Estimation of vertical diffusion coefficient and oxygen consumption rate in the interior western parts of Ariake Sea

In this study, in order to clarify the generation mechanism of hypoxic water that occurs frequently in the interior parts of Ariake Sea, various field observations were conducted in summer of 2005 and vertical diffusion coefficient and oxygen consumption rate in the study area were analyzed by the two-layer box model using Saga Prefecture research data in 1972-2000. Temporal variations of DO near sea bottom during 23 July-17 August in 2005 were strongly influenced by typhoons and strong wind-induced mixing of sea water and by the advection of hypoxic water from offshore area, besides tide and current velocity. From the data observed on 16 August in 2005, mixing condition of water column in the west coastal area was the weakly mixed-type and density stratification and pycnocline were formed at 3-5m depth from surface sea water at the time of occurrence of hypoxic water. There was a relationship between vertical diffusion coefficient obtained by the thermal stratification model and stratification parameter. That is, vertical diffusion coefficient decreased exponentially with increasing of stratification parameter. Thus, the development of density stratification in