Abstract:

In this paper, the seasonal variation characteristics of the bottom water temperature in the Great Wall Bay, Antarctica are analysed by means of the successive observational data (once per hour) acquired from March, 1987 to February 1988. The preliminary conclusions are as follows: 1. The bottom water temperature is relatively low throughout the year and has no obvious change in the Great Wall Bay, Antarctica. The annual mean temperature is -0.77℃, the maximum temperature, 2.56℃ , and the minimum temperature, -1.97℃. According to monthly statistics, the monthly mean maximum temperature, 1.49℃, occurs in January and February and the monthly mean minimum temperature, -1.88 ℃, occurs in July and August The monthly mean temperature above 0℃ occurs in 4 months of a year, and that below 0℃ in the other months. 2. The temperature-decreasing season of the bottom water is in autumn,and the temperature-decreasing speed is about 0.05℃/d on an average. The temperature-increasing season is in spring, and the temperature increasing speed is about 0.04 ℃/d on an average. Winter ( approximately from May to October ) is the coldest season and the bottom water temperature, about -1.87℃, keeps basically unchanged. Summer is the warmest season and the averaged temperature is 1.10℃. 3. The bottom water temperature interacts with the sea surface air temperature. The annual range of the former is relatively small (4.53℃),and that of the latter is relatively large (39.20℃). The sea surface air temperature rapidly changes from May to October, but the bottom water temperature still keeps the critical temperature, -1.88℃, before freezing and basically unchanged due to the shielding effect of sea ice. 4. The Great Wall Bay is close to the Antarctic Circle. Both the bottom water temperature and the sea surface air temperature have no clear diurnal variations in the winter semi-year, but the difference in temperature of either of them between the daytime and the nighttime is slight in the summer semi-year. It is found by analysing their diurnal change in summer that the difference in the bottom water temperatures between the daytime and the nighttime is relatively small, i.e. 0.11℃ and the difference in the sea surface air temperations is relatively large, 0.78℃. The diurnal change of the bottom water temperature has a time lag, its averaged daily maximum occurring about 2h later than that of sea air temperature and its averaged daily minimum occurring about 5h later than that of air temperature. Contrasting the summer of 1987 with that of 1988, the averaged diurnal changes are roughly identical.