posted on 2022-01-20, 01:05authored byMartin Jiskra, Stéphane Guédron, Julie Tolu, Sherilyn C. Fritz, Paul A. Baker, Jeroen E. Sonke
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.