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Moderate elevated vertical methane (CH 4 ) flux is associated with sediment accretion and raised fluid expulsion at the Hikurangi subduction margin, located along the northeast coast of New Zealand. This focused CH 4 flux contributes to the cycling of inorganic and organic carbon in solid phase sediment and pore water. Along a 7 km offshore transect across the Porangahau Ridge, vertical CH 4 flux rates range from 11.4 mmol·m −2 ·a −1 off the ridge to 82.6 mmol·m −2 ·a −1 at the ridge base. Stable carbon isotope ratios (δ 13 C) in pore water and sediment were variable across the ridge suggesting close proximity of heterogeneous OPEN ACCESSEnergies 2014, 7 5333 carbon sources. Methane stable carbon isotope ratios ranging from −107.9‰ to −60.5‰ and a C1:C2 of 3000 indicate a microbial, or biogenic, source. Near ridge, average δ 13 C for pore water and sediment inorganic carbon were 13 C-depleted (−28.7‰ and −7.9‰, respectively) relative to all core subsamples (−19.9‰ and −2.4‰, respectively) suggesting localized anaerobic CH 4 oxidation and precipitation of authigenic carbonates. Through the transect there was low contribution from anaerobic oxidation of CH 4 to organic carbon pools; for all cores δ 13 C values of pore water dissolved organic carbon and sediment organic carbon averaged −24.4‰ and −22.1‰, respectively. Anaerobic oxidation of CH 4 contributed to pore water and sediment organic carbon near the ridge as evidenced by carbon isotope values as low as to −42.8‰ and −24.7‰, respectively. Carbon concentration and isotope analyses distinguished contributions from CH 4 and phytodetrital carbon sources across the ridge and show a low methane contribution to organic carbon.