Decadal change of dissolved inorganic carbon in the subarctic western North Pacific Ocean

Dissolved inorganic carbon (DIC) was measured from 1992 to 2008 at two time-series sites in the subarctic western North Pacific; this region is a source of atmospheric CO 2 in winter due to vertical mixing of deep waters rich in DIC. To estimate the decadal DIC increase resulting from CO 2 uptake from the atmosphere, we corrected DIC for the contribution of biological activity below the temperature minimum ( T min ) layer (∼100 m), which is the remnant of the mixed layer from the preceding winter. Decadal DIC increases in the T min layer and upper intermediate water (1.3–1.5 μmol kg -1 yr -1 ; 100–200 m) were higher than those expected from oceanic equilibration with increasing atmospheric CO 2 and those previously reported in the open North Pacific. The increase in water column CO 2 was estimated to be 0.40 ± 0.08 mol m -2 yr -1 . The decadal DIC change in the T min layer affects winter CO 2 emission. The increase of atmospheric x CO 2 in winter (2.1 ± 0.0 ppm yr -1 ) is higher than that of oceanic x CO 2 (0.7 ± 0.5 ppm yr -1 ) that calculated from DIC and total alkalinity in the T min layer. This difference suggests reduction of CO 2 emission in winter is possibly controlled by the increase of total alkalinity. DOI: 10.1111/j.1600-0889.2010.00476.x