Publications

2017

November 2017: Palaeogeography, Palaeoclimatology, Palaeoecology

Palaeogeography, Palaeoclimatology, Palaeoecology

Understanding the response of sensitive Arctic and subarctic landscapes to climate change is essential to determine the risks of ongoing and projected climate warming. However, these responses will not be uniform in terms of timing and magnitude across the landscape because of site–specific differences in ecosystem susceptibility to climate forcing. Here we present a multi–proxy analysis of a sediment record from the 330–km2 lake Torneträsk to assess the sensitivity of the Fennoscandian subarctic landscape to climate change over the past ~ 9500 years. By comparing responses of this large–lake system to past climatic and environmental changes with those in small lakes in its catchment, we assessed when the magnitude of change was sufficient to affect an entire region rather than only specific sub–catchments that may be more sensitive to localized environmental changes such as, e.g., tree–line dynamics. Our results show three periods of regional landscape alteration with distinct change in sediment composition: i) landscape development following deglaciation and through the Holocene Thermal Maximum, ~ 9500–3400 cal yr BP; ii) increased soil erosion during the Little Ice Age (LIA); and iii) rapid change during the past century coincident with ongoing climate change. The gradual landscape development led to successive changes in the lake sediment composition over several millennia, whereas climate cooling during the late Holocene caused a rather abrupt shift occurring within ~ 100 years. However, this shift at the onset of the LIA (~ 750 cal yr BP) occurred > 2000 years later than the first indications for climate cooling recorded in small lakes in the Torneträsk catchment, suggesting that a critical ecosystem threshold was not crossed until the LIA. In contrast, the ongoing response to recent climate change was immediate, emphasizing the unprecedented scale of ongoing climate changes in subarctic Fennoscandia.

Meyer–Jacob, C, Bindler, R, Bigler, C, Leng, M J, Lowick, S E, Biester, H, Vogel, H. 2017. Regional Holocene climate and landscape changes recorded in the large subarctic lake Tornetrask, N Fennoscandia. Palaeogeography, Palaeoclimatology, Palaeoecology, 487, 1–14.

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October 2017: Journal of Archaeological Science

Archaeological discussions of early agriculture have often used the Neolithic village of Çatalhöyük in central southern Turkey as a key example of the restricting effect of environment on agricultural production and organization. Central to these discussions is the palaeoenvironmental reconstruction of the landscape surrounding the site. This paper presents an important new dataset from an intensive coring programme undertaken between 2007 and 2013 in the immediate environs of the site, designed to improve significantly the spatial resolution of palaeoenvironmental data. Using sediment analyses including organic content, magnetic susceptibility, particle size, total carbon and nitrogen contents and carbon isotope analysis, coupled with 3D modelling, we are able to present a new reconstruction of the palaeotopography and sedimentary environments of the site. Our findings have major implications for our understanding of Neolithic agricultural production and social practice.

We present four phases of environmental development. Phase 1 consists of the final phases of regression of Palaeolake Konya in the later parts of the Pleistocene, dominated by erosion due to wind and water that created an undulating surface of the marl deposited in the palaeolake. Phase 2 occurs in the latest Pleistocene and early Holocene, and indicates increased wetness, probably characteristic of a humid anabranching channel system, in which there are localized pockets of wetter conditions. In Phase 3a, this infilling continues, producing a flatter surface, and there are fewer pockets being occupied by wetter conditions. The fluvial régime shifts from humid to dryland anabranching conditions. The earliest period of occupation of the Neolithic East Mound coincides with this phase. Phase 3b coincides with the shift of occupation to the West Mound in the Chalcolithic, when there is evidence for a very localized wetter area to the southeast of the West Mound, but otherwise a continuation of the dryland anabranching system. Finally, Phase 4 shows a shift to the pre-modern style of fluvial environment, modified by channelization. This reanalysis demonstrates the importance of extensive spatial sampling as part of geoarchaeological investigations.

With this new evidence we demonstrate that the landscape was highly variable in time and space with increasingly dry conditions developing from the early Holocene onwards. In contrast to earlier landscape reconstructions that have presented marshy conditions during the early Holocene that impacted agriculture, we argue that localized areas of the floodplain would have afforded significant opportunities for agriculture closer to the site. In this way, the results have important implications for how we understand agricultural practices in the early Neolithic.

Ayala, G, Wainwright, J, Walker, J, Hodara, R, Lloyd, J M, Leng, M, Doherty, C. 2017. Palaeoenvironmental reconstruction of the alluvial landscape of Neolithic Çatalhöyük, central southern Turkey: The implications for early agriculture and responses to environmental change. Journal of Archaeological Science, 87C, 30-43.

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October 2017: Plant and Soil

The dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (Po) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction. We asked a group of experts to consider the global issues associated with Po in the terrestrial environment, methodological strengths and weaknesses, benefits to be gained from understanding the Po cycle, and to set priorities for Po research. We identified seven key opportunities for Po research including: the need for integrated, quality controlled and functionally based methodologies; assessment of stoichiometry with other elements in organic matter; understanding the dynamics of Po in natural and managed systems; the role of microorganisms in controlling Po cycles; the implications of nanoparticles in the environment and the need for better modelling and communication of the research. Each priority is discussed and a statement of intent for the Po research community is made that highlights there are key contributions to be made toward understanding biogeochemical cycles, dynamics and function of natural ecosystems and the management of agricultural systems.

George, T S, Giles, C D, Menezes-Blackburn, D. et al. Plant Soil (2017).

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September 2017: Journal of Paleolimnology

The Makgadikgadi–Okavango–Zambezi basin (MOZB) is a structural depression in the south–western branch of the East African Rift System of the northern and middle Kalahari, central southern Africa. In the present day, the mainly dry subbasins of the MOZB are part of a long–lived lacustrine system that has likely existed since Early Pleistocene and from which an extant freshwater fish radiation emerged seeding all major river systems of southern Africa. During hydrologically favourable periods the subbasins were connected as a single mega–lake termed Lake Palaeo–Makgadikgadi. Previous geomorphological studies and OSL dates have provided evidence for repeated mega–lake periods since approximately 300 ka. The environmental and climatic implications of such large scale late Quaternary lake–level fluctuations are controversial, with the duration of mega–lake phases poorly constrained. Here, we present the first evidence for a Marine Isotope Stage (MIS) 5 mega–lake period (about 935–940 m a.s.l.) reconstructed from a diatom–rich, 30–cm–thick lacustrine sediment section, exposed close to a palaeo–shoreline of the Makgadikgadi Basin. Based upon the environmental setting and in comparison with sedimentation rates of other similar lake environments, we tentatively estimated that the highstand lasted approximately 1 ka during MIS 5d–b. The 30–cm section was sampled in 0.5–cm steps. Diatom species diversity ranges from 19 to 30 through the section. The dominant species are Pseudostaurosira brevistriata, Rhopalodia gibberula, Cyclotella meneghiniana and Epithemia sorex. The total of 60 sediment samples provide us with a record at decadal to bi–decadal resolution. Based on diatom assemblages and their oxygen isotope composition (δ18O) we infer an alkaline and mostly oligohaline lake with shallow water conditions prevailing in MIS 5, and is potentially analogous to a Heinrich event. The climate over southern Africa during MIS 5 has been considered very arid but the hydromorphological context of our sediment section indicates that we captured a mega–lake period providing evidence that short–term excursions to significantly higher humidity existed. A hydrologically more favourable environment during MIS 5 than formerly presumed is in line with the early human occupation of the Kalahari.

Schmidt, M, Fuchs, M, Henderson, A C G, Kossler, A, Leng, M J, Mackay, A W, Shemang, E, and Riedel, F. 2017. Paleolimnological features of a mega–lake phase in the Makgadikgadi Basin (Kalahari, Botswana) during Marine Isotope Stage 5 inferred from diatoms. Journal of Paleolimnology, 58, 373–390.

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September 2017: Quaternary Science Reviews

The southern Cape coastal region is important for understanding both the behavioural history of modern humans, and regional and global climate dynamics, because it boasts a long archaeological record and occupies a key geographical location near the intersection of two major oceans. The western boundary Agulhas Current, implicated in global heat exchange dynamics, is an important modulator of southern African climates and yet we understand its past behaviour only broadly as the Current itself scours the coastal shelf and marine sediment core records necessarily provide little detail. Numerous archaeological sites from both the late Pleistocene and Holocene provide the opportunity for reconstruction of near–shore seasonal SST records, which respond both to localized wind–driven upwellings and Agulhas temperature shifts, corresponding in turn with terrestrial precipitation trends in the near–coastal and summer rainfall regions. Here we present a record of seasonal SSTs extending over MIS5, MIS4, and the Holocene, from serial δ18O measurements of a single gastropod species, Turbo sarmaticus. The results show that mean SST shifts accord well with global SST trends, although they are larger than those recorded in the Agulhas Current from coarser–scale marine sediment records. Comparison with a record of Antarctic sea–ice suggests that annual SST amplitude responds to Antarctic sea–ice extent, reflecting the positioning of the regional wind systems that drive upwelling dynamics along the coast. Thus, near–shore SST seasonality reflects the relative dominance of the westerly and easterly wind systems. These data provide a new climate archive for an important but understudied climate system.

Loftus, E, Sealy, J, Leng, M J, and Lee–Thorp, J A. 2017. A late Quaternary record of seasonal sea surface temperatures off southern Africa, Quaternary Science Reviews, Volume 171, 1 September 2017, Pages 73-84.

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August 2017: Rapid Communications in Mass Spectrometry

Potential post–mortem alteration to the oxygen isotope composition of biogenic silica is critical to the validity of palaeoclimate reconstructions based on oxygen isotope ratios (δ18O values) from sedimentary silica. We calculate the degree of oxygen isotope alteration within freshly cultured diatom biogenic silica in response to heating and storing in the laboratory. The experiments used freshly cultured diatom silica. Silica samples were either stored in water or dried at temperatures between 20°C and 80°C. The mass of affected oxygen and the associated silica–water isotope fractionation during alteration were calculated by conducting parallel experiments using endmember waters with δ18O values of –6.3 to –5.9‰ and –36.3 to –35.0‰. Dehydroxylation and subsequent oxygen liberation was achieved by stepwise fluorination with BrF5. The 18O/16O ratios were measured using a ThermoFinnigan MAT 253 isotope ratio mass spectrometer. Significant alterations in silica δ18O values were observed, most notably an increase in the δ18O values ollowing drying at 40–80°C. Storage in water for seven days between 20–80°C also led to significant alteration in δ18O values. Mass balance calculations suggest that the amount of affected oxygen is positively correlated with temperature. The estimated oxygen isotope fractionation during alteration is an inverse function of temperature, consistent with the extrapolation of models for high temperature silica–water oxygen isotope fractionation. Routinely used preparatory methods may impart significant alterations to the δ18O values of biogenic silica, particularly when dealing with modern cultured or field collected material. The significance of such processes within natural aquatic environments is uncertain; however, there is potential that similar processes also affect sedimentary diatoms, with implications for the interpretation of biogenic silica–hosted δ18O palaeoclimate records.

Tyler, J J, Sloane, H J, Rickaby, R E M, Cox, E J, and Leng, M J. 2017. Post–mortem oxygen isotope exchange within cultured diatom silica. Rapid Commun Mass Spectrom.

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August 2017: Palaeogeography, Palaeoclimatology, Palaeoecology

Palaeogeography, Palaeoclimatology, Palaeoecology

Understanding the response of sensitive Arctic and subarctic landscapes to climate change is essential to determine the risks of ongoing and projected climate warming. However, these responses will not be uniform in terms of timing and magnitude across the landscape because of site–specific differences in ecosystem susceptibility to climate forcing. Here we present a multi–proxy analysis of a sediment record from the 330–km2 lake Torneträsk to assess the sensitivity of the Fennoscandian subarctic landscape to climate change over the past ~9500 years. By comparing responses of this large–lake system to past climatic and environmental changes with those in small lakes in its catchment, we assessed when the magnitude of change was sufficient to affect an entire region rather than only specific sub–catchments that may be more sensitive to localized environmental changes such as, e.g., tree–line dynamics. Our results show three periods of regional landscape alteration with distinct change in sediment composition: i) landscape development following deglaciation and through the Holocene Thermal Maximum, ~9500–3400 cal yr BP; ii) increased soil erosion during the Little Ice Age (LIA); and iii) rapid change during the past century coincident with ongoing climate change. The gradual landscape development led to successive changes in the lake sediment composition over several millennia, whereas climate cooling during the late Holocene caused a rather abrupt shift occurring within ~100 years. However, this shift at the onset of the LIA (~750 cal yr BP) occurred > 2000 years later than the first indications for climate cooling recorded in small lakes in the Torneträsk catchment, suggesting that a critical ecosystem threshold was not crossed until the LIA. In contrast, the ongoing response to recent climate change was immediate, emphasizing the unprecedented scale of ongoing climate changes in subarctic Fennoscandia.

Meyer–Jacob, C, Bindler, R, Bigler, C, Leng, M J, Lowick, S E, Biester, H, and Vogel, H. 2017. Regional Holocene climate and landscape changes recorded in the large subarctic lake Tornetrask, N Fennoscandia. Palaeogeography, Palaeoclimatology, Palaeoecology – in press.

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July 2017: Proceedings of the Yorkshire Geological Society

Yorkshire Geological Society

A sedimentological study was conducted at two localities exposing the Mississippian Eyam Limestone Formation ofthe Derbyshire carbonate platform, UK. Ricklow Quarry comprises seven facies with diverse skeletal assemblages, representingdeposition on the inner to middle ramp within open marine waters. Once–a–Week Quarry comprises four facies, dominated bycrinoidal debris representing deposition on the inner ramp. Both localities expose Gigantoproductus shell beds. Palaeoecological analysis of a single shell bed from each locality enabled investigation of the rapid colonization andsuccess of this taxon on the platform. At Ricklow Quarry, on the eastern side of a localized mud mound, both life (>72% of thinand thick–shelled brachiopods in life position) and neighbourhood assemblages are present. A low–moderate diversitycommunity (<1.37 and <0.8 Shannon diversity index) rapidly established over relict Brigantian mud mounds. Shell beds arepreluded by intervals of decreased energy that allowed larvae to settle. Once established, the dominance of thick–shelledindividuals enabled baffling, potentially providing localized shelter for larvae and nearby individuals. At Once–a–Week Quarry,where no mud mound is present, only thick–shelled Gigantoproductus species and a low diversity community (<1.07 Shannondiversity index) exclusively comprising neighbourhood assemblages (37% in life position) is present. The presence of inactivemud mounds at Ricklow Quarry appears to have been the key to the success of Gigantoproductus species enabling the onset ofstable communities in the shelter provided by the relict mound. Once the first palaeocommunities were established, larvaedispersed and colonized higher energy settings, such as at Once–a–Week Quarry.

Nolan, L S P, Angiolini, L, Jadoul, F, Della Porta, G, Davies, S J, Banks, V J, Stephenson, M H, and Leng, M J. 2017. Sedimentary context and palaeoecology of Gigantoproductus shellbeds in the Mississippian Eyam Limestone Formation, Derbyshire carbonate platform, central England. Proceedings of the Yorkshire Geological Society, http://dx.doi.org/10.1144/pygs2017–393.

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June 2017: Marine and Petroleum Geology

Marine and Petroleum Geology

During the Serpukhovian (late Mississippian) Stage the Pennine Basin, now underlying much of northern England, consisted of a series of interlinked sub-basins that developed in response to the crustal extension north of the Hercynic orogenic zone. For the current study, mudstone samples of the Morridge Formation from two sub–basins located in the south–eastern part of the Pennine Basin were collected from the Carsington Dam Reconstruction C3 Borehole (Widmerpool Gulf sub–basin) and the Karenight 1 Borehole (Edale Gulf sub–basin). Detailed palynological analyses indicate that aside from the dominant (often 90% or more) heterogeneous amorphous organic matter (AOM), variable abundances of homogeneous AOM and phytoclasts are present. To complement the palynological dataset, a suite of geochemical and mineralogical techniques were applied to evaluate the prospectivity of these potentially important source rocks. Changes in the carbon isotope composition of the bulk organic fraction (δ13COM) suggest that the lower part (Biozone E2a) of Carsington DR C3 is markedly more influenced by terrigenous kerogen than the upper part of the core (Biozones E2a3–E2b1). The Karenight 1 core yielded more marine kerogen in the lower part (Marine Bands E1–E2b) than the upper part (Marine Band E2b). Present day Rock–Eval™ Total Organic Carbon (TOC) surpasses 2% in most samples from both cores, a proportion suggested by Jarvie (2012) that defines prospective shale gas reservoirs. However, when the pyrolysable component that reflects the generative kerogen fraction is considered, very few samples reach this threshold. The kerogen typing permits for the first time the calculation of an original hydrogen index (HIo) and original total organic carbon (TOCo) for Carboniferous mudstones of the Pennine Basin. The most prospective part of Carsington DR C3 (marine bands E2b1–E2a3) has an average TOCo of 3.2% and an average HIo of 465 mg/g TOCo. The most prospective part of Karenight 1 (242.80–251.89 m) is characterized by an average TOCo of 9.3% and an average HIo of 504 mg/g TOCo. Lastly, X–ray diffraction (XRD) analysis confirms that the siliceous to argillaceous mudstones contain a highly variable carbonate content. The palynological, geochemical and mineralogical proxies combined indicate that marine sediments were continuously being deposited throughout the sampled intervals and were punctuated by episodic turbiditic events. The terrestrial material, originating from the Wales–Brabant High to the south of the Pennine Basin, was principally deposited in the Widmerpool Gulf, with much less terrigenous organic matter reaching the Edale Gulf. As a consequence, the prospective intervals are relatively thin, decimetre–to meter–scale, and further high resolution characterization of these intervals is required to understand variability in prospectivitiy over these limited intervals.

Hennissen,J A I, Hough, E, Vane, C H, Leng, Melanie J, Kemp, S J, and Stephenson, M H. 2017. The prospectivity of a potential shale gas play: An example from the southern Pennine Basin (central England, UK), Marine and Petroleum Geology, ISSN 0264–8172.

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June 2017: Journal of Foraminiferal Research

Journal of Forminiferal Research

As part of an on–going re-assessment of the Cretaceous/Paleogene boundary in the Brazos River area, Falls County, Texas a number of new exposures have been described. One of these, at River Bank South, provides a near–continuous record of the lowermost Paleocene. It is from this succession that stable isotope analysis of bulk organic matter (δ13C and C/N) and mono–specific samples of the benthic foraminifera Lenticulina rotulata Lamarck (δ18O and δ13C) yields an orbitally–tuned stable isotope record, which allows the timing of events adjacent to the Cretaceous/Paleogene boundary to be determined. Using this cyclicity, it is suggested that the on–set of biotic recovery began ~40,000 years after the impact (near the base of Zone Pα) and that more significant recovery of planktic foraminifera and calcareous nannofossils began close to the base of Zone P1a, some 85,000–100,000 years post–impact. The data also appear to record the presence of the earliest Paleocene DAN–C2 and Lower C29n hyperthermal events and that these events appear to be an accentuated segment of this orbital cyclicity.

Leighton, A D, Hart, M B, Smart, C W, Leng, M J, and Hampton, M. 2017. Timing recovery after the Cretaceous/Paleogene boundary: evidence from the Brazos River, Texas, USA. Journal of Foraminiferal Research, 47(3), 229–238.

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June 2017: Marine Chemistry

Marine Chemistry

The isotope composition of seawater is an efficient method for detecting mixing between water masses to measure long term or large scale hydrological processes at the ocean surface, it is necessary to be able to precisely compare datasets produced by different laboratories. The oxygen and hydrogen isotope (δ18O and δ2H) composition of marine waters can be measured using isotope ratio mass spectrometry (IRMS) and near–infrared laser absorption spectroscopy (LS) techniques. The IRMS and equilibration method is thought to provide results on the activity scale, while LS provides results on the concentration scale. However, the effect of dissolved seawater salts on the measurement is not sufficiently assessed and seems sometimes contradictory in the literature. For this purpose, we made artificial seawater and a pure NaCl solution from a freshwater of known isotope composition. The solutions were measured by four different laboratories allowing us to compare the two techniques. We show that minor corrections are necessary to correct seawater measurements for the salt effect and report them on the concentration scale. Interestingly, seawater measurements using LS (type Picarro) coupled to a liner are not on the concentration scale and require a correction of ~ 0.09‰ for δ18O, while the correction is relatively less significant for δ2H (~ 0.13‰). Moreover, we found for IRMS measurements that the salt effect can differ between different laboratories but seems reproducible for a given laboratory. A natural sea water sample was then analyzed by the different laboratories participating in the study. We found that applying the corrections increases the reproducibility of the isotope measurement significantly, with inter–laboratory standard deviation decreasing from 0.06 to 0.02‰ and 0.55 to 0.23‰ for δ18O and δ2H, respectively. Thus, comparing sea water datasets produced in different laboratories requires that each laboratory carries out its own calibration with artificial seawater and presents measurements on the concentration scale.

Benetti, M, Sveinbjörnsdóttir, A E, Ólafsdóttir, R, Leng, M J, Arrowsmith, C, Debondt, K, Fripiat, F, Aloisi, G. 2017. Inter–comparison of salt effect correction for δ18O and δD measurements in seawater by CRMS and IRMS using the gas–H2O equilibration method. Marine Chemistry, 194, 114–123.

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May 2017: Deep Sea Research Part II: Topical Studies in Oceanography

Deep Sea Research Part II

The Western Antarctic Peninsula has recently undergone rapid climatic warming, with associated decreases in sea ice extent and duration, and increases in precipitation and glacial discharge to the ocean. These shifts in the freshwater budget can have significant consequences on the functioning of the regional ecosystem, feedbacks on regional climate, and sea–level rise. Here we use shelf–wide oxygen isotope data from cruises in four consecutive Januaries (2011–2014) to distinguish the freshwater input from sea ice melt separately from that due to meteoric sources (precipitation plus glacial discharge). Sea ice melt distributions varied from minima in 2011 of around 0% up to maxima in 2014 of around 4–5%. Meteoric water contribution to the marine environment is typically elevated inshore, due to local glacial discharge and orographic effects on precipitation, but this enhanced contribution was largely absent in January 2013 due to anomalously low precipitation in the last quarter of 2012. Both sea ice melt and meteoric water changes are seen to be strongly influenced by changes in regional wind forcing associated with the Southern Annular Mode and the El Niño–Southern Oscillation phenomenon, which also impact on net sea ice motion as inferred from the isotope data. A near–coastal time series of isotope data collected from Rothera Research Station reproduces well the temporal pattern of changes in sea ice melt, but less well the meteoric water changes, due to local glacial inputs and precipitation effects.

Meredith, M P, Stammerjohn, S E, Venables, H J, Ducklow, H W, Martinson, D G, Iannuzzi, R A, Leng, M J, van Wessem, J M, Reijmer, C H, and Barrand, N E. 2017. Changing distributions of sea ice melt and meteoric water west of the Antarctic Peninsula, Deep Sea Research Part II: Topical Studies in Oceanography, Volume 139, 40–57, ISSN 0967–0645.

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April 2017: PALAIOS

PALAIOS

Mean seasonal extreme temperatures on the seafloor calculated from the shell δ18O of the scallop Placopecten clintonius from the basal part of the early Pliocene Sunken Meadow Member (Yorktown Formation) in Virginia are very similar to those from the same horizon at the latitude of Cape Hatteras in North Carolina (˜ 210 km to the south). The lowest and highest temperatures calculated from each shell (using δ18Oseawater = +0.7‰) give mean values for winter and summer of 8.4 ± 1.1 °C (± 1σ) and 18.2 ± 0.6 °C in Virginia, and 8.6 ± 0.4 °C and 16.5 ± 1.1 °C in North Carolina (respective median temperatures: 13.3 °C and 12.6 °C). Patterns of ontogenetic variation in δ18O, δ13C and microgrowth increment size indicate summer water–column stratification in both areas, with summer surface temperatures perhaps 6 °C higher than on the seafloor. The low winter paleotemperatures in both areas are most simply explained by the greater southward penetration of cool northern waters in the absence of a feature equivalent to Cape Hatteras. The same current configuration but a warmer general climate can account for the high benthic seasonal range (over 15.0 °C in some cases) but warmer median temperatures (15.7–21.3 °C) derived from existing δ18O data from scallops of the higher Yorktown Formation (using δ18Oseawater = +0.7‰ for the upper Sunken Meadow Member and δ18Oseawater = +1.1‰ for the mid–Pliocene Rushmere, Morgarts Beach, and Moore House members). Existing δ18O data from the infaunal bivalve Mercenaria of the Rushmere Member yields a similarly high median temperature (21.6 °C) but a low seasonal range (9.2 °C), pointing to the periodic influence of warm currents, possibly at times when the Gulf Stream was exceptionally vigorous.

Johnson, A L A, Valentine, A M, Leng, M J, Sloane, H J, Schone, B R, and Balson, P S. 2017. Isotopic temperatures from the early Pliocene and mid–Pliocene of the US Middle Atlantic coastal plain, and their implications for the cause of regional marine climate change. PALAIOS, 32, 250–269.

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April 2017: Biogeosciences

Biogeosciences

This study reviews and synthesises existing information generated within the SCOPSCO (Scientific Collaboration on Past Speciation Conditions in Lake Ohrid) deep drilling project. The four main aims of the project are to infer (i) the age and origin of Lake Ohrid (Former Yugoslav Republic of Macedonia/Republic of Albania), (ii) its regional seismotectonic history, (iii) volcanic activity and climate change in the central northern Mediterranean region, and (iv) the influence of major geological events on the evolution of its endemic species. The Ohrid basin formed by transtension during the Miocene, opened during the Pliocene and Pleistocene, and the lake established de novo in the still relatively narrow valley between 1.9 and 1.3 Ma. The lake history is recorded in a 584 m long sediment sequence, which was recovered within the framework of the International Continental Scientific Drilling Program (ICDP) from the central part (DEEP site) of the lake in spring 2013. To date, 54 tephra and cryptotephra horizons have been found in the upper 460 m of this sequence. Tephrochronology and tuning biogeochemical proxy data to orbital parameters revealed that the upper 247.8 m represent the last 637 kyr. The multi–proxy data set covering these 637 kyr indicates long–term variability. Some proxies show a change from generally cooler and wetter to drier and warmer glacial and interglacial periods around 300 ka. Short–term environmental change caused, for example, by tephra deposition or the climatic impact of millennial–scale Dansgaard–Oeschger and Heinrich events are superimposed on the long–term trends. Evolutionary studies on the extant fauna indicate that Lake Ohrid was not a refugial area for regional freshwater animals. This differs from the surrounding catchment, where the mountainous setting with relatively high water availability provided a refuge for temperate and montane trees during the relatively cold and dry glacial periods. Although Lake Ohrid experienced significant environmental change over the last 637 kyr, preliminary molecular data from extant microgastropod species do not indicate significant changes in diversification rate during this period. The reasons for this constant rate remain largely unknown, but a possible lack of environmentally induced extinction events in Lake Ohrid and/or the high resilience of the ecosystems may have played a role.

Wagner, B, Wilke, T, Francke, A, Albrecht, C, Baumgarten, H, Bertini, A, Combourieu–Nebout, N, Cvetkoska, A, D'Addabbo, M, Timme, H D, Föller, K, Giaccio, B, Grazhdani, A, Hauffe, T, Holtvoeth, J, Joannin, S, Jovanovska, E, Just, J, Kouli, K, Koutsodendris, A, Krastel, S, Lacey, J H, Leicher, N, Leng, M J, Levkov, Z, Lindhorst, K, Masi, A, Mercuri, A M, Nomade, S, Nowaczyk, N, Panagiotopoulos, K, Peyron, O, Reed, J M, Regattieri, E, Sadori, L, Sagnotti, L, Stelbrink, B, Sulpizio, R, Tofilovska, S, Torri, P, Vogel, H, Wagner, T, Wagner Cremer, F, Wolff, G A, Wonik, T, Zanchetta, G, and Zhang, X S. 2017. The environmental and evolutionary history of Lake Ohrid (FYROM/Albania): Interim results from the SCOPSCO deep drilling project. Biogeosciences, 14, 2033–2054.

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March 2017: Nature communications

Nature communications

The impact of climatic change along the Antarctica Peninsula has been widely debated in light of atmospheric/oceanic warming and increases in glacial melt over the past half century. Particular concern exists over the impact of these changes on marine ecosystems, not only on primary producers but also on higher trophic levels. Here we present a record detailing of the historical controls on the biogeochemical cycling of silicic acid [Si(OH)4] on the west Antarctica Peninsula margin, a region in which the modern phytoplankton environment is constrained by seasonal sea ice. We demonstrate that Si(OH)4 cycling through the Holocene alternates between being primarily regulated by sea ice or glacial discharge from the surrounding grounded ice sheet. With further climate-driven change and melting forecast for the twenty-first century, our findings document the potential for biogeochemical cycling and multi-trophic interactions along the peninsula to be increasingly regulated by glacial discharge, altering food-web interactions.

Swann, G E A, Pike, J, Leng, M J, Sloane, H J, Snelling, A M. 2017.Temporal controls on silicic acid utilisation along the West Antarctic Peninsula. Nature Communications, 8.

