Biogeochemical processes accounting for the natural mercury variations in the Southern Ocean diatom ooze sediments

Abstract

Abstract. Due to its toxic nature and its high potential for biomagnification, mercury is a pollutant of concern. Understanding the marine biogeochemical cycle of mercury is crucial as consumption of mercury-enriched marine fish is the most important pathway of human exposure to monomethylmercury, a neurotoxin. However, due to the lack of long-term marine records, the role of the oceans in the global mercury cycle is poorly understood. We do not have well-documented data of natural mercury accumulations during changing environmental conditions, e.g., sea surface conditions in the ocean. To understand the influence of different sea surface conditions (climate-induced changes in ice coverage and biological production) on natural mercury accumulation, we used a continuous ∼170 m Holocene biogenic sedimentary record from Adélie Basin, East Antarctica, which mainly consists of silica-based skeletons of diatoms. We performed principal component analysis and regression analysis on element concentrations and corresponding residuals, respectively, to investigate the link between sediment mercury accumulation, terrestrial inputs, and phytoplankton productivity. Preindustrial mercury in the remote marine basin shows extremely high accumulation rates (median: 556 µg m−2 yr−1) that displayed periodic-like variations. Our analyses show that the variations in total mercury concentrations and accumulation rates are associated with biological production and related scavenging of water-phase mercury by rapidly sinking algae or algae-derived organic matter after intense algae blooms. High accumulation rates of other major and trace elements further reveal that, in regions of high primary productivity, settling of biogenic materials removes a large fraction of dissolved or particulate-bound elements from the free water phase through scavenging or biological uptake. The link between mercury cycling and primary production will need to be considered in future studies of the marine mercury cycle under primary production enhancement through climatic, temperature, and nutrient availability changes.

The Effect of Particle Composition and Concentration on the Partitioning Coefficient for Mercury in Three Ocean Basins

“…The Lack of a Resolved Intrinsic K d for Opal Zaferani et al have recently documented uncommonly high sediment accumulation fluxes of Hg that are also associated with high opal fluxes along parts of the Antarctic margin (e.g., Zaferani et al, 2018;Zaferani and Biester, 2020). This is seemingly inconsistent with our finding that there is little correlation between the values of bulk K d and f opal in overall datasets, resulting in undefined values for the intrinsic K d for Hg-opal, and implying either that biogenic silica is a poor sorbent material for Hg or that diatoms are not particularly effective at taking up Hg.…”

Sources of mercury varied in the Mariana Trench during the Last Glacial Maximum to the Holocene

“…The pronounced global environmental shifts during the LGM, which is manifested at depths of 215-325 cm and associated with an enhanced ux of Asian eolian dust, contributed to a marked increase in marine primary productivity in the western Paci c Ocean 34,55 . Recent research highlights the role of algae and algal-derived organic matter in aqueous-phase mercury removal, underscoring the signi cance of diatom laminations in Hg sequestration within marine environments 56,57 . The continuous existence of LDMs in the 215-325 cm sediment layer indicates that diatoms may be involved in the Hg cycle.…”

Transformation of Mercuric Ions to Mercury Nanoparticles in Diatom Chaetoceros curvisetus

“…This regulatory effect can be attributed to bioaccumulation and transformation of Hg by algae, which further influence the fate and transport flux of Hg in the ocean . The concentration factors (VCFs) of inorganic Hg in algae are 0.5–5 × 10 4 with intracellular Hg concentration at the range of 9.7–602.8 nmol g –1 (dry weight). , These make it difficult to calculate Hg transport flux via models due to the underestimated biological transformation of Hg . For better understanding of the marine Hg cycle and accurately assessing marine Hg flux, it is of vital importance to study the transformation of different Hg forms mediated by algae, particularly the formation of HgNPs in algae.…”

“…17,18 These make it difficult to calculate Hg transport flux via models due to the underestimated biological transformation of Hg. 19 of vital importance to study the transformation of different Hg forms mediated by algae, particularly the formation of HgNPs in algae. Until now, particulate HgS (β-HgS) has been detected in algae, while HgNPs have not been identified.…”