Climatic Controls on a Holocene Mercury Stable Isotope Sediment Record of Lake Titicaca

Martin Jiskra, Stéphane Guédron, Julie Tolu, Sherilyn C. Fritz, Paul A. Baker, Jeroen E. Sonke

Research output: Contribution to journalArticlepeer-review

Abstract

Mercury (Hg) records in sediment archives inform past patterns of Hg deposition and the anthropogenic contribution to global Hg cycling. Natural climate variations complicate the interpretation of past Hg accumulation rates (HgARs), warranting additional research. Here, we investigated Hg stable isotopes in a ca. 8k year-long sediment core of Lake Titicaca and combined isotopic data with organic biomarkers and biogeochemical measurements. A wet period in the early Holocene (8000-7300 BP) induced strong watershed erosion, leading to a high HgAR (20.2 ± 6.9 μg m-2 year-1), which exceeded the 20th century HgAR (8.4 ± 1.0 μg m-2 year-1). Geogenic Hg input dominated during the early Holocene (fgeog = 79%) and played a minor role during the mid- to late Holocene (4500 BP to present; fgeog = 20%) when atmospheric Hg deposition dominated. Sediment Δ200Hg values and the absence of terrestrial lignin biomarkers suggest that direct lake uptake of atmospheric Hg(0), and subsequent algal scavenging of lake Hg, represented an important atmospheric deposition pathway (42%) during the mid- to late Holocene. During wet episodes of the late Holocene (2400 BP to present), atmospheric Hg(II) deposition was the dominant source of lake sediment Hg (up to 82%). Sediment Δ199Hg values suggest that photochemical reduction and re-emission of Hg(0) occurred from the lake surface. Hg stable isotopes show promise as proxies for understanding the history of Hg sources and transformations and help to disentangle anthropogenic and climate factors influencing HgAR observed in sediment archives.

Original languageEnglish (US)
Pages (from-to)346-357
Number of pages12
JournalACS Earth and Space Chemistry
Volume6
Issue number2
DOIs
StatePublished - Feb 17 2022
Externally publishedYes

Keywords

  • Hg stable isotopes
  • Holocene
  • atmospheric deposition
  • climate variations
  • erosion
  • sediment archive

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Atmospheric Science
  • Space and Planetary Science

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