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February 2017: Journal of Geophysical Research

Journal of Geophysical Research

The salinity and water oxygen isotope composition (δ18O) of twenty-nine first-year (FYI) and second-year (SYI) Arctic sea ice cores (total length 32.0 m) from the drifting ice pack north of Svalbard were examined to quantify the contribution of snow to sea ice mass. Five cores (total length 6.4 m) were analyzed for their structural composition showing variable contribution of 10-30% by granular ice. In these cores snow had been entrained in 6 to 28% of the total ice thickness. We found evidence of snow contribution in about three quarter of the sea ice cores, when surface granular layers had very low δ18O values. Snow contributed 7.5-9.7% to sea ice mass balance on average (including also cores with no snow) using δ18O mass balance calculations. In SYI cores snow fraction by mass (12.7-16.3%) was much higher than in FYI cores (3.3-4.4%), while the bulk salinity of FYI (4.9) was distinctively higher than for SYI (2.7). We surmise that oxygen isotopes and salinity profiles can give information on the age of the ice and allows to distinguish between FYI and SYI (or older) ice in the area north of Svalbard. This article is protected by copyright. All rights reserved.

Granskog, M A, Rosel, A, Dodd, P A, Divine, D, Gerland, S, Martma, T, and Leng, M J. 2017. Snow contribution to first–year and second–year Arctic sea ice mass balance north of Svalbard. Journal of Geophysical Research Oceans. Journal of Geophysical Research Oceans, 122, 2539–2549.

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January 2017: Book Chapter- Developments in Paleoenvironmental Research

Applications of Paleoenvironmental Techniques in Estuarine Studies

The sediments that are preserved in estuarine environments (saltmarsh, riverine estuaries, mangrove habitats, lagoons, isolation basins and fjords) contain organic matter that allows investigation of the provenance of that material. These data can then be used specifically to investigate past sea level/land level changes and changes in freshwater flux. Where microfossils are poorly preserved or absent, C/N and δ13C analyses offer an alternative method to deduce environmental histories, but they are especially useful when used in conjunction with a range of other proxies, and when local modern end-member organic variables can be measured to 'calibrate' the sedimentary C/N and δ13C. There are a wide range of C/N-δ13C based carbon studies, here we describe examples of studies in a variety of estuarine environments.

Leng, M J, and Lewis, J P. 2017. Bulk C/N ratios and Carbon Isotopes in Estuarine Environments. In: Weckstrom, K. et al. 2017. Applications of Paleoenvironmental Techniques in Estuarine Studies. Developments in Palaeoenvironmental Research, volume 20, Springer.

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January 2017: Environmental Archaeology

Seasonal δ13C and δ18O data are presented from 14 Unio sub–fossil shells unearthed at the archaeological site of Çatalhöyük in central Turkey, spanning the occupation period ca. 9150–8000 cal years BP. The shells likely lived in the small lakes/wetlands around the site before being gathered and taken to Çatalhöyük. Wet–dry seasonal cycles are clearly apparent in the δ18Oshell profiles with low winter values reflecting winter precipitation and high δ18O in the summer resulting from evaporation. The most striking trend in the δ18O data is the drop in maximum summer δ18O ca. 8300 years BP, which we infer as indicating lower summer evaporation and hence a reduction in seasonality. Previous palaeoclimate records from the area have suggested cooler and more arid conditions, with reduced precipitation, around this time. While the drop in summer δ18O values could be due to reduced summer temperatures reducing summer evaporation, but there was little change in winter δ18O, perhaps suggesting winter growth cessation or reduced influence of winter climate change on δ18O. This shift in seasonal climate could be linked to solar-forced climate change beginning ca. 8600 years BP, and enhanced by the regional expression of the 8·2k event. Changing water balance over the occupation period is likely an important contributory factor behind observed cultural changes at Çatalhöyük in the Late Neolithic/Early Chalcolithic period. Our results might be considered to support the fission-fusion farming hypothesis as we provide additional evidence for wet winter/early spring conditions during the Early Holocene which likely caused flooding of the Çarşamba Fan. The changing water balance after ca. 8300 years BP (i.e. reduced seasonality and potentially reduced local summer evaporation) is also coincidental with the proposed end of this farming system due to multi–decadal drought.

Lewis, J P, Leng, M J, Dean, J R, Marciniak, A, Bar–Yosef Mayer, D E & Wu, X. 2016. Early Holocene palaeoseasonality inferred from the stable isotope composition of Unio shells from Çatalhöyük, Turkey. Environmental Archaeology, 22, 79–95.

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January 2017: Rapid Communications in Mass Spectrometry

Rational

The carbon isotope (δ13C value) composition of fossil plant material is routinely used as a proxy of past climate and environment change. However, palaeoclimate interpretation requires assumptions about the stability of δ13C values in plant material during its decomposition and incorporation into sediments. Previous work on modern angiosperm species shows δ13C changes of several per mille during simulated decomposition experiments. However, no such tests have been undertaken on non-flowering plants, which are found extensively within the geological record. These plants have distinctly different cellulose–to–lignin ratios from those of their angiosperm counterparts, potentially creating hitherto unknown variations in the original to fossil δ13C signatures.

Methods

To test the extent of δ13C change during decomposition we have subjected a number of plants, representing more basal, noδflowering plant lineages (cycads, ferns, horsetails and dawn redwood), to artificial decay using a hydrothermal maturation technique at two temperatures over periods of up to 273 hours. Subsamples were extracted every δ13C16 hours and analysed for their δ13C and %C values using a Carlo Erba 1500 elemental analyser, and VG TripleTrap and Optima mass spectrometers.

Results

The %C values increased for all samples through the maturation process at both temperatures with the largest increases observed within the first 24 hours. Decreases in δ13C values were observed for all plants at 300°C and for two of the species at the lower temperature (200°C). The maximum shift in the δ13C value related to experimental decomposition was –0.90‰ (horsetail), indicating a preferential loss of 13C during thermal maturation.

Conclusions

The reduction in the δ13C value potentially suggests a preferential loss of isotopically heavier cellulose in relation to the isotopically lighter lignin component during maturation. The isotopic offset observed here (<0.9‰) means that palaeoclimatic interpretation of δ13C values from non–flowering plant material within the geological record remains robust, but only where interpretations are based on variations in δ13C values greater than 1‰.

Smith, A C, Kendrick, C P, Moss–Hayes, V L, Vane, C H, and Leng, M J. 2017. Carbon isotope alteration during the thermal maturation of non–flowering plant species representative of those found within the geological record. Rapid Commun. Mass Spectrom, 31: 21–26. doi: 10.1002/rcm.7755.

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January 2017: Science of the Total Environment

Science of the Total Environment

The need to reduce both point and diffuse phosphorus pollution to aquatic ecosystems is widely recognised and in order to achieve this, identification of the different pollutant sources is essential. Recently, a stable isotope approach using oxygen isotopes within phosphate (δ18OPO4) has been used in phosphorus source tracing studies. This approach was applied in a one-off survey in September 2013 to the River Taw catchment in south-west England where elevated levels of phosphate have been reported. River water δ18OPO4 along the main channel varied little, ranging from + 17.1 to + 18.8‰. This was no > 0.3‰ different to that of the isotopic equilibrium with water (Eδ18OPO4). The δ18OPO4 in the tributaries was more variable (+ 17.1 to + 18.8‰), but only deviated from Eδ18OPO4 by between 0.4 and 0.9‰. Several potential phosphate sources within the catchment were sampled and most had a narrow range of δ18OPO4 values similar to that of river Eδ18OPO4. Discharge from two waste water treatment plants had different and distinct δ18OPO4 from one another ranging between + 16.4 and + 19.6‰ and similar values to that of a dairy factory final effluent (+ 16.5 to + 17.8‰), mains tap water (+ 17.8 to + 18.4‰), and that of the phosphate extracted from river channel bed sediment (+ 16.7 to + 17.6‰). Inorganic fertilizers had a wide range of values (+ 13.3 to + 25.9‰) while stored animal wastes were consistently lower (+ 12.0 to + 15.0‰) than most other sources and Eδ18OPO4. The distinct signals from the waste water treatment plants were lost within the river over a short distance suggesting that rapid microbial cycling of phosphate was occurring, because microbial cycling shifts the isotopic signal towards Eδ18OPO4. This study has added to the global inventory of phosphate source δ18OPO4 values, but also demonstrated the limitations of this approach to identifying phosphate sources, especially at times when microbial cycling is high.

Granger, S J, Heaton, T H E, Pfahler, V, Blackwell, M S A, Yuan, H, Collins, A L. The oxygen isotopic composition of phosphate in river water and its potential sources in the Upper River Taw catchment, UK, Science of The Total Environment, Volume 574, 1 January 2017, Pages 680-690.

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2016

December 2016: Global Change Biology

Global Change Biology

The forest–steppe ecotone in southern Siberia is highly sensitive to climate change; global warming is expected to push the ecotone northwards, at the same time resulting in degradation of the underlying permafrost. To gain a deeper understanding of long-term forest–steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimnological approach, based on sediment records from Lake Baikal. We reconstruct proxies that are relevant to understanding carbon dynamics including carbon mass accumulation rates (CMAR; g C m−2 yr−1) and isotope composition of organic matter (δ13CTOC). Forest–steppe dynamics were reconstructed using pollen, and diatom records provided measures of primary production from near- and off-shore communities. We used a generalized additive model (GAM) to identify significant change points in temporal series, and by applying generalized linear least-squares regression modelling to components of the multiproxy data, we address (1) What factors influence carbon dynamics during early Holocene warming and late Holocene cooling? (2) How did carbon dynamics respond to abrupt sub-Milankovitch scale events? and (3) What is the Holocene carbon storage budget for Lake Baikal. CMAR values range between 2.8 and 12.5 g C m−2 yr−1. Peak burial rates (and greatest variability) occurred during the early Holocene, associated with melting permafrost and retreating glaciers, while lowest burial rates occurred during the neoglacial. Significant shifts in carbon dynamics at 10.3, 4.1 and 2.8 kyr bp provide compelling evidence for the sensitivity of the region to sub-Milankovitch drivers of climate change. We estimate that 1.03 Pg C was buried in Lake Baikal sediments during the Holocene, almost one-quarter of which was buried during the early Holocene alone. Combined, our results highlight the importance of understanding the close linkages between carbon cycling and hydrological processes, not just temperatures, in southern Siberian environments.

Mackay, A W, Seddon, A W R, Leng, M J, Heumann, G, Morley, D W, Piotrowska, N, Rioual, P, Roberts, S and Swann, G E A. (2016), Holocene carbon dynamics at the forest–steppe ecotone of southern Siberia. Glob Change Biol. doi:10.1111/gcb.13583

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November 2016: American Journal of Physical Anthropology

Physical Anthropology

This is the first investigation of dietary practices amongst multiple early medieval populations (AD 500–1000) from Wales and the Isle of Man using carbon, nitrogen, and sulphur isotope analysis. The analysis will illuminate similarities or differences between the diets and subsistence strategies of populations occupying different geographical regions, specifically those living in marginal coastal regions in comparison to inland populations well-connected to ecclesiastical centres and high–status settlements. One hundred and two human skeletons were sampled for carbon and nitrogen isotope analysis, and 69 human skeletons were sampled for sulphur isotope analysis from nine cemetery sites from western Britain (Isle of Man = 3, southwest Wales = 4, southeast Wales = 2). Thirteen faunal skeletons from St Patrick's Chapel (southwest Wales) were sampled for carbon, nitrogen, and sulphur isotope analysis. Human δ13C values range from –19.4‰ to –21.2‰ (δ13C mean=–20.4 ±0.4‰, 1σ, n = 86), and δ15N values range from 9.1‰ to 13.8‰ (δ15N mean = 10.8 ±± 0.9‰, 1σ, n = 86). δ34S values range from 1.2‰ to 18.4‰ (δ34S mean = 11.6 ±4.5‰, 1σ, n = 66). Significant differences were noted between the mean δ13C, δ15N and δ34S values according to geographic region: Isle of Man (δ13C = –20.7 ± 0.4‰, δ15N = 11.4 ±0.6‰, n = 13/86; δ34S mean = 17.1 ±0.6, n = 4/66), southwest Wales (δ13C = –20.5 ± 0.4±, δ15N = 11.0 ±1‰, n = 32/86; δ34S = 16.1 ± 2.1, n = 21/66), and southeast Wales (δ13C =–20.3 ±0.4‰, δ15N = 10.4 ±0.7‰, n = 41/86; δ34S= 8.8 ±3‰, n = 41/66). Faunal δ13C values range from –23.1‰ to –21.2‰ (δ13C mean= –22.1 ±0.5‰, 1σ, n = 13), and δ15N values range from 6.3‰ to 9.8‰ (δ15N mean = 7.3 ± 1.1‰, 1σ, n = 13). δ34S values range from 4.7‰ to 18.4‰ (δ34S mean= 16.3 ± 3.6‰, 1σ, n = 13). The data reveal a reliance on terrestrial protein, however differences are observed between the resource consumption of populations from southwest Wales and the Isle of Man in comparison to the populations from southeast Wales. Populations from the west coast have a marine sulphur signature that reflects their coastal proximity and may also include a reliance on seaweed as a fertiliser/food source. Populations in the southeast were connected to ecclesiastical centres and high-status settlements and had access to inland–grown produce. The data add support to the suggestion that δ34S can be used as a mobility indicator.

Hemer, Katie A. Angela L. Lamb, Carolyn A. Chenery and Jane A. Evans, 2016. A multi-isotope investigation of diet and subsistence amongst island and mainland populations from early medieval western Britain. American Journal of Physical Anthropology. Version of Record online: 17 NOV 2016. DOI: 10.1002/ajpa.23127.

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November 2016: Journal of Archaeological Science

Journal of Archaeological Science

Fungi are a common part of modern human diets, but are rarely discussed in an archaeological context. Power et al. (2015) published data on bolete spores in human tooth calculus, suggesting that Upper Palaeolithic peoples ate mushrooms. Here we briefly consider the likelihood of mushroom consumption in the past, and examine whether or not stable isotopes may provide a way of seeing this in archaeological populations. We also consider the complexities of fungal stable isotopes using our own data and that from the literature. We conclude that fungi are highly variable isotopically, and are an additional dietary factor that should be considered when trying to interpret ‘terrestrial’ carbon isotope signatures combined with relatively high nitrogen isotope values in humans and other animals. Substantial mushroom ingestion could, in some cases, result in isotope values that may be interpreted as considerable meat consumption.

O'Regan, H J, Lamb, A L and Wilkinson, D M. (2016) The missing mushrooms: searching for fungi in ancient human dietary analysis. Journal of Archaeological Science, 75, 139-143.

