Onset of Neoglacial condition in South Orkney Plateau at 4.9ka

Abstract

A 533cm-long gravity core sediment retrieved from the northwestern end of the South Orkney Plateau, west Antarctica, records climatic and oceanographic changes during the last 8,700 years. Light grayish olive diatomaceous silt and mud are predominant throughout the core with several diatom-rich laminae below 498cm. Age of sediment was determined by AMS radiocarbon dating for organic matter in six sediment samples including one from box-core top, which shows a very old reservoir age of ~2,900 radiocarbon years. Sedimentation rate ranges from 46 and 84 cm/kyr with a higher rate in the upper part. The core is divided into two parts at 351 cm (4,900 cal yr B.P.) based on the contents of total organic carbon (TOC), carbonate (CaCO3) and biogenic opal (BSi). The lower part is characterized by variable TOC, high CaCO3, and BSi that varies similar to TOC. In the upper part, TOC is higher and CaCO3 is lower, and BSi does not correlate well with TOC. These characteristics imply that study area was under the influence of Scotia Sea Water prior to 4.9 ka and of Weddell Sea Water later. High concentration of open water diatom species and subpolar form of Eucampia antarctica in the lower part also suggests less winter sea ice during early Holocene. Cooling at 4.9 ka marks the onset of Neoglacial condition in the South Orkney Plateau and it accompanied northward shift of Weddell-Scotia frontal system.