A global perspective on mercury cycling in the ocean

Katlin L Bowman; Carl H Lamborg; Alison M Agather

doi:10.1016/j.scitotenv.2019.136166

A global perspective on mercury cycling in the ocean

Sci Total Environ. 2020 Mar 25:710:136166. doi: 10.1016/j.scitotenv.2019.136166. Epub 2019 Dec 18.

Authors

Katlin L Bowman¹, Carl H Lamborg², Alison M Agather³

Affiliations

¹ Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA; University of California Santa Cruz, Ocean Sciences Department, 1156 High Street, Santa Cruz, CA 95064, USA. Electronic address: klbowman@ucsc.edu.
² University of California Santa Cruz, Ocean Sciences Department, 1156 High Street, Santa Cruz, CA 95064, USA. Electronic address: clamborg@ucsc.edu.
³ National Oceanic and Atmospheric Administration, 1325 East West Highway, Silver Spring, MD 20910, USA. Electronic address: alison.agather@noaa.gov.

PMID: 32050358
DOI: 10.1016/j.scitotenv.2019.136166

Abstract

Mercury (Hg) is a ubiquitous metal in the ocean that undergoes in situ chemical transformations in seawater and marine sediment. Most relevant to public health is the production of monomethyl-Hg, a neurotoxin to humans that accumulates in marine fish and mammals. Here we synthesize 30 years of Hg measurements in the ocean to discuss sources, sinks, and internal cycling of this toxic metal. Global-scale oceanographic survey programs (i.e. CLIVAR and GEOTRACES), refined protocols for clean sampling, and analytical advancements have produced over 200 high-resolution, full-depth profiles of total Hg, methylated Hg, and gaseous elemental Hg throughout the Atlantic, Pacific, Arctic, and Southern Oceans. Vertical maxima of methylated Hg were found in surface waters, near the subsurface chlorophyll maximum, and in low-oxygen thermocline waters. The greatest concentration of Hg in deep water was measured in Antarctic Bottom Water, and in newly formed Labrador Sea Water, Hg showed a decreasing trend over the past 20 years. Distribution of Hg in polar oceans was unique relative to lower latitudes with higher concentrations of total Hg near the surface and vertical trends of Hg speciation driven by water column stratification and seasonal ice cover. Global models of Hg in the ocean require a better understanding of biogeochemical controls on Hg speciation and improved accuracy of methylated Hg measurements within the international community.

Keywords: Fluxes; GEOTRACES; Methylmercury; Sinks; Sources; Speciation.