On Quaternary time scales, the global biogeochemical cycle of silicon is interlocked with the carbon cycle through biotic enhancement of silicate weathering and uptake of dissolved silica by vascular plants and aquatic microalgae (notably diatoms, for which Si is an essential nutrient). Large tropical river systems dominate the export of Si from the continents to the oceans. Here, we investigate variations in Si cycling in the upper White Nile basin over the last 15 ka, using sediment cores from Lakes Victoria and Edward. Coupled measurements of stable O and Si isotopes on diatom separates were used to reconstruct past changes in lake hydrology and Si cycling, while the abundances of lipid biomarkers characteristic of terrestrial/emergent higher plants, submerged/floating aquatic macrophytes and freshwater algae document past ecosystem changes. During the late-glacial to mid-Holocene, 15–5.5 ka BP, orbital forcing greatly enhanced monsoon rainfall, forest cover and chemical weathering. Riverine inputs of dissolved silica from the lake catchments exceeded aquatic demand and may also have had lower Si-isotope values. Since 5.5 ka BP, increasingly dry climates and more open vegetation, reinforced by the spread of agricultural cropland over the last 3–4 ka, have reduced dissolved silica inputs into the lakes. Centennial-to millennial-scale dry episodes are also evident in the isotopic records and merit further investigation.
Cockerton, Helen E, Street-Perrott, F Alayne, Barker, Philip A, Leng, Melanie J, Sloane, Hilary J and Ficken, Katherine J. 2015. Orbital forcing of glacial/interglacial variations in chemical weathering and silicon cycling within the upper White Nile basin, East Africa: Stable-isotope and biomarker evidence from Lakes Victoria and Edward. Quaternary Science Reviews, 130, 57–71.
This study examines the role of tree canopies in processing atmospheric nitrogen (Ndep ) for four forests in the United Kingdom subjected to different Ndep: Scots pine and beech stands under high Ndep (HN, 13–19 kg N ha(–1) yr(–1) ), compared to Scots pine and beech stands under low Ndep (LN, 9 kg N ha(–1) yr(–1) ). Changes of NO3 –N and NH4 –N concentrations in rainfall (RF) and throughfall (TF) together with a quadruple isotope approach, which combines δ(18) O, Δ(17) O and δ(15) N in NO3 (–) and δ(15) N in NH4 (+) , were used to assess N transformations by the canopies. Generally, HN sites showed higher NH4 –N and NO3 –N concentrations in RF compared to the LN sites. Similar values of δ(15) N–NO3 (–) and δ(18) O in RF suggested similar source of atmospheric NO3 (–) (i.e. local traffic), while more positive values for δ(15) N–NH4 (+) at HN compared to LN likely reflected the contribution of dry NHx deposition from intensive local farming. The isotopic signatures of the N-forms changed after interacting with tree canopies. Indeed, (15) N–enriched NH4 (+) in TF compared to RF at all sites suggested that canopies played an important role in buffering dry Ndep also at the low Ndep site. Using two independent methods, based on δ(18) O and Δ(17) O, we quantified for the first time the proportion of NO3 (–) in TF, which derived from nitrification occurring in tree canopies at the HN site. Specifically, for Scots pine, all the considered isotope approaches detected biological nitrification. By contrast for the beech, only using the mixing model with Δ(17) O, we were able to depict the occurrence of nitrification within canopies. Our study suggests that tree canopies play an active role in the N cycling within forest ecosystems. Processing of Ndep within canopies should not be neglected and needs further exploration, with the combination of multiple isotope tracers, with particular reference to Δ(17) O.
Guerrieri, R, Vanguelova, E I, Michalski, G, Heaton, T H, and Mencuccini, M. 2015. Isotopic evidence for the occurrence of biological nitrification and nitrogen deposition processing in forest canopies. Global Change Biology, 21(12), 4613–4626.
A multiproxy record from Lake Parishan, SW Iran, shows human impact on the lake and its catchment over the last 4000 years. The Parishan recordprovides evidence of changes in lake hydrology, from ostracod, diatom and isotope analyses, that are directly linked to human activity in the catchment; recorded by pollen and charcoal and supported by regional archaeological and historical data. The lake ostracod fauna is particularly sensitive to human induced catchment alterations and allows us to identify changes in catchment hydrology that are due to more than a simple change in precipitation: evaporation state. Oxygen isotope data from endogenic carbonates follow these faunal changes but also display a longer trend to more positive values through the period, coincident with regional patterns of water balance for the late Holocene in the eastern Mediterranean.
Jones, M D, Djamali, M, Holmes, J, Weeks, L, Leng, M J, Lashkari, A, Alamdari, K, Noorollahi, D, Thomas, L and Metcalfe, S E. 2015. Human impact on the hydroenvironment of Lake Parishan, SW Iran, through the late Holocene. The Holocene, 25(10), 1651–1661.
The DEEP site sediment sequence obtained during the ICDP SCOPSCO project at Lake Ohrid was dated using tephrostratigraphic information, cyclostratigraphy, and orbital tuning through marine isotope record. Although this approach is suitable for the generation of a general chronological framework of the long succession, it is insufficient to resolve more detailed paleoclimatological questions, such as leads and lags of climate events between marine and terrestrial records or between different regions. In this paper, we demonstrate how the use of different tie points can affect cyclostratigraphy and orbital tuning for the period between ca. 140 and 70 ka and how the results can be correlated with directly/indirectly radiometrically-dated Mediterranean marine and continental proxy records. The alternative age model obtained shows consistent differences with that proposed by Francke et al. (2015) for the same interval, in particular at the level of the MIS6-5e transition. According to this 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 important a detailed study of independent chronological tie points is for synchronizing different records and to highlight asynchronisms of climate events.
Zanchetta, G, Regattieri, E, Giaccio, B, Wagner, B, Sulpizio, R, Francke, A, Vogel, L H, Sadori, L, Masi, A, Sinopoli, G, Lacey, J H, Leng, M L, and Leicher, N.: Aligning MIS5 proxy records from Lake Ohrid (FYROM) with independently dated Mediterranean archives: implications for core chronology, Biogeosciences Discuss., 12, 16979-17007, doi:10.5194/bgd-12-16979-2015, 2015.
