Clathrate eustasy: Methane hydrate melting as a mechanism for geologicallyrapid sea-level fall

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 bee n appreciated. Recent estimates of the total volume occupied by gas hydrate s in marine sediments vary 20-fold, from 1.2 x 10(14) to 2.4 x 10(15) m(3). Using a specific volume change on melting of -21%, dissociation of the cur rent global inventory of hydrate would result in a decrease of submarine hy drate volume of 2.4 x 10(13) to 5.0 x 10(14) m(3). Release of free gas bubb les present beneath hydrates would increase these volumes by 1.1-2.0 x 10(1 3) m(3). 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 sealevel rise associated with thermal ex pansion of the oceans. It could also explain anomalous sealevel drops durin g ice-free periods such as the early Eocene, the Cretaceous, and the Devoni an.