Chemosynthetic communities at oil and gas seeps

The Continental Slope of the northern Gulf of Mexico hosts diverse chemosynthetic communities at oil and gas seeps.  Professor Ian MacDonald and his students are participating in a new, multi-disciplinary study of sites in the 1000 to 2800 m range has been sponsored by the U.S. Minerals Management Service and NOAA Ocean Exploration.  This program will extend knowledge of the Gulf of Mexico chemosynthetic ecosystem in the zones anticipated to receive energy exploration and production activities over the coming decades. MacDonald developed a nested survey approach to identify representative sampling sites within this vast offshore area.  Potential sites where chemosynthetic community might occur were selected on the basis geophysical, geochemical, and satellite remote-sensing indicators.  A list of twenty high-priority targets was compiled from this review. Nineteen of these locations were surveyed during a reconnaissance cruise conducted on Research Vessel GYRE from 11 to 25 March 2006.   At each site, the seafloor was imaged using a drift camera system comprising a digital camera, CTD, and USBL navigation pinger.   Several previously unknown communities were discovered by this process and were targeted for follow-up sampling with submarine ALVIN.  The ALVIN cruise was completed on R/V ATLANTIS during 6 May through 3 June 2006.  Extensive collections were made at sites discovered during the reconnaissance cruise and at sites known from previous investigations.  Synoptic collections of over 50 RADARSAT SAR images were made to cover the entire region.  Preliminary results demonstrate that the benthic ecosystem supported by natural hydrocarbon seepages comprises potentially hundreds of sites occurring over a depth range of 500 to 2800 m and distributed over the entire continental slope.  Models developed from these investigations are essential for effective management of this ecosystem and for understanding the zoogeography of chemosynthetic species in the Gulf of Mexico and Western Atlantic Ocean.

Photo: Science and Technology students Shannon Strong (left) and Adriana Leiva prepare to launch MacDonald's deep-sea camera system while graduate student John Wood offers encouragement.