Large scale Multipurpose Ocean Observation System installed in the Central Arctic
The EU funded project High Arctic Ocean Observation System (HiAOOS) and the Office of Naval Research (ONR) funded project High Arctic Acoustic Thermometry and Soundscape (HiAATS) have successfully installed a large-scale mooring network in the Nansen and Amundsen Basin. The mooring system was deployed from the Norwegian Coast Guard ice breaker KV Svalbard during a six weeklong field campaign in August/September 2024. This is the first research infrastructure of its kind installed in the central Arctic.
The system is comprised of four moorings (Figure 1), two moorings in the Nansen Basin and two moorings in the Amundsen Basin. The distances between moorings are from 400 km up to 1000 km. Each mooring is anchored at the bottom and kept vertical with floatation installed on top of the 4-kilometre-long mooring wire line. Forty oceanographic and acoustic instruments are mounted along the wire line for temperature, salinity, pressure, currents, sea ice drift and draft, and ocean sound measurements.
Low frequency acoustic sources are incorporated into three of the moorings which create a triangle covering Nansen and Amundsen basins and crossing the Gakkel Ridge (Figure 2). These sources transmit 7-minute-long signals at the same time every other day. These signals are received by 800 m long vertical arrays of hydrophones placed at each of the four moorings. This setup of acoustic sources and receivers measures the speed of acoustic signals travelling in different layers of the ocean between each of the moorings. If the signal slows down it means that the mean ocean temperature is cooler, while if the signal goes faster the ocean is warmer. The new observing system will measure the mean ocean temperature along six sections. This is called acoustic thermometry or tomography. Spatially integrated measurements with acoustic thermometry combined with point measurements by oceanographic sensors provide a fuller picture of ocean temperature in the European sector of the Central Arctic Ocean.
The signals from the three acoustic sources can be received by drifting underwater floats, gliders and AUVs equipped with receivers. The distance of a mobile asset from the sources can be calculated from the signal reception time and its position can be obtained by triangulation. Procedures for underwater positioning will be also developed under the HiAOOS project. Underwater acoustic positioning will be tested using ice-tethered drifting acoustic receiver buoys equipped with surface GPS and developed in HIAOOS.
Development of the HiAOOS infrastructure builds on the previous Coordinate Arctic Acoustic Thermometry Experiment – CAATEX (2016-2022) funded by the Research Council of Norway and the Office of Naval Research. The HiAOOS system will be recovered in 2026.
The HiAOOS scientists onboard were from the Nansen Environmental and Remote Sensing Center (NERSC), the Norwegian Polar Institute, University of Bergen, Institute for Oceanology Polish Academy of Sciences, and NAXYS technology. The HiAOOS project is coordinated by Hanne Sagen, NERSC. The HiATTS scientists were from Scripps Institution of Oceanography, Woods Hole Oceanographic Institution, and Naval Postgraduate School. The HiAATS project is led by Matthew Dzieciuch, Scripps Institution of Oceanography.
*Cover photo: All the moorings were set out anchor first. The anchor and the double releases ready to go early mooring the 22 September 2024. A tube is fastened to the anchor to hold a bottom pressure recorder, which again is chained to the releases. In two years, we will send the release command to the acoustic release. The mooring detach from the heavy anchor, and come to the surface with all its instruments.
Check out our previous article about this expedition:
