A global perspective on mercury cycling in the ocean

Area of Science:

• * Marine chemistry and biogeochemistry
• * Environmental science and toxicology

Background:

• * Mercury (Hg) is a ubiquitous marine pollutant with significant public health implications due to the neurotoxin methylmercury (MeHg).
• * Understanding Hg sources, sinks, and cycling is crucial for assessing risks to marine life and human consumers.

Purpose of the Study:

• * To synthesize three decades of oceanographic Hg measurements to elucidate its global distribution, sources, sinks, and internal cycling.
• * To analyze Hg speciation (total Hg, methylated Hg, gaseous elemental Hg) across various ocean basins and depths.

Main Methods:

• * Compilation and analysis of over 200 high-resolution, full-depth oceanic profiles of Hg species.
• * Utilized data from global oceanographic survey programs (e.g., CLIVAR, GEOTRACES) and advanced clean sampling techniques.

Main Results:

• * Identified vertical maxima of MeHg in surface waters, near chlorophyll maxima, and in low-oxygen zones.
• * Observed highest deep-water Hg concentrations in Antarctic Bottom Water and a decreasing Hg trend in Labrador Sea Water over 20 years.
• * Noted unique Hg distribution in polar oceans, with higher surface total Hg and Hg speciation influenced by stratification and sea ice.

Conclusions:

• * Oceanic Hg distribution and cycling are complex, influenced by biogeochemical processes and water mass formation.
• * Accurate MeHg measurements and a better understanding of biogeochemical controls are essential for global Hg ocean modeling.
• * Continued monitoring and research are vital for managing the risks associated with mercury pollution in marine environments.