F LUORESCENCE AND F LUO RO PROBE

Vincent Taillandier, Diana Ruiz Pino (in collaboration with Felipe Artigas, not on board)

Aim: to evaluate the high frequency variability (including meso- and submesoscale) of total chlorophyll biomass and the main groups of phytoplankton at the sea-surface across the documented Austral Ocean and Weddell sea. The total/multispectral fluorometry from continuous pumping surface seawater data will be also used to be compared with ocean optics signals from satellite allowing the development of new color ocean algorithms.

FLUORESCENCE

Fluorescence continuous measurement was done during cruise. A turner sensor was installed on board the JCR, under the BAS responsibility. This sensor was used when the seawater flow rate was higher than a proposed threshold of 0.3 (Fig 2.8.1).

The total chlorophyll pigment measured by HPLC after the cruise (see section 4) will be used to calibrate the fluorescence sensor installed in the underway by BAS.

From the underway sea surface water arriving at the chemical laboratory were sampled regularly discrete samples, every 6 hours for the beginning of the cruise (local time 8h, 14h, 20h and 2h) between south of Falkland Island (55°S) and 75°S, then every 4 hours (local time 8h, 12h, 16h, 20h, 24h and 4h) at the end of the cruise. The discrete samples were stopped during the stations (cf figure A.1.1). The surface collected samples to measure total chlorophyll pigment by HPLC, after the cruise will be used to calibrate the fluorescence sensor installed in the underway by BAS. The sampling and storage protocols are described in annex N°3.3. Once calibrated the obtained continuous data from fluorescence will be also compared to the total chlorophyll obtained by the Fluoroprobe sensor (see following section).

49 FLUOROPROBE

Aim: To quantify the sea surface regional variability of main phytoplankton groups, and Yellow Substances (CDOM) in the Austral Atlantic Ocean and in the Weddel Sea.

A fluoroprobe sensor bbE+ was installed in the chemical laboratory and connected with the underway seawater flow during the entire cruise. The data frequency acquisition is 1 value/minute. The recorded raw data are the led 3 to 8 assumed to be used to evaluate the distribution of 5 groups of phytoplankton: diatoms, crysophites, yelow substances, green and bleu algae and also paheocystise. This method is based on the discrimination of spectral groups of algae characterised by specific composition of pigments and consequently, by a specific excitation spectrum of the chlorophyll-a a fluorescence, following sequential light excitation by different ligth-emitting diodes (LEDs) emitting at different wave length following the fluoroprobe.

Fluoroprobe allow determining total chlorophyll. Its principles are due to the fact that algae of the same division contains a similar quantity and quality of photosynthetic pigments, their fluorescence excitation spectrum (with a fixed emission wavelength at 680nm) is significant.

Thus, it is possible to differentiate divisions of algae by their fluorescence excitation spectrum. In addition to this, other fluorescing matter (for example, yellow substances) is detected to enhance the accuracy. The bbe fluorometers use 6 LEDs for fluorescence excitation for algae differentiation. The LEDs emit light at 6 selected wavelengths (370nm, 470nm, 525nm, 570nm, 590nm and 610nm).

The used algorithm to evaluate the groups from the row data and visualized by the +bbE software used the calibration provided by the instrument. After the cruise and once measured pigments and abundance of phytoplankton (taxonomic technic) it will be possible to determine and to adapt mathematic algorithm to the specific phytoplankton group and yellow subtances occurring in the Antarctic waters. Data were stored in ASCII files every days of cruise. Each file contains the raw 6 LEDS data available to be used with different algorithms to calculate the variability of 6 phytoplankton groups.

The determination of the different Algae classes with the fluoroprobe is based on the following hypothesis. The division of chlorophyceae (green algae) shows a broad maximum of fluorescence at the 470nm LED, which is caused by chlorophyll-a and -b. The cyanophyceae (blue-green algae) have their maximum at 610nm due to the photosynthetic antenna pigment phycocyanin.

Cyanophyceae also contains chlorophyll-a if there is low intensity at 470nm. This is due to the masking effect of the phycocyanin. Furthermore, the high peak at the 525nm region for the bacillariophyceae originates from xanthophyll fucoxanthin and for the dinophyceae from peridin.

