MacDonald, I. R.. Texas A&M Univev. GERG, ian@gerg.tamu.edu
Sager, W. R.. Texas A&M Univer. Oceanography Dept., wsager@ocean.tamu.ede
Guinasso, Jr., N. L.. Texas A&M Univ. GERG, norman@gerg.tamu.edu

 
DISTINCT SEAFLOOR ENVIRONMENTS CAUSED BY RAPID GAS FLUX ON THE GULF OF MEXICO SLOPE
 
Seep fluids in the Gulf of Mexico slope include high-molecular-weight hydrocarbons, fluidized mud, hypersaline brines, and C1 to C5 gaseous hydrocarbons. The process supports dense biological communities in which the dominant species possess bacterial symbionts that are able to oxidize dissolved H2S or CH4 in pore fluids and seawater near the interface. Gas venting has two robust consequences: brine pools and hydrate mounds. Where accompanied with discharge of brine and mud the result is fluid-filled craters that maintain a distinct density interface with seawater and contain thermal gradients of 10 C. Elsewhere, gas forms solid hydrates with water from the pore spaces that accrete as layers and mounds that breach the seafloor where gas flux is most vigorous. We obtained very high resolution seismic profiles of, respectively, a brine pool and a hydrate mound with use of a 2-12 kHz chirp system mounted on Submarine NR-1. We collected sediment cores of up to 1.8 m in length on the top and flanks of these features. These data confirm that the hydrate mounds included layers of carbonate and hydrate colonized by dense aggregations of tube worms (Vestimentifera). The brine pool appears to include a crater substantially larger than its present size, which has been buried by successive layers of clay. The present brine pool is surrounded by a continuous bed of seep mussels. Buried layers shown in the subbottom data may indicate previous, much older, mussel beds.
 
Day: Tuesday, Feb. 2
Time: 09:45 - 10:00am
Location: Sweeney Center
 
Code: SS27TU0945S