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

• Published in: Frontiers in Environmental Chemistry
• Main Authors: Cui, Xinyun, Lamborg, Carl H., Hammerschmidt, Chad R., Xiang, Yang, Lam, Phoebe J.
• Other Authors: National Science Foundation
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Frontiers Media SA 2021
• Subjects: Arctic; Pacific
• Online Access: http://dx.doi.org/10.3389/fenvc.2021.660267; https://www.frontiersin.org/articles/10.3389/fenvc.2021.660267/full

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.