Articles | Volume 18, issue 2
https://doi.org/10.5194/os-18-389-2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-18-389-2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Technical note
| 
24 Mar 2022
Technical note |
| 24 Mar 2022
| 24 Mar 2022
Technical note: Turbulence measurements from a light autonomous underwater vehicle
Geophysical Institute, University of Bergen and Bjerknes Center for Climate Research, Bergen, Norway
Tore Mo-Bjørkelund
Department of Marine Technology, Norwegian University of Science and Technology, Trondheim, Norway
Ilker Fer
Geophysical Institute, University of Bergen and Bjerknes Center for Climate Research, Bergen, Norway
Department of Arctic Geophysics, UNIS – The University Centre in Svalbard, Longyearbyen, Norway
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In the northwestern Barents Sea, we study the Barents Sea Polar Front formed by Atlantic Water meeting Polar Water. Analyses of ship and glider data from October 2020 to February 2021 show a density front with warm, salty water intruding under cold, fresh water. Short-term variability is linked to tidal currents and mesoscale eddies, influencing front position, density slopes and water mass transformation. Despite seasonal changes in the upper layers, the front remains stable below 100 m depth.
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The Arctic Ocean is a major sink for heat and salt for the global ocean. Ocean mixing contributes to this sink by mixing the Atlantic and Pacific waters with surrounding waters. We investigate the drivers of ocean mixing north of Svalbard based on observations collected during two research cruises in 2018 as part of the Nansen Legacy project. We found that wind and tidal forcing are the main drivers and that 1 % of the Atlantic Water heat loss can be attributed to vertical turbulent mixing.
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Measurements of ocean currents, stratification and microstructure collected northwest of Svalbard are used to characterize the evolution of the warm Atlantic current. The measured turbulent heat flux is too small to account for the observed cooling rate of the current. The estimated contribution of diffusion by eddies could be limited to one half of the observed heat loss. Mixing in the bottom boundary layer, driven by cross-slope flow of buoyant water, can be important.
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Atlantic water (AW) is a key driver of change in the Barents Sea. We studied an emerging pathway through the Svalbard Archipelago that allows AW to enter the Barents Sea. We found that the Atlantic sector near the study site has warmed over the past 2 decades; that Atlantic-origin waters intermittently enter the Barents Sea through the aforementioned pathway; and that heat transport is driven by tides, wind events, and variations in the upstream current system.
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In the northwestern Barents Sea, we study the Barents Sea Polar Front formed by Atlantic Water meeting Polar Water. Analyses of ship and glider data from October 2020 to February 2021 show a density front with warm, salty water intruding under cold, fresh water. Short-term variability is linked to tidal currents and mesoscale eddies, influencing front position, density slopes and water mass transformation. Despite seasonal changes in the upper layers, the front remains stable below 100 m depth.
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We quantify the mesoscale eddy field in the Lofoten Basin using Lagrangian model trajectories and aim to estimate the relative importance of eddies compared to the ambient flow in transporting warm Atlantic Water to the Lofoten Basin as well as modifying it. Water properties are largely changed in eddies compared to the ambient flow. However, only a relatively small fraction of eddies is detected in the basin. The ambient flow therefore dominates the heat transport to the Lofoten Basin.
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The Arctic Ocean is a major sink for heat and salt for the global ocean. Ocean mixing contributes to this sink by mixing the Atlantic and Pacific waters with surrounding waters. We investigate the drivers of ocean mixing north of Svalbard based on observations collected during two research cruises in 2018 as part of the Nansen Legacy project. We found that wind and tidal forcing are the main drivers and that 1 % of the Atlantic Water heat loss can be attributed to vertical turbulent mixing.
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Ocean Sci., 16, 685–701, https://doi.org/10.5194/os-16-685-2020, https://doi.org/10.5194/os-16-685-2020, 2020
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We analyzed 14-month-long observations from moored instruments to describe the average features and the variability of the Norwegian Atlantic Slope Current at the Lofoten Escarpment (13°E, 69°N). The slope current varies strongly with depth and in time. Pulses of strong current occur, lasting for 1 to 2 weeks, and extend as deep as 600 m. The average volume transport is 2 x 106 m3 s-1.
