Aqueous geochemistry of the melt pools on the McMurdo Ice Shelf : A collaboration with the RISE (Ross Ice Shelf Ecosystem) programme

A large freshwater ecosystem on the McMurdo Ice Shelf and the lower Koettlitz Glacier, in the Ross Dependency, is an area some 1500 km2 . The area is covered by pools, lakes, streams and rivers, many of which contain abundant growths of algae and cyanobacteria. The RISE (Ross Ice Shelf Ecosystem) programme was initiated in 1985 to gain an understanding of this ecosystem. A general survey of the major chemical constituents of the melt pools in the dirty ice area of the McMurdo Ice Shelf was conducted to determine the temporal and spatial variability in the chemical composition of the pools with the aim of delineating the source and concentration controls of the major elements. Six ponds were selected and sampled on a regular basis over a period of 5 to 6 weeks (temporal variability). A number of sampling trips were conducted to the west, east and southeast of Bratina Island with measurements made on site for temperature, pH and conductivity (spatial variability). Water samples for subsequent analysis in New Zealand of Na, K, Mg, Ca, SO4 and B(OH)4 were collected. Oxygen, Cl, pH and alkalinity were measured in the Bratina Island laboratory. This data, along with CO2 studies from a separate event, provide a comprehensive study of the CO2/carbonate system. The major element database will be used as an integral part of the RISE programme by providing a chemical component to the general envrionmental description of the ice shelf ecosystem and will enable some chemical processes to be investigated. An additional site was sampled from the Koettlitz, Walcott and Howchin Glaciers and at points along the length of the Alph River to extend sampling to the western edge of the McMurdo Ice Shelf. Samples were collected both early and late in the season to allow a comparison with the chemistry in the river later in the season.