Moderate elevated vertical methane (CH4) 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 CH4 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 CH4 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 (delta C-13) in pore water and sediment were variable across the ridge suggesting close proximity of heterogeneous carbon sources. Methane stable carbon isotope ratios ranging from -107.9 parts per thousand to -60.5 parts per thousand and a C1:C2 of 3000 indicate a microbial, or biogenic, source. Near ridge, average delta C-13 for pore water and sediment inorganic carbon were C-13-depleted (-28.7 parts per thousand and -7.9 parts per thousand, respectively) relative to all core subsamples (-19.9 parts per thousand and -2.4 parts per thousand, respectively) suggesting localized anaerobic CH4 oxidation and precipitation of authigenic carbonates. Through the transect there was low contribution from anaerobic oxidation of CH4 to organic carbon pools; for all cores delta 13C values of pore water dissolved organic carbon and sediment organic carbon averaged -24.4 parts per thousand and -22.1 parts per thousand, respectively. Anaerobic oxidation of CH4 contributed to pore water and sediment organic carbon near the ridge as evidenced by carbon isotope values as low as to -42.8 parts per thousand and -24.7 parts per thousand, respectively. Carbon concentration and isotope analyses distinguished contributions from CH4 and phytodetrital carbon sources across the ridge and show a low methane contribution to organic carbon.