Part of PUR due to photosynthetic pigments This is the sum of the light energy (expressed in megajoules) absorbed only by the photosynthetic pigments in phytoplankton in the water column under an area of 1 m² during a given 24 h period. Some of this energy in converted into chemical energy during the photosynthesis of organic matter in these cells, in contrast to the energy absorbed by photo-protecting pigments, which do not participate in photosynthesis. Part of the remaining absorbed energy is converted into heat, which is emitted from the cell to the surroundings,  while the rest radiates out of the cell as light produced during luminescence (mainly the luminescence of chlorophyll a).

The PUR energy is defined by (Woźniak, 2008):

$$PUR(z,t)=\int_{400nm}^{700nm}E_0(\lambda,z,t)a_{pl,PSP}(\lambda,t)d\lambda$$

where

$$E_0 (\lambda, z, t)$$– spectrum of scalar irradiation at depth z

$$a_{pl,PSP}(\lambda, z, t)$$ – spectrum of the coefficient of light absorption by photosynthetic pigments in phytoplankton at depth z

$$\lambda$$ - light wavelength [nm]

$$z$$ – depth [m]

$$t$$ - time [s]

The 24 h dose of PUR_PSP energy is obtained by integrating the PUR_PSP energy over depth (from the surface to 1.5 times the depth of the euphotic layer) and over time (24 hours). Methodology The PUR_PSP energy is determined using the DESAMBEM model (Woźniak et al., 2008). The input data for this model are the PAR radiation dose at the water surface and the concentration of chlorophyll a at the sea surface C_a(0). The DESAMBEM model can be used to determine light fields in the water, from which the irradiance at particular depths can be calculated. One can also calculate vertical concentration profiles of photosynthetic pigments in phytoplankton (Majchrowski et al., 2007) and spectral coefficients of light absorption by photosynthetic pigments in phytoplankton at the same depths (Ficek et al. 2004). With these magnitudes to hand, one can calculate the 24 h dose of PUR_PSP energy. Validation It is assumed that the errors in the method for determining the PUR_PSP energy flux are the same as for the PUR energy flux.

Link to parameter in the SatBaltic System: