Methane transport through submarine groundwater discharge to the North Pacific and Arctic Ocean at two Alaskan sites

Abstract

Here, we quantify the flux of methane to the coastal Arctic and North Pacific Oceans via submarine groundwater discharge (SGD), by use of naturally occurring radium isotopes as groundwater tracers, combined with methane concentration measurements of coastal groundwater. Our findings indicate the flux of methane through this process is much greater in the coastal North Pacific (35 ± 27 mg m−1 d−1) than the Arctic Ocean (4.1 ± 0.6 to 11.8 ± 3.9 mg m−1 d−1). The dominant controls on methane flux through SGD were not methane concentrations in the aquifer but rather the hydrologic characteristics of each site that mitigated or intensified the SGD water volume flux (120 ± 50 m3 m−1 d−1 in the North Pacific compared to 12 ± 4 m3 m−1 d−1 in the Arctic). Tidal pumping was observed to be an especially important control on SGD flux at the North Pacific site.