Articles | Volume 13, issue 15
Biogeosciences, 13, 4491–4512, 2016
Biogeosciences, 13, 4491–4512, 2016

Research article 11 Aug 2016

Research article | 11 Aug 2016

Massive asphalt deposits, oil seepage, and gas venting support abundant chemosynthetic communities at the Campeche Knolls, southern Gulf of Mexico

Heiko Sahling1,2, Christian Borowski2,3, Elva Escobar-Briones4, Adriana Gaytán-Caballero4, Chieh-Wei Hsu1, Markus Loher2, Ian MacDonald5, Yann Marcon6, Thomas Pape1,2, Miriam Römer1,2, Maxim Rubin-Blum3, Florence Schubotz2, Daniel Smrzka7, Gunter Wegener2,3, and Gerhard Bohrmann1,2 Heiko Sahling et al.
  • 1Department of Geosciences at the University of Bremen, Klagenfurter Str., 28359 Bremen, Germany
  • 2MARUM Center for Marine Environmental Sciences, Leobener Str., 28359 Bremen, Germany
  • 3Max-Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany
  • 4Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, A. P. 70-305 Ciudad Universitaria, 04510 Mexico City, México
  • 5Florida State University, P.O. Box 3064326, Tallahassee, FL 32306, USA
  • 6Alfred Wegener Institute Helmholz Centre for Polar and Marine Research, HGF-MPG Group for Deep Sea Ecology and Technology, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 7Center for Earth Sciences, University of Vienna, Althanstr. 14, 1090 Vienna, Austria

Abstract. Hydrocarbon seepage is a widespread process at the continental margins of the Gulf of Mexico. We used a multidisciplinary approach, including multibeam mapping and visual seafloor observations with different underwater vehicles to study the extent and character of complex hydrocarbon seepage in the Bay of Campeche, southern Gulf of Mexico. Our observations showed that seafloor asphalt deposits previously only known from the Chapopote Knoll also occur at numerous other knolls and ridges in water depths from 1230 to 3150 m. In particular the deeper sites (Chapopopte and Mictlan knolls) were characterized by asphalt deposits accompanied by extrusion of liquid oil in form of whips or sheets, and in some places (Tsanyao Yang, Mictlan, and Chapopote knolls) by gas emission and the presence of gas hydrates in addition. Molecular and stable carbon isotopic compositions of gaseous hydrocarbons suggest their primarily thermogenic origin. Relatively fresh asphalt structures were settled by chemosynthetic communities including bacterial mats and vestimentiferan tube worms, whereas older flows appeared largely inert and devoid of corals and anemones at the deep sites. The gas hydrates at Tsanyao Yang and Mictlan Knolls were covered by a 5-to-10 cm-thick reaction zone composed of authigenic carbonates, detritus, and microbial mats, and were densely colonized by 1–2 m-long tube worms, bivalves, snails, and shrimps. This study increased knowledge on the occurrences and dimensions of asphalt fields and associated gas hydrates at the Campeche Knolls. The extent of all discovered seepage structure areas indicates that emission of complex hydrocarbons is a widespread, thus important feature of the southern Gulf of Mexico.

Short summary
We were excited about nature’s diversity when we discovered spectacular flows of heavy oil at the seafloor with the remotely operated vehicle QUEST 4000 m in Campeche Bay, southern Gulf of Mexico. Vigorous methane gas bubble emissions lead to massive gas hydrate deposits at water depth as deep as 3420 m. The hydrates formed metre-sized mounds at the seafloor that were densely overgrown by vestimentiferan tubeworms and other seep-typical organisms.
Final-revised paper