| Summary: | Marine methane hydrate is one of the largest readily exchangeable carbon reservoirs near Earth’s surface. Small changes in temperature and pressure could perturb the stability of methane hydrate and release massive amounts of methane, a potent greenhouse gas, into the ocean and perhaps the atmosphere, causing ocean acidification and global warming. Documenting methane hydrate dissociation and methane release events in Earth’s history thus would provide insights into the fate of methane in a changing climate of the future. The history of hydrate dissociation, however, is difficult to constrain. My dissertation is focused on providing direct evidence of past hydrate dissociation and methane release events using lipid biomarkers of methanotrophic microorganisms and their compound-specific isotopes to better understand the behavior of marine methane hydrate over the Cenozoic era. In summary, I have led the investigation of (1) an ancient hydrate dissociation event across the Oligocene–Miocene Boundary (OMB; ~23 million years ago (Ma)), (2) the potential of archaeal lipid biomarker-based ‘Methane Index (MI)’ as a quantitative proxy for probing past methane cycling, and (3) methane cycling of the Arctic Ocean in a warmer and fresher condition during the Paleocene–Eocene Thermal Maximum (PETM, ~56 Ma).
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