VARIATIONS OF THE WATER TEMPERATURE OFFSHORE THE CHANGJIANG RIVER ESTUARY IN WINTERS AND SPRINGS
长江口外海域冬、春季水温变化规律研究

Using historical water temperature data offshore the Changjiang River estuary from 1963 to 1996, we analyzed seasonal and inter-annual temperature variations at sea surface, 10m, 20m and 30m depths and the variations of vertical structure. Seasonally, we found that the surface water temperature was the highest in August and the lowest in March; the bottom water temperature was the highest in September and the lowest in March. For inter-annual variations, the winter water temperatures shifted from cold phase to warm phase in 1979. Although the spring (defined as April here) water temperatures at all depths also shifted from cold phase to warm phase. The shifts occurred in different years. Horizontally, the winter surface water temperature had an increasing trend along coast and northern part of study area but a decreasing trend on southeastern part; spring water temperature had an increasing trend, whose magnitude decreased from sea surface to 30m depth, in northern and middle-southern areas. Vertically, winter water temperatures were homogenous and the correlation coefficient for inter-annual variations between sea surface and 20m depth was 0.97; water temperature difference of sea surface and 20m depth in spring presented an approximately 10 years periodic variation. We examined some possible factors affecting inter-annual variations in water temperature in spring and found significant correlation between sea surface water temperature and air temperature during cold period and the correlation coefficient was 0.79, which was greater than that during warm period. We also found significant correlation between net heat flux and water temperature difference of sea surface and 20m depth during warm period, with a correlation coefficient of 0.65.