Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 10 2009 10.5194/bg-6-2145-2009 http://www.biogeosciences.net/6/2145/2009/ http://www.biogeosciences.net/6/2145/2009/bg-6-2145-2009.html http://www.biogeosciences.net/6/2145/2009/bg-6-2145-2009.pdf 2145 2153 2009-10-09 CO₂ perturbation experiments: similarities and differences between dissolved inorganic carbon and total alkalinity manipulations K. G. Schulz kschulz@ifm-geomar.de J. Barcelos e Ramos R. E. Zeebe U. Riebesell Leibniz Institute of Marine Sciences (IFM-GEOMAR), Düsternbrooker Weg 20, 24105 Kiel, Germany University of Hawaii at Manoa SOEST Department of Oceanography 1000 Pope Road, MSB 504 Honolulu, HI 96822, USA Increasing atmospheric carbon dioxide (CO₂) through human activities and invasion of anthropogenic CO₂ into the surface ocean alters the seawater carbonate chemistry, increasing CO₂ and bicarbonate (HCO₃^&minus;) at the expense of carbonate ion (CO₃^2&minus;) concentrations. This redistribution in the dissolved inorganic carbon (DIC) pool decreases pH and carbonate saturation state (Ω). Several components of the carbonate system are considered potential key variables influencing for instance calcium carbonate precipitation in marine calcifiers such as coccolithophores, foraminifera, corals, mollusks and echinoderms. Unravelling the sensitivities of marine organisms and ecosystems to CO₂ induced ocean acidification (OA) requires well-controlled experimental setups and accurate carbonate system manipulations. Here we describe and analyse the chemical changes involved in the two basic approaches for carbonate chemistry manipulation, i.e. changing DIC at constant total alkalinity (TA) and changing TA at constant DIC. Furthermore, we briefly introduce several methods to experimentally manipulate DIC and TA. Finally, we examine responses obtained with both approaches using published results for the coccolithophore <I>Emiliania huxleyi</I>. 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