Anaerobic Methane Oxidation across the Last Glacial Cycle: Clumped Isotope Constraints from Atlantic Margin Seep Carbonates
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namphy-paolanam-bs-eaps-2026-thesis-unsigned.pdf
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Author(s)
Namphy, Paola D.S.
Advisor(s)
Bergmann, Kristin D.
Date Issued
May 2026
Publisher
Massachusetts Institute of Technology
Abstract
Methane gas has become a prominent contributor to air pollution and the greenhouse effect, making emissions a significant branch of climate change research. As a large component of natural gas, methane comes from many anthropogenic sources but also occurs naturally in various forms, including as a stable solid on the seafloor. However, processes are disturbing the gas hydrate stability zone (GHSZ) in which methane exists in its hydrate state, allowing the compound to dissociate as it encounters new temperature and pressure conditions. Furthermore, methane plumes have appeared above this zone on the slope, instigating questions about how methane migrates and gets consumed. These phenomena are taking place along the U.S. Atlantic Margin (USAM), a passive margin off the northeastern coast, where >1000 new methane seeps have been identified since 2014 in an area previously thought to possess only a handful. Using ∆₄₇ of methane-derived authigenic carbonates (MDACs), the anaerobic oxidation of methane (AOM) at these seeps can be characterized, helping resolve this important flux for the methane budget. Dual clumped isotope analysis (∆₄₇/∆₄₈) of MDACs from Baltimore and Shallop Canyons reveals near-equilibrium isotopic compositions in the Holocene but progressively negative ∆₄₇ disequilibrium beginning at ∼10 ka and reaching ∼ −0.16‰ at the Last Glacial Maximum. AOM rates derived from this disequilibrium remain low and stable through the Holocene (∼1–5 mol m−² yr−¹ ) but rise an order of magnitude at the LGM, suggesting a glacial-period intensification of methane oxidation along the margin. These results also highlight a preservation bias toward high-AOM intervals, since carbonate precipitation accelerates during AOM maxima, which must be accounted for when interpreting paleo-AOM records.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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