Postglacial climate-change record in biomarker lipid compositions of the Hani peat sequence, Northeastern China

The peat sequence at Hani in northeastern China accumulated over the past 16 cal kyr in a percolation mire in which rain water and ground water seeped through the peat system. The molecular compositions of n-alkanes, n-alkanols, and n-alkanoic acids extracted from the Hani peat sequence reveal different responses to the progressive evolution of climate and changes in the nature of the peat-forming vegetation. Long chain length components that originate from the waxy coatings of subaerial vascular plants dominate the n-alkane distributions throughout the Hani peat sequence. The paleoclimate integrity of these biomarker molecules appears to be well preserved. Most of the n-alkanol distributions are similarly dominated by long chain components that indicate their origins from subaerial plants. In contrast, n-alkanoic acid distributions are dominated by secondary components that record the importance of post-depositional microbial activity in this peat sequence, which evidently can be extensive in a percolation mire. Elevated n-alkane P(aq) values and C(23)/C(29) ratios, which are both molecular proxies for water-loving plants, record an especially moist local climate in the Bolling-Allerod (14.5 to 12.9 ka), Younger Dryas (12.9 to 11.5 ka), and Pre-Boreal (11.5 to 10.5 ka) portions of the Hard peat sequence. Depressed P(aq) values and C(23)/C(29) ratios and larger n-alkane average chain length values indicate that the Holocene Climatic Optimum (10.5 to 6 ka) was a period of warmer climate with lower effective precipitation, which contrasts with evidence of wetter climates in most of East Asia. (C) 2010 Elsevier B.V. All rights reserved.