Palaeoclimate records from northern Iberia are becoming increasingly sought after as this region is one of the most southerly terrestrial locations in Europe to have its climate dictated principally by the North Atlantic. Terrestrial records therefore have the potential to offer insights into changing oceanic and atmospheric circulation in the wider North Atlantic region. Cave speleothems offer one of the most promising archives from northern Iberia due to their wide geographic distribution and potential for accurately dated climate reconstruction. Cueva de Asiul, situated in Cantabria (N. Iberia; 43° 19' 0.63'' N, 3° 35' 28.32'' W; 285 m.a.s.l) within the Matienzo karst depression is one such site that offers the potential for palaeoclimate reconstructions. Here we present three years of climate and cave monitoring from Cueva de Asiul, giving detailed insight into local meteorology, hydrology and cave ventilation dynamics. In doing so, this paper presents a background to high resolution, Holocene duration speleothem records which have been extracted from this cave. Annual average cave temperatures are +13.7°C, with a maximum range of 1°C, reflecting the seasonality of external air temperature (average external temp +13.8°C). Cave ventilation is controlled by changes in external air temperature and variations in external air pressure during low pressure events. Local rainfall measurements show an average of 1400 mm/year with the majority of rainfall occurring during the winter, with periods of water excess between October and April. Speleothem drip rates are characterised by summer lows and a rapid transition to higher rates at the onset of the winter season. Stable isotope analysis (δ18O, δ2H) indicate that aquifer water is derived predominantly from the previous year’s rainfall and the rainfall feeding the karst system is controlled by a strong amount effect. Speleothems from this site are potentially suited to preserving extended records of rainfall amount in northern Spain and therefore have the potential to inform more clearly about Holocene scale changes in the rainfall source region, the North Atlantic.
Smith, Andrew C, Wynn, Peter M, Barker, Philip A, Leng, Melanie J, Noble, Steve R & Stott, Andrew. (2016) Cave monitoring and the potential for palaeoclimate reconstruction from Cueva de Asiul, Cantabria (N. Spain). International Journal of Speleology, 45(1), 1-9.
A tree ring oxygen isotope (δ18OTR) chronology developed from one species (Cedrela odorata) growing in a single site has been shown to be a sensitive proxy for rainfall over the Amazon Basin, thus allowing reconstructions of precipitation in a region where meteorological records are short and scarce. Although these results suggest there should be large-scale (> 100 km) spatial coherence of δ18OTRrecords in the Amazon, this has not been tested. Furthermore, it is of interest to investigate whether other, possibly longer -lived, species similarly record interannual variation of Amazon precipitation, and can be used to develop climate sensitive isotope chronologies. In this study, we measured δ18O in tree rings from seven lowland and one highland tree species from Bolivia. We found that cross-dating with δ18OTRgave more accurate tree ring dates than using ring width. Our "isotope cross-dating approach" is confirmed with radiocarbon "bomb-peak" dates, and has the potential to greatly facilitate development of δ18OTRrecords in the tropics, identify dating errors, and check annual ring formation in tropical trees. Six of the seven lowland species correlated significantly with C. odorata, showing that variation in δ18OTR has a coherent imprint across very different species, most likely arising from a dominant influence of source water δ18O on δ18OTR. In addition we show that δ18OTR series cohere over large distances, within and between species. Comparison of two C. odorata δ18OTRchronologies from sites several hundreds of kilometres apart showed a very strong correlation (r = 0.80, p< 0.001, 1901–2001), and a significant (but weaker) relationship was found between lowland C. odorata trees and a Polylepis tarapacana tree growing in the distant Altiplano (r = 0.39, p < 0.01, 1931–2001). This large-scale coherence of δ18OTR records is probably triggered by a strong spatial coherence in precipitation δ18O due to large-scale controls. These results highlight the strength of δ18OTRas a precipitation proxy, and open the way for temporal and spatial expansion of precipitation reconstructions in South America.
Baker, J, Hunt, S, Clerici, S, Newton, R, Bottrell, S, Leng, M J, Heaton, T H E, Helle, G, Argollo, J, Gloor, M, and Brienen, R. 2015. Oxygen isotopes in tree rings show good coherence between species and sites in Bolivia. Global and Planetary Change, 133, 298-308.
An early-to mid-Holocene humid phase has been identified in various Arabian geo-archives, although significant regional heterogeneity has been reported in the onset, duration and stability of this period. A multi-proxy lake and dune record from Wahalah in the United Arab Emirates (UAE) documents significant variations in hydrology, biological productivity and landscape stability during the first half of the Holocene. These data reveal that post-Last Glacial Maximum dune emplacement continued into the earliest part of the Holocene, with the onset of permanent lacustrine sedimentation at the site commencing ~8.5 ka cal. BP. A long-term shift towards more arid conditions is inferred between ~7.8 and 5.9 ka cal. BP, with intermittent flooding of the basin and distinct phases of instability throughout the catchment area. This transition is linked to the southwards migration of the Intertropical Convergence Zone (ITCZ) and associated weakening of monsoon rains. A peak in landscape instability is recorded between ~5.9 and 5.3 ka cal. BP and is marked by a pronounced increase in regional dune emplacement. These variations are considered alongside the record of human settlement raising important questions about the interactions between population demographics, climate and environment in southeast Arabia during the Neolithic.
Preston, G , Thomas, D S G, Goudie, A S, Atkinson, O A C, Leng, M J, Hodson, M J, Walkington, H, Charpentier, V, Méry, S, Borgi, F & Parker, A G. 2015. A multi-proxy analysis of the Holocene humid phase from the United Arab Emirates and its implications for southeast Arabia's Neolithic populations. Quaternary International.
