LATITUDINAL CHANGES IN 234TH DERIVED MERCURY, CARBON AND NUTRIENT PARTICLE FLUXES IN THE CENTRAL TROPICAL NORTH PACIFIC

A critical part of understanding the biogeochemistry of mercury (Hg) in marine systems is characterizing its transformations and export to depth on sinking particles. Water column samples were collected in August 2015 along a latitudinal transect (17.5 N to 5 N) in the North Pacific Subtropical Gyre. Using high resolution water column measurements of ²³⁸U-²³⁴Th disequilibria, we determined total particulate Hg flux on small (1-53 µm) and large (> 53 µm) particles collected using in situ pumps. Preliminary data show distinct latitudinal differences as sampling locations move closer to the equator as a result of changes in overlying biological productivity and the depth and intensity of the oxygen minimum zone. We hypothesize that Hg flux on large particles will be lower than on small particles at all stations, and that total Hg/Th ratios on particles will increase with declining oxygen concentrations due to microbially mediated remineralization. In addition to Hg/Th flux data, particulate carbon and nitrogen, and zooplankton data will provide insight into elemental particle fluxes and cycling in the region. We argue that differences total Hg flux on size fractionated particle are likely due to surface adsorption of inorganic Hg that scales with surface area to volume ratios, while organic carbon flux increases are due to changes in phytoplankton speciation and abundance and zooplankton grazing and export.