Upwelling of anoxic bottom water (Aoshio) frequently occur along the coast of Tokyo Bay, in the region extending from off Urayasu City to Chiba Port. According to the existing literatures, Aoshio occur when anoxic water mass formed in the bottom layer rises to the surface under the influence of wind, rainfall, temperature drop and other factors. However, actual observations of Aoshio during their emergence are scarce, except the continual observations conducted at four stations by the Environment Agency in 1992 to 1994. In the present report, we analyzed records of Tokyo Electric Company's observations, which, with the aim of obtaining real-time water quality conditions during Aoshio occurrence, were conducted in May to October at 2 water depths of 2 stations and at 2 layers of 6 stations in 1992 and 1993 respectively. Water temperature, salinity, and dissolved oxygen were measured. From the analyses it was shown that, before Aoshio emerged, continuous blowing of the south wind had preceded abrupt changes in water temperature, salinity and DO concentration of the bottom layer. And we estimate that a vertical movement of the pycnocline, which is induced by wind blowing, plays a major part in causing a large scale Aoshio phenomenon.
