Long-Term Trend and Inter-Annual Variation of Ocean Heat Content in the Bohai, Yellow, and East China Seas

Abstract

The long-term trend and interannual variation of ocean heat content (OHC) in the Bohai Sea, Yellow Sea, and East China Sea (BYECS) were examined using 27 years (1993–2019) of daily reanalysis data from the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2M). The annual mean OHC was 4.25 × 1021 J, with a linear warming rate of 0.13 W m−2 with a confidence level of 95%. The spatial distributions for the annual and linear trends of OHC in the BYECS were inhomogeneous, and a considerable quantity of heat was stored on the outer shelf. The warming rate was considerably elevated in the areas northeast of Taiwan and southwest of Kyushu, showing a rate greater than that of the Pacific and global oceans by a factor of 4–5. Heat budget analysis indicated that the Taiwan Strait (TAS) is the dominant source of heat for the BYECS. The mechanisms of the OHC interannual variation in the outer and inner shelves varied. On the outer shelf, the OHC interannual variation was dependent on the Kuroshio onshore intrusion, while on the inner shelf, the OHC interannual variation was related to the variation in air-sea heat flux. The rapid warming in the outer shelf corresponded to the increasing trends of heat transport across northeast Taiwan and southwest Kyushu, which were dominated by the temporal variation of current velocity.