Limited Acute Influence of Aerobic Methane Oxidation on Ocean Carbon Dioxide and pH in Hudson Canyon, Northern U.S. Atlantic Margin

Abstract

The ocean continental shelves host the largest global reservoir of methane (CH4). Despite the great extent of these CH4 reservoirs, much of the CH4 released into deep ocean environments appear to dissolve in seawater prior to atmospheric emission. Once dissolved in ocean water, the CH4 emitted can be aerobically oxidized and converted into either carbon dioxide (CO2) or biomass. While hypotheses have been levied suggesting that the CO2 produced from aerobic methane oxidation could enhance ocean acidification, no empirical research has been performed to confirm or refute this hypothesis. The work presented here investigates local changes in seawater-dissolved CO2 and pH in a region that is experiencing active CH4 seepage near the upper stability boundary of methane clathrate hydrates. We show that in an area of elevated CH4 concentrations and aerobic oxidation rates, Hudson Canyon, aerobic CH4 oxidation is only responsible for 0.3 ± 0.2% of the observed change in dissolved inorganic carbon. Measurements further show that the remineralization of both old marine and young terrestrial organic carbon is contributing more substantially to the observed changes. While this investigation did not investigate chronic, multiyear changes in ocean acidification due to CH4 oxidation, these results suggest that over short timescales, CH4 oxidation in seep fields does not have an acute influence on seawater pH.