Hydrographic structures of Tokyo Bay between 1992 and 2019 and evidence of temperature increase; observational results by the training vessel Seiyo-Maru

We investigated hydrographic conditions in Tokyo Bay recorded from 1992 to 2019 by the training vessel Seiyo Maru (retired in October 2021). We reviewed the basic features of hydrographic conditions discussed in the literature. The long-term trend of temperature differed from that reported in previous studies. The rates of temperature increase estimated in this study were 0.04–0.07 °C /year in the inner bay of Tokyo Bay. These rates were the same as those reported in other areas worldwide. The heat budget in the inner bay of Tokyo Bay also increased significantly from 2004 to 2019; this increase was related to the decrease in the loss of latent heat because of the increases of the atmospheric temperature and the decreases of wind speed. Because formation of the Tokyo Bay thermohaline front has been affected by the increase of water temperature and because the temperature increases have differed between months, the program of monthly monitoring should be continued to document future environmental changes in Tokyo Bay.