A biological inidication for Yellow Sea Bottom Cold Water

Abstract

Tintinnid ciliates, having distributional sensitivity to hydrological changes, have been applied as a useful tool to track the movements of water masses. The Yellow Sea Bottom Cold Water (YSBCW) is one of the most prominent summer oceanographic phenomena in the Yellow Sea. To examine the potential of tintinnid species as a biological indicator of the bottom cold water, the spatial distributions of the ciliates were investigated in the southeastern Yellow Sea. A dominant species, Tintinnidium primitivum, was found in the bottom cold waters during the summers 2010 and 2020. The temperature and salinity (T-S) diagram for the dominant species distribution was plotted against the T-S range for the YSBCW at low temperatures between 6 ℃ and 12 ℃ and salinity between 32 and 33. Distribution of the tintinnid indicative species for YSBCW, Tintinnidium primitivum, was monitored to trace the vertical mixing of the YSBCW by seasonal investigations along the 35°N line from 2019 to 2022. Bottom-oriented distribution of the species was observed in the whole season except in winter. Winter vertical mixing indicated by water temperature and salinity profiles was strongly supported by homogenous distribution of the species through the whole water column of Stns. 35-11 and 35-13. No occurrence of the species was a sensitive response on the different water mass in the upper layer of low salinity at Stn. 35-15 in the winter, indicating the invasion of neritic water mass from China. The sensitivity of the species occurrence on the hydrological changes provides further information on the vertical migration of the YSBCW. The synergetic analysis of physical and biological data can be an effective approach to trace the identity/origin of water mass in mixed seawater.