March 2014 – Congratulations to Hayley Manners on the successful defence of her thesis: A Multi-Proxy Study of the Palaeocene - Eocene Thermal Maximum in Northern Spain.
At the boundary between the Palaeocene and Eocene epochs (ca. 56 Ma) a significant global warming event, termed the Palaeocene-Eocene Thermal Maximum (PETM), occurred. Records of this event are characterised by a negative carbon isotope excursion (CIE) which has been associated with the release of thousands of petagrams of isotopically light carbon into the ocean-atmosphere system, initiating changes in the carbon cycle, the climate system, ocean chemistry and the marine and continental ecosystems. The amount of isotopically light carbon that was required to cause the event, its source and the rapidity of its release are, however, are still debated. This study uses δ13CTOC, δ13Cn-alkane, δ13<CCARB and palynological data to evaluate the PETM CIE in terms of the magnitude of the CIE in both continental and marine settings, rapidity of release and drawdown of carbon, and mobilisation of different organic matter (OM) pools as a response to the climate change. The sections studied span a continental to marine transect in northern Spain. This represents the first organic geochemical study of these PETM sections, one of the first comparisons of CIE magnitude between continental and marine sections within the same sediment routing system, and one of the first comparisons of the same OM proxies within different depositional
environments. The data suggest that different OM pools were mobilised in response to the PETM, with reworking of older material, soil residence times, and contemporaneous vegetation all contributing. CIE profile shapes predominantly suggest a rapid onset and recovery from the event. The magnitude of the CIE was also assessed. The current resolution of the data suggests that the differences between continental and marine CIE magnitudes could be minimal within a single sediment routing system, perhaps establishing a realistic CIE magnitude for the PETM, for use in future modelling scenarios.
Hayley’s main supervisor was Dr Stephen Grimes (Plymouth) and Prof Melanie Leng at BGS.
March 2014 – Congratulations to Jonathan Dean who gained his PhD entitled: Stable Isotope Analysis and U-Th Dating of Late Glacial and Holocene Lacustrine Sediments from Central Turkey.
Water is a politically sensitive resource in the Near East and water stress is increasing. It is therefore vital that there is a strong understanding of past hydrological variability, so that the drivers of change can be better understood, and so that the links between the palaeoclimate and archaeological records in this key region in the development of human civilisation can be investigated. To be of most use, this requires high resolution records and a good understanding of palaeoseasonality. A sediment sequence spanning ~14,000 years was retrieved from Nar Gölü, a lake in central Turkey. My thesis focussed in particular on oxygen isotope analysis of carbonates and comparing δ18Ocarbonate and δ18Odiatom data in order to examine palaeoseasonality. Due to the high resolution δ18Ocarbonate data, it was possible to show that the rapidity of the Younger Dryas to Holocene transition at Nar Gölü was similar to that seen in North Atlantic records and that centennial scale arid events in the Holocene seem to occur at the time of cold periods in the North Atlantic. Taken together, this suggests a strong teleconnection between the two regions. However, the longer duration of the aridity peaks ~9,300 and ~8,200 years BP at Nar Gölü, compared with the more
discrete cooling events at this time in the North Atlantic, suggest that there are additional controls on Near East hydroclimate. There is a multi-millennial scale trend of increasing δ18Ocarbonate values from the early to late Holocene. This ‘Mid Holocene Transition’ has previously been identified in the Near East, however here it is demonstrated that water balance and not a shift in the seasonality of precipitation was the primary cause. Finally, for the first time, the stability of Near East climate in the early Holocene is robustly demonstrated, suggesting that this could have been a key enabler of the development of agriculture at this time.
Jon was supervised at University of Nottingham by Dr Matthew Jones and Prof Sarah Metcalfe, at NIGL he was supported by Dr Stephen Noble and Prof Melanie Leng
December 2013 – congratulations to Sven Könitzer who was granted a doctorate for his PhD research entitled: Primary biological controls on UK Lower Namurian shale gas prospectivity: A step towards understanding a major potential UK unconventional gas resource.
Sven’s research is the first to analyse the abundance and type of organic matter preserved in deeper-water mudstones deposited in a Late Mississippian UK basin alongside a detailed sedimentological study to determine the key depositional processes and the palaeoenvironment. This study is a key step in understanding where, and why, organic matter is concentrated in fine-grained sedimentary rocks. Mudstones of this age, deposited across central and northern England, are known oil and gas source rocks and are currently the focus of attention for onshore shale gas exploration. Shale gas is formed from organic matter present during maturation and is mostly retained in the same rock formation.
Sven was supervised by Prof Sarah Davies (Leicester) and Prof Mike Stephenson, Prof Melanie Leng, and Dr Chris Vane at the BGS
December 2012 - Congratulations to Katie Egan, who has recently defended her Ph.D. entitled: New insights into Cenozoic silicon cycling in the Southern Ocean: refined application of silicon isotope ratios in biogenic opal".