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November 2016: Science and Technology of Archaeological Research

STAR: Science and Technology of Archaeological Research

This paper presents the results of the first comprehensive scientific study of the fallow deer, a non-native species whose medieval-period introduction to Britain transformed the cultural landscape. It brings together data from traditional zooarchaeological analyses with those derived from new ageing techniques as well as the results of a programme of radiocarbon dating, multi-element isotope studies and genetic analyses. These new data are here integrated with historical and landscape evidence to examine changing patterns of fallow deer translocation and management in medieval England between the 11th and 16th century AD.

Sykes, N, Ayton, G, Bowen, F, Baker, K, Baker, P, Carden, R F, Dicken, C, Evans, J, Hoelzel, A R, Higham, T F G, Jones, R, Lamb, A, Liddiard, R, Madgwick, R, Miller, H, Rainsford, C, Sawyer, P, Thomas, R, Ward, C and Worley, F. 2016. Wild to domestic and back again: the dynamics of fallow deer management in medieval England (c. 11th-16th century AD). STAR: Science & Technology of Archaeological Research, 2(1), 113-126.

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December 2016: Earth and Planetary Science Letters

Earth and Planetary Science Letters

The Early Jurassic was marked by multiple periods of major global climatic and palaeoceanographic change, biotic turnover and perturbed global geochemical cycles, commonly linked to large igneous province volcanism. This epoch was also characterised by the initial break–up of the super–continent Pangaea and the opening and formation of shallow–marine basins and ocean gateways, the timing of which are poorly constrained. Here, we show that the Pliensbachian Stage and the Sinemurian–Pliensbachian global carbon–cycle perturbation (marked by a negative shift in δ13C of 2–4‰), have respective durations of ~8.7 and ~2 Myr. We astronomically tune the floating Pliensbachian time scale to the 405 Kyr eccentricity solution (La2010d), and propose a revised Early Jurassic time scale with a significantly shortened Sinemurian Stage duration of 6.9±0.4 Myr. When calibrated against the new time scale, the existing Pliensbachian seawater 87Sr/86Sr record shows relatively stable values during the first ˜2 Myr of the Pliensbachian, superimposed on the long-term Early Jurassic decline in 87Sr/86Sr. This plateau in 87Sr/86Sr values coincides with the Sinemurian–Pliensbachian boundary carbon–cycle perturbation. It is possibly linked to a late phase of Central Atlantic Magmatic Province (CAMP) volcanism that induced enhanced global weathering of continental crustal materials, leading to an elevated radiogenic strontium flux to the global ocean.

Ruhl, M, Hesselbo, S P, Hinnov, L, Jenkyns, H C, Xu, W, Riding, J B, Storm, M, Minisini, D, Ullmann, C V, Leng, M J. 2016. Astronomical constraints on the duration of the Early Jurassic Pliensbachian Stage and global climatic fluctuations, Earth and Planetary Science Letters, 455, 149-165.

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November 2016: Chemical Geology

Chemical Geology

Stable (C and O) isotope data from carbonates are one of the most important methods used to infer genetic processes in carbonatites. However despite their ubiquitous use in geological studies, it is suspected that carbonates are susceptible to dissolution–reprecipitation and isotopic resetting, especially in shallow intrusions, and may not be the best records of either igneous or hydrothermal processes. Apatite, however, should be much less susceptible to these resetting problems but has not been used for O isotope analysis. In this contribution, a novel bulk–carbonatite method for the analysis of O isotopes in the apatite PO4 site demonstrates a more robust record of stable isotope values. Analyses of apatite from five carbonatites with magmatic textures establishes a preliminary Primary Igneous Apatite (PIA) field of δ18O = + 2.5 to + 6.0‰ (VSMOW), comparable to Primary Igneous Carbonatite (PIC) compositions from carbonates. Carbonate and apatite stable isotope data are compared in 10 carbonatite samples from Songwe Hill, Malawi. Apatite is heavy rare earth element (HREE) enriched at Songwe and, therefore, oxygen isotope analyses of this mineral are ideal for understanding HREE–related mineralisation in carbonatites. Carbonate C and O isotope ratios show a general trend, from early to late in the evolution, towards higher δ18O values (+ 7.8 to + 26.7‰, VSMOW), with a slight increase in δ13C (– 4.6 to – 0.1‰, VPDB). Oxygen isotope ratios from apatite show a contrary trend, decreasing from a PIA field towards more negative values (+ 2.5 to – 0.7‰, VSMOW). The contrasting results are interpreted as the product of the different minerals recording fluid interaction at different temperatures and compositions. Modelling indicates the possibility of both a CO2 rich fluid and mixing between meteoric and deuteric waters. A model is proposed where brecciation leads to depressurisation and rapid apatite precipitation. Subsequently, a convection cell develops from a carbonatite, interacting with surrounding meteoric water. REE are likely to be transported in this convection cell and precipitate owing to decreasing salinity and/or temperature.

Broom–Fendley, S, Heaton, T, Wall, F, Gunn, G. 2016. Tracing the fluid source of heavy REE mineralisation in carbonatites using a novel method of oxygen–isotope analysis in apatite: The example of Songwe Hill, Malawi. Chemical Geology 440, 275–287.

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September 2016: Polar Science

Polar Science

To understand the sources and sinks of sulphate and associated biogeochemical processes in a High Arctic environment, late winter snowpacks, the summer melt–waters and rock samples were collected and analysed for major ions and stable isotope tracers (δ18O, δ34S). The SO42¯/Cl¯ ratio reveal that more than 87% of sulphate (frequently > 95%) of total sulphate carried by the subglacial runoff and proglacial streams was derived from non–snowpack sources. The proximity of non–snowpack sulphate δ34S (~8–19‰) to the δ34S of the major rocks in the vicinity (~–6 to +18‰) suggest that the non–snowpack sulphate was principally derived from rock weathering. Furthermore, Ca2++Mg2+/SO4 molar shows that sulphate acquisition in the meltwaters was controlled by two major processes: 1) coupled-sulphide carbonate weathering (molar ratio ∼ 2) and, 2) re-dissolution of secondary salts (molar ratio ~ 1). The δ34S–SO4 = +19.4‰ > δ34S–S of rock, accompanied by increased sulphate concentration also indicates an input from re–dissolution of secondary salts. Overall, δ18O composition of these non–snowpack sulphate (–11.9 to –2.2‰) mostly stayed below the threshold δ18O value (–6.7 to –3.3‰) for minimum O2 condition, suggesting that certain proportion of sulphate was regularly supplied from anaerobic sulphide oxidation.

Ansari, A H. 2016. Stable isotopic evidence for anaerobic maintained sulphate discharge in a polythermal glacier. Polar Science, 10, 24–35.

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September 2016: Palaeoceanography

Palaeoceanography

The Bering Sea is one of the most biologically productive regions in the marine system and plays a key role in regulating the flow of waters to the Arctic Ocean and into the subarctic North Pacific Ocean. Cores from IODP Expedition 323 to the Bering Sea provide the first opportunity to obtain reconstructions from the region that extend back to the Pliocene. Previous research at Bowers Ridge, south Bering Sea, has revealed stable levels of siliceous productivity over the onset of major Northern Hemisphere Glaciation (NHG) (c. 2.85–2.73 Ma). However, diatom silica isotope records of oxygen (δ18Odiatom) and silicon (δ30Sidiatom) presented here demonstrate that this interval was associated with a progressive increase in the supply of silicic acid to the region, superimposed on shift to a more dynamic environment characterized by colder temperatures and increased sea ice. This concluded at 2.58 Ma with a sharp increase in diatom productivity, further increases in photic zone nutrient availability and a permanent shift to colder sea surface conditions. These transitions are suggested to reflect a gradually more intense nutrient leakage from the subarctic northwest Pacific Ocean, with increases in productivity further aided by increased sea–ice and wind–driven mixing in the Bering Sea. In suggesting a linkage in biogeochemical cycling between the south Bering Sea and subarctic Northwest Pacific Ocean, mainly via the Kamchatka Strait, this work highlights the need to consider the inter–connectivity of these two systems when future reconstructions are carried out in the region.

Swann, G E A, Snelling, A M, and Pike, J. 2016. Biogeochemical cycling in the Bering Sea over the onset of major Northern Hemisphere Glaciation, Paleoceanography, 31, doi:10.1002/2016PA002978.

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September 2016: Palaeogeography, Palaeoclimatology, Palaeoecology

Palaeogeography, Palaeoclimatology, Palaeoecology

The Lower Mississippian (Tournaisian) Ballagan Formation in SE Scotland yields tetrapod fossils that provide fresh insights into the critical period when these animals first moved onto land. The key to understanding the palaeoenvironments where they lived is a detailed analysis of the sedimentary architecture of this formation, one of the thickest and most completely documented examples of a coastal floodplain and marginal marine succession from this important transitional time anywhere in the world. Palaeosols are abundant, providing a unique insight into the early Carboniferous habitats and climate. More than 200 separate palaeosols are described from three sections through the formation. The palaeosols range in thickness from 0.02 to 1.85 m and are diverse: most are Entisols and Inceptisols (63%), indicating relatively brief periods of soil development. Gleyed Inseptisols and Vertisols are less common (37%). Vertisols are the thickest palaeosols (up to 185 cm) in the Ballagan Formation and have common vertic cracks. Roots are abundant through all the palaeosols, from shallow mats and thin hair–like traces to sporadic thicker root traces typical of arborescent lycopods. Geochemical, isotope and clay mineralogical analyses of the palaeosols indicate a range in soil alkalinity and amount of water logging. Estimates of mean annual rainfall from palaeosol compositions are 1000–1500 mm per year. The high mean annual rainfall and variable soil alkalinities contrast markedly with dry periods that developed deep penetrating cracks and evaporite deposits. It is concluded that during the early Carboniferous, this region experienced a sharply contrasting seasonal climate and that the floodplain hosted a mosaic of closely juxtaposed but distinct habitats in which the tetrapods lived. The diversification of coastal floodplain environments identified here may link to the evolution and movement of tetrapods into the terrestrial realm.

Kearsey,T I, Bennett, C E, Millward, D, Davies, S J, Gowing, C J B, Kemp, S J, Leng, M J, Marshall, J E A, Browne, M A E. The terrestrial landscapes of tetrapod evolution in earliest Carboniferous seasonal wetlands of SE Scotland, Palaeogeography, Palaeoclimatology, Palaeoecology, 457, 52–69.

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August 2016: Journal of Archaeological Science: Reports

Journal of Archaeological Science: Reports

The archaeological record concerning the distribution and timing of fallow deer translocation across the Mediterranean has been growing in the last years. This knowledge has provided important insights into the movement, trade patterns and ideology of past societies. Unfortunately, the dispersal of fallow deer to the western part of the Mediterranean is insufficiently understood. To fill this gap, this article presents the results of a multidisciplinary investigation (combining the zooarchaeological evidence with AMS radiocarbon dating, isotope analyses and preliminary aDNA results) from a set of remains recovered from archaeological sites on Mallorca (Balearic Islands, Western Mediterranean). The purpose is to explore the timing, circumstances and meaning of the fallow deer's introduction to this island, as well as their subsequent management and extirpation. The results of these proxies confirm the arrival of the fallow deer during the Roman period and, after a short expansion with the establishment of vivaria, its disappearance after the Byzantine period.

Valenzuela, A, Baker, K, Carden, R, Evans, J, Higham, T F G, Hoelzel, R, Lamb, A L, Madgwick, R, Miller, H, Alcover, J A, Ángel Cau, M, Sykes, N. 2016. Both introduced and extinct: The fallow deer of Roman Mallorca. Journal of Archaeological Science: Reports 9, 168-177.

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August 2016: Geology

The Geological Society of America

Large igneous provinces(LIPs) are proposed to have caused a number of episodes of abrupt environmental change by increasing atmospheric CO2 levels, which were subsequently alleviated by drawdown of CO2 via enhanced continental weathering and burial of organic matter. Here the sedimentary records of two such episodes of environmental change, the Toarcian oceanic anoxic event (T–OAE) and preceding Pliensbachian–Toarcian (Pl–To) event (both possibly linked to the Karoo–Ferrar LIP), are investigated using a new suite of geochemical proxies that have not been previously compared. Stratigraphic variations in osmium isotope (187Os/188Os) records are compared with those of mercury (Hg) and carbon isotopes (δ13C) in samples from the Mochras core, Llanbedr Farm, Cardigan Bay Basin, Wales. These sedimentary rocks are confirmed as recording an open-marine setting by analysis of molybdenum/uranium enrichment trends, indicating that the Os isotope record in these samples reflects the isotopic composition of the global ocean. The Os isotope data include the first results across the Pl–To boundary, when seawater 187Os/188Os increased from ~0.40 to ~0.53, in addition to new data that show elevated 187Os/188Os (from ~0.42 to ~0.68) during the T-OAE. Both increases in 187Os/188Os correlate with negative carbon isotope excursions and increased mercury concentrations, supporting an interplay between terrestrial volcanism, weathering, and climate that was instrumental in driving these distinct episodes of global environmental change. These observations also indicate that the environmental impact of the Karoo–Ferrar LIP was not limited solely to the T–OAE.

Percival, L M, Cohen, A S, Davies,M, Dickson, A J, Hesselbo, S P, Jenkyns, H C, Leng, M J, Mether, T A, Storm, M S, Xu, W. 2016. Osmium isotope evidence for two pulses of increased continental weathering linked to Early Jurassic volcanism and climate change. The Geological Society of America, doi:10.1130/G37997.1.

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August 2016: Sedimentary Geology

Sedimentary Geology

In a terrestrial Triassic–Jurassic boundary succession of southern Sweden, perfectly zoned sphaerosiderites are restricted to a specific sandy interval deposited during the end–Triassic event. Underlying and overlying this sand interval there are several other types of siderite micromorphologies, i.e. poorly zoned sphaerosiderite, spheroidal (ellipsoid) siderite, spherical siderite and rhombohedral siderite. Siderite overgrowths occur mainly as rhombohedral crystals on perfectly zoned sphaerosiderite and as radiating fibrous crystals on spheroidal siderite. Concretionary sparry, microspar and/or micritic siderite cement postdate all of these micromorphologies. The carbon isotope composition of the siderite measured by conventional mass spectrometry shows the characteristic broad span of data, probably as a result of multiple stages of microbial activity. SIMS (secondary ion mass spectrometry) revealed generally higher δ13C values for the concretionary cement than the perfectly zoned sphaerosiderite, spheroidal siderite and their overgrowths, which marks a change in the carbon source during burial. All the various siderite morphologies have almost identical oxygen isotope values reflecting the palaeo-groundwater composition. A pedogenic/freshwater origin is supported by the trace element compositions of varying Fe:Mn ratios and low Mg contents. Fluctuating groundwater is the most likely explanation for uniform repeated siderite zones of varying Fe:Mn ratios reflecting alternating physiochemical conditions and hostility to microbial life/activity. Bacterially–mediated siderite precipitation likely incorporated Mn and other metal ions during conditions that are not favourable for the bacteria and continued with Fe-rich siderite precipitation as the physico-chemical conditions changed into optimal conditions again, reflecting the response to groundwater fluctuations.

