Abstract. We report on methane (CH₄) dynamics in landfast sea ice, brine and under-ice seawater at Barrow in 2009. The CH₄ concentrations in under-ice water ranged from 25.9 to 116.4 nmol L⁻¹_sw, indicating a supersaturation of 700 to 3100% relative to the atmosphere. In comparison, the CH₄ concentrations in sea ice ranged from 3.4 to 17.2 nmol L⁻¹_ice and the deduced CH₄ concentrations in brine from 13.2 to 677.7 nmol L⁻¹_brine. We investigated the processes underlying the difference in CH₄ concentrations between sea ice, brine and under-ice water and suggest that biological controls on the storage of CH₄ in ice were minor in comparison to the physical controls. Two physical processes regulated the storage of CH₄ in our landfast ice samples: bubble formation within the ice and sea ice permeability. Gas bubble formation due to brine concentration and solubility decrease favoured the accumulation of CH₄ in the ice at the beginning of ice growth. CH₄ retention in sea ice was then twice as efficient as that of salt; this also explains the overall higher CH₄ concentrations in brine than in the under-ice water. As sea ice thickened, gas bubble formation became less efficient, CH₄ was then mainly trapped in the dissolved state. The increase of sea ice permeability during ice melt marked the end of CH₄ storage.