Ocean stagnation and end-Permian anoxia

Ocean stagnation has been invoked to explain the widespread occurrence of o rganic-carbon-rich, laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end-Permian mass extinction. However, to a first approximation, stagnation would severely reduce the upw elling supply of nutrients to the photic zone, reducing productivity. Moreo ver, it is not obvious that ocean stagnation can be achieved. Numerical exp eriments performed with st three-dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low e quator to pole temperature gradient could have produced weak oceanic circul ation and widespread anoxia in the Late Permian ocean. We find that polar w arming and tropical cooling of sea-surface temperatures cause anoxia throug hout the deep ocean as a result of both lower dissolved oxygen in bottom so urce waters and increased nutrient utilization. Buildup of quantities of H2 S and CO2 in the Late Permian ocean sufficient to directly cause a mass ext inction, however, would have required large increases in the oceanic nutrie nt inventory.