Weibel, R, Lindström, S, Pedersen, G K, Johansson, L, Dybkjær, K, Whitehouse, M, Boyce, A and Leng, M J. 2016. Groundwater table fluctuations recorded in zonation of microbial siderites from end–Triassic strata. Sedimentary Geology, 342, 47–65.

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August 2016: Global and Planetary Change

Global and Planetary Change

Sedimentary sequences in ancient or long–lived lakes can reach several thousands of meters in thickness and often provide an unrivalled perspective of the lake's regional climatic, environmental, and biological history. Over the last few years, deep–drilling projects in ancient lakes became increasingly multi– and interdisciplinary, as, among others, seismological, sedimentological, biogeochemical, climatic, environmental, paleontological, and evolutionary information can be obtained from sediment cores. However, these multi– and interdisciplinary projects pose several challenges. The scientists involved typically approach problems from different scientific perspectives and backgrounds, and setting up the program requires clear communication and the alignment of interests. One of the most challenging tasks, besides the actual drilling operation, is to link diverse datasets with varying resolution, data quality, and age uncertainties to answer interdisciplinary questions synthetically and coherently. These problems are especially relevant when secondary data, i.e., datasets obtained independently of the drilling operation, are incorporated in analyses. Nonetheless, the inclusion of secondary information, such as isotopic data from fossils found in outcrops or genetic data from extant species, may help to achieve synthetic answers. Recent technological and methodological advances in paleolimnology are likely to increase the possibilities of integrating secondary information. Some of the new approaches have started to revolutionize scientific drilling in ancient lakes, but at the same time, they also add a new layer of complexity to the generation and analysis of sediment–core data. The enhanced opportunities presented by new scientific approaches to study the paleolimnological history of these lakes, therefore, come at the expense of higher logistic, communication, and analytical efforts. Here we review types of data that can be obtained in ancient lake drilling projects and the analytical approaches that can be applied to empirically and statistically link diverse datasets to create an integrative perspective on geological and biological data. In doing so, we highlight strengths and potential weaknesses of new methods and analyses, and provide recommendations for future interdisciplinary deep–drilling projects.

Wilke, T, Wagner, B, Van Bocxlaer, B, Albrecht, C, Ariztegui, D, Delicado, D, Francke, A, Harzhauser, M, Hauffe, T, Holtvoeth, J, Just, J, Leng, M J, Levkov, Z, Penkman, K, Sadori, L, Skinner, A, Stelbrink, B, Vogel, H, Wesselingh, F, Wonik, T. 2016. Scientific drilling projects in ancient lakes: Integrating geological and biological histories. Global and Planetary Change, 143, 118–151.

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August 2016: Science – Technology of Archaeological Research

This paper presents the results of the first comprehensive scientific study of the fallow deer, a non–native species whose medieval–period introduction to Britain transformed the cultural landscape. It brings together data from traditional zooarchaeological analyses with those derived from new ageing techniques as well as the results of a programme of radiocarbon dating, multi–element isotope studies and genetic analyses. These new data are here integrated with historical and landscape evidence to examine changing patterns of fallow deer translocation and management in medieval England between the 11th and 16th century AD.

Sykes, N, Ayton, G, Bowen, F, Baker, K, Baker, P, Carden, R F, Dicken, C, Evans, J, Hoelzel, R, Higham, T F G, Jones, R, Lamb, A L, Liddiard, R, Madgwick, R, Miller, H, Rainsford, C, Sawyer, P, Thomas, R, Ward, C, – Worley, F. 2016. Wild to domestic and back again: the dynamics of fallow deer management in medieval England (c. 11th–16th century AD), STAR: Science & Technology of Archaeological Research, DOI: 10.1080/20548923.2016.1208027.

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June 2016: Journal of Quaternary Science

Journal of Quaternary Science

Carbon incorporated into diatom frustule walls is protected from degradation enabling analysis for carbon isotope composition (δ13Cdiatom). This presents potential for tracing carbon cycles via a single photosynthetic host with well-constrained ecophysiology. Improved understanding of environmental processes controlling carbon delivery and assimilation is essential to interpret changes in freshwater δ13Cdiatom. Here relationships between water chemistry and δ13Cdiatom from contemporary regional data sets are investigated. Modern diatom and water samples were collected from river catchments within England and lake sediments from across Europe. The data suggest dissolved, biogenically produced carbon supplied proportionately to catchment productivity was critical in the rivers and soft water lakes. However, dissolved carbon from calcareous geology overwhelmed the carbon signature in hard water catchments. Both results demonstrate carbon source characteristics were the most important control on δ13Cdiatom, with a greater impact than productivity. Application of these principles was made to a sediment record from Lake Tanganyika. δ13Cdiatom co-varied with δ13Cbulk through the last glacial and Holocene. This suggests carbon supply was again dominant and exceeded authigenic demand. This first systematic evaluation of contemporary δ13Cdiatom controls demonstrates that diatoms have the potential to supply a record of carbon cycling through lake catchments from sediment records over millennial timescales.

Webb, M, Barker, P A, Wynn, P M, Heiri, O, van Hardenbroek, M, Pick, F, Russell, J M, Stott, A W and Leng, M J. (2016), Interpretation and application of carbon isotope ratios in freshwater diatom silica. J. Quaternary Sci., 31: 300–309. doi: 10.1002/jqs.2837.

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June 2016: Journal of Quaternary Science

Journal of Quaternary Science

This study investigates hydrological responses to climatic shifts using sediment flux data derived from two dated palaeolake records in south-east Arabia. Flux values are generally low during the early Holocene humid period (EHHP) (˜9.0–6.4k cal a BP) although several short-lived pulses of increased detrital input are recorded, the most prominent of which is dated between ˜8.3 and 7.9k cal a BP. The EHHP is separated from the mid-Holocene humid period (MHHP) (˜5.0–4.3k cal a BP) by a phase of increased sediment flux and aridity, which began between ˜6.4 and 5.9k cal a BP and peaked between ˜5.2 and 5.0k cal a BP. The termination of the MHHP is marked by a phase of high detrital sediment flux between ˜4.3 and 3.9k cal a BP. While long-term shifts in climate are most likely linked to changes in the summer position of the Intertropical Convergence Zone and associated Indian and African monsoon systems, it is noted that the abrupt, short-term phases of aridity observed in both records are coeval with intervals of rapid climate change globally, which triggered non-linear, widespread landscape reconfigurations throughout south-east Arabia.

Parker, A G, Preston, G W, Parton, A, Walkington, H, Jardine, P E, Leng, M J and Hodson, M J. (2016), Low-latitude Holocene hydroclimate derived from lake sediment flux and geochemistry. J. Quaternary Sci., 31: 286–299.

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June 2016: Journal of Quaternary Science

Journal of Quaternary Science

The Valsequillo Basin in Central Mexico has been of interest due to the presence of megafaunal remains and evidence for early human occupation, but research has been controversial. It has been suggested that extensive and deep lakes characterized the Early Pleistocene environment but sediment exposure is highly fragmentary and reliable dating has been difficult. Here we report, for the first time, Early Pleistocene palaeoenvironmental reconstructions using stable isotopes, diatoms, tephra and pollen. We studied several stratigraphic sections of mainly non-volcanic rocks, containing the 1.3-Ma Xalnene Ash as a stratigraphic marker. The isotope and other proxy data show that topographically low points in the basin were occupied by spring-fed, shallow water lakes during the Early–Mid Pleistocene, with a trend to drier conditions. The basin was a dynamic volcaniclastic environment during this period, with the production of the Toluquilla volcanic sequence and other rhyolitic–dacitic volcanic ashes interbedded with the lake sediments at the sections studied. There is no evidence from the sections for extensive and deep lakes before or after deposition of the Xalnene Ash. Wetter conditions in the basin during the Early Pleistocene would have made it attractive for megafauna.

Metcalfe, S E, Leng, M J, Kirby, J R, Huddart, D, Vane, C H and Gonzalez, S. (2016), Early–Mid Pleistocene environments in the Valsequillo Basin, Central Mexico: a reassessment. J. Quaternary Sci., 31: 325–336. doi: 10.1002/jqs.2851.

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June 2016: Journal of Quaternary Science

Journal of Quaternary Science

Individual palaeoenvironmental records represent a combination of regional-scale (e.g. climatic) and site-specific local factors. Here we compare multiple climate proxies from two nearby maar lake records, assuming that common signals are due to regional-scale forcing. A new core sequence from Nar Lake in Turkey is dated by varves and U–Th to the last 13.8 ka. Markedly dry periods during the Lateglacial stadial, at 4.3–3.7 and at 3.2–2.6 ka BP, are associated with peaks in Mg/dolomite, positive δ18O, elevated diatom-inferred electrical conductivity, an absence of laminated sediments and low Quercus/chenopod ratios. Wet phases occurred during the early–mid Holocene and 1.5–0.6 ka BP, characterized by negative δ18O, calcite precipitation, high Ca/Sr ratios, a high percentage of planktonic diatoms, laminated sediments and high Quercus/chenopod ratios. Comparison with the record from nearby Eski Acıgöl shows good overall correspondence for many proxies, especially for δ18O. Differences are related to basin infilling and lake ontogeny at Eski Acıgöl, which consequently fails to register climatic changes during the last 2 ka, and to increased flux of lithogenic elements into Nar Lake during the last 2.6 ka, not primarily climatic in origin. In attempting to separate a regional signal from site-specific 'noise', two lakes may therefore be better than one.

Roberts, N, Allcock, S L, Arnaud, F, Dean, J R, Eastwood, W J, Jones, M D, Leng, M J, Metcalfe, S E, Malet, E, Woodbridge, J and YiğitbaŞıoğlu, H. (2016), A tale of two lakes: a multi-proxy comparison of Lateglacial and Holocene environmental change in Cappadocia, Turkey. J. Quaternary Sci., 31: 348–362. doi: 10.1002/jqs.2852.

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June 2016: Nature Communications

Nature Communications

Understanding the interaction between climate and biotic evolution is crucial for deciphering the sensitivity of life. An enigmatic mass extinction occurred in the deep oceans during the Mid Pleistocene, with a loss of over 100 species (20%) of sea floor calcareous foraminifera. An evolutionarily conservative group, benthic foraminifera often comprise >50% of eukaryote biomass on the deep-ocean floor. Here we test extinction hypotheses (temperature, corrosiveness and productivity) in the Tasman Sea, using geochemistry and micropalaeontology, and find evidence from several globally distributed sites that the extinction was caused by a change in phytoplankton food source. Coccolithophore evolution may have enhanced the seasonal 'bloom' nature of primary productivity and fundamentally shifted it towards a more intra-annually variable state at ˜0.8 Ma. Our results highlight intra-annual variability as a potential new consideration for Mid Pleistocene global biogeochemical climate models, and imply that deep-sea biota may be sensitive to future changes in productivity.

Kender, S, McClymont, E L, Elmore, A C, Emanuele, D, Leng, M J & Elderfield, H. (2016) Mid Pleistocene foraminiferal mass extinction coupled with phytoplankton evolution. Nature Communications, 7, 11970.

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June 2016: Palaeoceanography

Palaeoceanography

Over the last 5 million years, the global climate system has evolved toward a colder mean state, marked by large amplitude oscillations in continental ice volume. Equatorward expansion of polar waters and strengthening temperature gradients have been detected. However, the response of the mid- and high-latitudes of the southern hemisphere is not well documented, despite the potential importance for climate feedbacks including sea ice distribution and low-high latitude heat transport. Here, we reconstruct the Pliocene-Pleistocene history of both sea surface and Antarctic Intermediate Water (AAIW) temperatures on orbital timescales from DSDP Site 593 in the Tasman Sea, Southwest Pacific. We confirm overall Pliocene-Pleistocene cooling trends in both the surface ocean and AAIW, although the patterns are complex. The Pliocene is warmer than modern, but our data suggest an equatorward displacement of the subtropical front relative to present, and a poleward displacement of the subantarctic front of the Antarctic Circumpolar Current (ACC). Two main intervals of cooling, from c.3Ma and c.1.5Ma, are coeval with cooling and ice-sheet expansion noted elsewhere, and suggest that equatorward expansion of polar water masses also characterised the Southwest Pacific through the Pliocene-Pleistocene. However, the observed trends in SST and AAIW temperature are not identical despite an underlying link to the ACC, and intervals of unusual surface ocean warmth (c.2Ma) and large amplitude variability in AAIW temperatures (from c.1Ma) highlight complex interactions between equatorward displacements of fronts associated with the ACC and/or varying poleward heat transport from the subtropics.

McClymont, E L, Elmore, A C, Kender, S, Leng, M J, Greaves, M and Elderfield, H. 2016. Pliocene-Pleistocene evolution of sea surface and intermediate water temperatures from the Southwest Pacific. Paleoceanography, 31, 895–913.

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August 2016: Global and Planetary Change

Global and Planetary Change

Sedimentary sequences in ancient or long–lived lakes can reach several thousands of meters in thickness and often provide an unrivalled perspective of the lake's regional climatic, environmental, and biological history. Over the last few years, deep drilling projects in ancient lakes became increasingly multi– and interdisciplinary, as, among others, seismological, sedimentological, biogeochemical, climatic, environmental, paleontological, and evolutionary information can be obtained from sediment cores. However, these multi– and interdisciplinary projects pose several challenges. The scientists involved typically approach problems from different scientific perspectives and backgrounds, and setting up the program requires clear communication and the alignment of interests. One of the most challenging tasks, besides the actual drilling operation, is to link diverse datasets with varying resolution, data quality, and age uncertainties to answer interdisciplinary questions synthetically and coherently. These problems are especially relevant when secondary data, i.e., datasets obtained independently of the drilling operation, are incorporated in analyses. Nonetheless, the inclusion of secondary information, such as isotopic data from fossils found in outcrops or genetic data from extant species, may help to achieve synthetic answers. Recent technological and methodological advances in paleolimnology are likely to increase the possibilities of integrating secondary information, e.g., through molecular dating of molecular phylogenies. Some of the new approaches have started to revolutionize scientific drilling in ancient lakes, but at the same time, they also add a new layer of complexity to the generation and analysis of sediment core data. The enhanced opportunities presented by new scientific approaches to study the paleolimnological history of these lakes, therefore, come at the expense of higher logistic, communication, and analytical efforts. Here we review types of data that can be obtained in ancient lake drilling projects and the analytical approaches that can be applied to empirically and statistically link diverse datasets for creating an integrative perspective on geological and biological data. In doing so, we highlight strengths and potential weaknesses of new methods and analyses, and provide recommendations for future interdisciplinary deep drilling projects.

