Dynamique du mercure dans les neiges de hautes et moyennes latitudes : études in situ et en conditions simulées des mécanismes de réactivité chimique et d'échanges

Mercury (Hg) is a globally dispersed compound. In the atmosphere, it can be deposited onto snowpacks, which constitute a temporary reservoir of this toxic compound. We do not know what is the role of these reservoirs in the global cycle of Hg. We thus developed a new tool dedicated to the measurements of Hg° concentrations in the air of snowpacks. We investigated Hg° reactivity at the polar sunrise, during springtime and during the snowmelt in Greenland and in Canada. We then discriminated the main factors governing Hg reactivity in the snow. Here we show that snowpacks are both a sink and a source of atmospheric Hg°. Hg° can be oxidised by radicals and be accumulated in the snow during low irradiation periods. During springtime, Hg° can be produced by photochemical reactions. During the snowmelt, more than 85% of Hg present in the snow is discharged into snowmelt waters leading to a potential contamination of the surrounding ecosystems.