Impacts of Climate Change on Methylmercury Formation and Bioaccumulation in the 21st Century Ocean

Abstract

Climate change is altering marine biogeochemistry, thereby modifying factors affecting the formation and trophic transfer of the bioaccumulative neurotoxicant methylmercury (MeHg) in the global ocean. However, both the directionality and magnitude of future changes are unclear. Here we use a coupled 3-D atmosphere-ocean-ecology model to forecast how MeHg concentrations in the surface ocean will respond to changes in primary production and associated carbon export in 2100. Model results suggest a 68-93% increase in MeHg in the polar oceans and a 23% decrease in the high-latitude North Atlantic Ocean. Phytoplankton MeHg reservoirs will increase at high-latitudes and decrease in the mid- and low-latitude oceans due to a poleward shift in habitat. Ocean acidification is projected to increase phytoplankton MeHg reservoirs globally by promoting the growth of Synechococcus, a small phytoplankton species that efficiently accumulates MeHg. Changes in MeHg reservoirs in herbivorous zooplankton mimic their prey but with larger magnitudes due to non-linearity embedded in the food web structure. The effect of climate-driven shifts in marine biogeochemistry thus needs to be considered in evaluating future trajectories in biological MeHg concentrations.