Processes Controlling the Carbonate Chemistry of Surface Seawater Along the 150°E Transect in the Northwest Pacific Ocean

The problem of ocean acidification caused by the increase of atmospheric carbon dioxide concentration is becoming increasingly prominent. Field observation in the northwest Pacific Ocean was carried out along the 150°E transect in November 2019. The distribution characteristics and influencing factors of the surface seawater carbonate chemistry, including dissolved inorganic carbon (DIC), total alkalinity (TA), pH, partial pressure of carbon dioxide ( p CO 2 ) and aragonite saturation state (Ω arag ) were investigated. DIC and TA ranged from 1915 to 2014 µmol kg −1 and 2243 to 2291 µmol kg −1 , respectively; DIC in general decreased with decreasing latitude, but TA had no clear latitudinal gradient. p CO 2 values increased with the decrease of latitude and were all below the atmospheric p CO 2 level, ranging from 332 to 387 µatm. pH on the total hydrogen ion concentration scale (pH T ) decreased with the decrease of latitude in the range of 8.044–8.110, while Ω arag increased with the decrease of latitude in the range of 2.61–3.88, suggesting that the spatial distributions of pH T and Ω arag were out of phase. Compared with the present, the predicted values of pH T and Ω arag by the end of this century would decrease remarkedly; larger declines were found in the higher pH T and Ω arag regions, resulting in the differences along the meridional gradient becoming smaller for both pH T and Ω arag .