Author: Roman Majchrowski, last updated: 26 April 2016
Absorption by PSP per unit of chlorophyll at specified depths
The absorption of solar radiation by phytoplankton stimulates the photosynthesis of organic matter in the sea. Consequently, it is the principal factor responsible for supplying marine ecosystems with energy. In phytoplankton cells, solar energy is absorbed by both photosynthetic pigments and by photo-protecting pigments. Only the light quanta absorbed by photosynthetic pigments (PSP) can participate in photosynthesis. Hence, with a knowledge of the mean coefficient of absorption by PSP per unit of chlorophyll a, one can estimate the magnitude of primary production in the water with greater accuracy. The unit of the mean coefficient of light absorption by PSP at specified depths is [m2 (mg chl a)-1].
The definition of the mean coefficient of absorption by PSP per unit of chlorophyll a (Majchrowski et al., 2000):
- the spectral coefficient of absorption by PSP per unit of chlorophyll a (symbolized by the asterisk) at a given depth z.
Mean coefficients of absorption by PSP per unit of chlorophyll a at specified depths in the Baltic are calculated using the DESAMBEM model (Woźniak et al., 2008).
The input data for this model are the chlorophyll a concentration just below the surface and the daily dose of PAR. Vertical profiles of the concentrations of the main groups of PSPs are calculated: chlorophylls a, b, c and photosynthetic carotenoids and phycobilins (Majchrowski et al., 2007). With the aid of spectral reconstruction based on a total of 24 elementary absorption bands described by Gaussian functions (Ficek et al., 2004) and calculated levels of the main groups of pigments at a given depth, the DESAMBEM model determines the “unpackaged” (i.e. scattered) spectral coefficients of absorption by PSPs in phytoplankton. Then follows the “packaging” (i.e. the determination of absorption coefficients for the PSPs in phytoplankton cells) of absorption coefficients using the spectral function of the packaging effect. These calculations yield light absorption coefficients in vivo for PSPs in phytoplankton. The absorption for PSPs coefficients are then averaged over all wavelengths and divided by the chlorophyll a concentration. The relevant formulas for determining spectral coefficients of light absorption by phytoplankton in the Baltic can be found in the articles by Woźniak et al. (2008) and Ficek et al. (2004).
The standard deviations relating to calculations of PSP absorption per unit of chlorophyll are of the same magnitude as the those obtained by validating absorption per unit of chlorophyll (see the description of absorption per unit of chlorophyll).