A Reassessment of Air-Sea Exchange of Mercury and of the Global Mercury Cycle

University Of Maryland Center For Environmental Sciences, Cambridge MD

Investigators

Abstract

ABSTRACT OCE-0116925 Recently, studies on air-sea exchange have suggested that estimated evasion rates for Hg from the ocean are significantly higher that current deposition rates. One potential reason for this lack of balance is that elemental Hg is oxidized by hydroxyl or halogen radicals in the surface ocean, or via reactive halogen species in the marine boundary layer (MBL). The PI proposes to determine the importance of Hg oxidation at the air-sea exchange in controlling Hg cycling at the Earth's surface. To achieve this goal, the scientist from the University of Maryland will measure the spatial and temporal variation in the concentration of Hg species in both the surface ocean and in the MBL. In the atmosphere, reactive gaseous Hg (RGHg), particulate Hg and total gaseous Hg over the ocean will be measured on short timescales during both research cruises and from the atmospheric sampling tower at Bermuda and at a coastal site in Maryland. These measurements will be carried out across seasons to assess the temporal and spatial variability in Hg evasion and deposition. In conjunction with the air measurements, the speciation of Hg in the surface ocean (total Hg, Hg0 and methylated Hg) will be determined to allow the gas evasion from the ocean to be calculated. The parameters that affect RGHg concentrations and the controls of Hg oxidation and reduction in the MBL and in the surface ocean will be ascertained using a combination of field incubation experiments and laboratory tests. Results from this study will lead to an updated global Hg model and a revision of our understanding of how Hg cycles at the Earth's surface.