Schulz KG, Barcelos J, Ramos E, Zeebe RE, Riebesell U
review, mesocosm, co2, acidification, Dictyocha, alkalinity
Increasing atmospheric carbon dioxide (CO2)through human activities and invasion of anthropogenic CO2into the surface ocean alters the seawater carbonate chemistry,increasing CO2 and bicarbonate (HCO?3 ) at the expenseof carbonate ion (CO2?3 ) concentrations. This redistributionin the dissolved inorganic carbon (DIC) pooldecreases pH and carbonate saturation state (). Severalcomponents of the carbonate system are considered potentialkey variables influencing for instance calcium carbonateprecipitation in marine calcifiers such as coccolithophores,foraminifera, corals, mollusks and echinoderms. Unravellingthe sensitivities of marine organisms and ecosystems to CO2induced ocean acidification (OA) requires well-controlledexperimental setups and accurate carbonate system manipulations.Here we describe and analyse the chemical changesinvolved in the two basic approaches for carbonate chemistrymanipulation, i.e. changing DIC at constant total alkalinity(TA) and changing TA at constant DIC. Furthermore, webriefly introduce several methods to experimentally manipulateDIC and TA. Finally, we examine responses obtainedwith both approaches using published results for the coccolithophoreEmiliania huxleyi. We conclude that under mostexperimental conditions in the context of ocean acidificationDIC and TA manipulations yield similar changes in all parametersof the carbonate system, which implies direct comparabilityof data obtained with the two basic approaches forCO2 perturbation.