Seasonal variability of temperature profile in Thunnus obesus and Thunnus albacares fishing ground in the Indian Ocean

In order to study the spatial distribution seasonal characteristic of the upper boundary depth,temperature of the thermocline and vertical temperature difference of the fishing ground of Thunnus obesus and Thunnus alba-cares in the Indian Ocean,the subsurface temperature and thermocline characteristics parameters were estimated based on temperature data of Argo profile floats from 2007 to 2010.Based on these basic work,the monthly distribution figures of the upper boundary depth,temperature of the thermocline and vertical temperature difference from 10 to 200 m were plotted.The topography of the upper boundary depth,temperature of the thermocline and vertical temperature difference from 10 to 200 m showed obvious seasonal variability.The variability of the upper boundary depth of the thermocline on the annual mode is very weak between the equator and 15°S zonal where the upper boundary depth of the thermocline is present very shallow throughout the year and large away from the equator in the Arabian Sea and the southern tropic Indian Ocean.there is a seasonal deep zonal of the upper boundary depth of the thermocline between 15°S and 25°S during May to September and a seasonal shallow zonal in the south of 20°S during December to April of next year.In generally,the upper boundary temperature of the thermocline is low where the upper boundary depth of the thermocline is deep.On the annual mode,the upper boundary temperature of the thermocline presents a warm-pool region in the southeastern of Arabian sea and the southwestern of Bay of Bengal during February to May and a lower temperature zonal in south of 20°S throughout year.The upper boundary depth of the thermocline is very deep between 15°S and 25°S during May to September so that the temperature variation between sea surface and the upper boundary depth of the thermocline is very large,the upper boundary temperature of the thermocline is very low.The variability of the upper boundary temperature of the thermocline topography is large in the south of 10°S and weak below the warm-pool region.The variability of temperature difference from 10 to 200 m,on the annual model is similar to the upper boundary temperature of the thermocline.The spatial distribution of vertical temperature difference is divided by 10°S longitude line.The temperature difference is lower than 10℃ in the south and it is greater than 10℃ in the north.The Analysis results reveal the spatial distribution seasonal characteristic of the upper boundary depth,temperature of the thermocline and vertical temperature difference in major tuna fishing ground of T.obesus and T.albacares in the Indian Ocean,which provide reference to long line production operation in sea of tuna.