An anoxic Sea of Japan by the year 2200?

The Sea of Japan has experienced fluctuations in bottom-water properties over many time scales. These include increases in temperature and decreases in thickness of the bottom boundary layer and oxygen concentrations. Such temporal variations were thought to be transient and probably caused by a recent reduction or cessation of new bottom-water formation in the northern Sea of Japan. Such an event indeed occurred during the last glacial period when the Sea of Japan became anoxic, and it did not become oxic again until early in the Holocene. This study shows that an apparent stagnation started at least as early as 1950 and that it is still going on. The temperature increase is consistent with heat flow data. It also demonstrates that the estimated oxygen consumption rate and the phosphate and nitrate regeneration rates since the apparent stagnation began are in agreement with the rates calculated from one dimensional advection–diffusion and mass balance models. These rates average 0.8±0.4 μmol kg−1 year−1 for oxygen, 0.007±0.003 μmol kg−1 year−1 for phosphate and 0.10±0.04 μmol kg−1 year−1 for nitrate. It is concluded that if the oxygen consumption continues to outpace replenishment, the Sea of Japan below 2000 m could very well become anoxic again 180–530 years from now