Effects of CO₂ and light on the carbon acquisition of key diatom species in the Southern Ocean

The ecology and biogeochemistry of the Southern Ocean is strongly dominated by key diatom species (Fig. 1). The mechanisms regulating the dominance of these diatoms in the Southern Ocean ecosystem are poorly understood. According to the IPCC (scenario IS92a), surface water CO₂ concentrations are expected to increase almost three-fold for the year 2100 relative to preindustrial values and to lower the pH (‘ocean acidification’) by 0.4 units. Rising temperatures will impact surface ocean stratification, which in turn will affect light climate and nutrient input from deeper layers (Fig. 2). Climate models indicate that especially the Southern Ocean will be affected by these environmental changes. How will these changes shape diatom community structure and possibly alter productivity?



Fig. 1 Natural Antarctic phytoplankton community dominated by diatom species (Picture by Dr. Philipp Assmy).

Despite the fact that CO₂-related changes such as ocean acidification are considered to be especially pronounced in the Southern Ocean, the potential CO₂ sensitivity of Southern Ocean phytoplankton has not thoroughly been investigated yet. Since the mode of carbon acquisition determines how sensitive phytoplankton responds to changes in CO₂, investigation of these processes has gained increasing importance in phytoplankton ecology. In this project, phytoplankton responses to CO₂ will be assessed in conjunction with light availability at the cellular and the molecular levels to gain an ecophysiological explanation for the spatial distribution of diatom species in the present ocean and will further allow predicting changes in the community structure with regard to the predicted environmental changes.



Fig. 2 Main putative physico-chemical changes in the oceanic ecosystem occuring in this century. Modified after Rost and Riebesell (2004).

Scientists

Scarlett Trimborn
Alfred Wegener Institute for Polar and Marine Research
Bremerhaven

Research areas

Antarctic circumpolar current, Polar front, Ross Sea, Antarctic Peninsula

Publications

Tortell PD, Trimborn S, Li Y, Rost B, Payne CD, 2010. Inorganic carbon uptake by Ross Sea phytoplankton across natural and experimental CO2 gradients. Journal of Phycology 46, 433-443.

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

Tortell PD, Trimborn S, Li Y, Rost B, Payne CD, 2009. Inorganic carbon uptake by Ross Sea phytoplankton across natural and experimental CO₂ gradients. Journal of Phycology, in press.

Trimborn S, Lundholm N, Thoms S, Richter KU, Krock B, Hansen PJ, Rost B, 2008. Inorganic carbon acquisition in potentially toxic and non-toxic diatoms: the effect of pH-induced changes in the seawater carbonate chemistry. Physiologia Plantarum, doi:10.1111/j.1399-3054.2007.01038.x

Tortell PD, Payne CD, Li Y, Trimborn S, Rost B, Smith WO, Risselsman C, Dunbar R, Sedwick P, di Tullio GR, 2008. The CO₂ sensitivity of Southern Ocean phytoplankton, Geophysical Research Letters 35, L04605, doi:10.1029/2007GL032583.

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Research funding organisation

German Research Foundation

Project number: TR 899/2-1
Funding period: January 2010 - December 2011