Decadal change of the surface water pCO2 in the North Pacific: A synthesis of 35 years of observations

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Abstract

[1] Surface water pCO2 data observed over the 3 decades between 1970 and 2004 are analyzed for space and time (mean decadal) variability in thirty-two 10° × 10° box areas over the North Pacific Ocean north of 10°N. During this period, the pCO2 values at SST increased at a mean decadal rate of 12.0 ± 4.8 μatm decade−1 in all but four areas located in the vicinity of the Bering and Okhotsk Seas, where they decreased at a mean rate of −11.1 ± 5.7 μatm decade−1. The mean rate of increase for the open ocean areas is indistinguishable from the mean atmospheric CO2 increase rate of 15 μatm decade−1 (or 1.5 ppm yr−1) suggesting that the North Pacific surface waters as a whole have been following the atmospheric CO2 increase. However, the rate of increase varies geographically, reflecting differences in local oceanographic processes including lateral mixing of waters from marginal seas, upwelling of subsurface waters and biological activities. The decrease observed in the southern Bering Sea and the peripheries of the Okhotsk Sea may be accounted for by the combined effects of intensified biological production and changes in lateral and vertical mixing in these areas. The natural logarithm of wintertime pCO2 values normalized to a constant temperature and salinity of 14.3°C and 34.0 (the basin mean values, respectively) is correlated with winter SST. Using this relationship, the wintertime TCO2 in mixed layer can be expressed as a function of winter SST with a standard error of ±5 μmol kg−1.

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