The ocean has removed approximately a third of the CO2 released by human activities since the Industrial Revolution. It is one of the largest sinks of anthropogenic CO2 and the largest reservoir of carbon containing approximately 50 times more carbon than the atmosphere. Understanding the processes that control the exchange of carbon between the ocean and atmosphere is key for projecting the future effects of carbon dioxide on climate change, ocean acidification, marine ecosystems, and society. In addition, enhancing carbon sequestration by the ocean (blue carbon) is being explored for reducing the rapid accumulation of anthropogenic CO2. We discovered that the exchange of carbon between the atmosphere and ocean is modulated by a group of photosynthesizing plankton called coccolithophores, therefore we must ascertain the role of these organisms more precisely. These common microscopic organisms that live in the sun-lit layer of the world’s oceans form elaborate plates of the carbon bearing mineral calcium carbonate.
Concentrations of these plates are visible as chalk, for example, in the White Cliffs of Dover and via satellite images. We found that coccolithophores dominate the production of CaCO3. Coccolithophores are tiny algae which measure less than 1/100 of a millimeter and form the basis of the aquatic food web and contribute to the regulation of atmospheric CO2 levels through calcification and photosynthesis.
We found that coccolithophores comprise 90% of the total production of CaCO3 in the surface ocean with a large portion being dissolved, indicating they play a key role in controlling ocean chemistry and CO2. This research highlights that the other two main planktonic calcifying groups, pteropods and foraminifera (both zooplankton), play a secondary role.
