Summary
Around the Antarctic continent, polynyas form within the sea ice due to wind-forcing or upwelling of warm ocean water. Acting as ventillators in the ice cover, polynyas accelerate the exchange of energy, gas and aerosol at the ocean/atmosphere boundary, cause large-scale water mass modification and influence the global energy cycle. They are places of intense primary production and offer access to the ocean for animals higher in the trophic system. This study used a combination of data from the SSM/I passive microwave sensor and the JERS-1 SAR instrument to investigate the climatology of polynyas near Mawson in the winters 1992-1994. The study focused on the period from June to August 1994. the SAR images were used to identify ice types and polynya areas in the study region. The features in the SAR images were geolocated and compared with the bathymetry of the study area. Ice motion velocity fields were derived from the sequence of SAR images. The results from the SAR analysis were used to validate the passive microwave images. Study windows for each polynya were defined within the passive microwave images and ice concentration time series for these windows were produced. A comparison of the polynya time series with meteorological data from Mawson station was done in order to investigate the correspondence between synoptic events and polynya behaviour. The study of the meteorolgical data also allowed an estimate of the total heat transfer from the ocean to the atmosphere. Within the SAR images, land ice, fast ice, pack ice and two polynya areas (Taylor and Cape Darnley) were identified. The analysis of the passive microwave data showed a large polynya west of Cape Darnley reaching sometimes 23,500 sq.km in size. This polynya was nearly permanently visible and showed good correspondence to the meteorological conditions at Mawson. The Taylor study area included a much smaller polynya with a size of approximately 1300 sq.km. The Taylor