Collaborative proposal: Do arc-continent collisions in the tropics set the Earth's climate state?

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Over its history, Earth has experienced warm ice-free and cold glacial climates, but it is unknown if transitions between these background climate states were the result of changes in CO2 sources or sinks. On these multi-million year geological timescales, CO2 enters the ocean and atmosphere primarily by volcanic outgassing and is removed primarily though the chemical erosion of rocks, which delivers calcium and magnesium via rivers to the ocean where they react with CO2 to form carbonate. It is hypothesized that the tectonic closure of ocean basins and formation of mountains at equatorial latitudes could drive cooling by creating topography and eroding highly soluble oceanic rocks in the warm, wet tropics. This process increases global weatherability, thereby increasing Earth's potential to sequester CO2 in carbonates through chemical erosion. The investigators aim to test the hypothesis that changes in global weatherability have controlled the Earth's background climate state with coupled geological, geochemical, and modelling studies. This broader impact of this work will benefit society by generating and disseminating knowledge about geological climate change at both the K-12 and college level. The researchers have developed a global database of arc-continent collisions through the Phanerozoic, which mark the closure of former ocean basins, and reconstructed their position with state-of-the-art paleogeographic models. The results from this analysis revealed a temporal coincidence between the maximum global extent of arc-continent collision in the tropics and the occurrence of every major glacial period in the Phanerozoic. The investigators will refine geological constraints and tectonic reconstructions in five critical belts. Through these case studies, the researchers will generate thermochronological data and refine the exhumation history of New Guinea and construct a new paleogeographic model for suturing in the Alpine-Himalaya belt. The investigators will also acquire new stratigraphic, geochronological, geological, petrographic, geochemical, and paleomagnetic data along Permo-Carboniferous sutures from Mexico to South America, Ordovician sutures in the northern Appalachian, and Neoproterozoic sutures in the Arabian-Nubian Shield. These field and laboratory data will be integrated with paleogeographic, weathering, and climate models to develop estimates for the change in pCO2 resulting from arc-continent collisions in the tropics utilizing the GEOCLIM model framework. This framework integrates climate models run at varying pCO2 with global weathering models such that the variable climatology can be used to estimate the effect of changes in global weatherability model on long-term steady-state pCO2 levels. In this framework, the investigators will perform sensitivity tests to isolate the effects of specific parameters such as lithology or topography. The researchers will further calibrate these models with source-to-sink cation studies in modern and paleo ophiolite watersheds. Finally, they will develop statistical methods to evaluate the strength of correlation and test hypothesized causal mechanisms for environmental change. Through this research the investigators will directly train a postdoctoral researcher, 5 PhD students and numerous undergraduate research assistants. To disseminate this basic research, the team will hold public seminars and workshops with K-12 teachers, and construct classes on Tectonics and Climate with online course materials, both at the high-school and undergraduate level.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.