2012 Volume 118 Issue 3 Pages 172-183
In the Kujukuri-hama area of Chiba, Japan, Holocene series unconformably overlie the Pleistocene Kazusa Group, which was deposited mainly in a deep-sea environment and contains natural gas (methane) dissolved in water. These conditions allow gas to emerge from the ground as it moves upward through faults and sandy layers.
In May and August 2007, water in tidal pools at central and southern Kujukuri-hama became cloudy. A field survey revealed that methane gas was seeping into the pools where the cloudiness occurred and that bluish gray sand, the color of which indicates reducing conditions, occurs within the area of the gas seep. Yellow groundwater was found immediately beneath the area of bluish gray sand, and the groundwater became cloudy as it emerged into the tide pools.
Analyses of the pool water revealed a state of sulfate reduction (anoxic diagenesis) and that the cloudiness resulted from the presence of elemental sulfur. Therefore, the water in the tidal pools became yellow or cloudy in the presence of polysulfide ions or due to irregular reflections of sunlight induced by colloidal sulfur.
The 16S rRNA genes of anaerobic methanotrophic archaea belonging to ANME-1 were detected from yellow groundwater near the surface of a sandy beach, raising the possibility that anaerobic oxidation was involved in the reduction of the sulfate ions. Based on these findings, it is proposed that ANME-1 are active within methane gas seeping from the Kazusa Group to the surface, resulting in reducing conditions.
