Past sea-ice and ice sheet configurations in the eastern Weddell Sea. Insights from snow petrel stomach-oil deposits

To date, there are few records of past sea-ice variability in the eastern Weddell Sea, limiting our understanding of atmosphere-ocean-ice interactions in this region of the Southern Ocean. Sparse spatial and temporal data, uncertainties in palaeoclimate proxies, and overestimations of simulated winter sea ice complicate reconstructions of the East Antarctic Ice Sheet (EAIS) and sea-ice extent, especially over the past 2000 years. The EAIS is a vast freshwater reservoir and plays a key role in global sea level regulation and ice shelf dynamics, whilst sea ice helps regulate Antarctic Bottom Water (AABW) formation in the Weddell Sea. This thesis presents a new biological archive, snow petrel stomach-oil deposits, to help reduce uncertainties in ice sheet and sea-ice behaviours. These defensive regurgitated accumulations at ice-free nesting sites preserve geochemical evidence of past site occupation and diet, as snow petrels typically forage within intermediate sea-ice cover (30–60 %), the Marginal Ice Zone (MIZ).

Here, a combination of radiocarbon dating, carbon and nitrogen stable isotope, elemental and fatty acid analysis were used on deposits from the Theron Mountains and Shackleton Range to: (1) establish a chronology, (2) assess snow petrel diet, and (3) link dietary shifts to sea-ice variability. Results infer snow petrel occupation during intervals of relative warmth: putative Marine Isotope Stage (MIS) 5e, (c. 122-117 ka), MIS3, (c. 44 ka) and in the last 6000 years, absent during the Last Glacial Maximum (c. 26-19 ka). Snow petrel diet was inferred to have shifted from fish-dominated during peak MIS5e to a mixed, Antarctic krill and fish-based diet into the Holocene. Increased dietary variability and accumulation over the past 2000 years reflect productive coastal polynya(s) within c. 1,500 km. In combination, these findings offer novel observations of snow petrel diet, deglaciation and ocean-atmosphere-ecosystem interactions in a logistically challenging region across a long-term climate history.