Search

Abstract Volcanism is one of the major natural processes emitting mercury (Hg) to the atmosphere, representing a significant component of the global Hg budget. The importance of volcanic eruptions for local-scale Hg deposition was investigated using analyses of Hg, inorganic elemental tracers, and organic biomarkers in a sediment sequence from Lake Chungará (4520 m a.s.l.). Environmental change and Hg deposition in the immediate vicinity of the Parinacota volcano were reconstructed over the last 2700 years, encompassing the pre-anthropogenic and anthropogenic periods. Twenty eruptions delivering large amounts of Hg (1 to 457 μg Hg m−2 yr−1 deposited at the timescale of the event) were locally recorded. Peaks of Hg concentration recorded after most of the eruptions were attributed to a decrease in sedimentation rate together with the rapid re-oxidation of gaseous elemental Hg and deposition with fine particles and incorporation into lake primary producers. Over the study period, the contribution of volcanic emissions has been estimated as 32% of the total Hg input to the lake. Sharp depletions in primary production occurred at each eruption, likely resulting from massive volcaniclastic inputs and changes in the lake-water physico-chemistry. Excluding the volcanic deposition periods, Hg accumulation rates rose from natural background values (1.9 ± 0.5 μg m−2 yr−1) by a factor of 2.3 during the pre-colonial mining period (1400–900 yr cal. BP), and by a factor of 6 and 7.6, respectively, during the Hispanic colonial epoch (400–150 yr cal. BP) and the industrial era (~140 yr cal. BP to present). Altogether, the dataset indicates that lake primary production has been the main, but not limiting, carrier for Hg to the sediment. Volcanic activity and climate change are only secondary drivers of local Hg deposition relative to the magnitude of regional and global anthropogenic emissions. Graphical abstract Unlabelled Image Highlights • We studied mercury deposition in Lake Chungará (18°S) over the last ~2700 years. • Parinacota volcano produced 20 tephra layers recorded in lake sediments. • Lake primary production was the main, not limiting, carrier of Hg to the sediment. • Volcanoes contributed to ~30% of Hg inputs to the lake over the study period. • Last 400 years anthropogenic Hg emissions overwhelmed the volcanic activities. [ABSTRACT FROM AUTHOR]

Abstract Very few studies have focused on historical mercury (Hg) deposition in the Southern Hemisphere, especially for the pre-mining period. Therefore, the respective contributions of Hg emissions from anthropogenic and natural sources are not fully constrained and the long-term influence of climate variability is still in debate. In this study, we reconstructed Hg depositions over the last 13,500 years based on two sedimentary records located at the fringe between Amazonia and the Altiplano. Multiproxy analyses carried on the same sedimentary archives (i.e. Hg accumulation rates (AR), major elements, total organic carbon, δ13C and pollen analyses) show evidence that Hg deposition has risen according to Amazonian orographic moisture and precipitation during the Holocene, except for the last 200 years, for which modern industry and goldmining overwhelmed the natural signal. Comparisons with existing Hg records indicated that metallurgy and volcanic emissions were not perceptible due to the eastern down-wind position of the sites. Altogether, it argues that the historical variability of Hg deposition in the central eastern Andes has been primarily driven by changes in Amazonian moisture. At least six main phases of higher Hg AR (2.6 ± 1.4 μg m−2 y−1) compared to baseline values (0.9 ± 0.3 μg m−2 y−1) were identified over the Holocene. During the early and late Holocene, phases of higher Hg AR coincided with wet episodes recorded in Lake Titicaca and Sajama records. During the Middle Holocene arid phase, reconstructed wetter episodes by Hg together with vegetation dynamics were attributed to the set-up of moisture niches in the eastern flanks of the Andes. Comparisons to other paleoclimatic records supports the role of North Atlantic sea-surface temperature in forcing precipitation during the late Holocene period while other mechanisms allowing moisture niches by orography are discussed for the Mid-Holocene dry phase in the eastern Andes region. Graphical abstract Unlabelled Image Highlights • Two high-altitude sediment archives of the Eastern Andean Cordillera are studied. • Changes in mercury (Hg) deposition are recorded for the last 13,500 years. • Hg and pollen recorded changes in Amazonian orographic precipitation. • Moisture is likely to be driven by the Atlantic meridional overturning circulation. • Moisture niches maintained humidity during the arid mid-Holocene in eastern Andes. [ABSTRACT FROM AUTHOR]

Over the last decade, an increasing number of studies have used lake sediment DNA to trace past landscape changes, agricultural activities or human presence. However, the processes responsible for lake sediment formation and sediment properties might affect DNA records via taphonomic and analytical processes. It is crucial to understand these processes to ensure reliable interpretations for "palaeo" studies. Here, we combined plant and mammal DNA metabarcoding analyses with sedimentological and geochemical analyses from three lake-catchment systems that are characterised by different erosion dynamics. The new insights derived from this approach elucidate and assess issues relating to DNA sources and transfer processes. The sources of eroded materials strongly affect the "catchment-DNA" concentration in the sediments. For instance, erosion of upper organic and organo-mineral soil horizons provides a higher amount of plant DNA in lake sediments than deep horizons, bare soils or glacial flours. Moreover, high erosion rates, along with a well-developed hydrographic network, are proposed as factors positively affecting the representation of the catchment flora. The development of open and agricultural landscapes, which favour the erosion, could thus bias the reconstructed landscape trajectory but help the record of these human activities. Regarding domestic animals, pastoral practices and animal behaviour might affect their DNA record because they control the type of source of DNA ("point" vs. "diffuse"). [ABSTRACT FROM AUTHOR]