This study presents geochemical evidence for biogenic methane formation (methanogenesis) in the shallow sediments of the oligotrophic SE Mediterranean continental shelf at water depths between 46 and 88m. Depth-profiles of methane concentrations and related chemical parameters such as dissolved sulfate, dissolved inorganic carbon (DIC), and the stable carbon isotope composition of DIC and methane (δ13CDIC, δ13CCH4, respectively) were measured in six sediment cores (each 4.2-5.4 m long) in order to characterize the processes that involve methane production and decomposition. All the sediment cores reached the consumption depth of the entire sulfate pool and the in-situ microbial methane production (methanogenesis) zone. Methane concentrations reached saturation levels in one of the cores, but not in the others, probably because the zone of maximum methanogenesis was at a greater depth. Although the sediments exhibit a low TOC content of ~1%, the biogenic methane formation indicates a relatively high organic carbon lability capable of sustaining all redox microbial activity potential. Anaerobic oxidation of methane (AOM) was also evident in the sulfate-methane transition zone, showing a distinct isotope signature in diffusion limited conditions.
Bibliographical noteFunding Information:
We would like to thank associate editor Prof. Gary Fones and the anonymous reviewers for their thorough work on the manuscript. The authors thank the captain and crew of the R/V Shikmona and Yaron Gertner’s research assistant, all from the Israel Oceanographic and Limnological Research Institute, for their assistance during field sampling. We thank Ganor’s lab for assisting with the sulphate analyses, and Paradigm for their software support. This work was partly supported by a Grant # 212-17-024 named "Methane production and oxidation in the Eastern Mediterranean shelf" from the Israel Ministry of Infrastructure, Energy and Water (to OS and BH Y.M) , by the PERSEUS project, by EC Contract # 287600 (BH) and by the Ministry of Science and Technology , project # 3-9145 (to O.S. and Y.M).
© 2015 Elsevier Ltd.
- Eastern Mediterranean
- Stable isotopes
ASJC Scopus subject areas
- Aquatic Science