The role of algae for sequestration of atmospheric mercury in the ocean is largely unknown owing to a lack of marine sediment data. We used high-resolution cores from marine Antarctica to estimate Holocene global mercury accumulation in biogenic siliceous sediments (diatom ooze). Diatom ooze exhibits the highest mercury accumulation rates ever reported for the marine environment and provides a large sink of anthropogenic mercury, surpassing existing model estimates by as much as a factor of 7. Anthropogenic pollution of the Southern Ocean began ~150 years ago, and up to 20% of anthropogenic mercury emitted to the atmosphere may have been stored in diatom ooze. These findings reveal the crucial role of diatoms as a fast vector for mercury sequestration and diatom ooze as a large marine mercury sink.

Natural archives have been used to reconstruct mercury atmospheric deposition at different spatial and temporal scales during the Holocene in the Northern Hemisphere. In this study, we present the results from a Brazilian mountain mire (Pinheiro mire, Minas Gerais, SE Brazil), extending back to ∼57 ka. The core was analyzed for mercury concentration, organic matter content, organic carbon isotopic composition, and tracers of mineral matter flux. Principal components analysis followed by principal components regression enabled us to determine the evolution of the weight of the latent processes governing the accumulation of mercury through time. We show that climate change was the main driver for the variations of mercury concentrations, either indirectly by (i) enhancing soil erosion in the mire's catchment, which led to a decrease in mercury concentration due to dilution by low mercury-containing mineral matter, (ii) increasing regional dust deposition, which resulted in increased concentrations, or directly, by long-term changes in atmospheric wet deposition (arid vs humid periods). Internal peat processes (i.e., decomposition and mass loss) had a minor influence at the time scale represented by the core.

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Cyclic changes in total solar irradiance (TSI) during the Holocene are known to affect global climatic conditions and cause cyclic climatic oscillations, e.g., Bond events and related changes of environmental conditions. However, the processes how changes in TSI affect climate and environment of the Southern Hemisphere, especially in southernmost South America, a key area for the global climate, are still poorly resolved. Here we show that highly sensitive proxies for aquatic productivity derived from sediments of a lake near the Chilean South Atlantic coast (53 °S) strongly match the cyclic changes in TSI throughout the Holocene. Intra-lake productivity variations show a periodicity of ~200–240 years coherent with the time series of TSI-controlled cosmogenic nuclide 10Be production. In addition TSI dependent periodicity of Bond events (~1500 years) appear to control wetness at the LH site indicated by mineral matter erosion from the catchment to the lake assumingly through shifts of the position of the southern westerly wind belt. Thus, both intra-lake productivity and wetness at the southernmost South America are directly or indirectly controlled by TSI.

Mercury (Hg) is a toxic trace element known to highly accumulate in aquatic biota and uptake by algae is the main entry‐point into the aquatic food chain. However, the effect of changes in solar irradiance and climatic conditions on Hg uptake by algae is largely unknown. We analyzed the link between sediment Hg accumulation, cyclic changes in total solar irradiance (TSI), and related changes in lake productivity as well as climate during the past 4.5 thousand years (kyr) in sediments of a small highly productive lake in Southern Patagonia (53°S). The analyses encompass proxies for TSI (based on 10Be), sediment geochemical composition, and lake productivity (FTIR spectra, and hydrogen‐index). The sediment record shows high concentrations of organic matter (median 70%) and strong variations in Hg accumulation rates (14–53 μg m2 yr−1) which correspond to changes in aquatic productivity and TSI. Accumulation of Hg was highest during dryer periods when irradiance and lake productivity was high. During these periods, accumulation was up to fourfold higher compared to those of lower TSI, lower productivity, and wetter climatic conditions. Higher amounts of algae biomass can increase Hg scavenging by organic particles and Hg export to the sediment. To obtain mass balance, we assume that the increase in sediment Hg accumulation rates during periods of lower Hg fluxes from the catchment (drier) caused a decrease in water phase Hg and in rates of Hg evasion from the lake.