The Response of Marine Phytoplankton to Increasing [CO₂]

The concentration of CO₂ in surface seawater is increasing along with that of the atmosphere as a result of fossil fuel combustion and other human activities. In view of the critical role of the ocean biota in the global carbon cycle, the question of the response of marine phytoplankton to increasing [CO₂] is of prime importance. Aside from the indirect effect of lowered nutrient fluxes resulting from the increased stratification caused by warming, two direct effects must be considered: the effect of increasing [CO₂] on photosynthesis and the effects of decreasing pH on key chemical and biological processes such as the precipitation of calcium carbonate and the availability of major and trace nutrients. Our ongoing work on inorganic carbon acquisition in diatoms implies that increasing [CO₂] should increase carbon fixation rates in these organisms and that this effect may not be uniform among various families of marine phytoplankton.  Indeed, preliminary field experiments have shown that diatoms are favored under high [CO₂] conditions (Tortell et al. 2002).  We are presently examining in laboratory cultures the effects of [CO₂] changes on the growth of model phytoplankters under conditions of iron or nitrogen limitation.

Photos taken by Ken Bruland and Bettina Sohst.

2007 Summer Research Cruise Gulf of Alaska (Morel Group members Dalin Shi, Patrick McGinn, Yan Xu and Brian Hopkinson).

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Princeton University
Department of Geosciences