Mercury flux over West Antarctic Seas during winter, spring and summer

For the first time elemental mercury in air and surface seawater was measured continuously in the remote seas of western Antarctica. A major contributor to atmospheric emissions of the toxic and globally dispersed pollutant mercury is the re-evasion from water surfaces, due to a supersaturation of dissolved gaseous mercury (DGM) in surface water. In this study the degree of saturation and mercury flux at the air-sea surface interface have been estimated from continuous measurements of gaseous elemental mercury (GEM) or total gaseous mercury (TGM) in air, DGM in surface water and meteorological parameters. The measurements were performed during winter and spring (2013) in the Weddell Sea and during summer (2010/2011) in the Bellingshausen, Amundsen and Ross Seas, and show spatial and seasonal variations.

The average DGM concentration in surface water in open sea was highest during spring (12 ± 7 pg L− 1) and lowest during summer (7 ± 6.8 pg L− 1), resulting in a net evasion of mercury during spring (1.1 ± 1.6 ng m− 2 h− 1) and a net deposition during summer (− 0.2 ± 1.3 ng m− 2 h− 1). In open sea, higher average concentrations of GEM (or TGM) and DGM were found close to the Drake Passage compared to in the Bellingshausen and Weddell Seas. Emission sources from the South American continent, identified with back trajectories, were suggested to explain the observed variations. The yearly mercury evasion from open sea surfaces in the Southern Ocean was estimated to 30 (− 450–1700) tons, using the average (and min and max) flux rates obtained in this study. Higher DGM was measured under sea ice (19–62 pg L− 1) compared to in open sea due to a capsuling effect, resulting in a theoretical prevented evasion of 520 (0–3400) tons per year. Diminishing sea ice and higher water temperatures in polar regions could result in increased mercury evasion to the atmosphere. However, the contribution of the Southern Ocean to the global modeled annual emissions of mercury from sea surfaces would probably only be a few percent.

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