Spatiotemporal changes of ocean carbon species in the western North Pacific using parameterization technique

We constructed parameterizations for the estimation of dissolved inorganic carbon (DIC) and pH in the western North Pacific, including Japanese coastal regions. Parameterizations, determined as a function of potential temperature (θ) and dissolved oxygen (DO), provided strong correlations with direct measurements for DIC [the coefficient of determination (R2) = 0.99; the root mean square error (RMSE) = 8.49 µmol kg−1] and pH (R2 = 0.98, RMSE = 0.030). Predicted DIC and pH values were consistent with previous independent hydrographic observations, generally within 3 µmol kg−1 for DIC and 0.010 for pH. By applying these parameterizations to climatological seasonal θ and DO data and time-series θ and DO data from autonomous profiling floats (Argo) in the western North Pacific, large spatiotemporal variations in DIC and pH were demonstrated. Results indicated that the rate of increase in anthropogenic DIC above a depth of 400 m along 30° N in the western North Pacific was + 0.86 ± 0.11 µmol kg−1 year−1 between 1994 and 2004. This decreased by + 0.58 ± 0.05 µmol kg−1 year−1 after 2004 partly due to increasing anthropogenic nitrogen input, suggesting that the decrease has induced the slowdown of ocean acidification in the western North Pacific. The declining trend in anthropogenically induced ocean pH was found to be 0.0021 ± 0.0016 during 1994–2013.