Anthropogenic atmospheric CO2uptake by the ocean is causing a global ocean pH decline,resulting indirect‐anthropogenic ocean acidification (Ed‐anth). However, indirect‐anthropogenic effects ofchanges in biological and physical processes inthe oceanalso influence ocean pH (Ei‐anth). Therefore, distinguishing between Ed‐anth and Ei‐anth is essential for predicting the progress of overall ocean acidification. We demonstrate long‐term trends of Ed‐anth and Ei‐anth in the subarctic North Pacific using a parameterization technique with an observed pH (pHobs) time series. All Ei‐anthin the ocean interior under 150m cause a pH decrease of 0.0012 ± 0.0003 per year superimposed on an 18‐year oscillation. Subtracting the pH decrease by Ei‐anth from thepHobstrend for the same region yields a net linear pH decreasing trend of 0.0021 ± 0.0003 per year byEd‐anthfor the whole ocean, indicating that pH decreases by Ei‐anth account for ~40% of total ocean acidification.
Watanabe Y. W., Li B. F. & Wakita M., in press. Long‐term trends of direct‐and indirect‐anthropogenic effects on changes in ocean pH. Geophysical Research Letters. Article (subscription required).