Wilke, T, Wagner, B, Van Bocxlaer, B, Albrecht, C, Ariztegui, D, Delicado, D, Francke, A, Harzhauser, M, Hauffe, T, Holtvoeth, J, Just, J, Leng, M J, Levkov, Z, Penkman, K, Sadori, L, Skinner, A, Stelbrink, B, Vogel, H, Wesselingh, F, Wonik, T. 2016. Scientific drilling projects in ancient lakes: Integrating geological and biological histories, Global and Planetary Change, 143, 118–151.

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May 2016: The Holocene

The Holocene

The aim of this research was to create a decadal–scale terrestrial quantitative palaeoclimate record for NW Iceland from lake sediments for the last millennium. Geochemical, stable isotope and chironomid reconstructions were obtained from a lake sequence constrained by tephra deposits on the Snæfellsnes peninsula, western Iceland. Obtaining a quantitative record proved problematic, but the qualitative chironomid record showed clear trends associated with past summer temperatures, and the sedimentological records provided evidence for past changes in precipitation, mediated through catchment soil in–wash. When the full range of chronological uncertainty is considered, four clear phases of climatic conditions were identified: (1) a relatively warm phase between AD 1020 and 1310; (2) a relatively stable period between AD 1310 and 1510, cooler than the preceding period but still notably warmer than the second half of the millennium; (3) a consistent reduction of temperatures between AD 1560 and 1810, with the coolest period between AD 1680 and 1810; and (4) AD 1840–2000 has temperatures mainly warmer than in the preceding two centuries, with a rising trend and increased variability from c. AD 1900 onwards. The reconstructions show clearly that the first half of the millennium experienced warmer climatic conditions than the second half, with a return to the warmer climate only occurring in the last c. 100 years. Much of the variability of the chironomid record can be linked to changes in the North Atlantic Oscillation (NAO). The reconstructions presented can track low–frequency and long–term trends effectively and consistently but high–resolution and calibrated quantitative records remain more of a challenge – not just in finding optimal sedimentary deposits but also in finding the most reliable proxy. It is this that presents the real challenge for Holocene climate reconstruction from this key area of the North Atlantic.

Holmes, N, Langdon, P G, Caseldine, C J, Wastegård, S, Leng, M J, Croudace, I W, Davies, S M. 2016. Climatic variability during the last millennium in Western Iceland from lake sediment records. The Holocene, 26(5), 756–771.

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May 2016: Biogeosciences

Biogeosciences

The DEEP site sediment sequence obtained during the ICDP SCOPSCO project at Lake Ohrid was dated using tephrostratigraphic information, cyclostratigraphy, and orbital tuning through the marine isotope stages (MIS) 15-1. Although this approach is suitable for the generation of a general chronological framework of the long succession, it is insufficient to resolve more detailed palaeoclimatological questions, such as leads and lags of climate events between marine and terrestrial records or between different regions. Here, we demonstrate how the use of different tie points can affect cyclostratigraphy and orbital tuning for the period between ca. 140 and 70ka and how the results can be correlated with directly/indirectly radiometrically dated Mediterranean marine and continental proxy records. The alternative age model presented here shows consistent differences with that initially proposed by Francke et al. (2015) for the same interval, in particular at the level of the MIS6-5e transition. According to this new age model, different proxies from the DEEP site sediment record support an increase of temperatures between glacial to interglacial conditions, which is almost synchronous with a rapid increase in sea surface temperature observed in the western Mediterranean. The results show how a detailed study of independent chronological tie points is important to align different records and to highlight asynchronisms of climate events. Moreover, Francke et al. (2016) have incorporated the new chronology proposed for tephra OH-DP-0499 in the final DEEP age model. This has reduced substantially the chronological discrepancies between the DEEP site age model and the model proposed here for the last glacial-interglacial transition.

Zanchetta, G, Regattieri, E, Giaccio, B, Wagner, B, Sulpizio, R, Francke, A, Vogel, H, Sadori, L, Masi, A, Sinopoli, G, Lacey, J H, Leng, M J, and Leicher, N. Aligning and synchronization of MIS5 proxy records from Lake Ohrid (FYROM) with independently dated Mediterranean archives: implications for DEEP core chronology, Biogeosciences, 13, 2757-2768, doi:10.5194/bg-13-2757-2016, 2016.

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May 2016: Deep Sea Research Part II

Deep Sea Research Part II

Topical Studies in Oceanography The Western Antarctic Peninsula has recently undergone rapid climatic warming, with associated decreases in sea ice extent and duration, and increases in precipitation and glacial discharge to the ocean. These shifts in the freshwater budget can have significant consequences on the functioning of the regional ecosystem, feedbacks on regional climate, and sea-level rise. Here we use shelf-wide oxygen isotope data from cruises in four consecutive Januaries (2011 to 2014) to distinguish the freshwater input from sea ice melt separately from that due to meteoric sources (precipitation plus glacial discharge). Sea ice melt distributions varied from minima in 2011 of around 0% up to maxima in 2014 of around 4-5%. Meteoric water contribution to the marine environment is typically elevated inshore, due to local glacial discharge and orographic effects on precipitation, but this enhanced contribution was largely absent in January 2013 due to anomalously low precipitation in the last quarter of 2012. Both sea ice melt and meteoric water changes are seen to be strongly influenced by changes in regional wind forcing associated with the Southern Annular Mode and the El Niño-Southern Oscillation phenomenon, which also impact on net sea ice motion as inferred from the isotope data. A near-coastal time series of isotope data collected from Rothera Research Station reproduces well the temporal pattern of changes in sea ice melt, but less well the meteoric water changes, due to local glacial inputs and precipitation effects.

Meredith M P, Stammerjohn, S E, Venables, H J, Ducklow, H W, Martinson, D G, Iannuzzi, R A, Leng, M J, van Wessem, J M, Reijmer, C H and Barrand, N E. 2016. Changing distributions of sea ice melt and meteoric water west of the Antarctic Peninsula.

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April 2016: Scientific Reports

Scientific Reports

Century–to–millennial scale fluctuations in precipitation and temperature are an established feature of European Holocene climates. Changes in moisture delivery are driven by complex interactions between ocean moisture sources and atmospheric circulation modes, making it difficult to resolve the drivers behind millennial scale variability in European precipitation. Here, we present two overlapping decadal resolution speleothem oxygen isotope (δ18O) records from a cave on the Atlantic coastline of northern Iberia, covering the period 12.1–0 ka. Speleothem δ18O reveals nine –cyclical events of relatively wet–to–dry climatic conditions during the Holocene. Dynamic Harmonic Regression modelling indicates that changes in precipitation occurred with a ~1500 year frequency during the late Holocene and at a shorter length during the early Holocene. The timing of these cycles coincides with changes in North Atlantic Ocean conditions, indicating a connectivity between ocean conditions and Holocene moisture delivery. Early Holocene climate is potentially dominated by freshwater outburst events, whilst ~1500 year cycles in the late Holocene are more likely driven by changes internal to the ocean system. This is the first continental record of its type that clearly demonstrates millennial scale connectivity between the pulse of the ocean and precipitation over Europe through the entirety of the Holocene.

Smith, A C, Wynn, P M, Barker, P A, Leng, M J, Noble, S R, and Wlodeck T. 2016. North Atlantic forcing of moisture delivery to Europe throughout the Holocene. Scientific Reports, 6, 24745; doi: 10.1038/srep2474

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April 2016: Deep Sea Research Part II

Deep Sea Research

A continuous composite oxygen isotope (δ18O) stratigraphy from benthic foraminifera in the Bering Sea was reconstructed in order to provide insight into understanding sea–ice evolution in response to Northern Hemisphere Glaciation. Oxygen isotope records from multiple species of benthic foraminifera at Integrated Ocean Drilling Program (IODP) Expedition 323 Site U1343 (54°33.4'N, 176°49.0'E, water depth 1950 m) yield a highly refined orbital–scale age model spanning the last 1.2 Ma, and a refined age model between 1.2 and 2.4 Ma. An inter-species calibration was used to define species offsets and to successfully obtain a continuous composite benthic δ18O record, correlated with the global composite benthic δ18O stack curve LR04 to construct an orbital-scale age model. The consistency of the benthic δ18O stratigraphy with biostratigraphy and magnetostratigraphy confirms the reliability of both methods for constraining age. The time difference between cyclic changes in sedimentary physical properties and glacial interglacial cycles since 0.8 Ma is notable, and suggests that physical properties alone cannot be used to construct an orbital-scale age model. Amplitude changes in physical properties and a significant drop in the linear sedimentation rate during glacials after 0.9 Ma indicate that the glacial sea-ice edge extended beyond the Bering Sea Slope (Site U1343) at this time.

Asahi, H, Kender, S, Ikehara, M, Sakamoto, T, Takahashi, K, Ravelo, A C, Alvarez Zarikian, C A, Khim, B K, Leng, M J. 2016. Orbital–scale benthic foraminiferal oxygen isotope stratigraphy at the northern Bering Sea Slope Site U1343 (IODP Expedition 323) and its Pleistocene paleoceanographic significance. Deep Sea Research Part II: Topical Studies in Oceanography, 125–126, 66–83.

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April 2016: Global Change Biology

Global Change Biology

Quantitative reconstructions of terrestrial climate are highly sought after but rare, particularly in Australia. Carbon isotope discrimination in plant leaves (Δleaf) is an established indicator of past hydroclimate because the fractionation of carbon isotopes during photosynthesis is strongly influenced by water stress. Leaves of the evergreen tree Melaleuca quinquenervia have been recovered from the sediments of some perched lakes on North Stradbroke and Fraser Islands, south–east Queensland, eastern Australia. Here, we examine the potential for using M. quinquenervia ∆leaf as a tracer of past rainfall by analysing carbon isotope ratios (δ13C) of modern leaves. We firstly assess Δleaf variation at the leaf and stand scale and find no systematic pattern within leaves or between leaves due to their position on the tree. We then examine the relationships between climate and Δleaf for a 11–year time series of leaves collected in a litter tray. M. quinquenervia retains its leaves for 1–4 years; thus, cumulative average climate data are used. There is a significant relationship between annual mean ∆leaf and mean annual rainfall of the hydrological year for 1–4 years (i.e. 365–1460 days) prior to leaf fall (r2 = 0.64, P = 0.003, n = 11). This relationship is marginally improved by accounting for the effect of pCO2 on discrimination (r2 = 0.67, P = 0.002, n = 11). The correlation between rainfall and Δleaf, and the natural distribution of Melaleuca quinquenervia around wetlands of eastern Australia, Papua New Guinea and New Caledonia offers significant potential to infer past rainfall on a wide range of spatial and temporal scales.

Tibby, J, Barr, C, Mcinerney, F A, Henderson, A C G, Leng, M J, Greenway, M, Marshall, J C, McGregor, G B, Tyler, J J and McNeil, V. 2016. Carbon isotope discrimination in leaves of the broad–leaved paperbark tree, Melaleuca quinquenervia, as a tool for quantifying past tropical and subtropical rainfall. Glob Change Biol. doi:10.1111/gcb.13277

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April 2016: Biogeosciences

Biogeosciences

The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large–scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial–interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before ~320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe /Ca ratios in the sediments. While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high– to low–coercivity iron oxides. Glacial sediments are characterized by high concentration of high–coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial–interglacial behaviour are millennial–scale oscillations in the magnetic mineralcomposition that parallel variations in summer insolation. Like the processes on glacial–interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock–magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi–level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra–lake processes.

Just, J, Nowaczyk, N R, Sagnotti, L, Francke, A, Vogel, H, Lacey, J H, and Wagner, B. 2016. Environmental control on the occurrence of high–coercivity magnetic minerals and formation of iron sulphides in a 640 ka sediment sequence from Lake Ohrid (Balkans). Biogeosciences 13, 2093–2109.

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April 2016: PNAS

Explanations of the glacial–interglacial variations in atmospheric pCO2 invoke a significant role for the deep ocean in the storage of CO2. Deep-ocean density stratification has been proposed as a mechanism to promote the storage of CO2 in the deep ocean during glacial times. A wealth of proxy data supports the presence of a "chemical divide" between intermediate and deep water in the glacial Atlantic Ocean, which indirectly points to an increase in deep–ocean density stratification. However, direct observational evidence of changes in the primary controls of ocean density stratification, i.e., temperature and salinity, remain scarce. Here, we use Mg/Ca–derived seawater temperature and salinity estimates determined from temperature–corrected δ18O measurements on the benthic foraminifer Uvigerina spp. from deep and intermediate water–depth marine sediment cores to reconstruct the changes in density of sub–Antarctic South Atlantic water masses over the last deglaciation (i.e., 22–C2 ka before present). We find that a major breakdown in the physical density stratification significantly lags the breakdown of the deep–intermediate chemical divide, as indicated by the chemical tracers of benthic foraminifer δ13C and foraminifer/coral 14C. Our results indicate that chemical destratification likely resulted in the first rise in atmospheric pCO2, whereas the density destratification of the deep South Atlantic lags the second rise in atmospheric pCO2 during the late deglacial period. Our findings emphasize that the physical and chemical destratification of the ocean are not as tightly coupled as generally assumed.

Roberts, J, Gottschalk, J, Skinner, L C, Peck, V L, Kender, S, Elderfield, H, Waelbroeck, C, Vázquez Riveiros, N, and Hodell, D A. 2016. Evolution of South Atlantic density and chemical stratification across the last deglaciation. Proceedings of the National Academy of Science of the United States, 113(3), 514–519.

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March 2016: Palaeogeography, Palaeoclimatology, Palaeoecology

Palaeogeography, Palaeoclimatology, Palaeoecology

Understanding the transformations of the climate system may help to predict and reduce the effects of global climate change. The geological record provides a unique archive that documents the long–term fluctuations of environmental variables, such as seasonal change. Here, we investigate how seasonal variation in seawater temperatures varied in the Mediterranean Sea during the early Pleistocene, approaching the Early–Middle Pleistocene Transition (EMPT) and the beginning of precession–driven Quaternary–style glacial–interglacial cycles. We performed whole–shell and sclerochemical stable isotope analyses (δ18O, δ13C) on bivalves, collected from the lower Pleistocene Arda River marine succession (northern Italy), after checking shell preservation. Our results indicate that seawater temperature seasonality was the main variable of climate change in the Mediterranean area during the early Pleistocene, with the Northern Hemisphere Glaciation (NHG) exerting a control on the Mediterranean climate. We show that strong seasonality (14.4–C16.0 °C range) and low winter paleotemperatures (0.8–C1.6 °C) were likely the triggers leading to the establishment of widespread populations of so called "northern guests" (i.e., cold water taxa) in the Mediterranean Sea around 1.80 Ma. The shells postdating the arrival of the "northern guests" record a return to lower seasonal variations and higher seawater paleotemperatures, with seasonality increasing again approaching the EMPT; the latter, however, is not associated with a corresponding cooling of mean seawater paleotemperatures, showing that the observed seasonality variation represents a clear signal of progressive climate change in the Mediterranean Sea.

