Abstract
The behavior of the hypoxic water in the offshore hollows which were dug from 1982-1986 near Muromi River mouth in Hakata Bay, is studied.In these three years, 17 years after the construction of these hollows, the hypoxic condition of the bottom water of these hollows has been observed to be gradually worsening.Rapid formation of the hypoxic condition in June and rapid extinction in October were seen at the bottoms of the hollows in 2006.Piling up of the density layers in the sea water was thought to be the formation mechanism of hypoxic condition in June.The DO flux caused by the vertical mixing of the sea water or inflow of the sea water of high DO and high density from outside was thought to extinguish the hypoxic condition in October.