The marine silicon and carbon cycles are intrinsically linked by a unique group of primary producers; the diatoms. Diatoms play a significant role in carbon export, making them a critical component of the global biological carbon pump with the power to affect climatic change. In this thesis, the silicon isotope composition (δ30Si) preserved in diatom opal is used together with the δ30Si of sponge opal, a powerful new proxy for deepwater silicic acid concentration, to document the Cenozoic Silicon cycle, shedding light on its role in carbon cycling and global climatic change. This study has developed a novel size-separation methodology to produce the first core top calibration of diatom δ30Si. This calibration demonstrates that diatom &delta30Si exhibits a strong negative correlation with surface water silicic acid concentration, supportive of its application as a proxy for silicic acid utilisation. The refined method is used to produce a diatom δ30Si record, for the first time combined with sponge δ30Si, to gain insight into the Southern Ocean silicon cycle over one of the largest Cenozoic
climatic shifts; the onset of Antarctic glaciation (~33.7Ma). The two proxy records yield the first geochemical footprint which demonstrates the coincident proliferation of diatoms with the onset of Antarctic circumpolar flow as a precursor event to the Eocene-Oligocene boundary.
Katie was supervised by Ros Rickerby at the University of Oxford and Melanie Leng at NIGL
November 2012 - Congratulations to Helen Cockerton, who has recently defended her Ph.D. entitled: "Late-glacial and Holocene variations in the Si cycle in the Nile Basin: multi-isotope evidence from modern waters and lake sediments".
Until recently the continental Si cycle at Quaternary (decadal to million-year) time scales has been largely neglected. Emphasis was placed on silicate-rock weathering and resulting CO2 drawdown on geological time scales, rather than on shorter-term biogenic processes occurring along the land-ocean continuum. The ability of some terrestrial plants (e.g. tropical rainforest trees, savanna and wetland grasses, Papyrus) and aquatic organisms (e.g. diatoms in lakes, rivers and swamps) to take up, store and recycle significant amounts of Si is increasingly being recognised, although their impact on the continental Si cycle and Si export to the oceans under different climatic regimes remains unquantified. The main aim of this thesis was to reconstruct spatial and temporal patterns of Si cycling in the Nile Basin during the last 15,000 years.Seasonal variations in hydrology and Si cycling in the Nile Basin were investigated using stable isotope (H, O, and Si) compositions of surface waters, as a basis for interpreting lacustrine diatom sequences. Si- and O-isotope analysis of diatom silica in cores from Lakes Victoria and Edward, in the headwaters of the White Nile, were employed to reconstruct changes in biotic Si cycling and palaeohydrology, respectively. The relative abundances of lipid biomarkers (hydrocarbon-fraction) permitted major changes in terrestrial and aquatic ecosystems to be tracked. During drier conditions (e.g. the last glacial and late Holocene) (high δ18Odiatom), Si cycling was greatly reduced.
Diminished biomass, reduced biotic weathering, a declining soil stock of amorphous silica (ASi) and decreased run-off in the catchment resulted in biological demand for Si (high δ30Sidiatom). In contrast, enhanced monsoon rainfall (low δ18Odiatom) during the early to mid-Holocene enabled the proliferation of vegetation in the catchment, which in turn accelerated silicate-rock weathering and the mobilisation of DSi in surface runoff, providing a plentiful supply of Si (low δ30Sidiatom). Both the modern waters and palaeo-records indicate that the riverine flux of Si to the oceans on glacial \ interglacial time scales was not constant; resulting in important implications for the marine Si budget and consequently the global C cycle.
Helen was based at the University of Swansea
April 2012 - Congratulations to Holly Miller who recently passed her PhD entitled "The Origins of Nomadic Pastoralism in the Southern Levant: stable isotope, chipped stone and architectural analysis of archaeological evidence".
Herded sheep and goats were introduced to the steppic region of Eastern Jordan late in the seventh millennium cal BC. The evidence for initial pastoral activities in this arid area, some 500 years after domestic caprines are known to have been kept at large village sites in the neighbouring and more hospitable Mediterranean regions, suggests that these early herding groups began to develop a lifeway that pastoral nomads continue to live in some regions of the world today.
13C/12C and 15N/14N ratios from the bone collagen of animal remains from Mediterranean sites, where C4 plants were less common and water availability was greater, was compared to those of the steppic sites, where C4 vegetation was abundant and water scarce. The results of this study were used to pinpoint the foraging range of the herded animals, suggesting the regions in which they, and their accompanying herders, spent lengths of time. It was determined that differences in the isotopic ratios of animals from two sites in the arid region signify different herding strategies used to bring animals to the area. Animals from one site have indications of a diet that included Mediterranean vegetation, suggesting that their herders had more frequent contact with village groups. At the second site, animal diets, and thus movements, were restricted to the steppe, suggesting the development of a lifestyle based around frequent mobility within the arid regions, and allowing the rejection of a theory that stated early Neolithic Southern Levantine herding was village based.
In combination with chipped stone and architectural analysis, the results of the stable isotope study have allowed an investigation of the social and economic behaviours and practices of the communities that initially saw the potential of the Southern Levantine steppe as an area for pastoral activities.
Liverpool supervisors- Drs Jessica Pearson and Douglas Baird, NIGL- Dr Angela Lamb and Mrs Carolyn Chenery