Effects of Elevated CO₂ on a Marine Antarctic Diatom

Boelen et al. (2011) assessed the photophysiology of the Antarctic diatom Chaetoceros brevis in seawater equilibrated with ambient CO₂ air (380 ppm) and air of approximately twice-ambient CO₂ (750 ppm) and half-ambient CO₂ (190 ppm), under four different irradiance regimes: two of which simulated deep and shallow vertical mixing, and two of which mimicked limiting and saturating stable water column conditions.

According to the authors, no significant differences between the enhanced and reduced CO₂ levels were found, with respect to either "growth, pigment content and composition, photosynthesis, photoprotection and RuBisCO activity," and so they concluded that "within the range tested, CO₂ does not significantly affect the photophysiological performance of C. brevis." In these respects, they also note that their results "agree with other studies on marine diatoms showing little or no effect of elevated CO₂ on growth (Burkhardt et al., 1999) or maximum rates of photosynthesis (Rost et al., 2003; Trimborn et al., 2009)," although they say that in still other studies "elevated CO₂ concentrations enhanced growth rates (e.g., Riebesell et al., 1993; Clark and Flynn, 2000)," while adding that "a recent field study in the Southern Ocean (Tortell et al., 2008) showed an increase in phytoplankton productivity and the promotion of large chain-forming Chaetoceros species under elevated CO₂."

In summing up the implications of their findings, the six scientists say their results suggest that "under saturating and limiting, as well as under dynamic and constant irradiance conditions, the marine Antarctic diatom C. brevis has the ability to adjust its cellular physiology in response to changing CO₂ levels with minimal effects on growth and photosynthesis." And although this maintenance of the status quo could validly be considered to be a neutral response to elevated CO₂, it could also be regarded as a positive finding, in light of the fact that climate alarmists generally contend that atmospheric CO₂ enrichment will be bad for almost all oceanic life.

Additional References
Burkhardt, S., Riebesell, U. and Zondervan, I. 1999. Effects of growth rate, CO₂ concentration, and cell size on the stable carbon isotope fractionation in marine phytoplankton. Geochimica et Cosmochimica Acta 63: 3729-3741.

Clark, D.R. and Flynn, K.J. 2000. The relationship between the dissolved inorganic carbon concentration and growth rate in marine phytoplankton. Proceedings of the Royal Society of London Series B 267: 953-959.

Riebesell, U., Wolf-Gladrow, D.A. and Smetacek, V. 1993. Carbon-dioxide limitation of marine-phytoplankton growth-rates. Nature 361: 249-251.

Rost, B., Riebesell, U., Burkhardt, S. and Suitemeyer, D. 2003. Carbon acquisition of bloom-forming marine phytoplankton. Limnology and Oceanography 48: 55-67.

Tortell, P.D., Payne, C.D., Li, Y.Y., Trimborn, S., Rost, B., Smith, W.O, Riesselman, C., Dunbar, R.B., Sedwick, P. and DiTullio, G.R. 2008. CO₂ sensitivity of Southern Ocean phytoplankton. Geophysical Research Letters 35: 10.1029/2007GL032583.

Trimborn, S., Wolf-Gladrow, D., Richter, K.U. and Rost, B. 2009. The effect of pCO₂ on carbon acquisition and intracellular assimilation in four marine diatoms. Journal of Experimental Marine Biology and Ecology 376: 26-36.