Hydrogen isotopic ratios of plant wax n-alkanes in a peat bog deposited in northeast China during the last 16 kyr

Osamu Seki, Philip Meyers, Kimitaka Kawamura, Yanhong Zheng, Weijian Zhou

Research output: Contribution to journalArticle (Academic Journal)peer-review

71 Citations (Scopus)

Abstract

Based on paleoclimatic reconstructions using various proxies, the Holocene Climate Optimum (10.5–6 ka)
has been characterized as a warmer and wetter period in most of East Asia. The summer monsoons associated
with the East Asian Monsoon evidently intensified and extended further inland from the Pacific
Ocean, a source region of moisture. A notable exception to this general pattern exists in northeast China,
where less wet conditions are recorded. We determined molecular compositions of individual plant wax
hydrocarbons and their hydrogen isotope compositions (dD values) in a radiocarbon-dated peat core
recovered from the Hani marsh in Jilin Province (China) and confirmed that the temperature-dependent
effective precipitation in northeast China decreased during the Holocene Climate Optimum. A combination
of Paq, an indicator of the relative contribution of aquatic to terrestrial plants, and the difference in dD
between low (C23, C25 and C27) and high molecular weight (C31) n-alkanes in the Hani peat bog indicates a
dramatic change in vegetation from the deglaciation to the Holocene. No significant differences were
observed between the dD values of low and high molecular weight n-alkanes with relatively high dD values
and low Paq during the early Holocene, indicating that all n-alkanes were produced by evapotranspiration-
sensitive terrestrial plants during that time. However, lower dD values of mid-chain n-alkanes (C23,
C25 and C27) relative to the long chain n-alkane (C31), together with higher Paq values during the deglaciation
(14–11 ka), suggest an increase in the contribution of aquatic plants and a higher water level during
the period. The study demonstrates that northeast China was under a markedly wetter climate condition
during the late deglaciation. For the 16 kyr record in the Hani peat sequence, we infer that moisture delivery
by the East Asian Monsoon was relatively invariable in northeast China, but increased evaporation
during the warmer Holocene Climate Optimum reduced the effective precipitation, defined by the balance
between precipitation and evaporation.
Original languageEnglish
Article numberB
JournalOrganic Geochemistry
Publication statusPublished - 2009

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