Variation Characteristics of Salinity in the Pacific in Twentieth Century

As an important parameter to describe the properties of ocean, salinity is often taken into consideration together with temperature and pressure when studying the physical or chemical process in the ocean. In the past salinity cannot be directly observed, but now it is often directly recorded by CTD, XBT observation or calculated by satellite data. In this paper, 744 months of ISHII ocean salinity data is used to analyze the differences and connections between variations of the salinity in Pacific Ocean in different depth from surface to 700 meters, and to try to find long-term trend, and decadal characteristics of the salinity by means of EOF analysis, power spectrum analysis, correlation analysis and other methods. The results show that there is basically an oscillation period of 2-5 years in the variation of surface salinity, in spite of a sharp increase in both north and south subtropical ocean and a sharp decrease in equatorial area after 1995. Besides, the variation of surface salinity in Pacific Ocean shows the reverse every 5 years after 1980, while in subsurface ocean it only takes about 3 years. As respect to decadal variations, the salinity variation of the surface and middle water in subtropical area in the North Pacific is consistent with that in the South Pacific during 20th century, but is opposite to that in central equatorial Pacific. Most of salty regions in the middle water of the Pacific get saltier and fresh regions get fresher, which happens only after 1970s in the surface and subsurface water. Salinity variations of the surface water are highly tied to Nino4 index.