About one third of anthropogenic CO₂ emissions to the Earth’s atmosphere dissolves in surface seawater increasing its CO₂ concentration and decreasing its pH. These changes in the chemistry of their environment may affect the growth and the species assemblages of marine phytoplankton. Predicting such biological and ecological effects is made difficult by the fact that several chemical parameters change along with pCO₂ and pH, in particular the chemical form of phytoplankton macro- and micro-nutrients.   Our aim is to understand the physiological response of marine phytoplankton to the direct and indirect chemical and physiological changes caused by ocean acidification. 

An expected effect of increasing pCO₂ is a decrease in the energy expended to concentrate CO₂ (see Inorganic Carbon Acquisition by Phytoplankton) and, hence, a higher photosynthetic efficiency. But this effect is not always seen experimentally. Available data show that an equally important effect is a decrease in the rate of respiration in phytoplankton, which appears to be due to the lowering of the external pH. We have also shown that acidification decreases the rate of uptake of essential metals such as iron and zinc. This effect is due to a decrease in the binding of the metals by inorganic and weak organic complexing agents. (This unexpected result led to the discovery of the role of weak ligands in metal availability described in Metal Uptake by Phytoplankton.) Acidification of seawater reduces the degree of supersaturation of calcium carbonate and has been shown to sometimes decrease calcification in calcifying organisms such as coccolithophores.