Comparison of air-sea exchange of mercury from the GEOTRACES GP15 cruise with data from other cruises in the Pacific Ocean: From similarity to discrepancy

Air-sea exchange of mercury (Hg) is an important process of the global biogeochemical Hg cycle, which affects the input and output of Hg from surface seawater, and prolongs the residence time of Hg in the biosphere. For charactering the air-sea exchange of Hg and methylated Hg, we measured Hg species in the atmosphere as well as in the surface seawater with high temporal resolution, and determined their flux on the GP15 GEOTRACES expedition, 2018 (Central Pacific Ocean, 55°N to 20°S).To better understand the evasion of Hg⁰ from the marine boundary layer and contribute to the global Hg cycle, therefore, we compared the air-sea exchange Hg data from GP15 with other cruises which are available currently in the Pacific Ocean, including the GP16 (Equatorial South Pacific Ocean, zonal 80°W to 155°W), METZYME cruise (Central Pacific Ocean, meridional 20°N to 15°S) and the CHINARE cruise (Western Pacific Ocean, meridional 30°N to 5°S). We quantified the spatial and temporal variability in dissolved Hg⁰ concentrations and fluxes among these cruises and further explain these variabilities by examining the associated environmental factors (wind speed, temperature, salinity, density, fluorescence, DOC, DON (if available)), which can provide new insights into the factors controlling the cycling of Hg across the marine boundary layer.