POM samples with environmental data were collected from 2016 to 2021 in the southern part of the SOJ between 35°N and 41°N and between 131°15'E and 139°50'E (Fig. 1) during 28 cruises using R/V Hokko-maru, Shunyo-Maru, Yoko-Maru, T/V Tenyo-Maru (Japan Fisheries Research and Education Agency), and R/V Dai-Go Kaiyo-Maru (Kaiyo Engineering Co., Ltd.). The cruises were held yearly from February to September, except for March (Fig. 1). The observations were repeated 14 times after 2018 along the monitoring line established off the Sado Island (SI-line) (Fig. 1) (in September 2016, July 2018, August 2018, September 2018, February 2019, April 2019, June 2019, September 2019, February 2020, April 2020, June 2020, September 2020, February 2021, April 2021, and June 2021).