Search for: All records

Abstract Inorganic mercury (iHg) is an anthropogenic pollutant that forms monomethylmercury, a neurotoxicant affecting human health through seafood consumption. Despite iHg emissions reductions, the impact on oceanic concentrations remains unclear due to limited long-term data. Here, we present a four-year weekly time series of oceanic iHg concentrations at Scripps Pier in La Jolla, California, capturing interannual and seasonal variability. Interannual variability is driven by wet season precipitation, with wet years exhibiting sevenfold higher iHg concentration variance than dry years, potentially linking to El Niño-Southern Oscillation. Seasonally, precipitation and wave dynamics influence iHg inputs, with wet seasons driven by precipitation and runoff and dry seasons by upwelling. These parameters informed a model built to reconstruct a 20-year record of iHg concentrations, suggesting a long-term decline of 0.005 pM yr⁻¹due to climate-driven effects alone. This study highlights challenges in detecting long-term trends and emphasizes the need for sustained monitoring of oceanic iHg. 

California’s mining legacy continues to threaten water quality and ecosystem health throughout the state. This study focuses on mercury (Hg) releases from the former New Idria Mercury Mine, which was the second largest historic Hg producer in North America. San Carlos Creek, which flows adjacent to the mine, is impacted by acid mine drainage (AMD) as well as mining waste piles that sit at a high angle of repose over the channel. We documented total mercury (HgT) concentrations exceeding California’s 50 ng L^-1water quality objective for almost 10 km, from New Idria to a ~ 0.25 km²perennial wetland at the confluence of San Carlos Creek and Silver Creek within the Panoche Creek watershed. During baseflow and low flow storm conditions, unfiltered total Hg (U-HgT) in creek water downstream from the mine typically ranged from 1,100–9,200 ng Hg L^-1, with >90% of Hg in the particulate phase. U-HgT correlated (R² = 0.6) with suspended particulate matter (SPM) that was presumably a mixture of AMD-derived flocculant, weathered calcines (i.e., roasted ore), and sediment from the local watershed. The flocculant is easily resuspended in baseflow conditions and scoured from the channel during high flow events, resulting in seasonal patterns of Hg transport in San Carlos Creek that do not always align with the stream hydrograph. Mercury from New Idria, along with AMD flocculant, metals, sulfate, and other anions, presumably accumulate or infiltrate at the Silver Creek wetland until larger storms remobilize sediments further downstream towards the ~ 0.65 km²Panoche Creek Wetland, the Panoche Fan, and ultimately to the Fresno Slough, Mendota Wildlife Area, Mendota Pool and San Joaquin River. 

Bluefin tuna (BFT), highly prized among consumers, accumulate high levels of mercury (Hg) as neurotoxic methylmercury (MeHg). However, how Hg bioaccumulation varies among globally distributed BFT populations is not understood. Here, we show mercury accumulation rates (MARs) in BFT are highest in the Mediterranean Sea and decrease as North Pacific Ocean > Indian Ocean > North Atlantic Ocean. Moreover, MARs increase in proportion to the concentrations of MeHg in regional seawater and zooplankton, linking MeHg accumulation in BFT to MeHg bioavailability at the base of each subbasin's food web. Observed global patterns correspond to levels of Hg in each ocean subbasin; the Mediterranean, North Pacific, and Indian Oceans are subject to geogenic enrichment and anthropogenic contamination, while the North Atlantic Ocean is less so. MAR in BFT as a global pollution index reflects natural and human sources and global thermohaline circulation. 

Abstract The Greenland Ice Sheet is currently not accounted for in Arctic mercury budgets, despite large and increasing annual runoff to the ocean and the socio-economic concerns of high mercury levels in Arctic organisms. Here we present concentrations of mercury in meltwaters from three glacial catchments on the southwestern margin of the Greenland Ice Sheet and evaluate the export of mercury to downstream fjords based on samples collected during summer ablation seasons. We show that concentrations of dissolved mercury are among the highest recorded in natural waters and mercury yields from these glacial catchments (521–3,300 mmol km −2 year −1 ) are two orders of magnitude higher than from Arctic rivers (4–20 mmol km −2 year −1 ). Fluxes of dissolved mercury from the southwestern region of Greenland are estimated to be globally significant (15.4–212 kmol year −1 ), accounting for about 10% of the estimated global riverine flux, and include export of bioaccumulating methylmercury (0.31–1.97 kmol year −1 ). High dissolved mercury concentrations (~20 pM inorganic mercury and ~2 pM methylmercury) were found to persist across salinity gradients of fjords. Mean particulate mercury concentrations were among the highest recorded in the literature (~51,000 pM), and dissolved mercury concentrations in runoff exceed reported surface snow and ice values. These results suggest a geological source of mercury at the ice sheet bed. The high concentrations of mercury and its large export to the downstream fjords have important implications for Arctic ecosystems, highlighting an urgent need to better understand mercury dynamics in ice sheet runoff under global warming. 

