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

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.

Byrne, R. H., Mecking, S., Feely, R. A., & Liu, X., 2010. Direct observations of basin-wide acidification of the North Pacific Ocean. Geophysical Research Letters 37: L02601 doi:10.1029/2009GL040999. Article (subscription required).

2 Responses to “Direct observations of basin-wide acidification of the North Pacific Ocean”

  1. 1 artesian 21 January 2010 at 13:50

    The oceans are alkaline because they are in contact with limestone. You are talking about lowering the alkalinity not increasing the acidity. Very alarming ‘science’.

    • 2 Jean-Pierre Gattuso 22 January 2010 at 07:02

      The pH scale describes how acidic or basic a liquid is. It is based on the concentration of hydrogen ions (H+). The pH scale ranges from 0 to 14, with 0 being highly acidic, 14 being highly alkaline, and 7 being neutral. The pH scale is logarithmic, like the Richter scale used to measure earthquakes. Therefore, any change on the pH scale corresponds to a 10-fold higher change in the concentration of H+, hence of acidity. For example, the H+ concentration and the acidity of a solution at pH 7 is 10 times more than at pH 8. Ocean acidification refers to the increase in the acidity of seawater. The mean pH of surface seawater has decreased from about 8.2 at preindustrial time to 8.1 today, representing a 26% increase in the H+ concentration and acidity. Note that despite the process of ocean acidification, the oceans are alkaline and will not become acidic (pH lower than 7) even in the distant future.

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