CLATHRATE EUSTASY: METHANE HYDRATE MELTING AS A MECHANISM FOR GEOLOGICALLY RAPID SEA-LEVEL FALL

Abstract

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 x 10¹⠴ to 2.4 x 10¹⠵ 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 x 10¹³ to 5.0 x 10¹⠴ m³. Release of free gas bubbles present beneath hydrates would increase these volumes by 1.1 --2.0 x 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.