Intellectual Merit: The ocean is the largest sink for anthropogenic CO2 and has absorbed nearly 130 PgC of the 380 PgC emitted to the atmosphere since the onset of the Industrial Revolution. If emissions continue to rise unabated for the next three centuries, an additional 4000 PgC or more will be input to the atmosphere and ocean. Published model simulations of the ocean/atmosphere response to the eventual complete utilization of fossil fuels indicate that atmospheric CO2 will rise to levels that Earth likely hasn't experienced for at least 40 million years, and the surface ocean may undergo acidification to the extent that corals and other calcifying organisms will be unable to precipitate their skeletons. Confidence in and refinement of these model simulations will benefit from application to, and comparison with, analogous events in Earth history. Approximately 55 million years ago (Mya), Earth experienced a similar episode of rapid and extreme transient warming, the Paleocene-Eocene Thermal Maximum (PETM), likely the product of massive carbon release. Intense study of the PETM over the last five years has led to a far clearer understanding of the consequences of this event on climate, biota, and biogeochemical cycles. One of the more prominent advances is the documentation of evidence for widespread ocean acidification and buffering, consistent with carbon cycle theory. A related advance was the discovery of second warming and ocean acidification event at ~53 Mya. This event, known as ELMO, was less extreme than the PETM in every sense, from the carbon cycle perturbation to the magnitude of warming. These global warming events, termed hyperthermals, provide a unique opportunity to gain insight into the long-term impacts of rapidly rising CO2 levels on modern climate, ocean carbonate chemistry, and biotas. They also provide an opportunity to identify potential non-linear feedbacks, and test climate and biogeochemical model sensitivity. To this end, an interdisciplinary group of scientists with expertise in carbon cycle dynamics, sediment geochemistry, paleoceanography and paleobiology has been assembled, and will embark on a 4-year project to address critical questions regarding two hyperthermals, and their implications for understanding of the carbon cycle including: 1) what were the mass, rate, and origin of carbon released during the hyperthermals? 2) what were the rates of sequestration and recovery and what biogeochemical feedbacks came into play? and 3) how did associated extreme changes in ocean carbonate chemistry affect planktonic calcifiers? The strategy will involve integration of the observational database with numerical models. The observational database will be used to constrain and test the carbon cycle models. This includes records of biogenic carbonate production, accumulation and preservation in 3-dimensions through the PETM and ELMO. This will also require substantial refinement of age models. With a highly resolved and multifaceted data set for input, three modeling approaches will be used, each involving specific opportunities and compromises in terms of the time scales and scope of processes that can be modeled. Earth system models (GENIE and CCSM) will provide boundary conditions for the process-oriented models. Process model simulations will be designed to investigate problems identified during data/model validation of the Earth system models and to develop hypotheses to be tested with model simulations. Broader Impacts: This highly interdisciplinary project will provide important insight into the short-term and long-term fate of anthropogenic CO2 on the global carbon cycle, climate, and biota. Such information is essential to providing scientific leaders and policy makers with a better sense of the consequences of unabated anthropogenic CO2 emissions for global climate, ocean carbon chemistry and marine food chains. Moreover, the project places significant emphasis on a number of closely integrated research and educational activities that will lead to the development and circulation of educational materials related to abrupt climate change and training in how to integrate them in curricula. In addition, we will take advantage of highly successful existing programs to provide opportunities for undergraduates from under-represented groups to participate in cutting-edge, relevant, carbon-cycle research.
