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<p><strong>Abstract.</strong> Producing very extensive blooms in the world's oceans in both hemispheres, a coccolithophore <i>E. huxleyi</i> is capable of affecting both the marine ecology and carbon fluxes at the atmosphere-ocean interface. At the same time, it is subject to the impact of multiple co-acting environmental forcings, which determine the spatio-temporal dynamics of <i>E. huxleyi</i> blooming phenomenon.</p> <p>To reveal the individual importance of each forcing factor (FF) that is known to significantly control the extent and intensity of <i>E. huxleyi</i> blooms and can be retrieved from remote sensing data, we used long-term spatial time series (1998&amp;ndash;2016) of sea surface temperature and salinity, incident photosynthetically active radiation, and Ekman layer depth relevant to the marine environments located in the North Atlantic, Arctic and North Pacific oceans, namely the North, Norwegian, Greenland, Labrador, Barents and Bering seas.</p> <p>The FFs retrieved were subjected to statistical analyses. The descriptive statistical approach has shown that <i>E. huxleyi</i> phytoplankton were highly adaptive to the environmental conditions and capable of arising and developing within wide FFs ranges, which proved to be expressly sea-specific. It was also found that there were FFs optimal ranges (also sea-specific), within which the blooms were particularly extensive.</p> <p>The application of the Random Forest Classifier (RFC) approach to each target sea allowed to reliably rank the FFs considered in terms of their role in the spatio-temporal dynamics of <i>E. huxleyi</i> blooms. With the only exception of the Bering Sea, allegedly due to temporally established untypical hydrological conditions, the prediction ability of RFC modeling characterized in terms of precision, recall, and <i>f1</i>-score generally was in excess of 70&amp;thinsp;%, thus indicating the adequacy of the developed models for FFs prioritization with regard to <i>E. huxleyi</i> blooms.</p>

Blooms of a coccolithophore E. huxleyi are generally huge, occur annually and in the oceans of both Hemispheres. As a calcifying algal species, E. huxleyi is known to enhance the partial pressure of dissolved CO 2 in the surface ocean, thus reducing its ability to absorb atmospheric CO 2. Here we report on the results of our satellite study of CO 2 enhancement in the atmospheric column over E. huxleyi blooms in the North, Greenland, Iceland and Barents seas. The study is based on OCO-2 and wind force and direction data, and E. huxleyi bloom masks developed by us earlier. Eight case studies are discussed herein relating to the time period 2015-2018. The results obtained are strongly indicative that, indeed, the phenomenon of E. huxleyi blooms noticeably affects the carbon fluxes between the atmosphere and the surface ocean: the quantified enhancement of CO 2 content in the atmospheric column over the bloom area in five out of eight case studies proved to be in the range of 0.6-3.0 ppm. It is also shown that the magnitude of CO 2 enhancement in the atmospheric column is significantly controlled by air advection in the boundary layer. K e y w o r d s: satellite remote sensing; OCO-2 data; enhancement of atmospheric columnar CO 2 content over E. huxleyi blooms in Subarctic and Arctic seas; Emiliania huxleyi; wind and atmospheric advection.