A Biological Indication of Vertical Mixing of the Yellow Sea Bottom Cold Water

The identities and origins of water masses in mixed seawater can be effectively traced by comprehensively analyzing physicochemical and biological data. In this study, distribution of an indicator species of the Yellow Sea Bottom Cold Water, Tintinnidium primitivum, was monitored to trace vertical mixing across seasons along the 35 °N line from 2019 to 2022. A bottom-oriented distribution was observed in every season except for winter. Winter vertical mixing was supported by water temperature and salinity profiles and the homogenous distribution of T. primitivum throughout the water column at Stns. 35-11 and 35-13. The absence of this species in response to the difference in the low-salinity surface water mass at Stn. 35-15 during winter indicated the invasion of shallow water mass from China. The sensitivity of this species to such hydrological changes provides a valuable insight into the vertical migration of the YSBCW.