Intervals of significant biotic and climatic change, such as those occurring in the Neoproterozoic, the late Ordovician, the latest Permian, and the Cretaceous/Tertiary boundary, are commonly associated with marked excursions in the chemical and isotopic composition of the ocean. Some explanations of these events have been based largely on intuitive reasoning that invokes dramatic decreases in the rate of thermohaline circulation, i.e. "ocean stagnation." Rarely have physical oceanographic constraints, such as heat, salt and momentum balance been brought to bear on such problems. We therefore request funding to conduct a suite of dynamic ocean circulation/biogeochemical model simulations to quantitatively assess the efficacy of these "ocean stagnation" hypotheses. Although we focus our efforts on the Late Permian event, the results will be broadly applicable to other intervals of Earth history as well.
The GFDL Modular Ocean Model will be used to study the three-dimensional general circulation of the Late Permian ocean, with atmospheric boundary conditions being provided through collaboration with our colleagues at the University of Wisconsin and University of Chicago. These boundary conditions are expected to yield both vigorous and sluggish thermohaline circulation states. A small number of biogeochemical constituents will be added to this model, allowing us to assess the spatial distribution of anoxia. The circulation fields generated by the 3-D model will then be zonally averaged and used in a 2-D, multi-constituent biogeochemical model to study the biogeochemical consequences of sluggish circulation. In addition to phosphate and oxygen, the 2-D model will calculate distributions of dissolved inorganic carbon, sulfur and strontium isotopic compositions. Thus we will be able to investigate the hypothesis that an invigoration of ocean, releasing toxic amounts of carbon dioxide to the atmosphere, and to compare the predicted and observed isotopic records of such an event. A number of sensitivity analyses will be performed, including the model response to variations in riverine and hydrothermal input, to various kinetic and isotopic parameters, and to the drift of Pangea off the South Pole.
