Massive methane blow-outs may be responsible for clusters of kilometer-wide craters in the Barents Sea.

It is established that late-twentieth and twenty-first century ocean warming has forced dissociation of gas hydrates with concomitant seabed methane release. However, recent dating of methane expulsion sites suggests that gas release has been ongoing over many millennia. Here we synthesize observations of ∼1,900 fluid escape features—pockmarks and active gas flares—across a previously glaciated Arctic margin with ice-sheet thermomechanical and gas hydrate stability zone modelling. Our results indicate that even under conservative estimates of ice thickness with temperate subglacial conditions, a 500-m thick gas hydrate stability zone—which could serve as a methane sink—existed beneath the ice sheet. Moreover, we reveal that in water depths 150–520 m methane release also persisted through a 20-km-wide window between the subsea and subglacial gas hydrate stability zone. This window expanded in response to post-glacial climate warming and deglaciation thereby opening the Arctic shelf for methane release.

Significance: Shallow Arctic Ocean gas hydrate reservoirs experienced distinct episodes of subglacial growth and subsequent dissociation that modulated methane release over millennial timescales.

We find that summer methane (CH₄) release from seabed sediments west of Svalbard substantially increases CH₄ concentrations in the ocean but has limited influence on the atmospheric CH₄ levels. Our conclusion stems from complementary measurements at the seafloor, in the ocean, and in the atmosphere from land‐based, ship and aircraft platforms during a summer campaign in 2014. We detected high concentrations of dissolved CH₄ in the ocean above the seafloor with a sharp decrease above the pycnocline. Model approaches taking potential CH₄ emissions from both dissolved and bubble‐released CH₄ from a larger region into account reveal a maximum flux compatible with the observed atmospheric CH₄ mixing ratios of 2.4–3.8 nmol m⁻² s⁻¹. This is too low to have an impact on the atmospheric summer CH₄ budget in the year 2014. Long‐term ocean observatories may shed light on the complex variations of Arctic CH₄ cycles throughout the year.

Sub-sea Arctic methane and gas hydrate reservoirs are expected to be severely impacted by ocean temperature increase and sea-level rise. Our understanding of the gas emission phenomenon in the Arctic is however partial, especially in deep environments where the access is difficult and hydro-acoustic surveys are sporadic. Here, we report on the first continuous pore-pressure and temperature measurements over 4 days in shallow sediments along the west-Svalbard margin. Our data from sites where gas emissions have not been previously identified in hydro-acoustic profiles show that tides significantly affect the intensity and periodicity of gas emissions. These observations imply that the quantification of present-day gas emissions in the Arctic may be underestimated. High tides, however, seem to influence gas emissions by reducing their height and volume. Hence, the question remains as to whether sea-level rise may partially counterbalance the potential threat of submarine gas emissions caused by a warmer Arctic Ocean.