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

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 (f geog = 79%) and played a minor role during the mid-to late Holocene (4500 BP to present; f geog = 20%) when atmospheric Hg deposition dominated. Sediment Δ 200 Hg 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 Δ 199 Hg 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.

The altitude of the depths: use of inland water archaeology for the reconstruction of inundated cultural landscapes in Lake Titicaca

“…3804 metres. This wet period in the Lake Titicaca region (Baker et al 2009;Thompson et al 2013;Jiskra et al 2022) has thus resulted in the inundation of large surfaces of the inland territory, and probably forced the populations to migrate to higher elevations. This may have particularly contributed to the emergence of the Tiwanaku culture, through the migration of the populations towards its capital Tiahuanaco located at 3850 m a.s.l.…”

Sediments: sink, archive, and source of contaminants

“…Let us not forget about heavy metals and trace element that have recorded contamination from industrial activities and other anthropogenic activity (Hsu et al 2016 ; Magesh et al 2011 ). Furthermore, sediment records have helped to decipher the impact of climate change by using biogeochemical molecules, inorganic markers, stable isotopes, and natural forcings, to name a few (Jiskra et al 2022 ; Wanner et al 2008 ; Zander et al 2021 ).…”

Holocene variations in Lake Titicaca water level and their implications for sociopolitical developments in the central Andes

“…Elsewhere in the lake, higher CaCO 3 values reflect lower lake level and the resultant higher chemical precipitation of CaCO 3 with increasing salinity ( 30 , 37 ). Finally, because soils are enriched in Ti compared to lake sediments ( 38 ), Ti was used as an inorganic tracer of detrital inputs to the lake. Soil erosion from the catchment is mainly recorded at water depths less than ~2.5 m, because the dense totora sedges on the lake’s shore intercept more than 90% of terrestrial eroded particles ( 39 ).…”