MERCURY SPECIATION AND DISTRIBUTION IN A POLAR DESERT LAKE (LAKE HOARE, ANTARCTICA) AND 2 GLACIAL MELTWATER STREAMS

Total (Hg-T), reactive (Hg-R) and monomethylmercury (MMHg) have been d etermined in unfiltered collections from Lake Hoare and two glacial me ltwater streams (Canada and von Guerard streams) located in the Taylor Valley (McMurdo Dry Valleys, South Victoria Land, Antarctica). Sampli ng 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 br own dust and crustal weathering) to the glacial meltwater streams. Ero sion of crustal material accounts for 35-75% of the inorganic Hg load in streamwater. Oceanic production and sea-air exchange of elemental H g (Hg degrees) and dimethylmercury (DMHg) followed by atmospheric oxid ation/decomposition, transport and deposition may deliver MMHg and ino rganic Hg tin addition to crustal weathering) to glacial streams. Volc anically derived Hg may also contribute significantly to the streamwat er Hg load. In Lake Hoare, Hg, 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 Hg-T and Hg-R distributio n. Interestingly, the percent of Hg-T as MMHg (%MMHg) was approx. 30% below 22 m and approx. 10% from 4 to 20 m. In situ methylation of Hg i n the sediment (followed by diffusion into the overlying waters) of La ke Hoare is implied. (C) 1998 Published by Elsevier Science B.V.