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. Some pond types exhibit ... high conductivity with the principal contributing ions being Na+ and SO4. These attributes lend themselves to the hypothesis that reduced sulphur gases could be produced in significant amounts. Reduced sulphur gases were measured from pond water, water beneath mat communities and from the atmosphere at Bratina Island. Pond water column samples were taken from ponds with a high density of cyanobacterial mats. Replicate samples were obtained from ponds at a depth of 10-15cm and analysed within 6-12 hours of sampling. The samples were heated and the trapped sulphur gases separated and were analysed using gas chromatography with a flame photometric detector. Water samples from beneath mats were from a range of ponds and analysed as above. Atmospheric gases were drawn through a sulphur gas trap with the sulphur gases extracted and analysed as above. Measurements for atmospheric samples were only qualitative as the volume sampled were unknown. Samples from 40 ponds and 248 chromatograms were recorded.