ALBERT

Description: M87/2 COSY set out to investigate the geological processes that may cause significant migration of carbon from the subsurface into the ocean and ultimately into the atmosphere. Understanding these processes is fundamental for understanding episodic climate forcing by geological processes, for assessing the role that subsurface fluid migration plays for slope stability, and for assessing the economic potential of hydrate-bearing sediments as a future energy source. As such the cruise contributed mainly to two scientific projects: the Excellence Cluster Future Ocean and here in particular the sub-project Ocean Controls, and the BMBF funded project Sugar2.The two main objectives of the cruise were (1) to find out if the Giant Gjallar Vent on the north-western Vøring Margin can serve as a window to the deeper structures of the Vøring Basin, which were strongly influenced by hydrothermal activity related to break-up volcanism, and (2) to provide a controlled-source electromagnetic (CSEM) data set in an area where coexisting 3D ocean bottom seismometer data exist. We managed to achieve both objectives. Although we did not manage to collect a highresolution 3D seismic data set because of technical problems in the beginning of the cruise and adverse weather conditions later on, we can now show that the Giant Gjallar Vent is still active to some extent, but much less than hoped before the cruise. The main phase of activity, which generated the present seafloor morphology, must have occurred during deposition of the late Kai Formation. The rugged seafloor has been draped by hemipelagic sediments ever since. However, there are strong indications for ongoing neotectonic activity, significant accumulation of free gas below the Top Kai horizon, and minor evidence for formation of seepage-related authigenic carbonates. We also achieved the second objective of collecting a benchmark dataset of different types of controlled source electromagnetic data. We surveyed a pipe structure called CN03 which is located in the Nyegga area on the northern flank of the Storegga Slide, and which is characterized by high hydrate concentration at approximately 300 mbsl. In this area we collected high-resolution EM data with Sputnik and deep-penetration EM data with DASI as well as towed, continuously recording surface data with VULCAN. These data will keep a generation of marine electromagnetic geophysicists busy until all ways have been found to invert them jointly with the existing 3D P- and S-wave data for determining the hydrate and free gas distribution in the top 300 m of sediments. Additionally, we managed to carry out a detailed survey of sea floor crevasses on the northern sidewall of the Storegga Slide. The excellent sub-bottom sediment profiler records obtained with the Parasound system strongly indicate very recent, i.e. post-Storegga Slide, deformation of the northern sidewall of the Storegga Slide. Although it was not possible to prove unequivocally this late age of activity by a HyBIS video survey that we carried out for this purpose, the Parasound data are strongly indicative of this late phase of activity. The high-resolution seismic, multibeam bathymetry, Parasound, and video dataset that we managed to acquire provide deep insight into the ways that continental margins fail due to gravitational forces.