My research interests range from modern marine science to the co-evolution of Earth environment and life on geologic time scales. I generally focus on shallow-water tropical carbonate systems in both the modern and deep time because they are exceptional archives of Earth system processes and are genetically linked to tectonic, climatic, biologic, and chemical conditions.

How do patterns of ocean environmental change influence the spatial and temporal distribution of marine biodiversity? The magnitude and rate of environmental change have influenced the creation, retention, and depletion of marine biodiversity throughout the history of life on Earth. Reefs and other tropical benthic communities are among the most complex and diverse ecosystems, and they are the key carbonate sediment producers in shallow-marine environments. Although reef-building organisms construct massive frameworks of calcium carbonate and have excellent fossil and stratigraphic records, they also tend to be ecologically fragile and vulnerable to changes in environmental conditions. Consequently, reefs are valuable indicators of global marine ecosystem health on geologic time scales. A current research project is designed to investigate the controls on the absence of diverse reefs for millions of years following the end-Permian extinction, the pattern and timing of their recovery in the early Mesozoic, and the advent of modern-style reef ecosystems and scleractinian corals during the Middle Triassic.

How do tectonic, climatic, chemical, and biological systems evolve to influence the architecture and distribution of carbonate depositional systems? To improve the understanding of controls on patterns of carbonate sedimentation, I study depositional systems that span intervals of global change. These intervals provide an opportunity to more directly link environmental mechanisms with resulting sedimentary architecture. A current research project is designed to investigate the oceanic controls that influenced the spatial and stratigraphic variability of carbonate platform morphology across the Paleozoic to Mesozoic transition.

My research is focused on understanding the causes and consequences of ocean anoxia and oxygenation in Earth’s history. Anoxic conditions can be caused by large increases in atmospheric pCO2, which drives continental weathering and delivery of nutrients (such as phosphate) to the oceans—a perturbation that stimulates primary productivity and oxygen demand. The redox conditions of the oceans are in turn closely linked to many biogeochemical cycles, from carbon to trace metals. Oxygenation and de-oxygenation help to define the habitability of ancient oceans and thus impact patterns of animal evolution and extinction. I implement a combination of methods, including analyses of geochemical proxies in marine sedimentary rocks (carbonates and shales) and numerical modeling. In particular, isotopic proxies, such as uranium, offer a new perspective on past biogeochemical cycling and the potential to quantitatively reconstruct the redox conditions of oceans present many millions of years ago. My research also extends to improving our understanding of geochemical proxies, including (1) evaluating how diagenesis affects the geochemistry of marine carbonates and (2) characterizing how local depositional conditions affect isotope signatures recorded in reducing marine sediments.

Current research projects include:

• Understanding controls on U isotopes in reducing environments
• Determining the silicate weathering feedback strength during critical Earth history events
• Reconstructing the marine redox state and Earth system feedbacks around the Ediacaran-Cambrian Transition