The marine gastropod Conomurex fasciatus (Born 1778) is the main component of thousands of shell middens on the Farasan Islands in the southern Red Sea. The middens date from 6500 to 4500 cal BP and cover the period of increased aridification over the region. No general research on C. fasciatus has been carried out before and basic information about the species is mostly speculative. To test if C. fasciatus shells can be used as a recorder of climate variability, we collected living specimens from the Farasan Islands, in Saudi Arabia, over a 1.5 year period. This area receives almost no precipitation and sea surface salinity is extremely high (38–39 psu), and sea surface temperature (SST) ranges from +26.5 °C to +34.9 °C.Raman spectroscopy results on modern C. fasciatus shell samples show these specimens to be aragonitic. Ground fragments from archaeological C. fasciatus shells used for isotope analyses were also measured by Raman spectroscopy and shown to be well preserved against diagenetic alterations leading to aragonite to calcite transformation. Measured shell–edge δ18O values range from –0.5‰ to –1.7‰. Calculated modern shell edge temperatures from these δ18O values correlate with modern SST measured on site with an error of ±2.4 °C. Two different growth rates occurred in the shells of C. fasciatus. The measurement of growth increments in the lip part of adult specimens indicates a tide–related growth rate of ~13 mm/year. Sequential δ18O data from juvenile parts of the shell indicates a faster growth rate of ~90 mm/year. This growth rate and the correlation of δ18O with measured temperatures allows the use of C. fasciatus shell δ18O as a palaeoclimate proxy.
Hausmann, N, Colonese, A C, de Lima Ponzoni, A, Hancock, Y, Meredith–Williams, M, Leng, M J, Bailey, G N. 2015. Isotopic composition of Conomurex fasciatus shells as an environmental proxy for the Red Sea. Quaternary International, 10.1016/j.quaint.2015.08.051.
Solenopora jurassica is a fossil calcareous alga that functioned as an important reef-building organism during the Palaeozoic. It is of significant palaeobiological interest due to its distinctive but poorly understood pink and white banding. Though widely accepted as an alga there is still debate over its taxonomic affinity, with recent work arguing that it should be reclassified as a chaetetid sponge. The banding is thought to be seasonal, but there is no conclusive evidence for this. Other recent work has, however demonstrated the presence of a unique organic boron-containing pink/red pigment in the pink bands of S. jurassica. We present new geochemical evidence concerning the seasonality and pigmentation of S. jurassica. Seasonal growth cycles are demonstrated by X-ray radiography, which shows differences in calcite density, and by varying δ13C composition of the bands. Temperature variation in the bands is difficult to constrain accurately due to conflicting patterns arising from Mg/Ca molar ratios and δ18O data. Fluctuating chlorine levels indicate increased salinity in the white bands, when combined with the isotope data this suggests more suggestive of marine conditions during formation of the white band and a greater freshwater component (lower chlorinity) during pink band precipitation (δ18O). Increased photosynthesis is inferred within the pink bands in comparison to the white, based on δ13C. Pyrolysis Gas Chromatography Mass Spectrometry (Py-GCMS) and Fourier Transform Infrared Spectroscopy (FTIR) show the presence of tetramethyl pyrrole, protein moieties and carboxylic acid groups, suggestive of the presence of the red algal pigment phycoerythrin. This is consistent with the pink colour of S. jurassica. As phycoerythrin is only known to occur in algae and cyanobacteria, and no biomarker evidence of bacteria or sponges was detected we conclude S. jurassica is most likely an alga. Pigment analysis may be a reliable classification method for fossil algae.
Barden, H E, Behnsen, J, Bergmann, U, Leng, M J, Manning, P L, Withers, P, Wogelius, R A, van Dongen, B E. 2015. Geochemical evidence of the seasonality, affinity and pigmentation of Solenopora jurassica. PLOS ONE, DOI: 10.1371/journal.pone.0138305.
Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high-resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, δ13Ccalcite, δ18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, Rock Eval pyrolysis). The data identifies 3 main zones: (1) the Late Glacial–Holocene transition represented by low TIC and TOC contents, (2) the early to mid-Holocene characterised by high TOC and increasing TOC/N and (3) the Late Holocene–Present which shows a marked decrease in TIC and TOC. In general, an overall trend of increasing δ18Ocalcite from 9 ka to present suggests progressive aridification through the Holocene, consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the best-dated and highest resolution archive of past Late Glacial and Holocene climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north-eastern Mediterranean. The data presented set the context for the International Continental scientific Drilling Program Scientific Collaboration On Past Speciation Conditions in Lake Ohrid project cores recovered in spring–summer 2013, potentially dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history.
Lacey, J H, Francke, A, Leng, M J, Vane, C H, and Wagner, B. 2015. A high-resolution Late Glacial to Holocene record of environmental change in the Mediterranean from Lake Ohrid (Macedonia/Albania). International Journal of Earth Sciences, 104(6), 1623-1638.
Palaeo-hydrological interpretations of lake sediment proxies can benefit from a robust understanding of the modern lake environment. In this study, we use Nar Gölü, a non-outlet, monomictic maar lake in central Turkey, as a field site for a natural experiment using observations and measurements over a 17–year monitoring period (1997–2014). We compare lake water and sediment trap data to isotopic, chemical and biotic proxies preserved in its varved sediments. Nar Gölü underwent a 3 m lake–level fall between 2000 and 2010. δ18Olakewater is correlated with this lake–level fall, responding to the change in water balance. Endogenic carbonate is shown to precipitate in isotopic equilibrium with lake water and there is a strong relationship between δ18Olakewater and δ18Ocarbonate, which suggests the water balance signal is accurately recorded in the sediment isotope record. Over the same period, sedimentary diatom assemblages also responded, and conductivity inferred from diatoms showed a rise. Shifts in carbonate mineralogy and elemental chemistry in the sediment record through this decade were also recorded. Intra–annual changes in δ18Olakewater and lake water chemistry are used to demonstrate the seasonal variability of the system and the influence this may have on the interpretation of δ18Ocarbonate. We use these relationships to help interpret the sedimentary record of changing lake hydrology over the last 1725 years. Nar Gölü has provided an opportunity to test critically the chain of connection from present to past, and its sedimentary record offers an archive of decadal– to centennial–scale hydro–climatic change.
Dean, J R, Eastwood, W J, Roberts, N, Jones, M D, Yiğitbaşıoğ lu, H, Allcock, S L, Woodbridge, J, Metcalfe, S E and Leng, M J. 2015. Tracking the hydro–climatic signal from lake to sediment: A field study from central Turkey. Journal of Hydrology, 529(2), 608–621.
