Concentrations and Carbon Isotopic Compositions of CH4 and CO2 in Gas from Sediments of the Blake Outer Ridge, Deep Sea Drilling Project Leg 76

The principal gaseous carbon-containing components identified in the first 400 m of sediment at Deep Sea Drilling Project Site 533, Leg 76, are methane (CH 4 ) and carbon dioxide (CO 2 ). Below a sub-bottom depth of about 25 m, sediment cores commonly contained pockets caused by the expansion of gas upon core recovery. The carbon isotopic composition ( 13 C % 0 relative to PDB standard) of CH 4 and CO 2 in these gas pockets has been measured, resulting in the following observations: (1)