Significance of different n-alkane biomarker distributions in four same-age peat sequences around the edges of a small maar lake in China

Abstract

A decade-resolution study of peat cores from four different locations around Yuanchi Lake, a small shallow maar lake in the Changbai Mountains of northeastern China, has established that peat deposition around this lake amplified at ca. 1800 CE with accumulation rates that differ among the four closely spaced sites. Comparisons of the n-alkane distributions of typical plants and the distributions in the peat cores indicate that the differences in the n-alkane contents at the four sites around the lake are consequences of differences in the peat-forming plant communities that have developed on the lake edges. These floral differences likely resulted from different littoral water depths from small but significant variations in bottom topography around the lake, compounded by progressive infilling of the edges at different rates as peat accumulated. Moreover, several n-alkane-inferred variations in peat accumulation rates from 1800 to 1950 CE are common to the four sites and appear to reflect local cold and dry periods. We infer that these periods are associated with nearby volcanic eruptions in the Changbai Mountains and possibly to distal eruptions in the tropical Pacific. Since 1950 CE, decreases in peat accumulations around the lake may result from enhanced peat decomposition as the water table declined in response to a warm and dry climate and to anthropogenic impacts on the lake catchment.