Figure 8. Expanded plots of the upper 80 m of the sedimentary section at Sites 994, 995, and 997 highlight (A) variations in pore-fluid concentrations of SO₄^2- and total dissolved carbon dioxide (CO₂), and the ¹³C values of the dissolved inorganic carbon (DIC) pool; and (B) the ¹³C of carbonate minerals. The sulfate/methane interface marks a biogeochemical interface where methane (building up in sediments below) is consumed along with sulfate (diffusing downward from the seafloor) by microbially mediated anaerobic methane oxidation (AMO). The process of AMO produces conditions that are conducive to carbonate precipitation. Decreases in ¹³C values of both DIC and CaCO₃ at the SMI indicate that AMO is currently active.