The Observation of Growth-decay Process of Hypoxic Water Mass in the head of Ariake Bay

Abstract

In summer 2006, a large survey was conducted in the head of Ariake bay to investigate the relationship between growth-decay process of hypoxic water mass and the behavior of river plume after the flood induced by the monsoonal rainfall.After the flood, at first, low salinity water mass was formed along the coast with the coast to the west of its direction of travel.Then a river plume spread from the mouth of the Chikugo River toward offshore to form a bulge. Finally the bulge covered whole the region of the bay head.The formation of the bulge was followed by the development of a hypoxic water mass below the halocline.The stratification induced by the flood gradually weakened by tidal mixing with a neap-spring tidal cycle.Simutaneously, the bottom DO gradually increased.Then, the hypoxic water mass completely disappeared by the coastal upwelling and vertical mixing induced by the strong northerly wind by the typhoon 10.