Mercury (Hg) concentrations and speciation within surface waters of the Arctic Ocean are controlled by a complex set of processes including photochemical and microbial transformations, redox reactions, and air-sea exchange of gaseous and particulate Hg species. In this study, our aim was to estimate the magnitude of volatile Hg fluxes across the air-sea interface, and examine the influence of ice cover on this process. While gas exchange in the open ocean has been modeled as a function of wind speed, the parameterization is problematic in the presence of sea ice, which can physically block gas exchange, as well as reduce fetch and dampen waves. By using measurements of Radon-222 (Rn-222) gas and it parent isotope, Radium-226 (Ra-226), to accurately measure gas exchange velocities (k), the relative impacts of chemical and biological processes on mercury distributions within the surface waters can then be deduced.
This dataset contains Radon-222 and Radium-226 activity concentrations from R/V Sikuliaq cruise SKQ202108S in the Bering Sea, through the Bering Strait, and in shelf waters of the Chukchi Sea during May – June 2021. Samples include seawater (16 water column profiles), as well as ice cores and brine from four ice stations. At the time of the cruise, sampling locations in the Bering Sea were ice free and gas transfer velocities (k) estimated from Rn-222 deficits (with respect to Ra-226 concentrations) were in general agreement with published parameterizations of k as a function of wind speed. The springtime retreating ice edge was located at 69-70 degrees north latitude in the Chukchi Sea, and sampling locations there were located along the ice edge, in areas of open water, and at sites within the pack ice up to ~10 kilometers (km) from the ice edge. Gas transfer velocities in the marginal ice zone also reflected recent wind histories, with k values generally at the high end of or exceeding those predicted from the wind speed parameterizations.
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This content will become publicly available on May 25, 2024
Linked mercury methylation and nitrification across oxic subpolar regions
Methylmercury (MeHg) is a neurotoxin that bioaccumulates to potentially harmful concentrations in Arctic and Subarctic marine predators and those that consume them. Monitoring and modeling MeHg bioaccumulation and biogeochemical cycling in the ocean requires an understanding of the mechanisms behind net mercury (Hg) methylation. The key functional gene pair for Hg methylation,
- NSF-PAR ID:
- 10468068
- Publisher / Repository:
- Frontiers
- Date Published:
- Journal Name:
- Frontiers in Environmental Chemistry
- Volume:
- 4
- ISSN:
- 2673-4486
- Page Range / eLocation ID:
- 1109537
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Humans are exposed to potentially harmful amounts of the neurotoxin monomethylmercury (MMHg) through consumption of marine fish and mammals. However, the pathways of MMHg production and bioaccumulation in the ocean remain elusive. In anaerobic environments, inorganic mercury (Hg) can be methylated to MMHg through an enzymatic pathway involving the
hgcAB gene cluster. Recently,hgcA ‐like genes have been discovered in oxygenated marine water, suggesting thehgcAB methylation pathway, or a close analog, may also be relevant in the ocean. Using polymerase chain reaction amplification and shotgun metagenomics, we searched for but did not find thehgcAB gene cluster in Arctic Ocean seawater. However, we detected Hg‐cycling genes from themer operon (including organomercury lyase,merB ), andhgcA ‐like paralogs (i.e.,cdhD ) in Arctic Ocean metagenomes. Our analysis of Hg biogeochemistry and marine microbial genomics suggests that various microorganisms and metabolisms, and not just thehgcAB pathway, are important for Hg methylation in the ocean. -
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Abstract Monomethylmercury (CH3Hg) is the only form of mercury (Hg) known to biomagnify in food webs. Here we investigate factors driving methylated mercury [MeHg = CH3Hg + (CH3)2Hg)] production and degradation across the global ocean and uptake and trophic transfer at the base of marine food webs. We develop a new global 3‐D simulation of MeHg in seawater and phyto/zooplankton within the Massachusetts Institute of Technology general circulation model. We find that high modeled MeHg concentrations in polar regions are driven by reduced demethylation due to lower solar radiation and colder temperatures. In the eastern tropical subsurface waters of the Atlantic and Pacific Oceans, the model results suggest that high MeHg concentrations are associated with enhanced microbial activity and atmospheric inputs of inorganic Hg. Global budget analysis indicates that upward advection/diffusion from subsurface ocean provides 17% of MeHg in the surface ocean. Modeled open ocean phytoplankton concentrations are relatively uniform because lowest modeled seawater MeHg concentrations occur in oligotrophic regions with the smallest size classes of phytoplankton, with relatively high uptake of MeHg and vice versa. Diatoms and synechococcus are the two most important phytoplankton categories for transferring MeHg from seawater to herbivorous zooplankton, contributing 35% and 25%, respectively. Modeled ratios of MeHg concentrations between herbivorous zooplankton and phytoplankton are 0.74–0.78 for picoplankton (i.e., no biomagnification) and 2.6–4.5 for eukaryotic phytoplankton. The spatial distribution of the trophic magnification factor is largely determined by the zooplankton concentrations. Changing ocean biogeochemistry resulting from climate change is expected to have a significant impact on marine MeHg formation and bioaccumulation.