Erik M. Bruvik, Ilker Fer, Kjetil Våge, and Peter M. Haugan
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A concept of small and slow ocean gliders or profiling floats with wings is explored. These robots or drones measure the ocean temperature and currents. Even if the speed is very slow, only 13 cm s1, it is possible to navigate the (simulated) ocean using a navigation method called Eulerian roaming. The slow speed and size conserve a lot of energy and enable scientific missions of years at sea.
Eivind Kolås and Ilker Fer
Ocean Sci., 14, 1603–1618, https://doi.org/10.5194/os-14-1603-2018, https://doi.org/10.5194/os-14-1603-2018, 2018
Short summary
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Measurements of ocean currents, stratification and microstructure collected northwest of Svalbard are used to characterize the evolution of the warm Atlantic current. The measured turbulent heat flux is too small to account for the observed cooling rate of the current. The estimated contribution of diffusion by eddies could be limited to one half of the observed heat loss. Mixing in the bottom boundary layer, driven by cross-slope flow of buoyant water, can be important.
Jenny E. Ullgren, Elin Darelius, and Ilker Fer
Ocean Sci., 12, 451–470, https://doi.org/10.5194/os-12-451-2016, https://doi.org/10.5194/os-12-451-2016, 2016
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One-year long moored measurements of currents and hydrographic properties in the overflow region of the Faroe Bank Channel have provided a more accurate observational-based estimate of the volume transport, entrainment, and eddy diffusivities associated with the overflow plume. The data set resolves the temporal variability and covers the entire lateral and vertical extent of the plume.
E. Darelius, I. Fer, T. Rasmussen, C. Guo, and K. M. H. Larsen
Ocean Sci., 11, 855–871, https://doi.org/10.5194/os-11-855-2015, https://doi.org/10.5194/os-11-855-2015, 2015
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Quasi-regular eddies are known to be generated in the outflow of dense water through the Faroe Bank Channel. One year long mooring records from the plume region show that (1) the energy associated with the eddies varies by a factor of 10 throughout the year and (2) the frequency of the eddies shifts between 3 and 6 days and is related to the strength of the outflow. Similar variability is shown by a high-resolution regional model and the observations agree with theory on baroclinic instability.
I. Fer, M. Müller, and A. K. Peterson
Ocean Sci., 11, 287–304, https://doi.org/10.5194/os-11-287-2015, https://doi.org/10.5194/os-11-287-2015, 2015
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Over the Yermak Plateau northwest of Svalbard there is substantial energy conversion from barotropic to internal tides. Internal tides are trapped along the topography. An approximate local conversion-to-dissipation balance is found over
shallows and also in the deep part of the sloping flanks. Dissipation of
tidal energy can be a significant contributor to turbulent mixing and cooling of the Atlantic layer in the Arctic Ocean.
T. Vihma, R. Pirazzini, I. Fer, I. A. Renfrew, J. Sedlar, M. Tjernström, C. Lüpkes, T. Nygård, D. Notz, J. Weiss, D. Marsan, B. Cheng, G. Birnbaum, S. Gerland, D. Chechin, and J. C. Gascard
Atmos. Chem. Phys., 14, 9403–9450, https://doi.org/10.5194/acp-14-9403-2014, https://doi.org/10.5194/acp-14-9403-2014, 2014
M. Bakhoday Paskyabi and I. Fer
Nonlin. Processes Geophys., 21, 713–733, https://doi.org/10.5194/npg-21-713-2014, https://doi.org/10.5194/npg-21-713-2014, 2014
E. Støylen and I. Fer
Nonlin. Processes Geophys., 21, 87–100, https://doi.org/10.5194/npg-21-87-2014, https://doi.org/10.5194/npg-21-87-2014, 2014
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Short summary
A turbulence instrument was installed on a light autonomous underwater vehicle (AUV) and deployed in the Barents Sea in February 2021. We present the data quality and discuss limitations when measuring turbulence from the AUV. AUV vibrations contaminate the turbulence measurements, yet the measurements were sufficiently cleaned when the AUV operated in turbulent environments. In quiescent environments the noise from the AUV became relatively large, making the turbulence measurements unreliable.
A turbulence instrument was installed on a light autonomous underwater vehicle (AUV) and...
