Summer sea-ice dynamics and ecosystem changes over the last glacial period along the Dronning Maud Land margin recovered from snow petrel stomach-oil deposits

The annual cycle of Antarctic sea ice increases from ∼2.5 km² in summer to ∼18 km² in winter and is the largest physical change occurring on the Earth’s surface today, with a significant impact on its surroundings. Southern Ocean ecosystems are fine-tuned to these seasonal changes and play a crucial role in modulating the global carbon and nutrient cycles. Since 2017, Antarctic summer sea-ice has experienced a regime shift towards reduced sea-ice extent, creating uncertainty around its impact on global and local geobiological processes due to few geological archives available to contextualise the changes occurring today. This PhD project explores the extent of the summer sea-ice and geochemical processes occurring within the summer sea-ice zone using snow petrel (Pagodroma nivea) stomach-oil deposits, created by snow petrels’ defensive regurgitations at their nest sites. Collected during the GEOMAUD 1995/96 expedition from Untersee Oasis, the deposits presented in this thesis span 1-63 ka BP, recording the centennial to millennial-scale summer sea-ice zone (70-60°S) response of changes in glacial-interglacial climate variability along the Dronning Maud Land margin of East Antarctica. Through developing robust age-depth models and a multi-proxy approach of stable isotopes, X-Ray Fluorescence and fatty acid biomarkers, changes in snow petrel diet and geochemical properties of the summer sea-ice zone are recovered. Stomach-oil deposits reveal that open water likely prevailed south of 60°S during summer, either as polynyas or as a nonconsolidated marginal sea-ice zone, throughout the last glacial period, including the summer sea-ice maxima (30-22 ka BP). Stomach-oil deposit accumulation rate, δ¹³Corg and δ15Ntot and diet reconstructions show that snow petrels and their prey dynamically responded to physical and geochemical changes in the sea-ice zone, in line with the bipolar seesaw. Together, these findings provide new insights into past dynamics and geochemical cycling within the glacial seaice zone, showing that both primary productivity and air-sea gas exchange took place along the Dronning Maud Land margin throughout the last glacial period. This research has implications for our understanding of the biological and physical aspects of the Antarctic summer sea-ice zone and highlights the importance of including air-sea gas exchange at high southern latitudes in glacial carbon cycle models.