Gas hydrate dissociation linked to contemporary ocean warming in the southern hemisphere

Marcelo Ketzer,Luiz F Rodrigues,Adriano R Viana,Daniel Praeg,José A Cupertino,Mahboubeh Rahmati-Abkenar,Maria A G Pivel,Dennis J Miller,Adolpho Augustin

doi:10.1038/s41467-020-17289-z

Abstract

Ocean warming related to climate change has been proposed to cause the dissociation of gas hydrate deposits and methane leakage on the seafloor. This process occurs in places where the edge of the gas hydrate stability zone in sediments meets the overlying warmer oceans in upper slope settings. Here we present new evidence based on the analysis of a large multi-disciplinary and multi-scale dataset from such a location in the western South Atlantic, which records massive gas release to the ocean. The results provide a unique opportunity to examine ocean-hydrate interactions over millennial and decadal scales, and the first evidence from the southern hemisphere for the effects of contemporary ocean warming on gas hydrate stability. Widespread hydrate dissociation results in a highly focused advective methane flux that is not fully accessible to anaerobic oxidation, challenging the assumption that it is mostly consumed by sulfate reduction before reaching the seafloor.

Highlights

Ocean warming related to climate change has been proposed to cause the dissociation of gas hydrate deposits and methane leakage on the seafloor
The feather edge typically lies in upper slope depths (300–600 m), where ocean warming and sea-level lowering are capable of reducing the volume of the gas hydrate stability zone (GHSZ) to drive sediment degassing[5]
Our multi-disciplinary and multi-scale investigation of a bottom simulating reflector (BSR) outcrop on the southern Brazilian margin allows an investigation of gas hydrate dynamics and ocean interactions over long- to short- scales and provides the first robust evidence from the southern hemisphere of hydrate destabilization related to contemporary climate change

Summary

Introduction

Ocean warming related to climate change has been proposed to cause the dissociation of gas hydrate deposits and methane leakage on the seafloor. Geochemical and geophysical data, including the first autonomous underwater vehicle (AUV)-borne sub-bottom profiles of a BSR outcrop, allow us to document a massive advective flux of methane through the feather edge of the GHSZ, resulting in the formation of an elongate pockmark field associated with hundreds of water column gas flares.

Results

Conclusion