Mercury speciation and distribution in a polar desert lake (Lake Hoare, Antarctica) and two glacial meltwater streams

Total (HgT), reactive (HgR) and monomethylmercury (MMHg) have been determined in unfiltered collections from Lake Hoare and two glacial meltwater streams (Canada and von Guerard streams) located in the Taylor Valley (McMurdo Dry Valleys, South Victoria Land, Antarctica). Sampling was undertaken as part of a larger project examining the origin of dissolved organic matter and trace elements in these systems. Here we evaluate the possible sources of Hg and MMHg (marine aerosols, wind blown dust and crustal weathering) to the glacial meltwater streams. Erosion of crustal material accounts for 35–75% of the inorganic Hg load in streamwater. Oceanic production and sea–air exchange of elemental Hg (Hg°) and dimethylmercury (DMHg) followed by atmospheric oxidation/decomposition, transport and deposition may deliver MMHg and inorganic Hg (in addition to crustal weathering) to glacial streams. Volcanically derived Hg may also contribute significantly to the streamwater Hg load. In Lake Hoare, HgT ranged from 3.3 to 6.8 pM; the highest concentrations were found at 8 and 25m. MMHg levels varied from<0.4 to 2.1 pM. A peak in MMHg at 8 m follows the HgT and HgR distribution. Interestingly, the percent of HgT as MMHg (%MMHg) was approx. 30% below 22 m and approx. 10% from 4 to 20 m. In situ methylation of Hg in the sediment (followed by diffusion into the overlying waters) of Lake Hoare is implied.