Methane in Red Sea brines

Concentrations of hydrocarbon gases and stable carbon isotope ratios of met hane from the water column of Shaban, Kebrit, Atlantis II and Discovery dee ps. Red Sea, have been determined. Methane concentrations (yield C-1) range from < 50 nL/L (Red Sea deep water) to ca. 22 x 10(-3) L/L (Kebrit brine). Stable carbon isotopes of methane are between -30 and 43 parts per thousan d. Hydrocarbon gases in the brines are originally of thermogenetic origin ( Kebrit: C-1/C(2)similar to 57; delta(13)C(1) similar to 30 parts per thousa nd). Methane concentrations in the transition zones between brines and Red Sea deep water decreased, especially in the Atlantis II/Discovery deeps: as sociated with a strong shift of delta(13)C(1) to positive values. This shif t is related to bacterial oxidation of methane in the transition zone betwe en brine layers and overlying Red Sea deep water. Oxidized methane mixes wi th Red Sea deep water methane. A connection between the Atlantis II and the Discovery brine is postulated on the basis of the geochemical data. (C) 19 98 Elsevier Science Ltd. All rights reserved.