3. Data Report: Carbon Isotopic Composition of Dissolved CO2, CO2 Gas, and Methane, Blake-Bahama Ridge and Northeast Bermuda Rise, ODP Leg 172¹

Walter S. Borowski,^{2, 3} Namik Cagatay,⁴ Yann Ternois,⁵ and Charles K. Paull^{2, 6}

ABSTRACT

Carbon isotopic data of interstitial dissolved CO₂ (CO₂), CO₂ gas, and methane show that a variety of microbial diagenetic processes produce the observed isotopic trends. Anaerobic methane oxidation (AMO) is an important process near the sulfate-methane interface (SMI) that strongly influences the isotopic composition of CO₂ in the sulfate reduction and upper methanogenic zones, which in turn impacts methane isotopic composition. Dissolved CO₂ and methane are maximally depleted in ¹³C near the SMI, where ¹³C values are as light as -31.8 and -101 PDB for CO₂ and methane, respectively. CO₂ reduction links the CO₂ and methane pools in the methanogenic zone so that the carbon isotopic composition of both pools evolves in concert, generally showing increasing enrichments of ¹³C with increasing depth. These isotopic trends mirror those within other methane-rich continental rise sediments worldwide.