中海に出現する貧酸素水塊の海況学的特性と海洋構造

This paper attempts to describe the oceanographic structure of Lake Nakaumi, a semi-closed brackish water body connected to the Japan Sea, focusing on hydrographic feature of oxygen-deficient water mass. The study is based on monthly hydrographic observations made from April 2000 through to March 2001. The water mass characteristics were investigated by the station graph analysis. Three different types of water masses, namely, upper layer water, bottom layer water and riverine water appeared through the year. An oxygen-deficient water mass occurred from May to December. Its maximum volume was estimated to be c.40% of the entire volume of the Lake Nakaumi. The volume of the oxygen-deficient water mass increased from June to November corresponding to the occurrence of the bottom layer water mass, indicating that the bottom layer water induced from the Japan Sea rapidly turned into the oxygen deficient water mass during the high-temperature season. The decrease in volume of oxygen-deficient water mass in September was probably caused by the exchange of water mass due to the occurrence of a flush flood.