National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2010

Direct observations of basin-wide acidification of the North Pacific Ocean

Byrne, R.H., S. Mecking, R.A. Feely, and X. Liu

Geophys. Res. Lett., 37, L02601, doi: 10.1029/2009GL040999 (2010)

Global ocean acidification is a prominent, inexorable change associated with rising levels of atmospheric CO2. Here we present the first basin-wide direct observations of recently declining pH, along with estimates of anthropogenic and non-anthropogenic contributions to that signal. Along 152°W in the North Pacific Ocean (22–56°N), pH changes between 1991 and 2006 were essentially zero below about 800 m depth. However, in the upper 500 m, significant pH changes, as large as −0.06, were observed. Anthropogenic and non-anthropogenic contributions over the upper 800 m are estimated to be of similar magnitude. In the surface mixed layer (depths to ~100 m), the extent of pH change is consistent with that expected under conditions of seawater/atmosphere equilibration, with an average rate of change of −0.0017/yr. Future mixed layer changes can be expected to closely mirror changes in atmospheric CO2, with surface seawater pH continuing to fall as atmospheric CO2 rises.

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