Variable fluorescence was measured using a Fastracka submersible fluorometer (Chelsea Instruments Ltd). Two different sampling protocols were used for the continuous monitoring of surface waters. The first one was applied for:

1. The spatial description of the Morocco upwelling area (two times)

2. The continuous monitoring performed while moving from station to station between the UPW and MOI sites.

The second protocol was applied at MOI and DYF sites, as well as while moving between these sites.

In the first sampling protocol, water was pumped at ca. 3 m through PVC tubing, passed through a de-bubbling device and distributed to different instruments, including the Fastracka. The transit from sea surface to the Fastracka lasted ca. 7 minutes and was in darkness and dim light (ca. one minute in the de-bubbling device). The Fastracka was operated in a flow-through configuration, using only the dark chamber.

In the second sampling protocol, water was pumped from sea surface at ca. 3 m to a 50-L aquarium placed on the front deck away from any shadow, as far as possible. After passing through the pumping system (ca. 5 minutes) water was thus re-exposed to full sunlight during about 10 minutes before passing through the dark chamber of the Fastracka.

Measurement protocol was the same for for sampling strategies. Each Fastracka measurement consisted of train 100 1.1- microsec saturation flashes generated at 0.36 MHz, followed by 20 relaxation 1.1-microsec flashes at 12 kHz. The model published by Kolber et al. (1998) was adjusted by best fit to the observed fluorescence transient assuming no energy transfer between photosynthetic units. Baseline and reference function calibrations were conducted as recommended by the instruments manufacturer.

The following parameters were derived:

FoD: Minimal fluorescence yield measured in the dark (rel. units)

FmD: Maximal fluorescence yield measured in the dark (rel. units)

FvD: Variable fluorescence (Fo - Fm) measured in the dark (rel. units)

Fv/FmD: Normalised variable fluorescence measured in the dark (dimensionless), often assumed to be the photochemical conversion efficiency of photosystem 2

SigD: Functional cross section of photosystem 2 measured in the dark (square A°)

TauD: Turnover time for electron transport from photosystem 2 to photosystem 1 (microsec).

PAR at the level of the aquarium was measured using the PR46 PAR irradiance metter (Chelsea Instrument Ltd) equipped with an hemispherical collector, interfaced with the Fastracka. Note that in the current version, PAR data are in rel. units.

A total of 10 data files were generated from surface sampling. The first two correspond to the 2 spatial surveys conducted in the upwelling area:

1. "survey1.txt"

2. "survey2.txt"

These are followed by 6 time monitoring performed between short stations:

1. "monitoring_1to2.txt" : between stations 1 and 2

2. "monitoring_2to3.txt" : between stations 2 and 3

3. "monitoring_3to4.txt" : between stations 3 and 4

4. "monitoring_4to5.txt" : between stations 4 and 5

5. "monitoring_5to6.txt" : between stations 5 and 6

6. "monitoring_6toMIO.txt" : between stations 6 and MOI

Finally, two additional files contain the time monitoring performed while occupying the MIO and DYF sites. Note that the former also contains measurements performed continuously after we left the MOI site, toward the DYF site:

1. "MIO.txt"

2. "DYF.txt"

 

Kolber, ZS, Prasil O and Falkowski PG, 1998. Measurements of variable chlorophyll fluorescence using fast repetition rate techniques: defining methodology and experimental protocols. Biochimica et Biophysica Acta, 1367, 88-106.