Regan E. Dunn

Paleoecology & Paleobotany

Quantifying Canopy Change During the Paleocene-Eocene Thermal Maximum (PETM)

If humans continue to emit greenhouse gasses at the current rate, we can expect atmospheric carbon dioxide (pCO2) levels to increase from their present value of ~400 ppmv to ~1800 ppmv within 300 years, a value not known on Earth in the last 50 million years. One of the most salient questions for land-based life is: How will vegetation respond to this exponential increase in pCO2 and the associated climate changes? While vegetation feeds us and gives us shelter, it is also the interface between terrestrial ecosystems and the atmosphere. It directly affects the climate system by controlling primary productivity, energy flux, hydrology, carbon storage, atmospheric gas concentrations, albedo and erosion. Our present knowledge about the effects of pCO2 on plant growth comes climate modeling studies and from small-scale experimental work where plants are exposed to increased pCO2 concentrations in growth chambers, greenhouses, or in large field plots. How large-scale ecosystems will be affected remains largely unknown. One way to empirically test the effects of such environmental perturbations on Earth’s systems is to study similar events in the fossil record, and the best known CO2 bubble event is the Paleocene-Eocene Thermal Maximum (PETM) which occurred ~56 Ma.

The PETM is often considered the best analog to examine the impacts of anthropogenic climate change. It was an abrupt carbon cycle perturbation (~200,000 years) in which thousands of petagrams of carbon where released into Earth’s oceans and atmosphere in <10,000 years. At the same time, global mean annual temperature rose 5­–8ºC and profound biotic and abiotic changes occurred. These changes include a major extinction of benthic foraminiferans, large-scale migrations of plants and animals, increased insect folivory, turnover in vertebrate faunas and dwarfism in mammals and changes in precipitation and runoff patterns. While much paleoecological research has been done on this event, a quantitative reconstruction of vegetation structure is lacking. Since vegetation structure is vital for understanding ecosystem organization and function, a record of rLAI will put into context all of the existing paleoecological datasets.

I am working in a PETM section in the Hanna Basin of southeastern WY in collaboration with Ellen Currano (U Wyoming), Marieke Deschesne (USGS), Penny Higgins (U Rochester), and Brady Foreman (Western Washington U) to develop a unique PETM section. We are tracking LAI through the duration of the PETM using the rLAI method in development for leaf cuticles.

Rainbow over the Hanna Basin
Rainbow over the Hanna Basin
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