Crippa, G, Angiolini, L, Bottini, C, Erba, E, Felletti, F, Frigerio, C, Hennissen, J A I, Leng, M J, Petrizzo, M R, Raffi, I, Raineri, G, Stephenson, M H. 2016. Seasonality fluctuations recorded in fossil bivalves during the early Pleistocene: Implications for climate change. Palaeogeography, Palaeoclimatology, Palaeoecology, 446, 234–251.

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March 2016: Geochimica et Cosmochimica Acta

Geochimica et Cosmochimica Acta

The carbonate clumped isotope thermometer is a promising tool for determining past ocean temperatures. It is based on the temperature dependence of rare isotopes 'clumping' into the same carbonate ion group in the carbonate mineral lattice. The extent of this clumping effect is independent of the isotope composition of the water from which carbonate precipitates, providing unique advantages over many other paleotemperature proxies. Existing calibrations of this thermometer in cold–water and warm–water corals suggest clumped isotope 'vital effects' are negligible in cold–water corals but may be significant in warm–water corals. Here, we test the calibration of the carbonate clumped isotope thermometer in cold–water corals with a recently collected and well characterised sample set spanning a range of coral genera (Balanophyllia, Caryophyllia, Dasmosmilia, Desmophyllum, Enallopsammia and Javania). The clumped isotope compositions (Δ47) of these corals exhibit systematic dependences on their growth temperatures, confirming the basis of the carbonate clumped isotope thermometer. However, some cold–water coral genera show Δ47 values that are higher than the expected equilibrium values by up to 0.05‰ (equivalent to underestimating temperature by ~9 °C) similar to previous findings for some warm–water corals. This finding suggests that the vital effects affecting corals Δ47 are common to both warm– and cold–water corals. By comparison with models of the coral calcification process we suggest that the clumped isotope offsets in these genera are related to the kinetic isotope effects associated with CO2hydration/hydroxylation reactions in the corals' calcifying fluid. Our findings complicate the use of the carbonate clumped isotope thermometer in corals, but suggest that species– or genus-specific calibrations could be useful for the future application of this paleotemperature proxy.

Spooner, P T, Guo, W, Robinson, L F, Thiagarajan, N, Hendry, K R, Rosenheim, B E, Leng, M J. 2016. Clumped isotope composition of cold–water corals: A role for vital effects? Geochimica et Cosmochimica Acta, 179, 123–141.

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March 2016: Biogeosciences

Biogeosciences

Lake Ohrid (Macedonia/Albania) is an ancient lake with unique biodiversity and a site of global significance for investigating the influence of climate, geological, and tectonic events on the generation of endemic populations. Here, we present oxygen (δ18O) and carbon (δ13C) isotope data from carbonate over the upper 243 m of a composite core profile recovered as part of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project. The investigated sediment succession covers the past ca. 637 ka. Previous studies on short cores from the lake (up to 15 m, < 140 ka) have indicated the total inorganic carbon (TIC) content of sediments to be highly sensitive to climate change over the last glacial–interglacial cycle. Sediments corresponding to warmer periods contain abundant endogenic calcite; however, an overall low TIC content in glacial sediments is punctuated by discrete bands of early diagenetic authigenic siderite. Isotope measurements on endogenic calcite (δ18Oc and δ13Cc) reveal variations both between and within interglacials that suggest the lake has been subject to palaeoenvironmental change on orbital and millennial timescales. We also measured isotope ratios from authigenic siderite (δ18Os and δ13Cs) and, with the oxygen isotope composition of calcite and siderite, reconstruct δ18O of lake water (δ18Olw) over the last 637 ka. Interglacials have higher δ18Olw values when compared to glacial periods most likely due to changes in evaporation, summer temperature, the proportion of winter precipitation (snowfall), and inflow from adjacent Lake Prespa. The isotope stratigraphy suggests Lake Ohrid experienced a period of general stability from marine isotope stage (MIS) 15 to MIS 13, highlighting MIS 14 as a particularly warm glacial. Climate conditions became progressively wetter during MIS 11 and MIS 9. Interglacial periods after MIS 9 are characterised by increasingly evaporated and drier conditions through MIS 7, MIS 5, and the Holocene. Our results provide new evidence for long–term climate change in the northern Mediterranean region, which will form the basis to better understand the influence of major environmental events on biological evolution within Lake Ohrid

Lacey, J H, Leng, M J, Francke, A, Sloane, H J, Milodowski, A, Vogel, H, Baumgarten, H, Zanchetta, G, Wagner, B. 2016. Northern Mediterranean climate since the Middle Pleistocene: a 637 ka stable isotope record from Lake Ohrid (Albania/Macedonia). Biogeosciences, 13, 1801–1820.

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March 2016: Journal of Geophysical Research Biogeosciences

Journal of Geophysical Research Biogeosciences

The stable carbon isotopic composition of dissolved organic matter (δ13C–DOC) reveals information about its source and extent of biological processing. Here we report the lowest δ13C–DOC values (–43.8‰) measured to date in surface waters. The streams were located in the High Arctic, a region currently experiencing rapid changes in climate and carbon cycling. Based on the widespread occurrence of methane cycling in permafrost regions and the detection of the pmoA gene, a proxy for aerobic methanotrophs we conclude that the low δ13C–DOC values are due to organic matter partially derived from methanotrophs consuming biologically produced, 13C–depleted methane. These findings demonstrate the significant impact that biological activity has on the stream water chemistry exported from permafrost and glaciated environments in the Arctic. Given that the catchments studied here are representative of larger areas of the Arctic, occurrences of low δ13C–DOC values may be more widespread than previously recognized, with implications for understanding C cycling in these environments.

Hindshaw, R S, Lang, S Q, Bernasconi, S M, Heaton, T H E, Lindsay, M R, Boyd, E S. 2016. Origin and temporal variability of unusually low δ13C–DOC values in two high Arctic catchments, Journal of Geophysical Research Biogeosciences, 121, doi:10.1002/2015JG003303.

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March 2016: MEPS

Biogeosciences

Scientific information about European sea bass Dicentrarchus labrax stocks in the NE Atlantic is limited and a more accurate definition of the stock boundaries in the area is required to improve assessment and management advice. We investigated the connectivity and movement patterns of D. labrax in Wales (UK) using the stable isotope (δ13C and δ15N) composition of their scales. Analysis of δ13C and δ15N values in the last growing season was performed on 189 adult sea bass caught at 9 coastal feeding grounds. Fish >50 cm total length (TL) caught in estuaries had very low δ13C, which is characteristic of freshwater (organic/soil) input, indicating the primary use of estuaries as feeding areas. A random forest classification model was used to test for any differences in δ15N and δ13C values between north, mid and south Wales and whether it was possible to correctly assign a fish to the area where it was caught. This analysis was restricted to fish of a similar size (40–50 cm TL) caught in open coastal areas (n = 156). The classification model showed that about 75% of the fish could be correctly assigned to their collection region based on their isotope composition. The majority of the misclassifications of fish were of fish from north Wales classifying to mid Wales and vice versa, while the majority of fish from south Wales were correctly assigned (80%). Our findings suggest that 2 sub–populations of sea bass in Welsh waters use separate feeding grounds (south vs. mid/north Wales), and may need separate management.

Cambiè, G, Kaiser, M J, Marriott, A L, Fox, J, Lambert, G, Hiddink, J G, Overy, T, Bennet, S A, Leng, M J, McCarthy, I D. 2016. Stable isotope signatures reveal small–scale spatial separation in populations of European sea bass. Marine Ecology Progress Series, 546, 213–223.

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March 2016: Biogeosciences

Biogeosciences

Lake Ohrid (Macedonia and Albania) is a rare example of a deep, ancient Mediterranean lake and is a key site for palaeoclimate research in the northeastern Mediterranean region. This study conducts the analysis of diatoms as a proxy for Lateglacial and Holocene climate and environmental change in Lake Ohrid at a higher resolution than in previous studies. While Lake Ohrid has the potential to be sensitive to water temperature change, the data demonstrate a highly complex diatom response, probably comprising a direct response to temperature–induced lake productivity in some phases and an indirect response to temperature–related lake stratification or mixing and epilimnetic nutrient availability in others. The data also demonstrate the possible influence of physical limnological (e.g. the influence of wind stress on stratification or mixing) and chemical processes (e.g. the influence of catchment dynamics on nutrient input) in mediating the complex response of diatoms. During the Lateglacial (ca. 12 300–11 800 cal yr BP), the low–diversity dominance of hypolimnetic Cyclotella fottii indicates low lake productivity, linked to low water temperature. Although the subsequent slight increase in small, epilimnetic C. minuscula during the earliest Holocene (ca. 11 800–10 600 cal yr BP) suggests climate warming and enhanced stratification, diatom concentration remains as low as during the Lateglacial, suggesting that water temperature increase was muted across this major transition. The early Holocene (ca. 10 600–8200 cal yr BP) is characterised by a sustained increase in epilimnetic taxa, with mesotrophic C. ocellata indicating high water-temperature-induced productivity between ca. 10 600–10 200 cal yr BP and between ca. 9500–8200 cal yr BP and with C. minuscula in response to low nutrient availability in the epilimnion between ca. 10 200–9500 cal yr BP. During the middle Holocene (ca. 8200–2600 cal yr BP), when sedimentological and geochemical proxies provide evidence for maximum Holocene water temperature, anomalously low C. ocellata abundance is probably a response to epilimnetic nutrient limitation, almost mimicking the Lateglacial flora apart from the occurrence of mesotrophic Stephanodiscus transylvanicus in the hypolimnion. During the late Holocene (ca. 2600 cal yr BP–present), high abundance and fluctuating composition of epilimnetic taxa are probably a response more to enhanced anthropogenic nutrient input, particularly nitrogen enrichment, than to climate. Overall, the data indicate that previous assumptions concerning the linearity of diatom response in this deep, ancient lake are invalid, and multi–proxy analysis is essential to improve understanding of palaeolimnological dynamics in future research on the long, Quaternary sequence.

Zhang, X S, Reed, J M, Lacey, J H, Francke, A, Leng, M J, Levkov, Z, and Wagner, B: Complexity of diatom response to Lateglacial and Holocene climate and environmental change in ancient, deep and oligotrophic Lake Ohrid (Macedonia and Albania), Biogeosciences, 13, 1351–1365, doi:10.5194/bg–13–1351–2016, 2016.

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March 2016: Chemical Geology

Chemical Geology

In order to investigate the effect of glaciation on mineral weathering, the stream water chemistry and the bacterial community composition were analysed in two catchments containing nominally identical sedimentary formations but which differed in the extent of glaciation. The stream waters were analysed for major ions, δ34S, δ18OSO4 and δ18OH2O and associated stream sediments were analysed by 16S rRNA gene tagged sequencing. Sulphate comprised 72–86% and 35–45% of the summer anion budget (in meq) in the unglaciated and glaciated catchments respectively. This indicates that sulfuric acid generated from pyrite weathering is a significant weathering agent in both catchments. Based on the relative proportions of cations, sulphate and bicarbonate, the stream water chemistry of the unglaciated catchment was found to be consistent with a sulphide oxidation coupled to silicate dissolution weathering process whereas in the glaciated catchment both carbonates and silicates weathered via both sulfuric and carbonic acids. Stable isotope measurements of sulphate, together with inferences of metabolic processes catalysed by resident microbial communities, revealed that the pyrite oxidation reaction differed between the two catchments. No δ34S fractionation relative to pyrite was observed in the unglaciated catchment and this was interpreted to reflect pyrite oxidation under oxic conditions. In contrast, δ34S and δ18OSO4 values were positively correlated in the glaciated catchment and were positively offset from pyrite. This was interpreted to reflect pyrite oxidation under anoxic conditions with loss of S intermediates. This study suggests that glaciation may alter stream water chemistry and the mechanism of pyrite oxidation through an interplay of biological, physical and chemical factors.

Hindshaw, R S, Heaton, T H E, Boy, E S, Lindsay, M R, Tipper, E T. 2016. Influence of glaciation on mechanisms of mineral weathering in two high Arctic catchments. Chemical Geology, 420, 37–50.

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Febuary 2016: Biogeosciences

Biogeosciences

Lake Ohrid (Macedonia, Albania) is thought to be more than 1.2 million years old and host more than 300 endemic species. As a target of the International Continental scientific Drilling Program (ICDP), a successful deep drilling campaign was carried out within the scope of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project in 2013. Here, we present lithological, sedimentological, and (bio-)geochemical data from the upper 247.8 m composite depth of the overall 569 m long DEEP site sediment succession from the central part of the lake. According to an age model, which is based on 11 tephra layers (first–order tie points) and on tuning of bio–geochemical proxy data to orbital parameters (second–order tie points), the analyzed sediment sequence covers the last 637 kyr. The DEEP site sediment succession consists of hemipelagic sediments, which are interspersed by several tephra layers and infrequent, thin (< 5 cm) mass wasting deposits. The hemipelagic sediments can be classified into three different lithotypes. Lithotype 1 and 2 deposits comprise calcareous and slightly calcareous silty clay and are predominantly attributed to interglacial periods with high primary productivity in the lake during summer and reduced mixing during winter. The data suggest that high ion and nutrient concentrations in the lake water promoted calcite precipitation and diatom growth in the epilimnion during MIS15, 13, and 5. Following a strong primary productivity, highest interglacial temperatures can be reported for marine isotope stages (MIS) 11 and 5, whereas MIS15, 13, 9, and 7 were comparably cooler. Lithotype 3 deposits consist of clastic, silty clayey material and predominantly represent glacial periods with low primary productivity during summer and longer and intensified mixing during winter. The data imply that the most severe glacial conditions at Lake Ohrid persisted during MIS16, 12, 10, and 6, whereas somewhat warmer temperatures can be inferred for MIS14, 8, 4, and 2. Interglacial–like conditions occurred during parts of MIS14 and 8.

Francke, A, Wagner, B, Just, J, Leicher, N, Gromig, R, Baumgarten, H, Vogel, H, Lacey, J H, Sadori, L, Wonik, T, Leng, M J, Zanchetta, G, Sulpizio, R, and Giacco, B. 2016. Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present. Biogeosciences, 13, 1179–1196.

