Atmospheric CO₂ has been increasing at an unprecedented rate since the industrial revolution and is expected to reach 1000ppm by the year 2100 (Beardall et al. 2009). Atmospheric CO₂ increases are diffusing into ocean waters, increasing the pCO₂. The CO₂ molecule reacts with H₂O, creating HCO₃^- and H⁺, decreasing water’s pH and acidifying the oceans (Caldeira and Wickett, 2003). Changes in seawater pH affect morphology, physiology and create shifting in the marine biota (Fu et al. 2007). Doney et al. (2009) found that most calcifying organisms are affected by the increases of atmospheric CO₂ and decreases in pH. But, primary producers, like phytoplankton, could benefit from CO₂ increases (Bowes, 1991).

    Phytoplankton have been evolving over the last two billion years, in a once very high, but steadily decreasing atmospheric CO₂ concentration. Because of this, the carboxylating phytoplankton enzyme RUBISCO may show varying degrees of sensitivity to CO₂, depending upon what atmospheric CO₂ conditions the host phytoplankton evolved under. We hypothesize that phytoplankton will vary in their CO₂ sensitivity dependent upon their evolutionary emergence.

Beardall, J., Stojkovic, S., Larsend, S., 2009. Living in a high CO₂ world: Impacts of global climate change on marine phytoplankton. Planet Ecology and Diversity 2, 191-205.

Caldeira, K., Wickett, M. E., 2003. Anthropogenic carbon and ocean pH. Nature 425, 365

Bowes, G., 1991. Growth at elevated CO₂: photosynthetic responses mediated through RUBISCO. Planet, Cell and Environment 14, 795-806.

Fu, F., Warner, M. E., Zhang, Y., Feng, Y., Hutchins, D. A., 2007. Effects of increased temperature and CO₂ on photosynthesis, growth, and elemental ratios in marine Synechococcus and Prochlorococcus (cyanobacterias). Journal of Phycology 43, 485-496.