Mercury and Trace Metal Cycling in the Surface North Pacific Ocean

The North Pacific Ocean contains chemically and ecologically distinct regions moving from the subtropical to subpolar gyre. This region also has latitudinally variable trace metal inputs from atmospheric deposition and deep water upwelling. While it is known that many trace metals are biologically important, others, such as mercury, are purely toxic in nature. In order to further our understanding of trace metal cycling at the air-sea interface and through the surface mixed layer, a cruise was conducted from Honolulu, HI to 42^oN in April 2019. Total and dissolved metal concentrations, as well as dissolved gaseous and atmospheric mercury, were measured along the transect. Diel surface samples were also collected from several sites to compare dark and light conditions and potentially the impact of vertical plankton migration on trace metal concentrations. The trace metal results will be compared to data collected in two similar, prior cruises which show atmospheric deposition and upwelling effects on trace metal concentrations at the ocean surface. Hg results will be compared to data collected from GP15 six months prior which similarly shows a spatially non-distinct signal in the gaseous Hg concentrations in the North Pacific. The comparison between Hg, a metal with both particulate deposition and gas exchange at the air-sea interface, and trace metals with a net deposition into the ocean surface, such as iron and lead, shed light onto both metal input and internal transformation reactions in the surface ocean. The spatial patterns in metal concentrations will also be discussed in part as they relate to changing biological regimes along the cruise transect.