Environmental Science and Engineering Seminar

The consumption of CO2 by the chemical weathering of silicate rocks provides a stabilizing feedback in the global carbon cycle, moderating atmospheric pCO2 to maintain equable climates throughout Earth history and driving the long-term recovery from carbon release events. This process is also the largest source of dissolved silica to the oceans, thus inexorably linking the marine silica cycle to the global carbon cycle and climate. I will use sedimentological records and a suite of geochemical models to explore this carbon-silica cycle coupling during two of the most profound carbon cycle perturbations in Earth history. The first event, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) saw the release of thousands of gigatons of carbon into the ocean-atmosphere, providing a geological point of comparison to our current release of fossil-fuel CO2. Recent ocean drilling has provided new insights into patterns of CaCO3 and SiO2 burial that illuminate carbon-silica cycle coupling during this event. The rest of my talk will ponder the implications for carbon-silica cycle coupling during proposed Neoproterozoic "snowball Earth" events. The dynamics of those geochemical interactions are quite different from the PETM example, due to the lack of calcifying and silicifying organisms which dominate the modern (and Paleogene) carbon and silica cycles. However, if these events are accurately described by the snowball Earth hypothesis, then the pulse of silicate weathering during the super-greenhouse conditions that are proposed to characterize the immediate aftermath of such events likely represents the largest perturbation of the coupled carbon and silica cycles in Earth History.