Determining the spectrum of the coefficient of light absorption by phytoplankton is a complex experimental problem. One of the most reliable methods is the nonextract spectrophotometric method - direct measurements of light absorption spectra in isolated phytoplankton in vivo samples. Such measurements are made on samples of natural phytoplankton (or cultivated cultures) concentrated on filters. In order to eliminate the scattered light, the spectrophotometers are equipped with integrating spheres or diffusers made of milky glass.
The measurement consists of following steps:
1. - filtering,
2. - measurement of spectrum,
3. - bleaching (depigmentation),
4. - second measurement of spectrum.
The difference between absorption measured before and after bleaching gives a value of absorption by living phytoplankton pigments. The after-bleaching spectrum gives information about the absorption by remaining particular matter.
Database contains the results of measurements carried out by various specialists from other institutes during joined cruises. So the methodological details vary in each dataset. The differences are briefly described in the table below.
| Vessel, expedition, year | Filters, pores size [micrometer] | Spectrometer, Regime of measurements | Correction | Bleaching method |
| "Vityaz" 64 1978 | SYNPOR N4 + BaCO3 layer 0.85 | SF-14 Sample and reference filters in the middle of Ulbricht's sphere | K factor Konovalov (1985) | UV+H2O2 |
| "Profesor Siedlecki" 14 1980 | Nucleopore 1 | Specord UV-VIS Shibata et al. (1954) method | For the number of filter layers | Freezing solvents alkali |
| Akademik Kurchatov" 39 1984 | SYNPOR N5 + BaCO3 layer 0.65 | SF-18 Sample and reference filters in the middle of Ulbricht's sphere | beta factor Konovalov (1992) (eq. 1) | UV+H2O2 |
| Experiment SOPOT'87 1987 | GF/C 1.2 | SF-18 Sample and reference filters in the middle of Ulbricht's sphere | beta factor Konovalov (1992) (eq. 2) | UV+H2O2 |
| "Professor Shtokman" 25 1990 | GF/F 0.6 | SF-18 Sample and reference filters in the middle of Ulbricht's sphere | beta factor Konovalov (1992) (eq. 2) | Ca(OCl)2 2% sol. |
| Campaign ULISSE 1993-1994 | GF/F 0.6 | PERKINS-ELMER LAMBDA 19 + integrating sphere combination of light reflection and light transmission measurements (Tassan and Ferrari 1995) | beta factor (Tassan and Ferrari 1995) (eq. 3) | Ca(OCl)2 |
1) beta(lambda)=(0.0021 lambda - 6.35) D + 0.00073 lambda + 4.38
2) beta(lambda)=(0.00234 lambda - 4.54) D + 0.00033 lambda + 2.92
3) beta(lambda)=0.49 D2 + 0.417 D
where D is the optical density of the sample on the filter and lambda is expressed in nanometers.
Please contact Slawomir Kaczmarek for more detailed information.
References:
Konovalow B. V., 1985, Light absorption capacity of phytoplankton pigment, In: O.J. Koblentz Mishke, B. Wozniak, I.E. Ochakovskii [Eds.], Utilization of solar energy in the process of photosynthesis by the Black Sea and Baltic phytoplankton, Moskva, 59-71, (in Russian).
Konovalov B. V., 1992, Opredelenie pokazatelia pogloshchniia sveta komponentami sestona po spektru pogloshcheniia ego osadka na membrannom filtre, Okeanologiia, 32(3), 588-593.
Tassan S., Ferrari M. G., An alternative approach to absorption measurements of aquatic particles retained on filters,
Shibata K., Benson A. A., Calvin M., 1954, The absorption spectra of suspension of living micro-organisms, Biochim. Biophys. Acta, 15, 461-471.