PALEOCEANOGRAPHIC CHANGES AT THE PERMIAN-TRIASSIC BOUNDARY: IMPLICATION FROM CLIMATE MODEL SIMULATIONS

Widespread anoxic and dysoxic deposition in marine sediments has been associated with a stagnant ocean at the Permian-Triassic (P-Tr) boundary. This P-Tr boundary is also associated with one of the largest mass extinctions of species of the Paleozoic, marking the transition to the Mesozoic. Two possible types of the ocean circulation for the Late Permian have been identified: A circulation driven from strong evaporation in the subtropics (haline mode with a stagnant deep sea) or a polar sinking circulation driven by heat loss at the poles (thermal mode with a well-ventilated deep-sea). Here we review recent three-dimensional climate model studies that have investigated possible circulation patterns at the P-Tr boundary in respect to changes in the hydrological cycle and greenhouse gas concentration. Strong simulated fresh water input in the high latitudes, particular along the coast of south polar Pangea produces a significant local minimum in oxygen in the eastern tropical Panthalassa ocean at intermediate depth and at the sea floor. Recent coupled three-dimensional ocean-atmosphere computer simulations indicate that an increase in the greenhouse gas concentration favors an increase in precipitation in the polar region and thus promote a switch from the thermal mode with a well-ventilated deep-sea to the haline mode with a stagnant deep sea. Moreover, biogeochemical changes such as a significant change in the oceanic nutrient inventories or a reorganization of the marine productivity associated with a stronger biological pump may be favorable together with a more sluggish circulation to explain the anoxic sedimentary deposits.