The past, present and future of the East/Japan sea in change: a simple moving-boundary box model approach

The East/Japan Sea is a mid-latitude marginal sea that has undergone dramatic changes during the last 50–60 years. One of the most prominent characteristics of these changes is a rapid decrease in the amount of dissolved oxygen in deep waters. As a consequence of these changes, some investigators have even argued that the East/Japan Sea might become an anoxic sea in the next 200 years. While the causes of these changes are still under investigation, it has been shown that they are mainly due to modifications in the mode of the deep water ventilation system in the East/Japan Sea: a slowdown and complete cessation of bottom water formation accompanied by an enhancement of upper water formation instead. A simple moving-boundary box model (MBBM) was developed in order to analyze and quantify the processes involved in such changes over the last 50–60 years. Using a MBBM, we estimated the levels of several conservative chemical tracers (CFCs, Tritium, SF6, 137Cs) and bioactive tracers (oxygen and phosphate) in the deep water masses of the East/Japan Sea, comparing these with the historical data available, and making predictions for the near future. The model predicts that the East/Japan Sea should remain well-oxygenated, despite recent rapid oxygen decreases in its deep waters, accompanied by such structural changes as a shrinking of its oxygen-depleted deeper waters and an expansion of its oxygen-rich upper waters over the next few decades.