Mineralogical and Geochemical Records of Changing Terrigenous Supply off Antarctica (wilkes Land) during the Quaternary

Multiproxy analyses (clay mineralogy, grain-size distribution, elemental geochemistry) of a core collected off Wilkes Land (Antarctica) revealed a major modification of terrigenous sedimentation during glacial intervals suggesting deep-currents reorganization. Sedimentological and geochemical data indicate that detrital sedimentation results from both proximal continental inputs (i.e. Wilkes Land Antarctica) and distal volcanic supplies during interglacial intervals (IG). The volcanic contribution seems to disappear during glacial (G) periods as the result of major alteration of deep circulation. These potential sources were constrained using radiogenic isotopes. 87Sr/86Sr ranges stress major changing provenance of the clay-size particles over the last climatic cycle with low Sr isotope ratios occurring during the Holocene contrasting with high ratio during the last deglaciation. The lowest Sr compositions clearly reflect distal oceanic supply from volcanic areas during the deglaciation while the highest Sr ratios is directly related with prominent proximal inputs from the adjacent Wilkes Land old continental crust during G. Moreover, maximum 87Sr/86Sr amplitude is observed during the oldest part of the record whereas minimum range characterizes the last termination. According to regional geology and previously published Sr isotopic ratios distribution around Antarctica, the less radiogenic Sr characterizing the Holocene may result from volcanic supply from either the Kerguelen Plateau; via the Antarctic Circumpolar Current (ACC) or the Antarctic Peninsula, via the westward flowing currents south of the ACC (Hemming et al., 2007; Roy et al., 2007; van de Flierdt et al., 2007). The ɛNd displays higher values during the IG and lower values during G. The last climatic cycle displays a striking feature with lower ɛNd during MIS1 than during MIS2-4. This result confirms the major modification/reorganization of deep circulation during the last climatic cycle compared with previous climatic cycles evidenced by the 87Sr/86Sr record. The whole set of data samples plot on a mixing line between a "young" volcanic end-member and an "old" crustal end-member in the eɛNd vs. 87Sr/86Sr diagram, but define rather distinct domains. The IG samples plot near the "volcanic" enc-member whereas the G samples are located near the "crustal" end-member. The Pb isotopic system was used to discriminate between the different volcanic sources. Indeed Kerguelen Archipelago and Antarctic Peninsula are characterized by close 87Sr/86Sr and ɛNd ratios but display rather distinct Pb isotopic ratios (Hole et al., 1993; Xu et al., 2007). The lead isotopic ratios display similar variations, exhibiting a larger range of variability over the older part of the record compared to the last climatic cycle. IG are characterized by higher lead isotopic ratios relative to G stages. The lead isotopic data suggests that the Kerguelen Archipelago was potentially a source for detrital particles during previous IG periods, but could not explain the last climatic cycle specific trend (Kempton et al., 2002).