Transitions in the Earth System
I study the chemical and biological oceanography of the transition from the Paleozoic to the Mesozoic era, a series of linked changes in the earth’s oceans and atmosphere. The glaciated climate that had predominated since the late Devonian was warming rapidly, and sometimes catastrophically: low-oxygen (anoxic) conditions proliferated in many areas of the ocean, and the Paleozoic-Mesozoic transition was punctuated by two major mass extinctions at the end-Permian and end-Triassic. Together, these events spelled the end of the largely sessile, surface-dwelling, filter-feeding fauna of the Paleozoic, and the rise of more energetic and mobile marine life.
My research focuses on understanding these biodiversity crises at the most fundamental level. The complex, multicellular animal fauna known from the fossil record sat atop a pyramid of energy flowing upward from marine primary producers and, even further below, from dissolved inorganic nutrients. Interfering with this flow of energy at the lowest level would be an extraordinarily effective mechanism of extinction, but it is not all clear that primary productivity declined during mass extinctions; the most devastating calamities of the Phanerozoic may have occurred against the green backdrop of a thriving microbial community.
Understanding productivity, and how it is controlled in a greenhouse ocean, is the key to understanding whether mass extinctions were crises in biomass as well as diversity. The role of nitrogen, a nutrient that can limit productivity but is also sensitive to changes in redox conditions, may be the key to understanding how anoxia is generated and maintained.
Click on the links below to learn more about my ongoing research projects: