Climate changes in the South Orkney Plateau during the last 8600 years

Abstract

Climatic and oceanographic changes in the South Orkney Plateau, western Antarctica, during the last 8600 years are reconstructed from a 525-cm-long gravity core based on sedimentological, geochemical, and diatom analyses. The core sediments are composed mostly of light greyish olive diatomaceous silt and mud with a few diatom ooze laminae in the basal part. The core can be divided at 350 cm into two units (4800 cal yr BP): the lower unit is characterized by variable total organic carbon (TOC) content and higher CaCO3 content, and the upper unit is characterized by higher TOC and lower CaCO3. The content of biogenic silica varies similar to TOC content in the lower unit but does not increase in the upper unit despite increased TOC. The variations in the organic matter composition and the amount of carbonate suggest that Scotia Sea water had been dominant in the study area prior to 4800 cal yr BP. A warmer condition during the middle Holocene is also supported by the fewer sea ice diatom taxa and a more sub-polar form of Eucampia antarctica in the lower unit. The increased sea ice and decreased influence of Scotia Sea water in the upper unit reflect climate cooling occurred at 4800 cal yr BP.