Acceleration of Ocean Acidification in the Western North Pacific

Because annual anthropogenic CO2 emissions have grown rapidly over the past decades, there is a concern that anthropogenic CO2 invasion into the ocean may also have caused the rate of ocean acidification to increase. Here, we report the decadal and longer-term variability in the rates of change of inorganic carbon variables since the early 1980s in surface seawaters of various oceanic regions along the 137 degrees E repeat line in the western North Pacific. In the subtropical frontal zone, we found that the mean rate of acidification tracked the acceleration of the atmospheric CO2 increase; during 2008-2017, the rate of acidification was 30% faster than during 1983-2017. In the Kuroshio Recirculation and tropical zone, acidification trends were clear, but the trends were modulated by decadal variability associated with temporal variability in regional ocean circulation.