Seabed Mapping in Norwegian Waters: Using Hullborne and AUV/ROV Mounted Acoustic, Optical and Chemical Systems for Habitat Mapping and Studies of Natural Gas Seepages

Terje Thorsnes

Geological Survey of Norway

Friday, Apr. 19, 2013, 3:00pm
Chase 130

The MAREANO program in Norway started in 2005, and is a fairly large seabed mapping funded by the Norwegian government (16.1 Mill. USD in 2013). It has so far documented 107 000 km2 of seabed by mapping bathymetry, sediment composition, habitats and biotopes, biodiversity, as well as pollution in the seabed in Norwegian coastal and offshore regions. The work in MAREANO is done by the Institute of Marine Research (marine biology), the Geological Survey of Norway (marine geology) and the Norwegian Hydrographic Service (hydrography). The results from the program feed directly into the documents and reports forming the decision support for the government.

The area studied from 2005 to 2011 encompasses continental shelf, slope and deep water zones and includes many extreme habitats including shelf-edge canyons and submarine slides. Some of the world’s largest cold water coral complexes occur in this area. Geological features include a narrow, glacially shaped continental shelf, a continental slope with extensive erosion by canyons and submarine slides, and a continental rise with large submarine fans. Hullborne multibeam systems together with HD video systems is the most important data source for the habitat classification.

In recent years, we have studied natural gas seepages in the Barents Sea, together with scientists from the oil company Lundin Norway, and the Norwegian Defence Research Establishment. Major questions asked are: Are there natural gas seepages from the seabed? How much gas is seeping from the seabed? What is the nature of the gas? What is the timing of the seeps? Are there any physical expressions on the seabed? Is there an influence on the seabed biology?

Several surveys using the research vessel H.U. Sverdrup II as the platform for hullborne multibeam echosounder (EM710), sub-bottom profiler and sampling, and the autonomous underwater vehicle (AUV) HUGIN HUS as platform, e.g., Synthetic Aperture Sonar, TFish photo system and a methane sniffer, have been conducted. In addition, a separate survey using ROV equipped with HD video and gas sampling equipment have been done.

This nested approach—with multibeam echosounder, Synthetic Aperture Sonar and the TFish photo system—has proven very efficient with regard to identifying natural gas seepages over large areas, eventually combined with a methane sniffer. Starting with surveys covering several hundred km2, it is possible to identify structures covering only a few m2 of the seabed. Using ROV, active gas leakages have been sampled, and carbonate crusts formed by the gas have been sampled for detailed analysis and dating.