Holocene climate change in northeastern China reconstructed from lipid biomarkers in a peat sequence from the Sanjiang Plain

Lipid biomarkers extracted from a sediment-peat sequence from the Sanjiang Plain were analyzed to assess the change in regional vegetation and climate during the last 8 ky. The combination of n-alkane and n-alkanoic acid distributions and published pollen and plant macrofossil records for the lake sediments underlying the peat reveal that the region experienced a warmer and wetter period before ca. 6 ka that corresponds to the monsoon maximum and Holocene climate optimum in northeast China. The climate then entered a cold and wet period from 6 to 4 ka. A shift to warmer and drier conditions starting 4 ka is recorded as a transformation from a shallow lake to a peat deposit. From 1.5 to 0.4 ka, the region entered a cold and wet period that was followed by warm and dry conditions for the most recent 0.4 ky. Our lipid-based paleoclimate reconstruction was compared with Holocene reconstructions based on lipid records from the nearby Hani peat sequence, peat cellulose δ13C results from the Jinchuan peat sequence, and pollen records from other lakes in northeast China. Most of the regional paleoclimate changes reconstructed from the lipid proxies in the Sanjiang Plain peat sequence have a strong link with sea surface temperature changes in the Sea of Japan that were influenced by summer solar insolation at 65°N and the East Asia summer monsoon. In contrast, the change to the warmer and drier conditions of the last four centuries seems to be mainly a consequence of human activity.