Calcification and organic production of coccolithophorids Emiliania huxleyi under different atmospheric pCO2 in a mesocosm experiment

The response of primary production and calcification of the coccolithophorid Emiliania huxleyi
to different partial pressures of CO2 (p CO2) have been investigated during a mesocosm bloom
experiment in a Norwegian fjord. Glacial, present and next century atmospheric p CO2
conditions (respectively 180, 370 and 700 ppmV) have been simulated above the surface of large
sea-water enclosures. If production of organic matter remains constant under elevated p CO2, the
production of inorganic carbon appears to be affected in two ways. First, the beginning of
calcification is delayed. Second, the production rate of inorganic carbon appears to be lowered
by 40% in the future conditions, decreasing subsequently the calcification/photosynthesis ratio
from 1 to 0.6. During the experiment a strong viral growth have been experienced, which have
seriously depressed calcification as well. We propose the threshold of 5.10 6 cell/ml for E
huxleyi virus abundance above which the production and calcification of the population of E.
huxleyi are severely affected.