CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; perturbation experiments: similarities and differences between dissolved inorganic carbon and total alkalinity manipulations

K G Schulz,R E Zeebe,J Barcelos E Ramos,U Riebesell

doi:10.5194/bg-6-2145-2009

CO&lt;sub&gt;2&lt;/sub&gt; perturbation experiments: similarities and differences between dissolved inorganic carbon and total alkalinity manipulations

K G Schulz, R E Zeebe + Show 2 more

Open Access

https://doi.org/10.5194/bg-6-2145-2009

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Abstract

Abstract. 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−) at the expense of carbonate ion (CO32−) 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 Emiliania huxleyi. We conclude that under most experimental conditions in the context of ocean acidification DIC and TA manipulations yield similar changes in all parameters of the carbonate system, which implies direct comparability of data obtained with the two basic approaches for CO2 perturbation.

Highlights

With the beginning of the industrial revolution and the increasing utilisation of fossil fuels such as coal, oil and gas, atmospheric CO2 levels started to increase from usual interglacial values of about 280 to about 390 ppmv at present day
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
While the carbonate system can be understood in terms of the acid-base equilibria of carbonic acid, two additional concepts have proven very useful, those of dissolved inorganic carbon (DIC) and total alkalinity (TA)

Summary

Introduction

With the beginning of the industrial revolution and the increasing utilisation of fossil fuels such as coal, oil and gas, atmospheric CO2 levels started to increase from usual interglacial values of about 280 to about 390 ppmv at present day. As the demand for fossil fuels is likely to further intensify, atmospheric CO2 is projected to almost double within the 100 years (see Fig. 1 and references therein) This has profound impacts on global climate (IPCC, 2007), and on the world’s oceans. As a result of air-sea gas exchange dissolved CO2 in the surface ocean is increasing in concert with its atmospheric counterpart. This forces redistributions in the marine carbonate system, most importantly, decreasing pH and carbonate ion (CO23−) concentrations together with calcite and aragonite saturation states, often referred to as ocean acidification. Experimental assessment of possible sensitivities of marine organisms to ocean acidification and carbonation requires an understanding of the chemical background of CO2induced changes in carbonate chemistry, the design of suitable CO2 perturbation experiments for which a variety of manipulation approaches are available (see Riebesell et al, 2009), and the monitoring and measurement of various carbonate chemistry parameters

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