Atmospheric deposition enhances marine methane production and emissions from global oceans

Aerobic methane production from biological methylphosphonate degradation contributes to the observed supersaturation of oceanic methane in oxygenated surface waters. Atmospheric deposition is an important nutrient source and this process can affect nutrient ratios and biogeochemical cycle in the upper ocean. Here we present evidence that atmospheric nitrogen deposition modulates methane production by impacting microbial phosphorus acquisition. We found that methane production from methylphosphonate decomposition was enhanced (0.1-10.0 pmol L^-1 d^-1) by excessive nitrogen deposition from the atmosphere which altered nitrogen to phosphorus ratios (increase by ~27% in mixed layer) and exacerbated phosphorus limitation. Enhanced methane production could increase methane emissions from the open oceans, partially offsetting the decreased radiative forcing of carbon sequestration caused by atmospheric deposition. Our findings reveal an important linkage between atmospheric deposition and surface ocean methane cycling, suggesting a broader impact of atmospheric deposition on the feedback to the climate system that was not previously recognized.