Although submarine methane hydrates or clathrates have been highlighted as potential amplifiers of modern global climate change and associated glacio-eustatic sea-level rise, their potential role in sea-level fall has not been appreciated. Recent estimates of the total volume occupied by gas hydrates in marine sediments vary 20-fold, from 1.2 × 1014 to 2.4 × 1015 m3. Using a specific volume change on melting of −21%, dissociation of the current global inventory of hydrate would result in a decrease of submarine hydrate volume of 2.4 × 1013 to 5.0 × 1014 m3. Release of free gas bubbles present beneath hydrates would increase these volumes by 1.1–2.0 × 1013 m3. The combined effects of hydrate melting and subhydrate gas release would result conservatively in a global sea-level fall of 10–146 cm. Such a mechanism may offset some future sea-level rise associated with thermal expansion of the oceans. It could also explain anomalous sea-level drops during ice-free periods such as the early Eocene, the Cretaceous, and the Devonian.

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