The quantum efficiency of photosynthesis is the ratio of the number of atoms (or moles) of photosynthetically assimilated carbon to the number (or moles) of quanta of solar radiation absorbed by phytoplankton. Knowledge of the value of this parameter is of key importance for determining the magnitude of primary production. The maximum theoretical quantum efficiency of photosynthesis is 0.125 mol C Ein^-1, i.e. 8 quanta need to be absorbed for one molecule of CO₂ to be assimilated. In real conditions, a far greater number of absorbed quanta of light are required in order to assimilate one atom of carbon, which means that the quantum efficiency of photosynthesis of phytoplankton takes very small values. The quantum efficiency of photosynthesis at a given depth Φ_i(z) depends on many factors and can be defined as follows (Woźniak et al., 2008; Woźniak et al., 2007):

$$\Phi_i(z) = \Phi_{max} f_a(z) f\Delta f_c f_{E, t}$$

$$\Phi_{max}$$ – the theoretical maximum quantum efficiency of photosynthesis, which takes a value of 0.125 molC Ein^-1,

Fig.1 Comparison of empirical Φ_pomiar and modelled Φ_model quantum efficiencies of photosynthesis at different depths z in the euphotic layer of the Baltic. Empirical values of the quantum efficiency of photosynthesis Φ_pomiar were measured during research in 2006-2011, while modelled values of the quantum efficiency Φ_model were obtained using the DESAMBEM algorithm – one of the input data was the chlorophyll a concentration at the surface measured in situ from on board the research vessel.

where:

$$f_a(z)$$ - the index of non-photosynthetic pigment content at depth z, $$f\Delta$$ - the so-called inefficiency factor of energy transfer and charge recombination at photosynthetic centres, $$f_c$$ - the relative number of functioning reaction centres RC, i.e. the ratio of the number of functioning RCs (where the reactions of photosynthesis take place) to the total number of functioning and non-functioning RCs. This is a complex factor, dependent on nutrient concentrations and irradiance, and takes account of the influence of light inhibition on the number of functioning RCs, $$f_{E, t}$$ – a factor describing the relationship between the quantum efficiency of photosynthesis on the level of irradiance and temperature in the sea, colloquially known as the light response curve of photosynthesis.

Methodology

The quantum efficiency of photosynthesis at selected depths in the Baltic is determined using the DESAMBEM algorithm (Woźniak et al., 2008).

Validation

Validation of the quantum efficiency of photosynthesis at selected depths in the euphotic layer in studied basins of the Baltic. Measurements of 118 sets of parameters essential for calculating the quantum efficiency of photosynthesis were made in 2006-2011 during research cruises on the research vessels Oceania and Baltica. The standard error factor x (see the table below) characterizing the method for calculating the quantum efficiency of photosynthesis Φ using the DESAMBEM algorithm is relatively small at 1.439, which means that the logarithmic statistical error is from σ- = -30.5% to σ+ =43.9%.

Table 1. Systematic and statistical errors of estimated values of the quantum efficiency of photosynthesis at selected depths in the euphotic layer of the Baltic in arithmetical and logarithmic statistics when the sea surface chlorophyll a concentration, measured from on board ship, is used as an input datum for the DESAMBEM algorithm. N denotes the number of estimated values in the euphotic layer.

Links to the parameter in SatBaltic System:

Quantum efficiency of photosynthesis: 0m

Quantum efficiency of photosynthesis: 1 m (for registered users)

Quantum efficiency of photosynthesis: 3 m (for registered users)

Quantum efficiency of photosynthesis: 5 m (for registered users)

Quantum efficiency of photosynthesis: 10 m (for registered users)

Quantum efficiency of photosynthesis: 20 m (for registered users)