Interannual variation of nutrients along a transect across the Kuroshio and shelf area in the East China Sea over 40 years

Long-term datasets of water temperature, salinity, dissolved oxygen, phosphate and nitrate from 1973 to 2013 were used to study interannual variations of these parameters along a transect (section PN) across the Kuroshio and shelf area in the East China Sea. Water temperature and salinity at depths of 0–200 m showed a low-high-low-high pattern over the 40-year period. Water temperature and salinity at 500 m were relatively high from 1985 to 1990 and decreased continuously thereafter. Salinity at 800 m was lowest around 1993 and increased thereafter. Nutrients were highest between 1980 and 1985. After 1985, nutrients at 500 m were increasing. The range of variation in nutrients was large before 1985 and the magnitude increased with greater depths. Apparent oxygen utilization at 500 m depth was decreasing before 1990 and started to increase after 1992. Significant changes after 1990 at 500 m depth may be due to the upward trend of the upper boundary of Kuroshio intermediate water. Interannual variation of water temperature, salinity, dissolved oxygen, phosphate and nitrate along section PN has a significant correlation with the Pacific Decadal Oscillation index.