Thin chlorophyll layer concomitant of the thermohaline intrusion in the confluence of the Gulf Stream and Labrador Current (a case study)

Based on the depth-cycling data of a fluorometer probe in the northwestern Atlantic ocean, this paper considers features of the chlorophyll fluorescence layer against a background of concurrent variability of seawater temperature and fluorescence of CDOM (Colored Dissolved Organic Matter). The vertical distributions of chlorophyll fluorescence complied with the criteria of a thin chlorophyll layer at the site where changes of temperature and CDOM fluorescence were indicative of the intrusion of Labrador waters into adjacent warmer waters below the upper mixed layer. As may be supposed, the thin chlorophyll layer was due to the gyrotactic trapping of phytoplankton cells induced by water shear between the upper mixed layer and the intrusion.