Quasi-tropical cyclone caused anomalous autumn coccolithophore bloom in the Black Sea

Abstract. Short-period action of the quasi-tropical cyclone in September 2005 caused strong autumn coccolithophores bloom in the Black Sea lasted for more than 1.5 months. The cyclone induced intense upwelling of deep waters with temperature on 10–13 °C lower than surrounding waters and acceleration of the Rim Current up to extreme values of 0.75 m s⁻¹. The Rim current transported nutrient-rich waters from the north-western shelf to the zone of the cyclone action. Mixing of the shelf and upwelled waters triggers the initial growth of remote sensing reflectance (R_rs) indicating the beginning of the coccolithophore bloom. After two weeks, the bloom shifted directly to the zone of maximum upwelling in the western cyclonic gyre, where R_rs reached values of 0.018 sr⁻¹, corresponding to estimates of 107 cells l⁻¹. Advection by the Rim Current spread the bloom over the entire south part of the Black Sea on more than 1000 km from its initial source.