February 2016: Climate Dynamics

Understanding the modern day relationship between climate and the oxygen isotopic composition of precipitation (δ118OP) is crucial for obtaining rigorous palaeoclimate reconstructions from a variety of archives. To date, the majority of empirical studies into the meteorological controls over δ118OP rely upon daily, event scale, or monthly time series from individual locations, resulting in uncertainties concerning the representativeness of statistical models and the mechanisms behind those relationships. Here, we take an alternative approach by analysing daily patterns in δ118OP from multiple stations across the British Isles (n = 10–70 stations). We use these data to examine the spatial and seasonal heterogeneity of regression statistics between δ118OP and common predictors (temperature, precipitation amount and the North Atlantic Oscillation index; NAO). Temperature and NAO are poor predictors of daily δ118OP in the British Isles, exhibiting weak and/or inconsistent effects both spatially and between seasons. By contrast δ118OP and rainfall amount consistently correlate at most locations, and for all months analysed, with spatial and temporal variability in the regression coefficients. The maps also allow comparison with daily synoptic weather types, and suggest characteristic δ118OP patterns, particularly associated with Cylonic Lamb Weather Types. Mapping daily δ18OP across the British Isles therefore provides a more coherent picture of the patterns in δ118OP, which will ultimately lead to a better understanding of the climatic controls. These observations are another step forward towards developing a more detailed, mechanistic framework for interpreting stable isotopes in rainfall as a palaeoclimate and hydrological tracer.

Tyler, J J, Jones, M, Arrowsmith, C, Allott, T, Leng, M J. 2016. Spatial patterns in the oxygen isotope composition of daily rainfall in the British Isles. Climate Dynamics, 47(5), 1971–1987.

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January 2016: Journal of Palaeolimnology

We present new stable isotope (δ18Ocalcite and δ113Ccalcite) and diatom data from a 67–m sediment core (BAN II) from Lake Banyoles, northeastern Spain. We reassessed the chronology of the sequence by correlating stable isotope data with a shorter U–series–dated record from the lake, confirming a sedimentological offset between the two cores and demonstrating that BAN II spans Marine Isotope Stages (MIS) 3–1. Through comparison with previous records, the multi–proxy data are used to improve understanding of palaeolimnological dynamics and, by inference, western Mediterranean climate and environmental change during the past ca. 50,000 years. Three main zones, defined by isotope and diatom data, correspond to the MIS. The basal zone (MIS 3) is characterised by fluctuating δ118Ocalcite and benthic diatom abundance, indicating a high degree of environmental and climate variability, concomitant with large lake–level changes. During the full glacial (MIS 2), relatively constant δ118Ocalcite and a poorly preserved planktonic–dominated diatom assemblage suggest stability, and intermittently, unusually high lake level. In MIS 1, δ118Ocalcite and δ113Ccalcite initially transition to lower values, recording a pattern of Late Glacial to Holocene change that is similar to other Mediterranean records. This study suggests that Lake Banyoles responds limnologically to changes in the North Atlantic ocean–atmosphere system and provides an important dataset from the Iberian Peninsula, a region in need of longer-term records that can be used to correlate between marine and terrestrial archives, and between the western and eastern Mediterranean.

Lacey, J H, Leng, M J, Hobig, N, Reed, J M, Valero–Garces, B, Reicherter, K. 2016. Western Mediterranean climate and environment since Marine Isotope Stage 3: a 50,000–year record from Lake Banyoles, Spain. Journal of Paleolimnology, 55, 113–128.

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January 2016: Biogeosciences

Biogeosciences Discussions

The first δ30Sidiatom data from lacustrine sediment traps are presented from Lake Baikal, Siberia. Data are compared with March surface water (upper 180 m) δ30SiDSi compositions for which a mean value of +2.28‰ ± 0.09 (95 % confidence) is derived. This value acts as the pre–diatom bloom baseline silicic acid isotopic composition of waters (δ30SiDSi initial). Open traps were deployed along the depth of the Lake Baikal south basin water column between 2012 and 2013. Diatom assemblages display a dominance (> 85 %) of the spring/summer bloom species Synedra acus var radians, so that δ30Sidiatom compositions reflect predominantly spring/summer bloom utilisation. Diatoms were isolated from open traps and, in addition, from 3–monthly (sequencing) traps (May, July and August 2012) for δ30Sidiatom analyses. Mean δ30Sidiatom values for open traps are +1.23‰ ± 0.06 (at 95 % confidence and MSWD of 2.9, n = 10). Total dry mass sediment fluxes are highest in June 2012, which we attribute to the initial export of the dominant spring diatom bloom. We therefore argue that May δ30Sidiatom signatures (+0.67‰± 0.06, 2σ) when compared with mean upper water δ30SiDSi initial (e.g. pre-bloom) signatures can be used to provide a snapshot estimation of diatom uptake fractionation factors (ϵuptake) in Lake Baikal. A ϵuptake estimation of –1.61 ‰ is therefore derived, although we emphasise that synchronous monthly δ30SiDSi and δ30Sidiatom data would be needed to provide more robust estimations and therefore more rigorously test this, particularly when taking into consideration any progressive enrichment of the DSi pool as blooms persist. The near–constant δ30Sidiatom composition in open traps demonstrates the full preservation of the signal through the water column and thereby justifies the use and application of the technique in biogeochemical and palaeoenvironmental research. Data are finally compared with lake sediment core samples, collected from the south basin. Values of +1.30‰ ± 0.08 (2σ) and +1.43‰ ± 0.13 (2σ) were derived for cores BAIK13–1C (0.6–0.8 cm core depth) and at BAIK13–4F (0.2–0.4 cm core depth) respectively. Trap data highlight the absence of a fractionation factor associated with diatom dissolution (ϵdissolution) (particularly as Synedra acus var radians, the dominant taxa in the traps, is very susceptible to dissolution) down the water column and in the lake surface sediments, thus validating the application of δ30Sidiatom analyses in Lake Baikal and other freshwater systems, in palaeoreconstructions.

Panizzo, V N, Swann, G E A, Mackay, A W, Vologina, E, Sturm, M, Pashley, V, Horstwood, M S A. 2016. Insights into the transfer of silicon isotopes into the sediment record. Biogeosciences, 13 (1). pp. 147–157.

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January 2016: Review of Palaeobotany and Palynology

Review of Palaeobotany and Palynology

Carboniferous mudstones in central and northern England are shale gas prospects but the controls on the amount and composition of organic matter are not well understood, even though these parameters define the volumes of gas generated in fine–grained sediments. Organic matter in samples from basinal late Mississippian (Arnsbergian) mudstones in the Widmerpool Gulf was characterised by using semi–quantitative (n = 58) and quantitative palynofacies (n = 16) analyses, sporomorph counts and bulk rock geochemistry (total organic carbon, δ13C of bulk organic matter, Rock–Eval Pyrolysis). The results of this study suggest that most organic matter at this location was delivered to the sediment–water interface as aggregates of a granular translucent type of amorphous organic matter (AOMGr, mean 66.7±19.3%) via hemipelagic suspension settling. AOMGr represents fragments of algal material with subordinate inclusions of small plant fragments and pyrite framboids held together by microbial colonies. AOMBr (brown granular amorphous organic matter) is the second most abundant group (mean 15.6±8.5%) comprising similar microbial colonies that grew on suspended land plant–derived fragments in the water column. Palynofacies components representing clearly terrestrial organic matter are much less abundant and include gelified organic matter (G, mean 9.6±12.6%), black phytoclasts (PhBl mean 2.7±4.7%), brown phytoclasts (PhBr, mean 3.3±3.6%) and sporomorphs (mean 1.4±1.3%). Sediment delivery processes influence the balance between terrestrial organic matter and AOMGr. During low sea–level times, turbidity currents and debris flows delivered terrestrial organic matter (representing 12 to 40% of the palynofacies). Kerogen composition varies between Type II and III. In contrast, thin–bedded carbonate–bearing mudstones deposited during rising and high sea–level contain up to 95% AOMGr and these high abundances correspond to higher total organic carbon. Carbonate and AOMGr were generated by high bioproductivity in the water column. Type II (oil– and gas–prone) kerogens are dominant in these mudstones and therefore these intervals represent the best potential targets for thermogenic shale gas.

Koenitzer, S F, Stephenson, M H, Davies, S J, Vane, C H, Leng, M J. 2016. Significance of sedimentary organic matter input for shale gas generation potential of Mississippian mudstones, Widmerpool Gulf, UK. Review of Palaeobotany and Palynology, 224(2), 146–168.

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January 2016: Environmental Archaeology

Mummies are faunal remains that include the preservation of soft tissues, such as skin, muscle, nails and hair as well as bone. These soft tissues are generally rich in collagen or keratin proteins and thus provide potentially suitable material for stable isotope studies. When preserved, such tissues can provide high–resolution information about the diet and migration of humans in the weeks and months before death. Hair, nails and soft tissue provide short–term (months) dietary information in contrast to bone which will represent 5–20 years of dietary history prior to death, depending on the bone analysed. Such high–resolution data can answer questions on the season of death, seasonality of food resources and the movement and relocation of people. This review begins with a summary of the most common isotope techniques (13C/12C, 15N/14N) and the tissues concerned, followed by an analysis of the key questions that have been addressed using these methods. Until relatively recently work has focused on bulk protein isotope analysis, but in the last 10 years this has been expanded to on-line compound-specific amino acid analysis and to a wider variety of isotopes (18O/16O, 2H/1H and 34S/32S) and these applications are also discussed.

Lamb, A L. 2016. Stable isotope analysis of soft tissues from mummified human remains. Environmental Archaeology, 21(3).

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January 2016: Quaternary Science Reviews

Quaternary Science Reviews

With the substantial number of lake sediment δ18O records published in recent decades, a quantitative, process-based understanding of these systems can increase our understanding of past climate change. We test mass balance models of lake water δ18O variability against five years of monthly monitoring data from lakes with different hydrological characteristics, in the East-Midlands region of the UK, and the local isotope composition of precipitation. These mass balance models can explain up to 74% of the measured lake water isotope variability. We investigate the sensitivity of the model to differing calculations of evaporation amount, the amount of groundwater, and to different climatic variables. We show there is only a small range of values for groundwater exchange flux that can produce suitable lake water isotope compositions and that variations in evaporation and precipitation are both required to produce recorded isotope variability in lakes with substantial evaporative water losses. We then discuss the potential for this model to be used in a long-term, palaeo-scenario. This study demonstrates how long term monitoring of a lake system can lead to the development of robust models of lake water isotope compositions. Such systematics-based explanations allow us to move from conceptual, to more quantified reconstructions of past climates and environments.

Jones, M D, Cuthbert, M O, Leng, M J, McGowan, S, Mariethoz, G, Arrowsmith, C, Sloane, H J, Humphrey, K K, Cross, I. 2016. Comparisons of observed and modelled lake δ18O variability. Quaternary Science Reviews, 131B, 329–340.

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January 2016: Rapid Communications in Mass Spectrometry

Rapid Communications in Mass Spectrometry

Current studies which use the oxygen isotope composition from diatom silica (δ18Odiatom) as a palaeoclimate proxy assume that the δ18Odiatom value reflects the isotopic composition of the water in which the diatom formed. However, diatoms dissolve post mortem, preferentially losing less silicified structures in the water column and during/after burial into sediments. The impact of dissolution on δ18Odiatom values and potential misinterpretation of the palaeoclimate record are evaluated. Diatom frustules covering a range of ages (6 samples from the Miocene to the Holocene), environments and species were exposed to a weak alkaline solution for 48 days at two temperatures (20°C and 4°C), mimicking natural dissolution post mucilage removal. Following treatment, dissolution was assessed using scanning electron microscope images and a qualitative diatom dissolution index. The diatoms were subsequently analysed for their δ18O values using step-wise fluorination and isotope ratio mass spectrometry. Variable levels of diatom dissolution were observed between the six samples; in all cases higher temperatures resulted in more frustule degradation. Dissolution was most evident in younger samples, probably as a result of the more porous nature of the silica. The degree of diatom dissolution does not directly equate to changes in the isotope ratios; the δ18Odiatom value was, however, lower after dissolution, but in only half the samples was this reduction outside the analytical error (2σ analytical error = 0.46‰). We have shown that dissolution can have a small negative impact on δ18Odiatom values, causing reductions of up to 0.59‰ beyond analytical error (0.46‰) at natural environmental temperatures. These findings need to be considered in palaeoenvironmental reconstructions using δ18Odiatom values, especially when interpreting variations in these values of <1‰.

Smith, A C, Leng, M J, Swann, G E A, Barker, P A, Mackay, A W, Ryves, D B, Sloane, H J, Chenery, S R N and Hems, M. 2016. An experiment to assess the effects of diatom dissolution on oxygen isotope ratios. Rapid Communications in Mass Spectrometry, 30, 293–300.

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January 2016: Water Research

Water Research

Eutrophication is a globally significant challenge facing aquatic ecosystems, associated with human induced enrichment of these ecosystems with nitrogen (N) and phosphorus (P). However, the limited availability of inherent labels for P and N has constrained understanding of the triggers for eutrophication in natural ecosystems and appropriate targeting of management responses. This paper proposes and evaluates a new multi-stable isotope framework that offers inherent labels to track biogeochemical reactions governing both P and N in natural ecosystems. The framework couples highly novel analysis of the oxygen isotope composition of phosphate (δ18OPO4) with dual isotope analysis of oxygen and N within nitrate (δ15NNO3, δ18ONO3) and with stable N isotope analysis in ammonium (δ15NNH4). The River Beult in England is used as an exemplar system for initial evaluation of this framework. Our data demonstrate the potential to use stable isotope labels to track the input and downstream fate of nutrients from point sources, on the basis of isotopic differentiation for both P and N between river water and waste water treatment work effluent (mean difference = +1.7‰ for δ18OPO4; +15.5‰ for δ15NNH4 (under high flow); +7.3‰ for δ18ONO3 and +4.4‰ for δ15NNO3). Stable isotope data reveal nutrient inputs to the river upstream of the waste water treatment works that are consistent with partially denitrified sewage or livestock sources of nitrate (δ15NNO3 range = +11.5 to +13.1‰) and with agricultural sources of phosphate (δ1OPO4 range = +16.6 to +19.0‰). The importance of abiotic and metabolic processes for the in-river fate of N and P are also explored through the stable isotope framework. Microbial uptake of ammonium to meet metabolic demand for N is suggested by substantial enrichment of δ15NNH4 (by 10.2‰ over a 100 m reach) under summer low flow conditions. Whilst the concentration of both nitrate and phosphate decreased substantially along the same reach, the stable isotope composition of these ions did not vary significantly, indicating that concentration changes are likely driven by abiotic processes of dilution or sorption. The in-river stable isotope composition and the concentration of P and N were also largely constant downstream of the waste water treatment works, indicating that effluent-derived nutrients were not strongly coupled to metabolism along this in-river transect. Combined with in-situ and laboratory hydrochemical data, we believe that a multi-stable isotope framework represents a powerful approach for understanding and managing eutrophication in natural aquatic ecosystems.

Gooddy, D C, Lapworth,D J, Sarah ,A, Bennett, Heaton, T H E, Williams, Peter J, Surridge, B W J. 2016. A multi-stable isotope framework to understand eutrophication in aquatic ecosystems. Water Research, 88, 623–633.

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Contact Béatrice Bullock-von Moos for further information about the Stable isotope facility.