Optimal Assimilation Number of Phytoplankton in the Siberian Seas: Spatiotemporal Variability, Environmental Control and Estimation Using a Region-Specific Model
Andrey B. Demidov | Tatiana A. Belevich | Sergey V. Sheberstov
The maximal value of the chlorophyll-specific carbon fixation rate in the water column or the optimal assimilation number (P<sup>b</sup><sub>opt</sub>) is an important parameter used to estimate water column integrated primary production (IPP) using models and satellite-derived data. The spatiotemporal variability in the P<sup>b</sup><sub>opt</sub> of the total and size-fractionated phytoplankton in the Siberian Seas (SSs) and its links with environmental factors were studied based on long-term (1993–2020) field and satellite-derived (MODIS-Aqua) observations. The average value of P<sup>b</sup><sub>opt</sub> in the SSs was equal to 1.38 ± 0.76 mgC (mg Chl <i>a</i>)<sup>–1</sup> h<sup>–1</sup>. The monthly average values of P<sup>b</sup><sub>opt</sub> decreased during the growing season from 1.95 mgC (mg Chl <i>a</i>)<sup>–1</sup> h<sup>–1</sup> in July to 0.64 mgC (mg Chl <i>a</i>)<sup>–1</sup> h<sup>–1</sup> in October. The average value of P<sup>b</sup><sub>opt</sub> for small (<3 μm) phytoplankton 1.6-fold exceeded that for large (>3 μm) phytoplankton. The values of P<sup>b</sup><sub>opt</sub> depend mainly on incident photosynthetically available radiation (PAR). Based on the relationship between P<sup>b</sup><sub>opt</sub> and PAR, the empirical region-specific algorithm (E<sub>0reg</sub>) was developed. The E<sub>0reg</sub> algorithm performed better than commonly used temperature-based models. The application of E<sub>0reg</sub> for the calculation of P<sup>b</sup><sub>opt</sub> will make it possible to more precisely estimate IPP in the SSs.
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