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

Abstract Observed subsurface methane (CH 4 ) maxima in the Arctic Ocean challenge traditional benthic‐centered models. Here, we integrate a water‐column CH 4 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 CH 4 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 CH 4 accumulation across regions: both lateral transport and biological production (via zooplankton) contribute to shelf CH 4 dynamics, with physical transport emerging as the dominant process, while zooplankton fecal pellet production and bacterial activity govern offshore CH 4 accumulation. Seasonal variability is tightly linked to primary production, stratification, and vertical mixing. Our findings underscore the critical role of non‐benthic CH 4 sources in shaping Arctic methane distributions, with implications for projecting CH 4 fluxes under future climate change.