Late winter observation of the Kuroshio: Hakuho-maru KH-25-1 cruise

The Kuroshio transports a large amount of heat, nutrients, fish eggs and larvae, and affects climate and marine ecosystem in the North Pacific. To investigate turbulence and transport processes of heat, nutrient and fish larvae in the Kuroshio during winter, KH-25-1 cruise of R/V Hakuho-maru (Tite: Turbulence, heat, nutrient and larvae fish transport processes in the winter Kuroshio, PI: Prof. Ichiro Yasuda, U. Tokyo) was conducted from February 8 through March 6, 2025.

The A01-1 group and another research project (Grant-in-Aid for Scientific Research (A)) led by Prof. Akira Kuwano-Yoshida (Kyoto Univ.) took part in this cruise to measure water vapor over the Kuroshio in winter. We conducted radiosonde observations and also used a small-sized microwave radiometer that can measure water vapor.

Despite bad weather conditions during winter and several serious troubles, all the six Kuroshio cross-sections and glider observational data were obtained. It was unfortunate, however, that only a few sardine and/or anchovy larvae were caught. (April 2025, Yoshimi Kawai@A01-1)

Sea surface temperature in the middle of the cruise (color) and ship track (bold line). Did the large meander of the Kuroshio end? The Kuroshio appears to have returned to the large-meander state after this cruise.
Vertical micro-structure profiler (VMP2000), its winch, and Prof. Yasuda (right). The winch malfunctioned at the beginning of the cruise, the crew in the engine department fixed it. (Photo: Daigo Yanagimoto, U. Tokyo)
We launched radiosondes with balloons filled with helium. The jet stream is stronger in winter. Wind speed sometimes exceeded 80 m/s (more than 300 km/h) in the upper troposphere during this cruise. (Photo: Yuta Ando, Kyusyu U. and Daigo Yanagimoto, U. Tokyo)
Drawing a neuston net. Sardine and/or anchovy larvae were scarcely found …
Underwater glider. This instrument can conduct vertical observations while moving in the targeted direction through two-way satellite communication.
There were a lot of drifting seaweeds in the East China Sea. I had a bad feeling …
It turned out like this. It was a relief that the glider was recovered successfully.