Since 2008 scientists have been studying the effects of increasing concentrations of carbon dioxide in seawater on Antarctic marine microbial communities at Davis. These communities include bacteria, phytoplankton and protozoa, which sit at the base of the food web and directly, or indirectly, support all life in the Southern Ocean. This 2013–14 Antarctic season the team is returning to Davis to continue their experiments.

The scientists have installed six 650 litre ‘minicosms’ or incubation tanks in a shipping container on the shore at Davis. The tanks are filled with seawater which is filtered to remove any organisms larger than 0.2mm.

Different volumes of CO2-saturated sterile seawater is then added to each of the tanks to achieve different CO2 concentrations, ranging from ambient Antarctic concentrations in summer (84 ppm — parts per million), to the maximum seawater CO2 concentration predicted for the year 2300 (2423 ppm). For comparison, the current atmospheric CO2 concentration is about 400 ppm.

Research so far has shown that Antarctic marine microbes can tolerate the natural large seasonal fluctuations of CO2 concentrations from 84 to 643 ppm. However, above 1281 ppm there are dramatic changes in the species composition and size of microbial cells. Large phytoplankton above 0.02mm in size greatly decline, while smaller species less than 5 µm increased.

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