Chlorophyll variable fluorescence data (discrete samples) from the Prosope cruise.

Ondrej Prasil¹, Flavienne Bruyant², Bernard Genty³, Marcel Babin²

1Laboratory of Photosynthesis, Institute of Microbiology, Opatovicky mlyn, 37981, Trebon, Czech Republic

2Laboratoire de Physique et Chimie Marines Quai de la Darse BP 08, 06238 Villefranche sur Mer, France

3Laboratoire d'Ecophysiologie Vegetale, CNRS UPRES-A 8079, Universite Paris Sud, 91405 Orsay, France

(420)-333-724860/721101

prasil@alga.cz

Chlorophyll-a variable fluorescence was used a convenient tool to study the photosynthetic processes in vivo. The method is highly sensitive, allows for measurements of highly diluted samples and can provide (indirect) information about photochemical events related to Photosystem II (PSII), e.g. photochemical yield of PSII, kinetics of electron transfer on the acceptor side of PSII, effective size of PSII antenna etc. During the PROSOPE cruise we have used two methods for variable fluorescence measurements – Fast Repetition Rate (FRR) technique with Fastracka (Chelsea Instr.)instrument for in situ profiling and for continuous measurements on flow-through surface samples. For measurements of discrete samples in the laboratory we used the sensitive version of the Pulse Amplitude Modulation (PAM) fluorimeter from Walz that are presented in this dataset.

Bottles from surface to 200 m were sampled on every CTD cast during the cruise.

50 ml of samples were transferred from Niskin bottles first to dark glass bottles and then in the laboratory into clean plastic syringes that were wrapped in black tape. The samples in syringes were left for 30 minutes in the dark to dissipate the light-induced changes and to equilibrate the temperature. The last sample of each CTD series was measured within 30-45 minutes after the start of the first measurement.

The samples were measured in standard 3 ml quartz fluorescence cuvettes. The fluorometer was operated in a standard pump-and-probe setup as suggested by manufacturer: Samples were excited by a short (m sec) measuring flash that was provided by xenon flashlamp filtred by a BG39 blue-green excitation filter. Chlorophyll fluorescence was detected by photodiode that was protected by emission filters RG65 and RG645. The single turnover (ST) actinic flash was provided by xenon flashlamp XST-101, the multiple turnover (MT) actinic pulse of 500 ms duration was provided by halogen lamp. The output signals from the control unit were monitored using the digital oscilloscope Lecroy 9310C. Each data point for Fo and FmST is an average of 5 measurements, FmMT was measured only once (due to significant decrease in FmMT induced by non-photochemical quenching by actinic pulse).

The file pambottles.xls gives the measured data Fo (column C), FmST (column D) and FmMT (column E). From these values the maximal photochemical yields of PSII in the dark Fv/Fm for Fm measured either by single turnover (Fv/Fm ST column F) or by multiple turnover excitation (Fv/Fm column G) were calculated. Fv stands for variable fluorescence, Fv = Fm – Fo.

The units of fluorescence yields are arbitrary and are proportional to the output voltage of the fluorescence detector. For profiles PRO001-PRO014 the direct reading of the display on the PAM fluorimeter was used (units in Volts), while all further data from PRO016 were measured using the digital oscilloscope (units millivolts).

Especially in the surface layers of the oligotrophic regions, the PAM instrument was working at the limit of its sensitivity and the signal was comparable with the drift in the baseline that occurred during some measurements. We tried to avoid this by frequent adjustment of the detector baseline by calibration against the filtered seawater or distilled water.