How does rising atmospheric CO2 affect marine organisms?

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Elevated CO2 Primes the Ocean's Biological Carbon Pump
Riebesell, U., Schulz, K.G., Bellerby, R.G.J., Botros, M., Fritsche, P., Meyerhofer, M., Neill, C., Nondal, G., Oschlies, A., Wohlers, J. and Zollner, E. 2007. Enhanced biological carbon consumption in a high CO2 ocean. Nature 450: 545-548.

What was done
Between 15 May and 9 June of 2005 at the Espegrend Marine Biological Station of the University of Bergen, located on a fjord in southern Norway, the authors maintained nine cylindrical mesocosms -- which extended from the water surface to a depth of 9-10 meters -- in equilibrium with air of either ambient CO2 concentration (350 ppm), doubled CO2 (700 ppm) or tripled CO2 (1050 ppm), while they measured several phytoplanktonic physiological parameters.

What was learned
During the period of their study, Riebesell et al. report that "net community carbon consumption under increased CO2 exceeded present rates by 27% (2 x CO2) and 39% (3 x CO2)," and they state that continuous oxygen measurements in the mesocosms indicated "enhanced net photosynthesis to be the source of the observed CO2 effect."

What it means
Noting that "the phytoplankton groups dominating in the mesocosm studies -- diatoms and coccolithophores -- are also the main primary producers in high productivity areas and are the principal drivers of biologically induced carbon export to the deep sea," the eleven researchers say their findings "underscore the importance of biologically driven feedbacks in the ocean to global change."

Further noting that "increased CO2 has been shown to enhance fixation of free nitrogen, thereby relaxing nutrient limitation by nitrogen availability and increasing CO2 uptake (Barcelos e Ramos et al., 2007)," Arrigo (2007) states in a News & Views discussion of Riebesell et al.'s paper that "neither these, nor other possible non-steady-state biological feedbacks, are currently accounted for in models of global climate -- a potentially serious omission, given that the biological pump is responsible for much of the vertical CO2 gradient in the ocean." And in this regard they additionally indicate that the phytoplankton growth-promoting effect of CO2 described and measured by Riebesell et al. has probably been responsible for limiting the rise in atmospheric CO2 experienced since the dawn of the Industrial Revolution to approximately 90% of what it likely would have been in its absence.

Arrigo, K.R. 2007. Marine manipulations. Nature 450: 491-492.

Barcelos e Ramos, J., Biswas, H., Schulz, K.G., LaRoche, J. and Riebesell, U. 2007. Effect of rising atmospheric carbon dioxide on the marine nitrogen fixer Trichodesmium. Global Biogeochemical Cycles 21: 10.1029/2006GB002898.

Reviewed 16 January 2008