Bromine, Iodine and Mercury Spatial Variability and Seasonal Accumulation Along the EAIIST Traverse

This research investigates the possible influence of the ozone hole on the geochemical cycles, between the cryosphere and the atmosphere, of iodine (I), bromine (Br), and mercury (Hg) in East Antarctica. Both Br and I promotes the destruction of the tropospheric ozone layer and while iodine is a photoreactive element, bromine is expected to have no significant post-depositional mechanisms in the snowpack. Hg is a toxic heavy metal present in the environment in several different chemical forms and as iodine, once in the snowpack, it can be photoactivated by the ultraviolet (UV) radiation (280-320 nm mainly) and released from the snowpack into the atmosphere. They have a well-known diurnal cycle of exchange between surface snow and the atmosphere, and here we try to identify the connection between the ozone hole cycle and the Hg and I spatial distribution and seasonal cycle. The increased amounts of UV radiation reaching the snow surface due to ozone layer depletion, could promote the photo-reactivity of mercury and iodine in the photic zone of the snow leading to their higher re-emission from the snow surface. In surface and bulk snow samples and in shallow core from the East Antarctic International Ice Sheet Traverse project (EAIIST), concentration measurements are performed by ICP-MS and experimental data are compared to data from atmospheric chemical models such as CAM-CHEM. Concentration results in surface snow show a decreasing trend for mercury and iodine moving inland along the EAIIST route, toward the centre of the ozone hole. Bromine has no significant post-depositional mechanisms and probably the inland surface snow concentration is influenced by spring coastal bromine explosions. Comparing the bulk and surface samples we can hypothesize that iodine undergoes spring summer snow recycling and accumulates in the snow during the winter months when photochemistry ceases. Mercury instead, seems controlled by an interplay of the oxidative capacity of the atmosphere and surface snow photochemistry emissions. On going shallow cores analysis are expected to improve our knowledge about the seasonal accumulation of the analytes and what influences them. Moreover, we expect to find a tipping point, a change into the iodine concentration, and possibly the mercury concentration, corresponding with the ozone hole formation. These results would define iodine and/or mercury as proxy for the stratospheric ozone layer.