Reconstruction of intermediate water properties is important for understanding feedbacks within the ocean-climate system, particularly since these water masses are capable of driving high–low latitude teleconnections. Nevertheless, information about intermediate water mass evolution through the late Pleistocene remains limited. This paper examines changes in Antarctic Intermediate Water (AAIW), the most extensive intermediate water mass in the modern ocean through the last 400 kyr using the stable isotopic composition (δ18O and δ13C) and trace element concentration (Mg/Ca and B/Ca) of two benthic foraminiferal species from the same samples: epifaunal Planulina wuellerstorfi and infaunal Uvigerina peregrina. Our results confirm that the most reasonable estimates of AAIW temperature and Δ[CO2−3] are generated by Mg/CaU. peregrina and B/CaP. wuellerstorfi, respectively. We present a 400 kyr record of intermediate water temperature and Δ[CO2−3] from a sediment core from the Southwest Pacific (DSDP site 593; 40°30′S, 167°41′E, 1068 m water depth), which lies within the core of modern AAIW. Our results suggest that a combination of geochemical analyses on both infaunal and epifaunal benthic foraminiferal species yields important information about this critical water mass through the late Pleistocene. When combined with two nearby records of water properties from deeper depths, our data demonstrate that during interglacial stages of the late Pleistocene, AAIW and Circumpolar Deep Water (CPDW) have more similar water mass properties (temperature and δ13C), while glacial stages are typified by dissimilar properties between AAIW and CPDW in the Southwest Pacific. Our new Δ[CO2−3] record shows short time-scale variations, but a lack of coherent glacial–interglacial variability indicating that large quantities of carbon were not stored in intermediate waters during recent glacial periods.
Elmore, A C, McClymont, E L, Elderfield, H, Kender, S, Cook, M R, Leng, M J, Greaves, M and Misra, S. (2015) Antarctic Intermediate Water properties since 400 ka recorded in infaunal (Uvigerina peregrina) and epifaunal (Planulina wuellerstorfi) benthic foraminifera. Earth and Planetary Science Letters, 428, 193-203.
A multiproxy Lateglacial environmental record is presented for a ca. 3.5-m lacustrine sequence retrieved from a small basin (ca. 2km2) at Thomastown Bog in County Meath, Ireland. Sediment chemistry, pollen, chironomid and stable isotope data provide a detailed picture of catchment and lake system changes from the end of the last glacial (GS-2a) to the early Holocene that correspond closely to existing local and regional models of climate change. Concomitant adjustments in independent proxy records are matched to the NGRIP oxygen isotope curve giving 12 event-episodes ranging from major climatic shifts to lower amplitude, centennial- to sub-centennial-scale adjustments, including a previously unreported regressive period of landscape instability during the north-west European ‘Rammelbeek Phase’. The study emphasizes the potential of palaeoenvironmental reconstruction from sediment chemistry where the sediment mixing system reflects autochthonous versus allochthonous inputs. The investigation also indicates problems of interpreting isotope data derived from bulk marl due to possible lag effects controlling the delivery of soil and groundwater and multiple sources of HCO3– (aq.). These research findings have implications for core site selection and for studies attempting to use stable isotopes for correlation purposes.
Turner, J N, Holmes, N, Davis, S R, Leng, M J, Langdon, C, and Scaife, R G. 2015. A multiproxy (micro-XRF, pollen, chironomid and stable isotope) lake sediment record for the Lateglacial to Holocene transition from Thomastown Bog, Ireland. Journal of Quaternary Science, 30 (6), 514–528.
The extent to which breeding populations of fallow deer were established in Roman Europe has been obscured by the possibility that the skeletal remains of the species, in particular Dama foot bones and antlers, were traded over long distances as objects in their own right. This paper sets out to refine our understanding of the evidence for the transportation of living and dead fallow deer in Iron Age and Roman Europe. To achieve this, museum archives containing purportedly early examples of Dama antler were searched, with available specimens sampled for carbon, nitrogen and strontium isotope analyses, and compared with data for archaeological fallow deer from across Europe. Importantly, the resulting isotope values can be interpreted in light of new modern baseline data for fallow deer presented here. Together these multi-isotope results for modern and archaeological fallow deer provide a more critical perspective on the transportation of fallow deer and their body parts in antiquity.
Miller, H, Carden, R F, Evans, J, Lamb, A, Madgwick, R, Osborne, D, Symmons, R, and Sykes, N. 2015. Dead or alive? Investigating long-distance transport of live fallow deer and their body parts in antiquity. Environmental Archaeology. DOI. 10.1179/1749631414Y.0000000043
There is a lack of high-resolution records of hydroclimate variability in the Eastern Mediterranean from the late glacial and early Holocene. More knowledge of the speed of climate shifts and the degree to which they were synchronous with changes in the North Atlantic or elsewhere is required to understand better the controls on Eastern Mediterranean climate. Using endogenic carbonate from a sediment sequence from Nar Gölü, a maar lake in central Turkey, dated by varve counting and uranium-thorium methods, we present high-resolution (~25 years) oxygen (δ18O) and carbon isotope records, supported by carbonate mineralogy data, spanning the late glacial and Holocene. δ18Ocarbonate at Nar Gölü has been shown previously to be a strong proxy for regional water balance. After a dry period (i.e. evaporation far exceeding precipitation) in the Younger Dryas, the data show a transition into the relatively wetter early Holocene. In the early Holocene there are two drier periods that appear to peak at ~9.3 ka and ~8.2 ka, coincident with cooling 'events' seen in North Atlantic records. After this, and as seen in other records from the Eastern Mediterranean, there is a millennial-scale drying trend through the Mid Holocene Transition. The relatively dry late Holocene is punctuated by centennial-scale drought intervals, at the times of 4.2 ka 'event' and Late Bronze Age societal 'collapse'. Overall, we show that central Turkey is drier when the North Atlantic is cooler, throughout this record and at multiple timescales, thought to be due to a weakening of the westerly storm track resulting from reduced cyclogenesis in the North Atlantic. However, some features, such as the Mid Holocene Transition and the fact the early Holocene dry episodes at Nar Gölü are of a longer duration than the more discrete 'events' seen in North Atlantic records, imply there are additional controls on Eastern Mediterranean hydroclimate.
Dean, J R, Jones, M D, Leng, M J, Noble, S R, Metcalfe, S E, Sloane, H J, Sahy, D, Eastwood, W J, Roberts, C N. 2015. Eastern Mediterranean hydroclimate over the late glacial and Holocene, reconstructed from the sediments of Nar lake, central Turkey, using stable isotopes and carbonate mineralogy. Quaternary Science Reviews, 124, 162-174.
We have used sediments from Nar lake in central Turkey to reconstruct climatic variability over timescales longer than can be obtained from direct meteorological observations. Because the sediments of this lake are annually layered and precisely dated, it has been possible to calibrate sedimentary climate proxies against meteorological records to derive a drought index; this has then been applied to time periods before instrumental data are available. In this study, δ18O from Nar lake carbonates have been used to generate a decadal average P/E index for central Anatolia, which highlights major drought events since 1400 AD.
Yiğitbaşıoğlu, H, Dean, J R, Eastwood, W J, Roberts, N, Jones, M D, Leng, M J. 2015. A 600 year-long drought index for central Anatolia. Journal of the Black Sea/Mediterranean Environment, 21, 84-88.
We examined the use of δ13C, TOC and C/N geochemistry of sedimentary organic matter to reconstruct former sea levels and paleoenvironments in the absence of suitable microfossil data. The modern distribution of δ13C, TOC and C/N of 33 vegetation and 74 surface sediment samples collected from four coastal wetlands in the Thames Estuary and Norfolk, UK are described. The δ13C, TOC and C/N geochemistry of sediments varied in relation to the input of in situ vascular vegetation versus allochthonous particulate organic matter and algae, which was controlled primarily by tidal inundation. We reviewed published and unpublished studies to produce an English database of vegetation (n = 257) and sediment (n = 132) δ13C, TOC and C/N geochemistry. Four elevation-dependent environments in the database had statistically distinct δ13C, TOC and C/N values: (1) tidal flat/low marsh (δ13C: –24.9 ± 1.2‰; TOC: 3.6 ± 1.7%; C/N: 9.9 ± 0.8); (2) middle marsh/high (δ13C: −26.2 ± 1.0‰; TOC: 9.8 ± 6.7%; C/N: 12.1 ± 1.8); (3) reed swamp (δ13C: −27.9 ± 0.7‰: TOC: 36.5 ± 11.5%; C/N: 13.9 ± 1.2); and (4) fen carr (δ13C: –29.0 ± 0.6‰; TOC: 41.6 ± 5.7%; C/N: 17.4 ± 3.1). The δ13C, TOC and C/N geochemistry database was applied to a Holocene sediment core collected from the Thames Estuary to produce three new sea-level index points and one limiting date, illustrating the utility of δ13C, TOC and C/N values to reconstruct Holocene relative sea levels.
Khan, N S, Vane, C H, Horton, B P, Hillier, C, Riding, J D, Kendrick, C. 2015. The application of δ13C, TOC and C/N geochemistry to reconstruct Holocene relative sea levels and paleoenvironments in the Thames Estuary, UK. Journal of Quaternary Science, 30, 417-433.
The Late Pliocene has been proposed as a possible analogue for understanding future climate change and for testing climate models. Previous work has shown that during the Pliocene the major upwelling systems were relatively warm, and that this meant they were either inactive, contracted, or were upwelling warmer waters than present. Here, we examine evidence from a site located on the margins of the modern Benguela Upwelling system to test whether the upwelling cells had migrated or contracted relative to present during the Pliocene.
We applied several organic geochemistry proxies and foraminiferal analyses to reconstruct the Pliocene history of ODP Site 1087 (31°28′S, 15°19′E, 1374 m water depth), including the UK37′and TEX86 indices (for reconstructing sea surface temperatures), phytoplankton biomarker concentrations and stable isotope ratios (for estimating export primary productivity, and for oxygen isotope statigraphy), and planktonic foraminifera assemblage abundances (for inferring water mass changes). These proxies show that, between 3.5 and 3.0 Ma, the southern Benguela region was cooler than the northern Benguela region by 5 °C, the latter being where the main upwelling cells are found today. From the multiproxy data obtained, we also infer that more extensive upwelling was present in the southern Benguela region during the Pliocene than at present, and that the Benguela Upwelling cells shifted northwards after the Pliocene epoch as a result of changes in the local wind field. We also find evidence that the Benguela Upwelling was sensitive to the pronounced cooling during the M2 and KM2 glacial stages, potentially associated with the expansion of sea ice and cooling in Antarctica in the Late Pliocene.
Petrick, B, McClymont, E L, Felder, S, Rueda, G, Leng, M J & Rosell-Meléc, A. 2015. Late Pliocene upwelling in the Southern Benguela region. Palaeogeography, Palaeoclimatology, Palaeoecology, 429, 62-71.
Phosphate dosing of drinking water supplies, coupled with leakage from distribution networks, represents a significant input of phosphorus to the environment. The oxygen isotope composition of phosphate (δ18OPO4), a novel stable isotope tracer for phosphorus, offers new opportunities to understand the importance of phosphorus derived from sources such as drinking water. We report the first assessment of δ18OPO4 within drinking water supplies. A total of 40 samples from phosphate-dosed distribution networks were analyzed from across England and Wales. In addition, samples of the source orthophosphoric acid used for dosing were also analyzed. Two distinct isotopic signatures for drinking water were identified (average = +13.2 or +19.7‰), primarily determined by δ18OPO4 of the source acid (average = +12.4 or +19.7‰). Dependent upon the source acid used, drinking water δ18OPO4 appears isotopically distinct from a number of other phosphorus sources. Isotopic offsets from the source acid ranging from −0.9 to +2.8‰ were observed. There was little evidence that equilibrium isotope fractionation dominated within the networks, with offsets from temperature-dependent equilibrium ranging from −4.8 to +4.2‰. While partial equilibrium fractionation may have occurred, kinetic effects associated with microbial uptake of phosphorus or abiotic sorption and dissolution reactions may also contribute to ‰18OPO4 within drinking water supplies.
Gooddy, D C, Lapworth, J D, Ascott, M J, Bennett, S A, Heaton, T H E, and Surridge, B W J. 2015. Isotopic Fingerprint for Phosphorus in Drinking Water Supplies. Environmental Science and Technology, DOI: 10.1021/acs.est.5b01137.
In this study, we have used stable isotopes of megafauna, microbial mats and particulate organic matter to examine the effect of depth and vent fluid composition on the carbon sources at two proximal, chemically distinct hydrothermal vent fields along the Mid-Cayman Rise. The basalt hosted Piccard vent field (4980 m) is twice as deep as the ultramafic hosted Von Damm vent field (2300 m) and has very different faunal assemblages. Of particular note is the presence of seep-associated fauna, Escarpia and Lamellibrachia tubeworms, at the Von Damm vent field. We identify a greater range of carbon sources and a suggestion of increased photosynthetic inputs to the Von Damm vent field compared to Piccard vent field. Rimicaris hybisae shrimp are the only abundant species shared between the two vent fields with δ13C values ranging between -22.7 to -10.1‰. Higher concentrations of hydrogen sulfide in the vent fluids at Piccard is proposed to be responsible for varying the relative contributions of the carbon fixation cycles used by their epibionts. Seep-associated fauna at Von Damm rely on elevated, thermogenic hydrocarbon content of the vent fluids for their carbon source (δ13C values ranging from -21.3 to 11.6‰). They also derive energy from hydrogen sulfide formed by the microbial reduction of sulfide (δ34S values ranging from -10.2 to -6.9‰). The tubeworms have very short roots (buried at most a centimeter into rubble), suggesting that microbial sulfate reduction must be occurring either in the shallow subsurface and/or in the anterior part of the tube. Overall, megafauna at Von Damm vent field appear to have a smaller food chain length (smaller δ15N range) but a greater breadth of trophic resources compared to the megafauna at the Piccard vent field.
Bennett, S A, Van Dover, C, Breier, J A, and Coleman, M. 2015. Effect of depth and vent fluid composition on the carbon sources at two neighboring deep-SEA Hydrothermal vent fields (mid-cayman rise). Deep Sea Research Part I: Oceanographic Research Papers. In Press.
In this paper we present surface water oxygen (δ18O), hydrogen (δD) and inorganic carbon (δ13CDIC) isotope data to gain a better understanding of the modern day hydrogeology of Cuatrociénegas Basin, a semi-arid region in northeastern Mexico. Our study focuses on 26 water samples collected in March 2008 to investigate: 1) current provenance and flow pathways of surface waters, 2) the use of stable isotopes in identifying water loss and environmental degradation, and 3) human influence on hydrogeology. δ18O for Cuatrociénegas water samples ranged from –7.99 to +4.97‰ (mean –5.23± 3.13‰), δD from –54.8 to +0.3‰ (mean –42.4 ± 14.4‰), and δ13CTDIC from –21.6 to –9.2‰ (mean –14.3 ± 3.4‰). Samples collected progressively away from their respective spring lines display increasing δ18O and δD values. Isotope data suggest that where the residence time of the groundwater is long and/or the system is hydrologically open, δ18O may not be a reliable indicator of water loss and environmental degradation. Our data suggest the central ciénega (area W(b)) is the most viable area for palaeoenvironmental study and long term monitoring is an essential tool in the identification of ecosystem damage and response, allowing for better future management of the complex and fragile CCB ecosystem.
Felstead, N J, Leng, M J, Metcalfe, S E, Gonzalez, S. 2015. Understanding the hydrogeology and surface flow in the Cuatrociénegas Basin (NE Mexico) using stable isotopes. Journal of Arid Environments, 121, 15-23.
The use of speleothems to reconstruct past climatic and environmental change through chemical proxies is becoming increasingly common. Speleothem chemistry is controlled by hydrological and atmospheric processes which vary over seasonal time scales. However, as many reconstructions using speleothem carbonate are now endeavouring to acquire information about precipitation and temperature dynamics at a scale that can capture short term hydrological events, our understanding of within cave processes must match this resolution. Monitoring within Cueva de Asiul (N. Spain) has identified rapid (hourly resolution) changes in drip water electrical conductivity (EC), which is regulated by the pCO2 in the cave air. Drip water EC is therefore controlled by different modes of cave ventilation. In Cueva de Asiul a combination of density differences, and external pressure changes control ventilation patterns. Density driven changes in cave ventilation occur on a diurnal scale at this site irrespective of season, driven by fluctuations in external temperature across the cave internal temperature threshold. As external temperatures drop below those within the cave low pCO2 external air enters the void, facilitating the deposition of speleothem carbonate and causing a reduction in measured drip water EC. Additionally, decreases in external pressure related to storm activity act as a secondary ventilation mechanism. Reductions in external air pressure cause a drop in cave air pressure, enhancing karst air draw down, increasing the pCO2 of the cave and therefore the EC measured within drip waters. EC thereby serves as a first order indicator of cave ventilation, regardless of changes in speleothem drip rates and karst hydrological conditions. High resolution monitoring of cave drip water electrical conductivity reveals the highly sensitive nature of ventilation dynamics within cave environments, and highlights the importance of this for understanding trace element incorporation into speleothem carbonate at the event scale.
Smith, A C, Wynn, P M, Barker, P A & Leng, M J. 2015. Drip water electrical conductivity as an indicator of cave ventilation at the event scale. Science of the Total Environment, 532, 517-527.
In a large study on early crop water management, stable carbon isotope discrimination wasdetermined for 275 charred grain samples from nine archaeological sites, dating primarily tothe Neolithic and Bronze Age, from the Eastern Mediterranean and Western Asia. This has revealed that wheat (Triticumspp.) was regularly grown in wetter conditions than barley(Hordeumsp.), indicating systematic preferential treatment of wheat that may reflect a culturalpreference for wheat over barley. Isotopic analysis of pulse crops (Lens culinaris,Pisum sativumand Vicia ervilia) indicates cultivation in highly varied water conditions atsome sites, possibly as a result of opportunistic watering practices. The results have alsoprovided evidence for local land-use and changing agricultural practices.
