Carbon and nitrogen stable isotopes across the last deglaciation: perspectives from snow petrel stomach oil deposits

Evidence from both marine and ice cores strongly indicates that surface ocean processes influencing air-sea gas exchange of the Southern Ocean played a crucial role in the transition from a glacial to interglacial climate state. However, few archives have been able to reconstruct how high latitude surface ocean processes affected the biogeochemical changes occurring in nutrient utilization, primary productivity, and their effects on carbon sequestering in ecosystems. An opportunity to explore these processes is provided by accumulated snow petrel (Pagodroma nivea) stomach oil deposits, defensively regurgitated by snow petrels at their nest sites. These deposits provide a record of biogeochemical processes in the austral summer, at a high trophic level and integrated over a relatively wide area defined by snow petrel foraging range. Here, we present a joint carbon and nitrogen stable isotope record from stomach oil deposits from the Lake Untersee nunataks in Dronning Maud Land (DML) integrating data from a coastal area of 65-70°S. Our results show a 3‰ offset in δ¹³C and 4‰ offset in δ¹⁵N between LGM and Holocene, indicating that the coastal high latitudes underwent large changes over the deglaciation. The δ¹⁵N depletion into the Holocene shows strong similarity to changes occurring in nutrient utilization along the margin of the polar front, indicating that the Southern Ocean high latitudes were not an isolated oasis during the LGM but biogeochemically connected to the surface ocean beyond the summer sea-ice margin. In addition, the presence of stomach oil deposits indicates that open water was present in summer along the coast of DML over both the LGM and Holocene. Such highly productive, open water areas were potentially an important factor in the air-sea gas exchange contributing to the deglacial atmospheric CO₂ -rise.