Upwelling Enhances Mercury Particle Scavenging in the California Current Ecosystem

Abstract

Coastal upwelling supplies nutrients supporting primary production, while also adding the toxic trace metal mercury (Hg), to the mixed layer of the ocean. This could be a concern for human and environmental health if it results in enhanced bioaccumulation of monomethylmercury (MMHg). Here we explore how upwelling influences the Hg cycling in the California Current Ecosystem (CCE) biome through particle scavenging and sea-air exchange. We collected suspended and sinking particle samples from an upwelled water parcel and a non-upwelled water parcel and observed higher total particulate Hg and sinking flux in the upwelling region compared to non-upwelling region. To further investigate the full dynamics of Hg cycling, we modeled Hg inventories and fluxes in the upper ocean under upwelling and non-upwelling scenarios. The model simulations confirmed and quantified that upwelling enhances sinking fluxes of Hg by 40% through elevated primary production. Such an enhanced sinking flux of Hg is biogeochemically important to understand in upwelling regions as it increases the delivery of Hg to the deep ocean where net conversion to MMHg may take place.