Abstract
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, Kd, in the water column. The data suggest that the Kd varies widely over three ocean basins. We also investigated the effect of particle concentration and composition on Kd 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 Kd 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 Kd. Particulate organic matter (POM) and calcium carbonate (CaCO3) 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 Kd, indicating that Kd has significant effect on Hg residence time.
Highlights
Removal of trace elements by particle scavenging has a first-order control on their concentrations in the ocean (Anderson, 2014)
In addition to discussion on some special features of Kd, we extended the study of Kd on Hg residence time at the end
We investigated into the Hg partition coefficient (Kd) in the water column across the Pacific, Atlantic and Arctic Ocean, and analyzed the impact of particle concentration and composition on variation of Kd
Summary
Removal of trace elements by particle scavenging has a first-order control on their concentrations in the ocean (Anderson, 2014). This is true for mercury (Hg) as well: particle scavenging represents the ultimate sink for Hg from the ocean over centuries, and it is eventually back to the deep mineral reservoir on the timescales of glacial cycle (e.g., Amos et al, 2013). Given the current oceanic inventory of Hg, these burial fluxes suggest a residence time of Hg of about 520 years (Outridge et al, 2018).
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