Pairing plant-wax H and C isotopes with lake-area – A method for evaluating the local amount effect in northern China during the late Quaternary

Yonaton Goldsmith*, Pratigya J. Polissar, Hai Xu, Peter deMenocal, Jianghu Lan, Peng Cheng, Weijian Zhou, Wallace S. Broecker

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

The correlation between modern tropical mean annual precipitation (MAP) and its isotopic composition (δp) has been extensively used to interpret terrestrial paleoclimate records. However, the existence of this phenomenon in the past and in individual regions remains a matter of debate. Here, we describe a method for evaluating the relationship between local δp and local MAP in the past (i.e. the “local amount effect”) and apply this method to a closed-basin lake in northeastern China. We measured compound specific hydrogen isotopes from plant-wax derived long-chain n-alkanes (δ2Hwax) and fatty acids (δ2HFA) from lake sediments, which primarily record local δp, and compared them with the lake level and area history of the lake, which records local MAP. Both the lake level reconstruction and the organic isotope proxies are derived from the same samples and thus enable a direct comparison. In addition, we explore the possibility of using chain-length distribution and δ2Hwax data to assess sediment reworking in the lake basin. Our results show that the n-C29 n-alkane δ2Hwax and C16:0n-acid δ2HFA are correlated with lake level over the past 15 to 3 ka from samples where both age and lake level are well constrained (n = 5 and n = 3, respectively). Over the past 2–3 ka this correlation breaks down: lake level remains low, following summer insolation, but the Chinese cave δ18O and modern δ2Hwax become progressively more negative. The reason for this ‘2 ka shift’, first identified in Chinese cave δ18O records, is unclear. Our data suggests that δp is decoupled from MAP during this time and thus adds an additional constraint to solving this issue. Our results show that combining lake-area reconstructions with organic isotope geochemistry from closed-basin lakes can be used to assess the relation between local rainfall amount and local δp in the past, but requires a thorough assessment of sediment dynamics of each individual sample.

Original languageAmerican English
Article number104403
JournalOrganic Geochemistry
Volume169
DOIs
StatePublished - Jul 2022

Bibliographical note

Publisher Copyright:
© 2022 Elsevier Ltd

Keywords

  • Biomarkers
  • Closed-basin lakes
  • Eastern Asia
  • Monsoon
  • Organic geochemistry
  • Paleoclimatology
  • Quaternary
  • Sedimentology
  • Speleothems
  • Stable isotopes

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