Wallace, M P, Jones, G, Charles, M, Fraser, R, Heaton, T H E, Bogaard, A. 2015. Stable CarbonIsotope Evidence for Neolithic and Bronze Age Crop Water Management in the Eastern Mediterraneanand Southwest Asia. PLoS ONE, DOI: 10.1371/journal.pone.0127085
Hydrothermal vents harbor ecosystems mostly decoupled from organic carbon synthesized with the energy of sunlight (photosynthetic carbon source) but fueled instead by oxidation of reduced compounds to generate a chemosynthetic carbon source. Our study aimed to disentangle photosynthetic and chemosynthetic organic carbon sources for the shrimp species Rimicaris hybisae, a primary consumer presumed to obtain its organic carbon mainly from ectosymbiotic chemoautotrophic bacteria living on its gill cover membrane. To provide ectosymbionts with ideal conditions for chemosynthesis, these shrimp live in dense clusters around vent chimneys; they are, however, also found sparsely distributed adjacent to diffuse vent flows, where they might depend on alternative food sources. Densely and sparsely distributed shrimp were sampled and dissected into abdominal tissue and gill cover membrane, covered with ectosymbiotic bacteria, at two hydrothermal vent fields in the Mid-Cayman rise that differ in vent chemistry. Fatty acids (FA) were extracted from shrimp tissues and their carbon isotopic compositions assessed. The FA data indicate that adult R. hybisae predominantly rely on bacteria for their organic carbon needs. Their FA composition is dominated by common bacterial FA of the n7 family (~41%). Bacterial FA of the n4 FA family are also abundant and found to constitute good biomarkers for gill ectosymbionts. Sparsely distributed shrimp contain fractions of n4 FA in gill cover membranes ~4% lower than densely packed ones (~18%) and much higher fractions of photosynthetic FA in abdominal tissues, ~% more (compared with 1.6%), suggesting replacement of ectosymbionts along with exoskeletons (molt), while they take up alternative diets of partly photosynthetic organic carbon. Abdominal tissues also contain photosynthetic FA from a second source taken up presumably during an early dispersal phase and still present to c. 3% in adult shrimp. The contribution of photosynthetic carbon to the FA pool of adult R. hybisae is, however, overall small (max. 8%). Significant differences in carbon isotopic values of chemosynthetically derived FA between vent fields suggest that different dominant C fixation pathways are being used.
Streita, K, Bennett, S A, Van Doverb, C L, & Coleman, M. 2015. Sources of organic carbon for Rimicaris hybisae: Tracing individual fatty acids at two hydrothermal vent fields in the Mid-Cayman rise. Deep Sea Research Part I: Oceanographic Research Papers, 100, 13-20.
The stable isotope composition of benthic sponge spicule silica is a potential source of palaeoceanographic information about past deep seawater chemistry. The silicon isotope composition of spicules has been shown to relate to the silicic acid concentration of ambient water, although existing calibrations do exhibit a degree of scatter in the relationship. Less is known about how the oxygen isotope composition of sponge spicule silica relates to environmental conditions during growth. Here, we investigate the vital effects on silica, silicon and oxygen isotope composition in a carnivorous sponge, Asbestopluma sp., from the Southern Ocean. We find significant variations in silicon and oxygen isotopic composition within the specimen that are related to unusual spicule silicification. The largest variation in both isotope systems was associated with the differential distribution of an unconventional, hypersilicified spicule type (desma) along the sponge body. The absence an internal canal in the desmas suggests an unconventional silicification pattern leading to an unusually heavy isotope signature. Additional internal variability derives from a systematic offset between the peripheral skeleton of the body having systematically a higher isotopic composition than the internal skeleton. A simplified silicon isotope fractionation model, in which desmas were excluded, suggests that the lack of a system for seawater pumping in carnivorous sponges favours a low replenishment of dissolved silicon within the internal tissues, causing kinetic fractionation during silicification that impacts the isotope signature of the internal skeleton. Analysis of multiple spicules should be carried out to "average out" any artefacts in order to produce more robust downcore measurements.
Hendry, K R, Swann, G E A, Leng, M J, Sloane, H J, Goodwin, C, Berman, J, and Maldonado, M: Technical Note: Silica stable isotopes and silicification in a carnivorous sponge Asbestopluma sp., Biogeosciences, 12, 3489-3498.
Oxygen isotope records of precipitation (δ18Oprecip) from Beringia are thought to reflect synoptic-scale circulation changes associated with the Aleutian Low. To delineate the spatial pattern of δ18Oprecip associated with the two dominant modes of Aleutian Low circulation, we combine modern δ18Oprecip and deuterium excess data with climate reanalysis and back-trajectory modelling. Aleutian Low strength and position are revealed to systematically affect regional moisture source and δ18Oprecip; whereby a strengthened Aleutian Low causes lower (higher) δ18Oprecip in western (eastern) Beringia. We compare a new 100-year-long δ18O record from the Aleutian Islands with the North Pacific Index, the primary indicator of Aleutian Low strength, and find a significant positive relationship (r = 0.43, p < 0.02, n = 28) that tracks late 20th century change. This study demonstrates synoptic-scale circulation controls on our isotope record, and provides a coherent framework for interpreting existing and emerging paleo-isotope data from the region.
Bailey, H L, Kaufman, D S, Henderson, A C G, and Leng, M J. 2015. Synoptic-scale circulation controls on the δ18O in precipitation across Beringia. Geophysical Research Letters, 42, DOI: 10.1002/2015GL063983.
The first molecular-based studies of microbes in snow and on glaciers have only recently been performed on the vast Greenland Ice Sheet (GrIS). Aeolian microbial seeding is hypothesized to impact on glacier surface community compositions. Localized melting of glacier debris (cryoconite) into the surface ice forms cryoconite holes, which are considered ‘hot spots’ for microbial activity on glaciers. To date, few studies have attempted to assess the origin and evolution of cryoconite and cryoconite hole communities throughout a melt season. In this study, a range of experimental approaches was used for the first time to study the inputs, temporal and structural transformations of GrIS microbial communities over the course of a whole ablation season. Small amounts of aeolian (wind and snow) microbes were potentially seeding the stable communities that were already present on the glacier (composed mainly of Proteobacteria, Cyanobacteria, and Actinobacteria). However, the dominant bacterial taxa in the aeolian samples (Firmicutes) did not establish themselves in local glacier surface communities. Cryoconite and cryoconite hole community composition remained stable throughout the ablation season following the fast community turnover, which accompanied the initial snow melt. The presence of stable communities in cryoconite and cryoconite holes on the GrIS will allow future studies to assess glacier surface microbial diversity at individual study sites from sampling intervals of short duration only. Aeolian inputs also had significantly different organic δ13C values (-28.0 to -27.0‰) from the glacier surface values (-25.7 to -23.6‰), indicating that in situ microbial processes are important in fixing new organic matter and transforming aeolian organic carbon. The continuous productivity of stable communities over one melt season makes them important contributors to biogeochemical nutrient cycling on glaciers.
