Interannual Variability of Bio-Optical Characteristics of the Barents and Kara Seas

The paper is devoted to the calculation of trends in the temporal variability of bio-optical characteristics in the subregions of the Barents Sea (chlorophyll a and coccolithophore concentrations for the period 1998–2024) and Kara Sea (chlorophyll a concentrations for the period 2003–2024) based on MODIS (Moderate Resolution Imaging Spectroradiometer) and SeaWiFS (Sea-Viewing Wide Field-of-View Sensor) satellite ocean color data processed using regional bio-optical algorithms. To expand the time series of bio-optical characteristics, the satellite ocean color data were combined. To assess the magnitude of climate change, the time series of sea surface temperature were also analyzed. When calculating the trends, the methods of harmonic analysis, singular spectrum analysis and quantile regression were used. Significant trends were recorded only for the sea surface temperature values. In the middle subregion of the Barents Sea, the periodogram of chlorophyll a concentration has two pronounced maxima corresponding to periods of 1 and 0.5 year. Significant trends were obtained in quantiles including 10% of the largest and smallest values of the chlorophyll a concentration series in the southwestern subregion of the Kara Sea. They amounted to 0.86 × 10–2 and –0.38 × 10–2 mg/m3 per year, respectively, with a confidence level of 75%. The use of the singular spectrum analysis method made it possible to record fluctuations in the chlorophyll a concentration values in the middle subregion of the Barents Sea with a period of 6–7 years.