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Observations of Anoxic Bottom Water (AOSHIO) in the Innermost of Tokyo Bay

Author(s): Ippei Fukuoka; Kouichi Kitahara; Akira Wada; Mitsuhito Kawanaga; Yuji Kagami; Tairyu Takano

Linked Author(s): Akira Wada

Keywords: Noxic bottom water (Aoshio); Upwelling; Wind-induced circulation; Tokyo Bay

Abstract: Aoshio frequently occurs along the coast of Tokyo Bay, in the region extending from off Urayasu City to Chiba Port. According to the existing literatures, the Aoshio occurs when anoxic water mass formed in the bottom layer rises to the surface under the influence of wind, rainfall, air temperature drop and other factors. However, actual observations conducted during the Aoshio season are scarce. One of the few is the then Environment Agency’s continual observations at 4 stations during the Aoshio seasons of 1992 to 1994. In the present report, we analyze 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 seasons and at 2 layers at 6 stations in 1992 and 1993. Water temperature, salinity and dissolved oxygen were measured. Before the Aoshio occurred, a south wind preceded abrupt changes in water temperature, salinity and DO of the bottom layer. Vertical movement of the pycnocline, induced by wind, plays a major part in causing a large-scale Aoshio phenomenon.


Year: 2005

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