Sea level and heat content changes in the western North Pacific

Altimetry-observed sea level rise (SLR) over the western North Pacific (WNP), including the South China Sea, Yellow Sea, East China Sea, and East/Japan Sea, has a rate of 5 mm/year over 1993-2010, which is about 1.5 times the rate of the global mean. Here we have examined sea level changes and related ocean heat content (OHC) in the WNP by comparing results from a non-Boussinesq ocean general circulation model (mass-conserved) with data sets from altimeters, the Gravity Recovery and Climate Experiment (GRACE), and in situ profiles. Our model reproduces the altimetry regional trends as well as their seasonal/interannual variations. Adding a GRACE-estimated mass to the model result further explains the altimetry SLR in a way that mass-induced effect contributes more in the midlatitudes than in the tropical WNP over the GRACE period. In addition, interannual variability and linear trend of regional sea levels are explained mainly by changes in the OHC due to heat convergence and divergence by ocean circulations, while seasonal variability is caused mainly by surface air-sea fluxes. To understand the underline physics, a comparative experiment was carried out, showing that the recent strengthening trends of SLR and OHC in the tropical regions are significantly attributed to the heat and water mass redistribution in the upper ocean caused by the intensified easterly trade wind over the past two decades.