In situ and remote-sensed chlorophyll fluorescence as indicator of the physiological state of phytoplankton near the Isles Kerguelen (Southern Ocean)

Shipboard and remote-sensed Chlorophyll fluorescence were determined in the natural phytoplankton assemblage above the iron-enriched Kerguelen Plateau and the adjacent high-nutrient, low-Chlorophyll open Southern Ocean. The variance between fluorescence yield and photosynthetic efficiency was determined in combination with Chlorophyll a concentrations, irradiance and phytoplankton species distribution. A co-variance between the fluorescence measurements would allow the refinement of remote-sensing primary production algorithms. Distinct differences were found in photosynthetic efficiency and water-leaving fluorescence, with relatively high values for the Kerguelen Plateau and low values in the open ocean, reflecting the differences in Chlorophyll a concentrations. The co-variance of the fluorescence properties suggested that remote-sensed fluorescence measurements could be used to infer differences in the physiological state of the phytoplankton, hence primary production. Fluorescence yield, however, did not show the differences in the research area, most likely due to the low signal and the diurnal variation in water-leaving fluorescence.