Mid-Holocene sea-ice dynamics and climate in the northeastern Weddell Sea inferred from an Antarctic snow petrel stomach oil deposit

Understanding past variability in Antarctic sea ice is of critical importance to determine how it regulates global climate processes, biogeochemistry, and Southern Ocean marine ecosystems. Records of changes in Holocene sea-ice conditions in the Weddell Sea are limited to a few marine sediment cores and inferences from continental ice cores. Here we present a novel record of sea ice and climate from ∼ 6390 to 1830 cal. yr BP based on accumulation rates and multi-proxy geochemical analyses of a snow petrel stomach-oil deposit from the Heimefrontfjella Range, Dronning Maud Land, East Antarctica. Three different sea-ice configurations are interpreted from the record. In the first interval, from 6390 to 5960 cal. yr BP, we see evidence of high productivity and inputs of krill, which suggests foraging both at the continental shelf edge in the marginal ice zone (MIZ) and extending offshore over pelagic waters. We infer that the MIZ lay within the foraging range of Heimefrontfjella. In the second interval, from 5960 to 4320 cal. yr BP, productivity remained high, but there was a reduced influence of krill and likely more fish in the diet. This is consistent with foraging both over the continental shelf edge and offshore, supportive of the summer sea ice retreat reaching the shelf edge more frequently. Finally, in the final interval, between 4320 to 1830 cal. yr BP we infer very low productivity where increased sea-ice conditions restricted access to foraging grounds and open waters, with a less accessible MIZ resulting in a more dense sea-ice pack. Our results highlight how specific Holocene sea-ice configurations can be interpreted from the geochemical composition of snow petrel stomach-oil deposits. We also show, for the first time, the utility of phytol and cholesterol analysis for tracking past avian diet.

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