Physical Oceanography Physical Oceanography 1573-160X 20250306 Mathematical modeling of marine systems Research Article Parameterization of the Dependence of Integral Phytoplankton Biomass on Chlorophyll Concentration at the Black Sea Surface Based on Expeditionary Research Data https://orcid.org/0000-0001-5430-2002 AAB-4397-2019 2356-4570 Kovalyova I. V.
Russian Federation
ilonavk@ibss-ras.ru A. O. Kovalevsky Institute of Biology of the Southern Seas of RAS Sevastopol Russia 30 06 2025 32 3 347 360 16 08 2024 03 03 2025 13 03 2025 Copyright © 2025, I. V. Kovalyova 2025 I. V. Kovalyova https://creativecommons.org/licenses/by-nc/4.0/ https://physical-oceanography.ru/repository/issues/2025/03/06/

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.

 integral biomass phytoplankton Black Sea calculation algorithm chlorophyll a concentration profiles The study was funded by the Russian Science Foundation and the Government of Sevastopol (Grant No. 24-27-20014, “Transformation of the structure and functional characteristics of the Black Sea phytoplankton off the Crimea coast in modern environmental conditions. Fundamental role and applied importance”, https://rscf.ru/project/24-27-20014/). The work was carried out at the Center for Collective Use of R/V Professor Vodyanitsky.

Article text not included.

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