Satellite monitoring of coccolithophore blooms in the Black Sea from ocean color data

- High backscattering in June is formed by both coccolithophore bloom and river runoff.
- Satellite algorithm to assess the coccolithophore concentration has been designed.
- Separation of the contributions from main factors in water turbidity in June was made.
- The results have been validated by in situ data and compared with PIC data product.

Satellite observation is an eminently suitable tool for monitoring and study of coccolithophore blooms but quantitative estimation needs perfected algorithms. The current satellite algorithm using the data of ocean color scanners, such as SeaWiFS and MODIS, is based on retrieval of the backscattering coefficient and then estimation of the calcite concentration via an empirical relationship. The regional algorithm for the Black Sea is also an empirical relationship between the coccolithophore concentration and the particle backscattering coefficient, based on in situ measured data. The drawback of the both algorithms is that “non-coccolithophore” backscattering is not accounted for. This shortcoming is particularly significant for the Black Sea which is strongly influenced by river runoff.We analyze the problem of taking into account the “non-coccolithophore” backscattering by using the integrated approach with the comprehensive data set including satellite data and optical, hydrological and biogeochemical parameters measured in situ in the eastern part of the Black Sea. The main result obtained is a new algorithm for retrieval of coccolithophore concentration in the Black Sea from satellite ocean color data. The algorithm is based on the two-parametric model of the particle backscattering coefficient, which takes into account both coccolithophore bloom and river runoff. Application of the new algorithm to satellite ocean color data in 1998-2011 gave an opportunity to separate the changes associated with the abovementioned factors. Several new interesting results were obtained. It was shown that coccolithophore blooms occupied only a part of the area with high values of the particle backscattering coefficient, and there were the years with no coccolithophore bloom in the Black Sea in June even though the high values of the particle backscattering coefficient were observed.The other problems to be solved for improvement of the satellite algorithm, providing a quantitative assessment of the intensity of coccolithophore blooms in the Black Sea, were discussed.