10 - Estimation of paleoenvironmental changes in the Eurasian continental interior during the past 5 million years inferred from organic components in the BDP96 1

Abstract

This chapter presents a study on the total organic carbon (TOC), total nitrogen (TN), hydrocarbons, fatty acids, and sterols in a BDP96/1 sediment core from the Academician Ridge in Lake Baikal in relation to BDP, and compares the results with marine d18O records, to estimate paleoenvironmental changes in the interior of the Eurasian continent during the past 5.2 million years. Low TOC content indicates low primary productivity in the drainage basin of the lake throughout the sedimentation. The TOC values fluctuates largely within a short period of time (less than 20 kilo years) reflecting short-term climate changes. The similarity of the TOC profile and marine records reveals that the climate changes in the interior of the continent occurred simultaneously with changes in the marine environment. The TOC profile is a useful proxy for global climate change. TOC and allocthonous organic matter data indicates a fairly warm climate from 4.3 to 2.8 Ma and from 2.0 to 1.5 Ma, and a cool climate from 2.8 to 2.2 Ma and from 1.5 Ma to the present. Allochthonous organic matter was mainly supplied by inflow of fiver water in warm periods. The decrease in relative abundance of n-C27 alkane and n-C26 alkanoic acid from about 4 Ma to the present, suggests a decrease in the contribution of Populas spp. and Salix spp. In the drainage basin of the lake, the increase in relative abundance of n-C31 alkane from about 4 Ma to the present probably reflects an increase in herbaceous plants due to aridification of the climate.