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キーワード:
geochemistry, lake sediments, palaeoenvironmental proxies, tso moriri lake, weathering indices
要旨:
We report the results of our investigations on the catchment area, lake surface sediments, and hydrology of the high altitude alpine Tso Moriri Lake, NW Himalayas (India). Our results indicate that the lake is currently alkaline, and thermally stratified with an oxic bottom layer. Results from hydrochemistry and isotopic composition (δ 18 O and δD) of inflowing streams and lake waters show that Tso Moriri Lake is an evaporative lake with contributions from both westerly source (snow melt) and Indian summer monsoon precipitation. Geochemical and mineralogical investigations on the catchment and lake surface sediments reveal the presence of authigenic aragonite in modern lake sediment. The lithogenic components reflect the inflow and sorting processes during transport into the lake, whereas the authigenic carbonate fraction can be linked to the changes in ([precipitation+meltwater]/evaporation) (I/E) balance within the lake. The spatial variability in grain size distribution within the lake surface sediments shows that the grain size data can be utilised as a proxy for transport energy and shoreline proximity in the lake basin. We have evaluated the applicability of commonly applied environmentally sensitive proxies (isotopes, mineralogy, weathering indices) for palaeoenvironmental reconstruction in the Tso Moriri Lake. Our results show that the commonly used weathering index (Rb/Sr) is not applicable due to Sr contribution from authigenic carbonates. The useful weathering indices in Tso Moriri Lake are the Si/Al and the Chemical Proxy of Alteration (CPA). Since the carbonates are formed by evaporative processes, their presence and isotopic values can be used as indicators of I/E changes in the lake.
