Preprint Review Version 1 Preserved in Portico This version is not peer-reviewed

Gas Seeps at the Edge of the Gas Hydrate Stability Zone on Brazil’s Continental Margin

Marcelo Ketzer
* ORCID logo ,
Daniel Praeg
ORCID logo ,
Maria A.G. Pivel
ORCID logo ,
Adolpho H. Augustin
,
Luiz F. Rodrigues
,
Adriano R. Viana
ORCID logo ,
Jose A. Cupertino
Version 1 : Received: 4 April 2019 / Approved: 5 April 2019 / Online: 5 April 2019 (12:04:25 CEST)

A peer-reviewed article of this Preprint also exists.

Ketzer, M.; Praeg, D.; Pivel, M.A.; Augustin, A.H.; Rodrigues, L.F.; Viana, A.R.; Cupertino, J.A. Gas Seeps at the Edge of the Gas Hydrate Stability Zone on Brazil’s Continental Margin. Geosciences 2019, 9, 193. Ketzer, M.; Praeg, D.; Pivel, M.A.; Augustin, A.H.; Rodrigues, L.F.; Viana, A.R.; Cupertino, J.A. Gas Seeps at the Edge of the Gas Hydrate Stability Zone on Brazil’s Continental Margin. Geosciences 2019, 9, 193.

Abstract

Gas hydrate provinces are present in at least in two areas along Brazil’s continental margin: (1) the Rio Grande Cone in the southeast, and (2) the Amazon deep-sea fan in the equatorial region. The occurrence of gas hydrates in these depocentres was first detected geophysically and has recently been proven by seafloor sampling of gas vents, detected as water column acoustic anomalies rising from seafloor depressions (pockmarks) and/or mounds, many associated with seafloor faults. The gas vents include typical features of cold seep systems, including shallow sulphate reduction depths (<4 m), authigenic carbonate pavements and chemosynthetic ecosystems. In both areas, gas sampled in hydrate and in sediments is dominantly formed by biogenic methane. Calculation of the methane hydrate stability zone for water temperatures in the two areas shows that gas vents occur along its feather edge (water depths between 510-760 m in the Rio Grande Cone and 500-670 m in the Amazon deep-sea fan) but also in deeper waters within the stability zone. Gas venting along the feather edge of the stability zone could reflect gas hydrate dissociation and release to the oceans, as inferred on other continental margins, or upward fluid flow through the stability zone facilitated by tectonic structures recording the gravitational collapse of both depocentres. The potential quantity of venting gas on the Brazilian margin under different scenarios of natural or anthropogenic change require further investigation. The studied areas provide a natural laboratory where these critical processes can be analysed and quantified.

Keywords

Gas hydrates, gas seeps, ocean acidification

Subject

Environmental and Earth Sciences, Geophysics and Geology

Copyright: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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