Multi-Element Dissolved Trace Metal Distributions in Surface Waters of the Texas-Louisiana Shelf: A Synthesis From Three Cruises 2017-2019 Showing the Influence of Rivers, Hurricanes, Sediments, and Biology

Trace metals cycling is important because trace metals can serve as essential nutrients for phytoplankton production, as toxins arising from anthropogenic pollution, and/or as critical tracers of oceanographic processes. The Gulf of Mexico is a model system for studying trace metal biogeochemical cycling in marginal seas, given its abundant continental shelves, multiple river inputs with varying anthropogenic influence, dust and sediment fluxes, and massive gradients in primary production from the shelf to the oligotrophic waters offshore. Despite these exciting biogeochemical gradients and features, however, almost no trace metal data exist in the Gulf of Mexico literature, likely because of previous sampling contamination issues. Here, we present surface water dissolved Fe, Mn, Zn, Cu, Cd, Ni, and Pb concentrations from three cruises to the Texas Louisiana Shelf: a 2017 nearshore transect along the West Texas Shelf following Hurricane Harvey, and 2018 and 2019 occupations of a triangular cruise transect connecting the Atchafalaya River to Galveston Bay to the Flower Garden Banks. Following Hurricane Harvey in 2017, most metals had linear relationships with salinity, consistent with a strong influence of hurricane floodwaters on surface metal distributions. Comparison of these distributions to metal:salinity relationships in Galveston Bay surprisingly disprove a Galveston Bay source of these floodwaters, instead requiring another source such as the Brazos River. In contrast, in the 2018-2019 cruises the metal:salinity relationships break down and instead point to local metal-specific fluxes. We use metal:metal relationships, spatiotemporal comparisons, and correlations to other hydrographic parameters to distinguish influences of dust, sediments, mixing, and biology on these trace metal distributions.