1. Ковалева И. В. (Kovalуоva I. V.)

Purpose. The purpose of the study is to present an algorithm for calculating the integral phytoplankton biomass in the Black Sea euphotic layer using expeditionary data, and to perform a comparative analysis of the variability of the studied characteristics obtained by means of calculations in two ways: using direct measurements of chlorophyll concentration along the horizons, and based on the parameterization results.

Methods and Results. The algorithm for calculating the integral biomass of phytoplankton is presented. Data from Crimean coastal waters at the depths of 20–1500 m, collected during R/V Professor Vodyanitsky cruises for different seasons of 2018–2022, were used in this study. The estimates resulted from parameterization and those obtained from calculations based on direct measurements of the individual input parameters at different depths are compared. The results of parameterization statistical analysis show that the determination coefficients varied in the range 0.70–0.74. In the photosynthesis zone, the monthly averages of integral phytoplankton biomass (calculated from the expeditionary data) in June and October constitute 768 ± 283 and 2277 ± 726 mg С/m², respectively. In the upper mixed layer, in June they are 556 ± 270 mg С/m², and in October – 2023 ± 725 mg С/m². The parameterization-derived monthly averages for the whole water area under study differ from the ones calculated using the direct measurements of input parameters at different depths by 0.9–4%. The chlorophyll a concentration profiles for individual months in 2018–2022 are considered and mathematically described using the function obtained in earlier studies. In autumn, maximum values of chlorophyll a are observed mainly in the upper mixed layer. In summer, they occur at the lower boundary of the euphotic zone, where up to ~ 0.1% of light reaching the sea surface penetrates.

Conclusions. The above parameterization of integral phytoplankton biomass is applicable to all the seasons, easy to use and agrees well with the results of calculations based on direct measurements of chlorophyll concentration at different depths. In the future, the calculation algorithm will be refined to facilitate computations based on satellite data.