Paleoceanographic changes in the Southern Ocean off Elephant Island since the last glacial period: Links between surface water productivity, nutrient utilization, bottom water currents, and ice-rafted debris

Abstract

To understand past changes in ocean–cryosphere interactions in the Southern Ocean off the Antarctic Peninsula, multi-proxy analyses of three sediment cores located off Elephant Island were used to reconstruct changes in paleoproductivity, nutrient utilization, bottom current intensity, and iceberg calving since the last glacial period. The glacial period was characterized by low surface water productivity with high nutrient utilization, indicating surface water stratification. During the deglaciation, surface water productivity increased with decreasing nutrient utilization, implying that the increase is associated with increased nutrient supply from the subsurface water by enhancing Antarctic Circumpolar Current (ACC) influence as fronts migrate southward with warming. Abundant occurrence of grains >1 mm during the deglacial period indicates rapid ice sheet retreat with large-scale melting and calving. During the glacial period, however, coarse silt–fine sand-sized fraction represented ice-rafted debris (IRD). The different IRD grain size characteristics are thought to be related to the IRD source material characteristics. Regardless of IRD input, the running downcore correlation (5 to 9-point) between sortable silt mean grain size and percentage showed that sediments are well sorted by bottom current. However, the cross plot of them showed different temporal relationships. Sediments were sorted by the ACC and southwestward flowing bottom current. Along with southward migration of fronts and the ACC, southwestward flowing bottom current influence diminished, whereas the ACC influence increased particularly from 7 ka. Our results indicate that the sedimentary processes in the Scotia Sea largely depend on the regional interactions between the ocean and the cryosphere.