Diatom evidence for Holocene paleoclimatic change in the South Scotia Sea, West Antarctica

摘要

Diatom data of the core sediment from a deep basin in the South Scotia Sea, West Antarctica provide high-resolution information on changes in oceanographic processes and paleoclimate during the late Quaternary. Three main climatic changes can be distinguished in diatom assemblages: Last Glacial Maximu (LGM), mid-Holocene climatic optimum and Neoglacial cold event. Diatom assemblages have been deposited in a variable sea ice condition over the last 25,000 yr in response to the climate change. During the LGM to early-Holocene (23,370–8,300 yr BP), the core site might be influenced by increased dense sea-ice cover, which could reduce biogenic flux from the surface water, depositing relatively increased amount of sea ice-related diatoms (Actinocyclas actinochilus, Eucampia antarctica, Fragilariopsis curta, andFragilariopsis cylindrus). During these periods, it is likely that the increased sea ice cover between the Weddell and Scotia seas would have severely preventedChaetoceros resting spores in the Weddell Sea ice margin from being laterally advected to the Scotia Sea, resulting in the reduction ofC. resting spore abundance in the sediment. Afterward, a warm period followed from 8,300 to 2,400 yr BP in the mid Holocene when open water assemblages (Rhizosolenia styliformis andThalassiosira antarctica (warn)) were deposited. Significant dilution of the number ofFragilariopsis kerguelensis indicates the opening of communication between the Weddell and Scotia seas allowing lateral advection ofC. resting spores from the Weddell Sea to the Scotia Sea. A colder condition (Neoglacial cooling) then resumed since <2,400 yr BP in the late Holocene supported by other paleoclimatic records in the Antarctic Peninsula. The assemblage is characterized either by the increase of sea ice-related diatoms (A. actinochilus andF. cylindrus) or by the decrease of open water taxa (R. styliformis andT. antarctica (warm)) compared to that in the mid-Holocene optimum. The loose sea-ice assemblage was, however, different from dense sea-ice assemblage deposited in the LGM. Similarity of abundance ofChaetoceros between the Neoglacial and the mid-Holocene implies that the loose sea ice condition was not able to sufficiently restrict the lateral advection ofC. resting spore to the Scotia Sea from the Weddell Sea.