COMPOSITIONAL VARIATIONS IN SEDIMENTARY LACUSTRINE ORGANIC-MATTER ANDTHEIR IMPLICATIONS FOR HIGH ALPINE HOLOCENE ENVIRONMENTAL-CHANGES - LAKE ST MORITZ, SWITZERLAND

Organic matter accumulation and preservation in lakes with different g eomorphological and climatic regimes, is directly influenced not only by local but also by regional and more global climatic conditions. Thu s, compositional variations in lacustrine organic matter can be used a s good indicators of paleoenvironmental conditions of deposition. Rela tively high average TOC (1.0-6.5 wt%) and good lamination characterize most of the Holocene sequence of Lake St. Moritz, an Alpine lake loca ted in SE Switzerland. However, variations in the type and quality of the organic matter at discrete intervals have been distinguished using bulk parameters and biomarker distributions. The most prominent chang e occurs at the Late Glacial-Holocene boundary, where delta(13)C((OM)) , Hydrogen Index and lipid concentrations indicate a substantial incre ase in primary productivity. Organic matter production and preservatio n appear to dominate from the early Holocene until approximately 3.8 K a BP, although variations in sterol contents and fatty acid distributi ons indicate superimposed fluctuations, such as between 8.3 and 8.1 Ka BP and 5.1 4.8 Ka BP. These variations in the lake trophic-state can be correlated with other proglacial lakes in the region, as well as wi th similar lacustrine records on both sides of the Alps. The result of this comparison indicates a synchronous character of major to medium- amplitude climatic shifts on a European scale. Copyright (C) 1996 Else vier Science Ltd.