Emiliania huxleyi algae are known to enhance CO₂ partial pressure in their ambient water, (pCO2)w. Thus, over such bloom areas, the atmospheric column-averaged dry air mole fraction of carbon dioxide (XCO₂) is likely to increase, which has not been yet quantified on basin scales. Here we report on an Orbiting Carbon Observatory (OCO-2) satellite study of the influence of E. huxleyi blooms on XCO2 over the Black Sea. We established that concurrently with a (pCO2)w significant rise, there is an increase in the overlying XCO2 within the range ~1 to nearly 2 ppmv, which is on the order of the planetary annual increase of XCO2. As we found, (∆pCO2)w in the Back Sea and Subpolar and Polar seas are closely comparable. This strongly indicates that E. huxleyi blooms do weaken carbon sinks in the ocean on a large scale, which can be consequential for global climatology and marine biogeochemistry.