CHLOROPHYLL NATURAL FLUORESCENCE RESPONSE TO UPWELLING EVENTS IN THE SOUTHERN-OCEAN

Variability of solar-induced (natural) fluorescence and chlorophyll we re measured on scales of hours to weeks in the upper layer of a cyclon ic eddy located south of the Antarctic Polar Front using a free-floati ng drifter. The fluorescence signal was analyzed both in terms of chlo rophyll concentration and as an indicator of energy distribution in th e photosynthetic apparatus. Long-term trends in fluorescence parallel changes in chlorophyll concentration. Considering a significant positi ve correlation between fluorescence and the relative depth of the eddy upper layer we hypothesize that the observed short-term variations in natural fluorescence are a physiological response of phytoplankton to changes in the supply of limiting nutrients. This interpretation is c onsistent with the Southern Ocean iron limitation hypothesis.