A high-resolution marine mercury model MITgcm-ECCO2-Hg with online biogeochemistry

Abstract. Mercury (Hg) is a global persistent contaminant. Modeling studies are useful means of synthesizing a current understanding of the Hg cycle. Previous studies mainly use coarse-resolution models, which makes it impossible to analyze the role of turbulence in the Hg cycle and inaccurately describes the transport of kinetic energy. Furthermore, all of them are coupled with offline biogeochemistry, so they cannot respond to short-term variability in oceanic Hg concentration. Here we use a high-resolution (horizontal resolution is 1/5°) ocean model (MITgcm-ECCO2, high-resolution-MITgcm) coupled with the online biogeochemistry of Darwin project to simulate the global Hg cycle. The finer portrayal of surface Hg concentrations in estuarine and coastal areas, strong western boundary flow and upwelling areas, and concentration diffusion as vortex shapes demonstrate the effects of turbulence that are neglected in previous models. Ecological events such as algal blooms can cause a sudden enhancement of phytoplankton biomass and chlorophyll concentrations, which can also result in a dramatic change in particle-bound mercury sinking flux at the same time in our simulation. In the global estuary region, the inclusion of riverine Hg input in the high-resolution model allows us to reveal the outward spread of Hg in an eddy shape driven by fine-scale ocean currents. With faster current velocities and diffusion rates, our model captures the transport and mixing of Hg from river discharge in a more accurate and detailed way and improves our understanding of Hg cycle in the ocean.