Reconstruction of postglacial paleoproductivity in Long Lake, King George Island, West Antarctica

Abstract

A sediment core (LS−1) collected from Long Lake in King George Island, South Shetland Islands (West Antarctica) was analyzed for a variety of textural, geochemical, iso− topic and paleontological properties together with 14 C age dates. These data combined with published records of other studies provide a detailed history of local/regional postglacial paleoproductivity variation with respect to terrestrial paleoclimate change. The lithologic contrast of a lower diamicton and an upper fine−grained sediment demonstrates glacial re− cession and subsequent lake formation. The upper fine−grained deposit, intercalated by mid−Holocene tephra−fallout followed by a tephra gravity flow, was formed in a lacustrine environment. Low total organic carbon (TOC) and biogenic silica (Sibio) contents with high C/N ratios characterize the diamicton, whereas an increase of TOC and Sibio contents char− acterize the postglacial lacustrine fine−grained sediments, which are dated at c. 4000 yrBP. More notable are the distinct TOC maxima, which may imply enhanced primary productiv− ity during warm periods. Changes in Sibio content and 13 C values, which support the in− creasing paleoproductivity, are in sympathy with these organic matter variations. The uni− form and low TOC contents that are decoupled by Sibio contents are attributed to the tephra gravity flows during the evolution of the lake rather than a reduced paleoproductivity. A very recent TOC maximum is also characterized by high Sibio content and 13 C values, clearly indicating increased paleoproductivity consequent upon gradual warming across King George Island. Comparable with changes in sediment geochemistry, the occurrence and abundance of several diatom species corroborate the paleoproductivity variations to− gether with the lithologic development. However, the paleoclimatic signature in local ter− restrial lake environment during the postglacial period (for example the Long Lake) seems to be less distinct, as compared to the marine environment.