Compositional variations in sedimentary lacustrine organic matter and their implications for high Alpine Holocene environmental changes: Lake St. Moritz, Switzerland

Abstract

Organic matter accumulation and preservation in lakes with different geomorphological and climatic regimes, is directly influenced not only by local but also by regional and more global climatic conditions. Thus, compositional variations in lacustrine organic matter can be used as good indicators of paleoenvironmental conditions of deposition. Relatively high average TOC (1.0–6.5 wt%) and good lamination characterize most of the Holocene sequence of Lake St. Moritz, an Alphine lake located 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 change occurs at the Late Glacial-Holocene boundary, where δ 13C (OM), Hydrogen Index and lipid concentrations indicate a substantial increase in primary productivity. Organic matter production and preservation appear to dominate from the early Holocene until approximately 3.8 Ka BP, although variations in sterol contents and fatty acid distributions indicate superimposed fluctuations, such as between 8.3 and 8.1 Ka BP and 5.1 to 4.8 Ka BP. These variations in the lake trophic-state can be correlated with other proglacial lakes in the region, as well as with 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.