PhD: The anatomy of an interglacial: interrogating the timing of Earth system responses to polar warming

Models of future climate change are, for the most part, informed by observational data spanning the last c.150 years – a period that has seen only limited climatic variability. To test our long-term projections of Earth system responses we exploit the geological record. Previous climatically warm periods, e.g. the Last Interglacial (LIG; 130-116 ka), provide natural laboratories to study landscape and ecosystem responses to warmer-than-present conditions.

A range of proxy-based approaches, e.g. pollen, sedimentology, have been used to reconstruct LIG environmental conditions across NW Europe. A key challenge however, is building age models that can describe the timing and rates of change described in the proxy records. Volcanic ash (tephra) layers, traceable often over many 1000s of kilometres from their source, provide isochrons for precise synchronisation of terrestrial, marine and ice core records. Tephrochronology has become a staple method for dating and correlating European Holocene and Last Glacial-age sequences, however its application in LIG sequences remains limited.

The project will improve our understanding of the nature, timing and propagation of environmental change in the North Sea region, e.g. vegetation development and sea level, under warmer-than-present LIG climate conditions,. Traditionally, terrestrial LIG sequences have been dated through correlation of pollen stratigraphies to regional stratotypes and few are directly dated (Turner, 2000). The development of a regional tephrostratigraphic framework will tie together and allow precise comparison of, key LIG sedimentary records. The work will extend the existing LIG tephrostratigraphy for the North Atlantic (Abbott et al., 2013).

This a collaboration between the Universities of Leeds (Prof Natasha Barlow, Dr Amy McGuire), Cambridge (Prof Christine Lane), Utrecht and the Dutch Geological Survey (TNO), and will build upon the RISeR project (riser.leeds.ac.uk), which seeks to constrain the rate of southern North Sea sea-level change during the LIG.

The project
During the project you will detect, geochemically characterise and correlate far-travelled tephra deposits within terrestrial sediment records from sites across the North Sea basin, the British Isles, the Netherlands, and northern Germany. Laboratory-based cryptotephra methods will be used to find far-travelled tephra layers, preserved in low concentration and not visible to the naked eye.

The study sites will be selected in collaboration with partners at the tephrochronology laboratory University of Cambridge and sampling will involve visits to other labs in the UK (e.g., Cambridge) and The Netherlands (e.g., TNO, Utrecht), where LIG sediments are under research. There is potential for incorporating fieldwork to access further LIG sequences in the British Isles and the opportunity to carry out pollen analysis on new or archive samples.

Data compilation and interpretation will involve developing improved age-depth models for important LIG sequences. Comparison of environmental proxy datasets, including vegetation and past sea-level change, within a unified chronology will establish the nature and rates of LIG environmental change both at individual sites and on a regional scale.

Training and wider research group
The supervisory team have a wealth of expertise and will support the student in gaining the necessary skills for this project. The successful candidate will have access to our extensive world-leading palaeo-chronology and geochemistry laboratories within the School of Earth and Environment. Training in cryptotephra research (including identification and geochemical analysis), age-modelling and pollen analysis will be carried out at the wording leading laboratories in the School of Earth and Environment at the University of Leeds, and the Department of Geography in Cambridge. External supervisors and members of the ERC-funded RISeR project will support broader research into past landscapes in the North Sea region, including the selection of study sites and interpretation of existing datasets. The successful candidate will also have access to a broad spectrum of training workshops facilitated by the DTP at the University of Leeds.

Student profile
The ideal candidate will have a background in geosciences, with a relevant degree e.g. Geology, Geography, Environmental Science, Oceanography, or Chemistry. An enthusiasm for careful and laborious laboratory work and an interest in past climate and environmental change is important.

Relevant literature
Field, M., Huntley, B. & Müller, H. Eemian climate fluctuations observed in a European pollen record. Nature 371, 779–783 (1994).
Cohen, K.M., Cartelle, V., Barnett, R., Busschers, F.S. and Barlow, N.L., 2022. Last Interglacial sea-level data points from Northwest Europe. Earth System Science Data, 14(6), pp.2895-2937.
Abbott, P.M., Austin, W.E., Davies, S.M., Pearce, N.J. and Hibbert, F.D., 2013. Cryptotephrochronology of the Eemian and the last interglacial–glacial transition in the North East Atlantic. Journal of Quaternary Science, 28(5), pp.501-514.