Musilova, M, Tranter, M, Bennett, S A, Wadham, J & Anesio, A M. 2015. Stable microbial community composition on the Greenland Ice Sheet. Frontiers in Microbiology, 6:193, doi: 10.3389/fmicb.2015.00193.
Lake Prespa, in the Balkans, contains an important palaeo-archive in a key location for understanding Quaternary climate variability in the transition between Mediterranean and central European climate zones. Previous palaeoenvironmental research on sediment cores indicates that the lake is highly sensitive to climate change and that diatoms are likely to be strong palaeohydrological proxies. Here, we present new results from diatom analysis of a ca. 91 ka sequence, core Co1215, which spans the time from the end of the last interglacial to the present. Fluctuations in the diatom data were driven primarily by changes in lake level, as a function of shifts in moisture availability. Warmer interglacial (MIS 5, MIS 1) and interstadial (MIS 3) phases exhibit higher lake levels in spite of enhanced evaporative concentration, underlining the importance of changes in precipitation regimes over time. Low lake levels during glacial phases indicate extreme aridity, common to all Mediterranean lakes. Evidence for fluctuations in trophic status is linked, in part, to lake-level change, but also reflects nutrient enrichment from catchment processes. MIS 5a is characterized by the highest lake productivity in the sequence, but low lake levels, which are ascribed primarily to very low precipitation. On a suborbital timescale, the diatoms provide evidence for correlation to the millennial-scale variability recorded in the Greenland oxygen isotope records and clearly reflect the impact of the Heinrich H6, H5 and H3–1 ice-rafting events, suggesting the dominant influence of North Atlantic forcing in this region. Although the highest-amplitude shift in the diatom assemblages occurs during the time of H4 (40–38 ka), it may be superimposed upon the impact of the 39.28 cal ka BP Campanian Ignimbrite volcanic eruption. Diatoms from Lake Prespa core Co1215 display the first strong evidence for the impact of Italian volcanic activity on lacustrine biota in this region. Results emphasize the complexity of diatom response thresholds in different studies across the region. In the case of Lake Prespa, the results highlight the important role of precipitation for maintaining the hydrological balance of the lake, and indirectly, its biodiversity.
Cvetkoska, A, Levkov, Z, Reed, J M, Wagner, B, Panagiotopoulos, K, Leng, M J, Lacey, J H. 2015. Quaternary climate change and Heinrich Events in the southern Balkans: Lake Prespa diatom palaeolimnology from the last interglacial to present. Journal of Paleolimnology, 53:2, 215-231.
Oxygen isotope geochemistry of Molluscan shell is an essential part of environmental archaeology and over the last decade has contributed significantly to the understanding of the past inhabitants of our planet. From the analysis of collected (and disposed of) shells we can gain information on environmental data from the species assemblages and also from the shell chemistry. In particular, intra-seasonal information can be gained from shells by analysing the isotope composition of the shell from successive growth increments. Here, we describe some of the recent developments in the use of oxygen isotopes in environmental archaeology. In particular, we consider preservation and sampling and describe how δ18O can provide us with information on seasonal climate, season of collection as well as changes in global climate.
Leng, M J, and Lewis, J P. 2015. Oxygen isotopes in Molluscan shell: Applications in environmental archaeology. Environmental Archaeology, DOI 10.1179/1749631414Y.0000000048.
The dispersal of human populations out of Africa into Arabia was most likely linked to episodes of climatic amelioration, when increased monsoon rainfall led to the activation of drainage systems, improved freshwater availability, and the development of regional vegeta-tion. Here we present the ﬁrst dated terrestrial record from southeast Arabia that provides evidence for increased rainfall and the expansion of vegetation during both glacial and inter-glacial periods. Findings from extensive alluvial fan deposits indicate that drainage system activation occurred during Marine Isotope Stage (MIS) 6 (ca. 160–150 ka), MIS 5 (ca. 130–75 ka), and during early MIS 3 (ca. 55 ka). The development of active freshwater systems during these periods corresponds with monsoon intensity increases during insolation maxima, suggesting that humid periods in Arabia were not conﬁned to eccentricity-paced deglaciations, and providing paleoenvironmental support for multiple windows of opportunity for dispersal out of Africa during the late Pleistocene.
Parton, A, Farrant, A R, Leng, M J, Telfer, M, Groucutt, H, Petraglia, M D, and Parker, A G. 2015. Alluvial fan records from southeast Arabia reveal multiple windows for human dispersal. Geology doi:10.1130/G36401.1.
In comparison to other sectors of the marine system, the palaeoceanography of the subarctic North Pacific Ocean is poorly constrained. New diatom isotope records of δ13C, δ18O, δ30Si (δ13Cdiatom, δ18Odiatom, and δ30Sidiatom) are presented alongside existing geochemical and isotope records to document changes in photic zone conditions, including nutrient supply and the efficiency of the soft-tissue biological pump, between Marine Isotope Stage (MIS) 4 and MIS 5e. Peaks in opal productivity in MIS 5b/c and MIS 5e are both associated with the breakdown of the regional halocline stratification and increased nutrient supply to the photic zone. Whereas the MIS 5e peak is associated with low rates of nutrient utilisation, the MIS 5b/c peak is associated with significantly higher rates of nutrient utilisation. Both peaks, together with other smaller increases in productivity in MIS 4 and 5a, culminate with a significant increase in freshwater input which strengthens/re-establishes the halocline and limits further upwelling of sub-surface waters to the photic zone. Whilst δ30Sidiatom and previously published records of diatom δ15N (δ15Ndiatom) (Brunelle et al., 2007, 2010) show similar trends until the latter half of MIS 5a, the records become anti-correlated after this juncture and into MIS 4, suggesting a possible change in photic zone state such as may occur with a shift to iron or silicon limitation.
Swann, G E A. and Snelling, A M. 2015. Photic zone changes in the north-west Pacific Ocean from MIS 4–5e. Climate of the Past, 11, 15-25
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