Does Sedimentary Organic δ13C Record Variations in Quaternary Ocean [CO2(aq)]?

Abstract

Ocean surface water [CO2(aq)] variations based on glacial/interglacial changes in sediment δ13Corg are shown to compare favorably with reconstructions based on ice core [CO2]. In particular, an approximate 80 uatm increase in atmospheric pCO2 during the last glacial-interglacial transition is calculated to correspond to a 3–4 umolar increase in ocean surface water [CO2(aq)] at atmospheric equilibrium. A widespread marine δ13Corg decrease of 1–2 ‰ accompanied this event and was not preceded by an equivalent isotopic change in surface water total dissolved inorganic carbon. These observations support the hypothesis that [CO2(aq)] influences photosynthetic isotope fractionation between marine inorganic and organic carbon pools, and therefore that plankton/sediment δ13Corg may serve as a proxy for surface water [CO2(aq)].