EFFECTS OF TSUGARU WARM CURRENT AS COASTAL BOUNDARY CURRENT ON THE WATER TEMPERATURE AND DISSOLVED OXYGEN IN OFUNATO BAY

Abstract

The effect of Tsugaru warm current (TWC) to the variation of temperature and dissolved oxygen (DO) wasinvestigated byfield observation data and sea surface temperature (SST) derived from NOAA/AVHRR data inOhfunato bay. From the field observation data, density intrusion, the phenomenon that outer seawater intrudes thesame density layer in inner bay, was observed under stratified season in Ohfunato bay. Since outer seawatertemperature was sameat the middle layer in inner bay, seawaterexchange occurred at the depthof middle layer. In August, we observed abrupt DOincrease. It seemed to affect ofdensity intrusion. However, this phenomenon didnot affect broken ofoxygen-deficient water mass because DO was consumed by seabed immediately. On the other hand, when typhoon passed through Tsugaru straight at the end of August, temperature changed abruptlywith DO increase. From SST data, it was suggested that Oyashio affect this phenomenon.In the end of oxygen-deficient water mass disappearance period, when temperature of the bottom of inner bay equal to that of outer seawater, DO changed largely. At that time, seeing SST datafrom satellite, the effect of TWC isweaker than in September and outer seawater is also low. Therefore, it was concluded thatthe strength and weaknesscondition of TWC is importantfor anoxic water disappearance.