Morpho-acoustic Characterization of Natural Seepage Features near the Macondo Wellhead (ECOGIG Site OC26, Gulf of Mexico)

Document Type

Article

Publication Date

7-2016

Department

Coastal Sciences, Gulf Coast Research Laboratory

Abstract

OC26 (R/V Oceanus Site 26) is one of three primary sites selected for study by the Ecosystem Impact of Oil and Gas Inputs to the Gulf (ECOGIG) consortium to determine the impacts of natural seepage versus large pulse inputs of hydrocarbons into the Gulf of Mexico (GOM) and to chart the long-term effects and mechanisms of ecosystem recovery from the Deep Water Horizon Oil Spill in 2010. OC26 is located on the western slope of the Gloria Dome, about five kilometers south-east of the Macondo wellhead. In 2011, the site was visited by the NOAA research vessel Okeanos Explorer. During this cruise, several natural oil/gas plumes originating from the seabed were identified. In order to establish precise locations for these naturally occurring sources of hydrocarbons and to inform biogeochemical and biological studies of the water-column, the seafloor, and the shallow subseafloor in the wake of the Deep Water Horizon spill, we conducted several Autonomous Underwater Vehicle (AUV) surveys. The surveys were designed to include swath bathymetry, chirp sub-bottom profiles, and seafloor still photos to augment the Okeanos Explorer and the 2012 ECOGIG Falkor multibeam bathymetric and water column data. These AUV high resolution datasets were collected to provide in-depth geophysical analyses of seafloor morphology and to link, where possible, morphological features to the subsurface structure and plumbing system at this site where natural seepage possibly intersects hydrocarbon inputs from the spill. The site exhibits many morphological seafloor features: depressions, elongated erosional structures, dome-shaped mud volcanoes/mounds, fault traces, and round pockmarks. Seabed photos show the presence of gas hydrate outcrops and benthic communities in the vicinity of maximum seafloor backscatter intensities and many of the morphological features. Subsurface profiles show gas-related anomalies (blanking and acoustic wipeout) where pockmarks, mud volcanoes/mounds and depressions are located. In addition to the discovery of novel seafloor features, these studies provide definitive links between seafloor seeps and particular morphologies and communities, contributing to the fundamental understanding of seeps in the deep sea. (C) 2016 Published by Elsevier Ltd.

Publication Title

Deep Sea Research Part II: Topical Studies in Oceanography

Volume

129

First Page

53

Last Page

65

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