Transformations of Mercury in the Marine Water Column

Kathleen Munson, Ph.D., 2014
Carl Lamborg, Advisor

Marine water column mercury (Hg) methylation may serve as the primary source of bioaccumulating monomethylmercury (MMHg) to marine food webs. However, mechanistic studies of Hg transformations in the marine water column face analytical challenges due to low femtomolar concentrations of dimethylmercury (DMHg) and MMHg in marine systems. Consideration of gaseous, dissolved, and particulate species of Hg are necessary to probe controls on its transfer into marine food webs.

We measured Hg species distributions and fluxes along a transect of the Tropical Pacific Ocean. Over significant gradients in oxygen utilization and primary productivity, we observed highest methylated Hg concentrations in the Equatorial Pacific. From the first full water column depth profiles of this region, we also observed the intrusion of elevated Hg into deep waters of the Equatorial and South Pacific Ocean.

We also observed substantial potential rates of mercury methylation in subsurface and low oxygen waters at sites in the Tropical Pacific Ocean and the Sargasso Sea using Hg isotope tracers. We observed dynamic production and decomposition of methylated Hg in both high productivity and oligotrophic waters. These experiments suggest that Hg methylation is not limited to anoxic environments and water column methylation may contribute to the bioaccumulation of MMHg.