The maxima at 470nm are caused by chlorophyll-a and -c. In our last analysed group, cryptophyceae, a significant maximum can be found at 570nm, which originates from phycoerythrin.

The different divisions of algae was first measured separately to calibrate the instrument an optics lab of Wimereux by Pr. Felipe Artigas. The measured spectra, or fingerprints, are then stored in the FluoroProbe.
During the measurement, the spectrum of the sample is loaded into the storage device of the instrument and sent to an external computer. The computer calculates the content of

the different divisions of algae in the sample from the sample spectrum and the spectra of the separately measured algae divisions. The concentration of every algae division is given in μg chlorophyll-a/l.

After subtracting the offset from the measured fluorescence signals, the remaining signals have to be assigned to the different algae classes. A statistical calculation procedure in the software finds the best combination of concentrations of algae classes for the measured pattern of signals. The total chlorophyll concentration is the sum of all detected concentrations of algae classes. The row LED measured signal hasi8t'e calibrated after the cruise. The different algae classes used for the statistical fit need to have significantly different fluorescence spectra. Moreover the different pigment signal measured at the discrete sample collected from the underway system will be used to calibrate the Fluoroprobe to reproduce the specific Antarctic algae groups.

Yellow substances may fluorescence and a priori abundant in the Ice Shelf of the Weddell sea could be also determined by the Fluoroprobe.
 The UV LED (370nm) is used to measure yellow substances in the water. At 370nm it is possible to differentiate between algae (low signal) and yellow substances (high signal). The result of this measurement is given in relative units and not in weight/volume, because very different substances are detected. The result is mainly used to obtain a more accurate determination of algae classes – but it is also possible to determine the variations of the yellow substances.

The transmission of the water is measured with a 710nm LED opposite the detector. It is measured in per cent, where 100% is pure water and complete “black water” is 0%. The transmission can be used to compensate errors in the chlorophyll measurement that are caused by particles in the water which absorb either the excitation light or the fluorescence light. The seawater sample temperature and temperature of the sensor were also measured.

The post-calibration of Fluoroprobe will be done again after the cruise using a strategy based on 2 sets of data. We will use first the 6 LED signals measured in a continuous way by the fluoroprobe together with the pigments to calibrate the fluoroprobe. Then a validation will be done comparing the variability of main phytoplankton groups determined by the fluoroprobe with the distribution obtained in key Antarctic region by taxonomy (optical microscope and SEM) and genomic (polar front, weddell gyre, marginal ice zone, ice shelf).

51 Fig. 2.8.2. Raw Fluoroprobe LED data a) the sum of all LEDs assumed to correspond to total Chl-a signal, and for the other LED : LED 3, 4, 5, 6, 7, 8 corresponding to different phytoplankton groups.

2.9. Oxygen

Maria Gelado, Vincent Taillandier

Sampling Contribution : Marion Benneti, Camille Akhoudas

Aim : to evaluate the surface variability in key regions of the Weddell sea of biological net production of Oxygen (DeltaO2) and to compare with the net Carbon biological pump evaluated from DIC and pC02 (DeltaDIC, DeltapC02).

Continuous measurement of Oxygen (02) from the underway sea surface water were obtained using an Optode sensor. This sensor is connected to the PLM (UK) PC02 instrument. The Optode system was collecting data during a large part of the cruise, from February 10 until March 10 (see Figure 2.9.1). No oxygen seasurface data were obtained during shorts periods due to the stop of seawater pump when the Vessel was
in areas surrounded by sea ice. In the same flow of seawater were collected discrete Oxygen samples, on duplicate during the first part of the cruise, then on triplicate during the last part. A total of 141 samples of 02 analyzed following the Winkler method will be used to calibrate the Optode sensor (see Table 3.1).

This calibration uses also the continuous temperature data obtained by the underway TSG.

Figure 2.9.1: Underway Oxygen-continuous data from Optode sensor and discrete data measured on board by Winkler titration (top) , Underway Sea water Flow rate (below).

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