Holocene foraminiferal assemblage and stable isotope analysis for the Gerlache Strait, Antarctic Peninisula.

摘要

The Antarctic Peninsula is one of the fastest warming regions on the planet. In the past 50 years, the temperature has increased by more than 2°C, leading to the retreat of large areas of the ice shelves fringing the Antarctic Peninsula. Recent environmental changes in the Antarctic Peninsula are well documented by meteorological and remote sensing data, but the behavior of the Holocene atmosphere-ocean-cryosphere system is not well understood. In this study foraminifera are used as a proxy for Holocene oceanographic conditions in the Gerlache Strait, western Antarctic Peninsula. The most abundant foraminifera identified in this study include the agglutinated taxa Miliammina arenacea and Paratrochammina lepida, which are associated with cold, saline water masses and periods of high sea-ice production. The most abundant calcareous species identified is the opportunistic Fursenkoina spp., which is associated with ice-proximal conditions and fresh water input due to glacial melting.;Deglaciation of the Gerlache following the Last Glacial Maximum is indicated by the appearance of foraminifera and diatoms at ∼7700 years BP. The Post-Deglaciation period is characterized by high frequency variation in foraminiferal assemblages between abundant agglutinated and calcareous taxa, indicating unstable glacial conditions. The beginning of the Mid-Holocene Climactic Optimum (MHCO) is indicated by a substantial decrease in sedimentation rates and a shift to more stable foraminiferal assemblages. A decline in diatom abundance and the absence of calcareous foraminifera indicates a glacial readvance at 6030 years BP. At 4470 years BP the calcareous taxa including Fursenkoina spp. become dominant, indicating glacial retreat and input of fresh water into the water column. After 3240 years BP agglutinated taxa are once again dominant and calcareous taxa absent. This marks the beginning of the Neoglacial period and the presence of colder, more saline shelf waters in the Gerlache Strait. Stratification of the water column is apparent during the Post-Deglaciation period and the latter part of the MCHO. A difference in delta18O values of >0.5 per mille between benthic and planktonic foraminifera indicates the presence of a less saline surface water layer which may be the result of freshwater input due to glacial melting and an estuarine circulation regime.