Estimating undersea methane gas reserves
Despite the fact that methane is a much stronger greenhouse gas than carbon dioxide, it often receives significantly less attention. However, the fact that significant reserves of methane are sequestered at the bottom of the Earth's oceans has drawn considerable interest of late. Fortunately, an oxidation barrier at the sulphate methane transition zone (SMTZ) prevents the release of this methane to the overlying water column and hence the atmosphere, but the mechanics and sensitivity of this barrier are not well understood. The Max Planck Institute for Marine Microbiology (MPI) led an investigation of sub-surface sediments that included eight other research institutes. During the METROL project, a research vessel collected data during several transects of the Arcona and Bornholm Basins in the Baltic Sea. The MPI was able to make advances in methane flux modelling by performing simultaneous high resolution hydroacoustic and water column measurements. A linear relationship between methane saturation depth and the vertical methane flux was discovered. This led to considerable improvement in the interpretation of seismic images with relation to free gas and methane saturation depth in the sediment. The outcome of the project was a net methane oxidation map for the greater Aarhus Bay. The map will be useful for marine geologists, microbiologists and climate modellers as well as coastal management authorities since the methane reserves have attracted the attention of oil and gas companies hoping to exploit this hidden hydrocarbon stockpile.
