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

Here, 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.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [8] ;  [3]
  1. California State Univ., Fullerton, CA (United States); Univ. of California, Los Angeles, CA (United States)
  2. Northern Arizona Univ., Flagstaff, AZ (United States)
  3. Univ. of California, Los Angeles, CA (United States); Univ. de Brest, Plouzane (France)
  4. Univ. of California, Los Angeles, CA (United States)
  5. Univ. of Bergen, Bergen (Norway)
  6. Oregon State Univ., Corvallis, OR (United States)
  7. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  8. Univ. of California, Riverside, CA (United States)
  9. Univ. of Washington, Seattle, WA (United States)
Publication Date:
Grant/Contract Number:
FG02-13ER16402; SC0010288
Type:
Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 7; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Research Org:
Univ. of California, Los Angeles, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES
OSTI Identifier:
1395567