MSM57

Methane hydrate research on the continental slope of Spitzbergen

An international team of researchers under the leadership of MARUM scientist Prof. Dr. Gerhard Bohrmann carried out an expedition to the Arctic in the summer of 2016. The six-week cruise with the research ship MARIA S. MERIAN took the team of researchers to the continental slope off Spitzbergen, where they investigated a methane hydrate occurrence in the sea floor with the help of the sea-floor drilling rig MARUM-MeBo70. Methane hydrate is a solid compound that is composed of methane and water and is only stable at conditions of low temperature and high pressure. Their aim was to study the distribution of methane hydrates and their stability in the sea floor because the warming of Arctic water masses also warms the sea floor. The warming could cause a breakdown of the methane hydrates and result in an increase in the methane being released from the sea floor.

MeBo being hauled up with a heavy load crane to the afterdeck of MERIAN. In the background the vessels SARMIENTO DE GAMBOA and NEIL ARMSTRONG.

British research vessel DISCOVERY and MARIA S. MERIAN at same pier in the port of Reykjavik.

At the first study area on the Vestnesa Ridge, MARUM-Mebo70 retrieved seven cores down to 62 meters into the sediment at a water depth of around 1200 meters. Methane gas escapes from funnel-shaped depressions called pockmarks that occur along the ridge. Coring operations were carried out both inside and outside of the pockmarks. With their colleagues from the Norwegian Excellence Cluster “CAGE” in Tromsø, MARUM scientists determined that the gas hydrates only occur in sediments inside the pockmarks. But even within the pockmarks large variations in the concentrations of gas hydrates were observed. Massive gas hydrate deposits here are associated with geological faults that enable methane to rise from greater depths. After successful coring, a borehole observatory (MeBoCORK) was installed in one of the holes in order to continuously record pressure, temperature and salinity. After about two years the system will be retrieved and the long-term data can be read out and downloaded.

White layers of methane hydrate appear parallel to sediment layering

After having been recovered by the deck crew, MeBo slides on a rail system to its position on deck for unloading of the core barrels.

On the second leg of the cruise an area on the western upper continental slope was studied along with scientists from GEOMAR in Kiel. Here, at a water depth of around 400 meters, a remarkably large number of sites of methane release occur on the sea floor. Until now, the reason for this was presumed to be a warming of bottom waters by 1 degree Celsius over the past 30 years, leading to the decomposition of methane hydrates in the depth range between 360 and 400 meters. From twelve MeBo holes the scientists were able to demonstrate that there was no evidence of existing or dissolved methane hydrates in these water depths, which would not have been possible to assess using conventional gravity or piston cores. The numerous sites of free methane gas release at 400 meters of water depth are most probably associated with geological structures of glacial till and not the result of methane hydrate breakdown due to bottom-water warming over the past 30 years.

Inner core barrels of MARUM seafloor drill rig MeBo70 on deck of MARIA S. MERIAN, ready for the next deployment.