From the deep earth to the atmosphere: new geochemical approaches to address marine productivity, long-term climate, and continental rifting

This dissertation, as indicated by its title, is eclectic, but is united around the theme of developing and applying new geochemical approaches to answer large-scale questions in earth science. And it represents an interdisciplinary contribution, drawing on paleobiology, paleoclimate and paleoceanography as well as incorporating near surface and deep earth seismic models and signal analysis techniques to expand the range of conclusions that can be extracted from large geochemical datasets. The first two chapters focus on the marine biosphere in the geologic past. Chapter 1 presents a new high-throughput method for establishing paleo export productivity as well as evidence that increased supply of Southern Ocean water masses during glacial intervals stimulated productivity off the coast of East Africa. The method presented in Chapter 1 enabled Chapter 2, in which an unprecedented global view of marine productivity reveals a global biological “heartbeat”: marine productivity varies at the same frequencies as Earth’s orbital obliquity and precession, indicating a fundamental link between astronomical and biological processes. Chapters 3 and 4 explore the information contained in the carbon in marine sediments to better constrain the amount and form of C subducting along the Sunda margin, Indonesia and to infer a multi-phased expansion of C4 grasslands on the Indian subcontinent, indicating punctuated episodes of aridification. The final chapter traces the He isotope signature of a mantle plume from the core-mantle boundary to elucidate the processes involved in forming and sustaining continental rifting in Ethiopia and Afar. The breadth of topics covered here reflects the range of my own curiosity in pursuing what Nietzsche termed fröliche wissenschaft – joyful science