n -alkanol ratios as proxies of paleovegetation and paleoclimate in a peat-lacustrine core in southern China since the last deglaciation

Abstract

High resolution records of long chain n-alkanol biomarkers were obtained from a peat-lacustrine core from the Dingnan profile in southern China. The n-alkanol distributions are characterized by the predominance of even-over-odd carbon number and maximize at C₂₄ or C₂₆. On the basis of the reported n-alkanol records in the literature and the n-alkane record in our samples, we concluded that the n-alkanol ratio of C₂₆/C₃₀ varying from 1.25 to 6.48, together with the n-alkanol ratio C₂₂/C₂₄ less than unity, is indicative of the presence of a dominant forest paleovegetation. A 2000-year cycling in the variation of the n-alkanol ratio C₂₆/C₃₀ is identifiable in our profile, and probably results from the change in the abundance of the grass relative to trees induced by a cyclic paleoclimate. The n-alkanol ratio C₂₄/C₂₆ appears to be more sensitive to change in precipitation than in temperature, and may be a potential indicator of precipitation/humidity, with increased values being associated with relatively dry conditions. The paleovegetation and the paleoclimate reconstructed on the basis of the n-alkanol records for the recent 18000 cal a BP in general accord with the pollen data and other lipid evidence recorded in the Dingnan region in southern China. In particular, both the n-alkanol records and the pollen data infer the different paleoclimate conditions for the two peat sequences, with a cool and wet climate dominating in the lower peat deposition formed during the latest Pleistocene and a change to a drier and cooler climate occurring in the upper peat sequence in mid-Holocene.

Keywords

southern China / n-alkanols / lipids / paleovegetation and paleoclimate / geobiology