Distribution of Methane in the Gulf of Mexico

Abstract

Methane (CH4) originating from thermogenic (e.g. seafloor seeps) and biogenic sources (e.g. methanogenesis) affects the distribution of methane concentrations at varying depths in the ocean. A comprehensive survey of CH4 concentrations throughout the Gulf of Mexico has been difficult to obtain due to international boundaries. For this study, samples were collected from the Northern and Western Gulf of Mexico, including areas within the Mexican Exclusive Economic Zone (EEZ). These samples were analyzed for CH4, ethane (C2H6), and propane (C3H8). The vertical and areal distribution of CH4 in the Gulf of Mexico is assessed. The lack of measurable concentrations of C2H6 and C3H8 in the samples suggest that there were no thermogenic sources. Methane concentrations were elevated in profiles with lower dissolved oxygen concentrations at the oxygen minimum. The calculated sea-to-air flux of CH4 averaged 19.1 µmol m-2 d-1 in the Northern Gulf of Mexico and is in agreement with previous measurements. For the Western Gulf of Mexico, where there is no prior reported surface CH4 data, the sea-to-air flux averaged 115.2 µmol m-2 d-1.