Methane seep carbonates yield clumped isotope signatures out of equilibrium with formation temperatures

S. J. Loyd (), J. Sample, R. E. Tripati, W. F. Defliese, K. Brooks, M. Hovland, M. Torres, J. Marlow, L. G. Hancock, R. Martin, T. Lyons and A. E. Tripati ()
Additional contact information
S. J. Loyd: California State University
J. Sample: School of Earth Sciences and Environmental Sustainability, Northern Arizona University
R. E. Tripati: Planetary and Space Sciences, University of California
W. F. Defliese: Planetary and Space Sciences, University of California
K. Brooks: Planetary and Space Sciences, University of California
M. Hovland: Centre for Geobiology, University of Bergen
M. Torres: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University
J. Marlow: California Institute of Technology
L. G. Hancock: University of California
R. Martin: University of Washington
T. Lyons: University of California
A. E. Tripati: Planetary and Space Sciences, University of California

Nature Communications, 2016, vol. 7, issue 1, 1-12

Abstract: Abstract Methane cold seep systems typically exhibit extensive buildups of authigenic carbonate minerals, resulting from local increases in alkalinity driven by methane oxidation. Here, we demonstrate that modern seep authigenic carbonates exhibit anomalously low clumped isotope values (Δ47), as much as ∼0.2‰ lower than expected values. In modern seeps, this range of disequilibrium translates into apparent temperatures that are always warmer than ambient temperatures, by up to 50 °C. We examine various mechanisms that may induce disequilibrium behaviour in modern seep carbonates, and suggest that the observed values result from several factors including kinetic isotopic effects during methane oxidation, mixing of inorganic carbon pools, pH effects and rapid precipitation. Ancient seep carbonates studied here also exhibit potential disequilibrium signals. Ultimately, these findings indicate the predominance of disequilibrium clumped isotope behaviour in modern cold seep carbonates that must be considered when characterizing environmental conditions in both modern and ancient cold seep settings.

Date: 2016
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DOI: 10.1038/ncomms12274

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