Methane in Red Sea brines

Concentrations of hydrocarbon gases and stable carbon isotope ratios of methane from the water column of Shaban, Kebrit, Atlantis II and Discovery deeps, Red Sea, have been determined. Methane concentrations (yield C1) range from < 50 nL/L (Red Sea deep water) to ca. 22 × 10−3 L/L (Kebrit brine). Stable carbon isotopes of methane are between −30 and 43‰. Hydrocarbon gases in the brines are originally of thermogenetic origin (Kebrit: C1/C2 57; δ13C1 −30‰). Methane concentrations in the transition zones between brines and Red Sea deep water decreased, especially in the Atlantis II/Discovery deeps, associated with a strong shift of δ13C1 to positive values. This shift is related to bacterial oxidation of methane in the transition zone between brine layers and overlying Red Sea deep water. Oxidized methane mixes with Red Sea deep water methane. A connection between the Atlantis II and the Discovery brine is postulated on the basis of the geochemical data.