Decomposition of Methylmercury in Surface Water of the Northwest Atlantic Ocean

Abstract

<p>Mercury (Hg) speciation measurements were performed on board the R/V Knorr during the first leg of the u.S. GEOTRACES North Atlantic Ocean zonal section in Fall 2010. All four of the principal mercury species (monomethylmercury, dimethylmercury, elemental Hg, and total Hg) were determined in high vertical and horizontal resolution at eight stations off the coast of North Africa, an ocean region that experiences significant coastal upwelling, atmospheric dust deposition, and associated high levels of biological productivity. Preliminary results suggest that filtered total Hg has both scavenging and nutrient-type vertical distributions at different locations in the northeast Atlantic. Elemental Hg, in contrast, has strong nutrient-like profiles, with deep water concentrations as much as 50% of total Hg. This is in contrast to the western side of the basin where elemental Hg in deep water is much less abundant. Monomethylmercury (MMHg) distributions have pronounced midwater maxima associated with the oxygen minimum zone. Increased levels in the oxygen minimum likely result from either in situ methylation or isopycnal transport from the margin. MMHg levels in the mixed layer and North Atlantic Deep Water on the eastern side of the ocean basin are similar to those we have recently measured in the western North Atlantic. High-quality Hg speciation results from the international GEOTRACES program will help constrain oceanic budgets and cycling models for toxic and bioaccumulative MMHg in the ocean.</p><p>This presentation occurred at the Wright State University Campus-Wide Celebration of Research, Scholarship and Creative Activities on April 8, 2011</p>