Comment on “Phytoplankton Calcification in a High-CO2 World”

coccolithophore Emiliania huxleyi doubles its organic matter production and calcification in response to high carbon dioxide partial pressures, contrary to previous laboratory and field studies. We argue that shortcomings in their experimental protocol compromise the interpretation of their data and the resulting conclusions. The uptake of anthropogenic CO2 by theocean is projected to drive seawater pH inthe course of this century to levels lower than have occurred over the past 20 million years (1). Despite much uncertainty about the resulting impacts on marine biota, there will be both win-ners and losers of ocean carbonation and acid-ification. Calcareous organisms will for the most part be on the losing side, as increasing seawater acidification (decreasing pH) incurs a greater meta-bolic energy requirement to precipitate calcium carbonate (2). Some photoautotrophic groups are likely to be on the winning side as increasin