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Surface and Subsurface Manifestations of Gas Movement through a North-South Transect of the Northern Gulf Of Mexico

By

Jean Whelan1, Deet Schumacher2, Harry Roberts3, Larry Cathles4 and Steven Losh4

1Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA

2ESRI, Merrill Engineering Bldg, University of Utah, Salt Lake City, Utah 84112

3Coastal Studies Institute, Louisiana State University, Baton Rouge, LA 70703

4Department of Geological Sciences, Snee Hall, Cornell University, Ithaca, N.Y. 14853

Large volumes of gas appear to have vented through a north-south transect of the offshore northern Gulf of Mexico. The specific sites of venting are generally highly localized and possibly episodic making the actual hydrocarbon fluxes involved difficult to estimate. This venting gas has caused significant changes in compositions of reservoired oils, both in the past (on the continental shelf) and at the present time (in reservoirs to the south). This upward gas movement produces a number of interesting effects at the seafloor, including support of a prolific and diverse biological community, formation of seafloor gas hydrates, and sometimes massive disruption of the subsurface and surface sediments including ejection of fossils from older deeper sediments to the modern seafloor. In some cases, methane gas bubbles appear to be vented directly into the atmosphere, possibly providing a deep sea source of the greenhouse gas, methane. Natural oil slicks are formed across the sea surface which can be followed for miles. An overview will be presented focusing on the effects of this migrating gas in the subsurface and its related surface sediment manifestations.