Abstract Microbes transform aqueous mercury (Hg) into methylmercury (MeHg), a potent neurotoxin that accumulates in terrestrial and marine food webs, with potential impacts on human health. This process requires the gene pair hgcAB , which encodes for proteins that actuate Hg methylation, and has been well described for anoxic environments. However, recent studies report potential MeHg formation in suboxic seawater, although the microorganisms involved remain poorly understood. In this study, we conducted large-scale multi-omic analyses to search for putative microbial Hg methylators along defined redox gradients in Saanich Inlet, British Columbia, a model natural ecosystem with previously measured Hg and MeHg concentration profiles. Analysis of gene expression profiles along the redoxcline identified several putative Hg methylating microbial groups, including Calditrichaeota, SAR324 and Marinimicrobia, with the last the most active based on hgc transcription levels. Marinimicrobia hgc genes were identified from multiple publicly available marine metagenomes, consistent with a potential key role in marine Hg methylation. Computational homology modelling predicts that Marinimicrobia HgcAB proteins contain the highly conserved amino acid sites and folding structures required for functional Hg methylation. Furthermore, a number of terminal oxidases from aerobic respiratory chains were associated with several putative novel Hg methylators. Our findings thus reveal potential novel marine Hg-methylating microorganisms with a greater oxygen tolerance and broader habitat range than previously recognized. 

The downward flux of sinking particles is a prominent Hg removal and redistribution process in the ocean; however, it is not well-constrained. Using data from three U.S. GEOTRACES cruises including the Pacific, Atlantic, and Arctic Oceans, we examined the mercury partitioning coefficient, K d , in the water column. The data suggest that the K d varies widely over three ocean basins. We also investigated the effect of particle concentration and composition on K d by comparing the concentration of small-sized (1–51 μm) suspended particulate mass (SPM) as well as its compositional fractions in six different phases to the partitioning coefficient. We observed an inverse relationship between K d and suspended particulate mass, as has been observed for other metals and known as the “particle concentration effect,” that explains much of the variation in K d . Particulate organic matter (POM) and calcium carbonate (CaCO 3 ) dominated the Hg partitioning in all three ocean basins while Fe and Mn could make a difference in some places where their concentrations are elevated, such as in hydrothermal plumes. Finally, our estimated Hg residence time has a strong negative correlation with average log bulk K d , indicating that K d has significant effect on Hg residence time. 

Abstract. Bioactive trace metals are critical micronutrients for marinemicroorganisms due to their role in mediating biological redox reactions,and complex biogeochemical processes control their distributions.Hydrothermal vents may represent an important source of metals tomicroorganisms, especially those inhabiting low-iron waters, such as in thesouthwest Pacific Ocean. Previous measurements of primordial 3Heindicate a significant hydrothermal source originating in the northeastern (NE)Lau Basin, with the plume advecting into the southwest Pacific Ocean at1500–2000 m depth (Lupton etal., 2004). Studies investigating the long-range transport of trace metalsassociated with such dispersing plumes are rare, and the biogeochemicalimpacts on local microbial physiology have not yet been described. Here wequantified dissolved metals and assessed microbial metaproteomes across atransect spanning the tropical and equatorial Pacific with a focus on thehydrothermally active NE Lau Basin and report elevated iron and manganeseconcentrations across 441 km of the southwest Pacific. The most intensesignal was detected near the Mangatolo Triple Junction (MTJ) and NortheastLau Spreading Center (NELSC), in close proximity to the previously reported3He signature. Protein content in distal-plume-influenced seawater,which was high in metals, was overall similar to background locations,though key prokaryotic proteins involved in metal and organic uptake,protein degradation, and chemoautotrophy were abundant compared to deepwaters outside of the distal plume. Our results demonstrate that tracemetals derived from the NE Lau Basin are transported over appreciabledistances into the southwest Pacific Ocean and that bioactive chemicalresources released from submarine vent systems are utilized by surroundingdeep-sea microbes, influencing both their physiology and their contributionsto ocean biogeochemical cycling.