Regional Report for PICES Region 23, 32 pp.
31 January 2023
Through the geostrophic balance, the depth of the main pycnocline shoals toward the center of the WSAG. [...] The slow acidification in the western subarctic region (Section 5.2) was considered to be attributed to the reduced rate of increase of dissolved inorganic carbon caused by the pycnocline depression, the weakened vertical mixing flux and warming, and the increase of total alkalinity (Wakita et al., 2017). [...] The reduction of the rate of increase of the nDIC in winter is attributed to a reduction of the surface water density due to the pycnocline depression associated with the northward shrinkage of the western subarctic gyre (Nagano et al., 2016) and surface water warming, and a decline of the vertical diffusion flux of deep water with high concentrations of nDIC from the top of the main pycnocline as. [...] Because the nTA increase in winter due to the decrease in density is cancelled out by the reduction of the vertical diffusion flux, the increase of winter nTA is possibly caused by weakening calcification in organisms in winter. [...] At the same time, specific areas in the southern ES region (where half of the catch occurred in the two recent years of strong recruitment, 2010 and 2012) are closed during the rest of fishing season, to conserve the spawning stock.