Chlorophyll natural fluorescence response to upwelling events in the Southern Ocean

R. M. Letelier¹, M. R. Abbott¹ and D. M. Karl²

¹College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon

²School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii

Abstract

Variability of solar-induced (natural) fluorescence and chlorophyll were measured on scales of hours to weeks in the upper layer of a cyclonic eddy located south of the Antarctic Polar Front using a free-floating drifter. The fluorescence signal was analyzed both in terms of chlorophyll concentration and as an indicator of energy distribution in the photosynthetic apparatus. Long-term trends in fluorescence parallel changes in chlorophyll concentration. Considering a significant positive correlation between fluoresence 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 consistent with the Southern Ocean iron limitation hypothesis.