Atlantic mercury emission determined from continuous analysis of the elemental mercury sea-air concentration difference within transects between 50°N and 50°S

Mercury in the environment deserves serious concern because of the mobility of volatile elemental mercury (Hg-0) in the atmosphere, in combination with the harmful effect of Hg compounds on human health and the ecosystem. A major source of global atmospheric mercury is presumed to be oceanic Hg-0 emission. However, available Hg-0 surface water data to reliably estimate the ocean's mercury emissions are sparse. In this study, high-resolution surface water and air measurements of Hg-0 were carried out between Europe and South Africa in November 2008 and between South America and Europe in April-May 2009. On each cruise a strong enrichment of Hg-0 in tropical surface water was determined that apparently followed the seasonal shift of the Intertropical Convergence Zone (ITCZ). A combination of a high Hg-0 production rate constant and the actual low wind speeds, which prevented emission, probably caused the accumulation of Hg-0 in surface waters of the ITCZ. Hg-0 emissions in the tropics were significant only if wind speed variability on a monthly scale was considered, in which case the observed significant decline of total Hg in tropical surface waters during the northern winter could be explained. In the midlatitudes, increased autumn Hg-0 emissions were calculated for November in the Northern Hemisphere and for May in the Southern Hemisphere; conversely, emissions were low during both the northern and the southern spring. Mercury removal from surface waters by Hg-0 emission and sinking particles was comparable to its supply through wet and dry deposition.