Phytoplankton take up dissolved carbon dioxide and fix it into organic carbon.
If they sink out of the surface mixed layer they effectively remove carbon dioxide from surface water into deep water or sediments. This is new production, and drives the so-called biological pump. The hypothesis that the biological pump plays a role in regulating carbon dioxide levels in the atmosphere, and hence climate, would be supported by the finding that phytoplankton productivity was higher in periods of low atmospheric carbon dioxide. Isotopic analysis of preserved phytoplankton organic matter, combined with knowledge of the carbon isotopic composition of the inorganic carbon pool derived from the study of calcium carbonate shells, can provide information on ancient levels of dissolved carbon dioxide in surface waters and the growth rates, or productivity, of phytoplankton. My research focuses on diatoms, the class of phytoplankton most likely to be responsible for new production.