Methane hydrates, ice-like cages of frozen gas beneath the seafloor, store roughly 1,800 gigatons of methane worldwide, and what happens to them as ice sheets retreat is a first-order climate question. An international team including Professor Mads Huuse of the University of Manchester has found that hydrates beneath the northwest Greenland continental shelf were rapidly destabilised by meltwater during past ice-sheet retreat, releasing large quantities of methane.
The evidence comes from two directions. Sediment cores drilled offshore northwest Greenland during International Ocean Discovery Program Expedition 400 showed unexpectedly low methane concentrations in layers where hydrates should be abundant. High-resolution 3D seismic imaging of the seafloor then revealed widespread pockmarks and fluid-escape structures, the fingerprints of methane-rich fluids migrating quickly up through the sediments. Together they indicate meltwater-driven dissolution emptied a hydrate store in the Melville Bay area over a geologically short period.
Published in Nature Geoscience, the study shows meltwater can destabilise hydrates even within zones previously considered stable. As the Greenland ice sheet retreats again under modern warming, the mechanism identifies a pathway by which the cryosphere's decline could unlock seabed carbon, and gives modellers concrete geological evidence against which to calibrate projections of future methane release.