Extremes of Ocean Biogeochemistry: Focus on the Permian-Triassic Boundary

Project Summary

Geologic evidence indicates that many periods of biotic and environmental crisis coincided with times when the world's oceans were highly stratified in their chemical and isotopic composition, with deep waters that were devoid of oxygen and likely strongly enriched in carbon dioxide and hydrogen sulfide. The Late Permian, notable as the time of the largest mass extinction in the fossil record (251 million years ago), is thought to represent such an interval. Stagnation of ocean circulation has been invoked to explain extreme oceanic conditions of widespread anoxia during this time, and reinvigoration of circulation has been suggested as a mechanism to bring toxic waters to the ocean's surface in a global Lake Nyos-type event, leading to mass extinction.

The project proposed here will explore the relationship between ocean stagnation and chemical stratification, and the mechanisms that sustain shallow-water anoxia in the face of wind-driven mixing, using numerical models to ensure that the scenarios proposed are consistent with fundamental principles of mass, energy, and isotopic balance. Model results will be compared with existing isotopic and lithologic data. In addition, new sulfur isotopic data will be obtained from one of the most continuous and well-studied Permian-Triassic boundary sections in the world, providing an important missing piece of biogeochemical information against which to evaluate the models. The modeling will also provide motivation and guidance for further data collection in specific locales.

The model will have the unique ability to explore the chemistry of an anoxic ocean, and as such, its availability should be of great interest to the scientific community. The intuition developed should help to guide subsequent formulation of conceptual models concerning the relationship between climate, ocean circulation, ocean biogeochemistry, and biological response.