This MODIS image of a coccolithophore bloom of the coast of Brittany, France was taken on June 15, 2004.
This particular coccolithophore, when it blooms consumes, dissolved carbon dioxide, nitrate, and phosphate while producing oxygen, ammonia, dimethyl sulfide. They incorporate huge quantities of carbon which, as they die, falls to the bottom of the ocean floor and is buried.
A bloom like the one above can contain billions of cells per litre of water and generate tens of thousands of metric tons of calcium carbonate in the upper layer of the bloom.
Of course anything trapped under this bloom that requires photosynthesis is in trouble as the water becomes darker with the amount of reduced light penetrating through the layers of coccolithopores. As wind and tides change, the bloom is dispersed and it begins again in another part of the ocean.