Subsurface Methane Accumulation in the Beaufort Sea Driven by Pelagic Processes: A Mechanistic Modeling Approach

Abstract

Observed subsurface methane (CH4) maxima in the Arctic Ocean challenge traditional benthic-centered models. Here, we integrate a water-column CH4 module into a coupled biogeochemical model to investigate methane cycling at contrasting coastal and offshore sites in the Beaufort Sea. Baseline simulations underestimated observed subsurface CH4 peaks, but introducing additional source terms―including lateral transport, zooplankton fecal methanogenesis, organic carbon decomposition, and methylphosphonate breakdown―substantially improved model performance. Results reveal that distinct processes control CH4 accumulation across regions: both lateral transport and biological production (via zooplankton) contribute to shelf CH4 dynamics, with physical transport emerging as the dominant process, while zooplankton fecal pellet production and bacterial activity govern offshore CH4 accumulation. Seasonal variability is tightly linked to primary production, stratification, and vertical mixing. Our findings underscore the critical role of non-benthic CH4 sources in shaping Arctic methane distributions, with implications for projecting CH4 fluxes under future climate change.