Researchers from the Nansen Center, the Norwegian Polar Institute, the University of Bergen, the Institute for Oceanology Polish Academy of Sciences, and American researchers are currently establishing an underwater observation system that will cover central parts of the Arctic Ocean. The system will be used to conduct sustainable long-term observations of the ocean, below the Arctic sea ice.
Through the EU project HiAOOS and the Office of Naval Research project HiAATS, a six-week research cruise is now being carried out with the Coast Guard’s icebreaker KV Svalbard.
The observation system consists of deep-water moorings that are deployed at four different locations, the first two are already placed in international waters in the eastern Arctic Ocean. Each mooring is equipped with a 1,500kg anchor, which is held up in the water column by powerful buoyancy elements. The anchor and buoyancy element hold a four-kilometre-long wire vertically in the water column. Around 40 instruments are attached along the wire. Each deployment is an extensive operation that can take up to three days.
The instruments deployed measure ice thickness, temperature, salinity and currents at various depths under the ice. Furthermore, variations in bottom pressure are measured at a depth of four kilometres. These are important measurements for use in studies of ocean conditions in the Arctic. The moorings are equipped with acoustic sources and hydrophones at different depths, which can receive acoustic signals for use in temperature measurements and earthquake studies. The sound recordings can also be used to investigate which marine mammals are found in the different areas of the Arctic Ocean.
It is important to establish and maintain observation systems in the Arctic Ocean in the years to come, so that we can use the data collected to understand how the climate is changing in the ocean under the ice.
An important part of the observation data is measurements of how fast sound signals travel between the moorings. Three of the moorings are equipped with low-frequency sound sources that emit sound signals at specific times and these are picked up by acoustic receivers on the moorings. The moorings are accurately positioned, and movements in the moorings are carefully measured to calculate the exact distance between the sound source and receivers. Advanced acoustic modelling is used to determine which paths the sound signal follows through the water masses from transmitter to receiver. Once the speed of sound has been measured, the data can be translated into temperature for the different water layers, such as cold polar water and warmer Atlantic water. The moorings will remain in the Arctic Ocean until 2026, when they will be retrieved. When the researchers get hold of the instruments, they will download the data and the work of extracting important information about the ocean under the ice will begin.
Three moorings that have been out for three years north of Svalbard have been retrieved during the research cruise. These have been positioned in an area where relatively warm and nutrient-rich water flows into the Arctic. One of the moorings was equipped with a hydrophone, and the data shows a variety of sounds from marine mammals and fish. The acoustic data will be further analysed by researchers at the Nansen Center and the University of Bath, England. Students associated with the Useful Arctic Knowledge project also participated in the cruise and will use the data collected in their studies.
During the research cruise, three polar bears were observed in the eastern part of the Nansen Basin. These were in good shape, and one of the bears stayed close to the boat for a long time, much to the delight of researchers and crew on board KV Svalbard.
Key researchers: Hanne Sagen, Espen Storheim, Astrid Stallemo
