Figure 4. A. Diagram showing how varying amounts of carbon derived from methane via anaerobic methane oxidation (Fraction AMO) affect the carbon isotopic composition of the CO₂ pool (¹³CCO₂). B. An enlargement of the shaded box in A. The measured carbon isotopic composition of the CO₂ pool at the sulfate-methane interface at Site 995 is -37.7. Using this value, the model predicts that the CO₂ pool has received ~24% of its carbon from methane, presumably through AMO.