WAS VOLCANOGENIC CO2 THE PRIMARY DRIVER OF CRETACEOUS CLIMATE?

The climate of the Cretaceous Period underwent considerable change from generally “cool greenhouse” conditions during the Berriasian through late Aptian (~145-113 Ma), “warm greenhouse” temperatures from the early Albian through early Cenomanian (~113-98 Ma), and “hot greenhouse” conditions from the middle Cenomanian through late Santonian (~98-84 Ma) with maximum sea surface temperatures (SSTs), reached during the Turonian (94-90 Ma), estimated as 36–42°C at 10°N and up to 30°C at 60°S. The Campanian-Maastrichtian (83-66 Ma) experienced long-term cooling with high latitude SSTs dropping to 6°C by the mid-Maastrichtian. Climate model outputs indicate that during the peak of the hot greenhouse climate pCO₂ was 4-8x higher than during the Holocene. The primary cause for changes in Cretaceous climate has been widely attributed to variations in the flux of pCO₂ sourced from arc and/or flood basalt volcanism. This is supported by correspondence between timing for peak eruption of the Caribbean Plateau eruption from 93-89 Ma, but the largest volcanic event of the Cretaceous occurred much earlier, during the early Aptian (125-120 Ma) eruption of the Ontong Java and Manihiki Plateaus when the global climate was much cooler. Such a discrepancy cannot be resolved by geochemical carbon cycle models as they indicate too broad a range of pCO₂ variations, and existing geochemical proxies lack the resolution necessary to characterize Cretaceous pCO2 changes. Until such uncertainties are better resolved consideration of volcanic CO₂ as a primary forcing mechanism for Cretaceous climate change will remain open for debate.