Foraminiferal assemboages and CaCO_3 dissolution since the last deglaciation in the Maxwell Bay, King George Island, Antarctica

摘要

Three sediment cores (A10-01, -02 and -08) from the Maxwell Bay, King George Island, Antarctica were quantitatively analyzed for foraminiferal fauna. Planktonic foraminifera of three cores the due to the special Antarctica environment. Benthic foraminifera is mainly composed of Globocassidulina biora, Globocassidulina crassa rossensis, Cassidulinoides parkerianus and Miliammina arenacea. G.biora and G.crassa rossensis show high percentages in the shallower Core A10-08 while M.arenacea displays obviously high percentage in deeper Core A10-02. The lower parts of the cores have a lower abundance of foraminifera, while the upper parts have a relatively higher abundance. The down-core variations of benthic foraminifera reflect the contrast of surface water environment between the last deglaciation and post glacial. During the last deglaciation (lower parts of the cores), the lower abundant foraminifera was consistent with the lower TOC, which reflected that the extensive sea ice prevented the production of primary organisms, and therefore, lower flux of organic particles was delivered to the sea floor. Abundant foraminifera together with higher TOC in the upper parts of the cores suggested a higher primary productivity after the glaciation. The shallowest-water-depth Core A10-08 (45m), displayed a better carbonate preservation than the other two cores (A10-01 and -02) from the depths of 85 and 105m, respectively in carbonate dissolution reflected the remarkable shallow lysocline and carbonate compensation depth (CCD) in the Antarctic area, and also reflected significant variations in water properties even within such a difference only about 60m in water depth .Down-core variations of benthic foraminifera dissolution index (BDI) and CaCO_3 content indicated the existence of stronger carbonate dissolution in the upper parts than those in the lower parts of the cores .The down-core variations of carbonate dissolution suggested changes of water properties linked to the shallow CCD in this area. It was supposed that the less influence of the Saline Shelf Water during the last deglaciation enhanced the carbonate preservation. With the sea-level increasing and retreat of the coastal ice after the glacial, erosive water masses and the higher CO_2 accumulated by the increased flux of organic material led to severe dissolution of CaCO_3 and foraminiferal shells in the sediment.