The sixth Antarctic survey cruise of R/V Kaiyo Maru was carried out in waters around the Shouth Shetland Islands. where are known as the fishing grounds of krill, during the 1990-91 austral summer. In order to investigate seasonal changes in oceanic structure. two observations were put into operation In the same area after an interval of 40 days. The more characteristic change was clearly recognized in the waters of the insular shelf from the first leg to the second leg. The Antarctic Surface Water over the insular shelf at the first leg entirely indicated the minus values of temperature. 40 days later, however, the temperature in the same waters rised above the plus values. The reason for the phenomenon of the temperature rise is considered that the Warm Deep Water intruded over the insular shelf. The following two processes were considered for the present intrusion. The first was the steady topographic upwelling of the Warm Deep Water, and the second was the wind-driven coastal upwelling. The distribution patterns of temperature, salinity, density. dissolved oxygen and nutrient salts supported this upwelling phenomenon.