Recent developments in chemical oceanography of the East (Japan) Sea with an emphasis on CREAMS findings: A review

Abstract

The understanding on the chemistry of the East (Japan) Sea, a typical mid-latitude marginal sea, has been dramatically improved through the CREAMS expeditions, an international cooperative study, carried out during 1990s. The CREAMS studies confirmed that the East Sea has undergone dramatic changes during the last 50–60 years. One of the most prominent characteristics of these changes is a rapid decrease of dissolved oxygen in deep waters. There even has been a claim that the East Sea might become an anoxic sea by next 200 years. While the causes for these changes are still under investigation, it has been shown that these changes are mainly due to the modification in the mode of deep water ventilation system in the East Sea: a slow down and complete stop 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 quantify the processes involved in such changes for the last 50–60 years. The model predicts that the East Sea may remain as a well-oxygenated sea despites recent rapid oxygen decreases in deep waters in association with structural changes such as a shrinking of oxygen-depleted deeper waters and an expansion of oxygen-rich upper in the East Sea in next few decades. The sedimentary record, however, shows that the East Sea has undergone oscillation between well-oxygenated environment and anoxic environment during last glacial period in association with the eustatic sea-level change. Several flooding processes such as intrusion of cold Oyashio Current and less saline, nutrient-rich seawaters from East China Sea and Yellow Sea has been proposed. Being a semi-closed basin, the carbon cycle of the East Sea has been a subject of CREAMS investigation. The East Sea serves as a strong sink of atmospheric CO2; penetration of anthropogenic CO2 all the way to the bottom is clear with its very rapid conveyor-belt system.