Abstract: Compared with the surrounding seawater, hydrothermal fluid has big differences in both physical and chemical characteristics. Detecting abnormal temperature and turbidity are important means for finding hydrothermal plumes signal. The towing CTD and the turbidity data from leg 20 and the CTD station data from leg 21 of “DaYang Yi Hao” expedition ship were studied. A neutral buoyancy level at the depth of 2 550~2 650 meters with a temperature anomaly about 0.01 degree, and the thickness about 100 meters is found in a hydrothermal field at 49.65°E in the Southwest Indian Ocean. It also shows that temperature anomaly appears at the depth of 2 750~2 800 meters, with the maximum value to 0.08 degree. Accompanied by temperature anomaly, turbidity anomaly also occurres at the same water levels. The potential temperature of background water shows a linear correlation with the potential density in the deep sea. In addition, it is estimated that the initial buoyancy flux is 8.78×10^-4 m⁴/s³, and the estimation value of the hydrothermal area heat flux is about 130±43 MW calculated from the neutral buoyancy level.

Key words: Southwest Indian Ocean, hydrothermal plumes, temperature anomaly, turbidity anomaly, heat flux