Changes in temperature, Southern Hemisphere Westerly winds and CO2 degassing of the Southern Ocean over the last 20,000 years

Project Background
The Southern Ocean (SO) is a key driver of present and past global climate because changes in circumpolar Southern Hemisphere westerly winds (SHW) help to regulate global CO2 levels in the atmosphere. Recent poleward shifts in the Antarctic Circumpolar Current and the SHW have driven late C20th warming of the SO and led to increased turbulence, mixing of deep water currents, degassing of previously-stored CO2 from the ocean, and possibly elevated the basal melting rates of some Antarctic ice-shelves. Our current understanding of how long-term changes circumpolar winds might affect future global temperature trends is limited by a lack of palaeotemperature records from the SO that can help constrain past, naturally-driven, variability. This project will address these issues by investigating spatial and temporal relationships between temperature and wind strength across the SO for the last c. 20,000 years using peat records from the sub-Antarctic region.

Project Aims and Methods
The overall project aim is to determine whether the Southern Ocean (SO) has acted net source or sink for global atmospheric CO2 in the past c. 20,000 years. The hypothesis being tested is that key warm periods since the last deglaciation were also associated with an increased SHW strength and a poleward shift in SHW intensity. Temperature-sensitive membrane-spanning biomarkers (branched glycerol dialkyl glycerol tetraether, brGDGTs, produced by bacteria, and found in peat deposits) will be used to generate quantitative biomarker-based palaeotemperatures for the last c.20,000 years from up to 5 strategically located peat records in the terrestrial sub-Antarctic region.

Specific talks include:
1. Analyse modern samples for brGDGTs distribution and compare results with meteorological data.
2. Update existing peat brGDGT temperature calibration datasets.
3. Establish laboratory and field experiments investigating seasonal and temperature driven changes in brGDGT distribution and abundance in active (sub-) Antarctic peatlands.
4. Quantify palaeotemperatures using brGDGTs from up to 5 SO peat records.
5. Test relationships between past temperature and wind strength at each location and across the SO and compare field data with model simulations. Figure highlighting the lack of quantitative temperature records from the Southern Ocean and there is currently only one terrestrial temperature record from the S. Hemisphere that encompasses the last deglaciation.

Candidate
A background in analytical Earth Sciences and/or analytical (bio- geo-) Chemistry is essential. The candidate should have good laboratory and data analytical skills coupled with a willingness to learn new techniques and develop existing ones. An aptitude for statistical analysis and an interest in climate modeling would be desirable.

Case Award description
The student will subsample peat cores and reference material collected on SHW/ACE expeditions (2013-2020). Laboratory-based moss-bank/peatland temperature/production experiments will be set up at BAS during the first year. Collaborative Antarctic Science Scheme (CASS) grant application(s) will be submitted to enable participation in an Antarctic summer field season where the student will assist with collection of moss/peat samples in up to 3 (sub)Antarctic locations.

Training
Training biomarker analysis will be undertaken at Bristol University. Fieldwork training and equipment will be provided by BAS. The student will also receive training in transferable skills, including seminars/workshops in project management, data analysis, oral and poster presentations, paper writing, thesis writing, compiling bibliographies. They will have access to the full range of training opportunities within the GW4+ set up at Bristol University, The University of Exeter, and at BAS, which has a partnership student training programme for transferable skills with the University of Cambridge.