How the onset of winter conditions affects the physical and chemical conditions within the melt water ponds on the McMurdo Ice Shelf (of which summer information is available) and how these changes affect the planktonic and benthic microbial communities within the ponds, was investigated in an extended field season until April, when the freezing process was well advanced. During the summer, four ... representative ponds were selected to make profiles of the physico-chemical variables at different depths in the pond. Samples were analysed for temperature, pH, conductivity, dissolved oxygen, major ions and nutrients, trace metals, sulphides, dissolved organic carbon and inorganic carbon, alkalinity, chlorophyll a, primary productivity, superoxide dismutase activity, nitrous oxide, irradiance and stable isotopes of both DOC and DIC to determine ?13C ratios. Two initial diel sampling events were carriend out in January and were sampled throughout February, March and April. This data in conjunction with information on the bathymetry of the ponds will be used to calculate the rates of whole pond processes (physical, chemical and biological) and how these varied with time and interacted with ice formation.