An Earth-system perspective on ocean deoxygenation during the end-Permian mass extinction

Abstract:

Global ocean anoxia has been proposed to be the cause of the end-Permian (252 Ma) marine extinction event. Evidence for global-scale anoxia mainly comes from the study of organic geochemistry, framboidal pyrite, and redox-sensitive elements, although disagreement exists with respect to the interpretation of the observed patterns. Climate models with biogeochemical components often fail to generate global-scale anoxia induced by warming alone, unless increased phosphate level is invoked. Here, I use the carbon isotope inversion approach in an Earth system model of intermediate complexity (GENIE) with modern phosphate levels to investigate ocean deoxygenation due to global warming through continuous CO­₂ emission. I evaluate the temporal and spatial extent of ocean deoxygenation for a best-fit scenario that represents contact metamorphism of organic-rich sediments (δ¹³C = -25‰) during Siberian Traps volcanism eruption. This scenario is characterized by total peak amount of ~30,000 Gt of carbon and global sea surface temperature increase of 5 ^oC (Cui et al., 2014). The global surface ocean oxygen concentration shows only a modest decrease (from 230 to 215 µmol kg^-1) during peak C emission, whereas the global deep ocean oxygen concentration shows a 70% decrease (from 160 to 50 µmol kg^-1). During peak C emission, the oxygen minimum zone (~800 m depth) expands vertically and horizontally, and vast regions in the deep northern Panthalassa becomes hypoxic (<50 µmol kg^-1) while the deep southern Panthalassa remains oxygenated. The minimum oxygen concentration is coincident with the peak extinction and minimum surface saturation state, suggesting ocean deoxygenation and ocean acidification might go hand in hand causing the largest extinction of all time.

Reference

Cui, Y., L. Kump, et al. (2014 in press). Spatial and temporal patterns of ocean acidification during the end-Permian mass extinction – An Earth system model evaluation. Volcanism and Global Environmental Change. L. T. elkins-Tanton, Fristad, K. Cambridge, Cambridge University Press.