This post has two objectives. First, to salute all those who made the Nuka Arctica project possible. Even though this is not a publication, a record of note is definitely in order. While serving on the ICES working group on ocean hydrography (WGOH) I learned from Dr. Bogi Hansen at the Faroes Marine Science Center that they had an ADCP they couldn’t use and that it might serve science better on another vessel. Almost in passing I mentioned this to a meteorologist at the Swedish Met Office (SMHI) and he immediately suggested the Royal Arctic Lines (RAL) freighter Nuka Arctica that operates between Nuuk, Greenland, and Aalborg, Denmark. This ship was already operating a thermosalinograph, a CO2 system, taking XBT sections and releasing weather balloons during its transits!
What followed became an impressive collaborative effort. Prof. Martin Mork and I paid a visit the RAL operations office in Aalborg where we proposed to install and operate the ADCP on their vessel – a suggestion they quickly endorsed. We now had the platform and the instrument. But we needed funds to build the seachest (the steel structure that is welded to the hull to house the ADCP), funds for the yardwork and funds for the GPS navigation system. My dean Margaret Leinen provided funds for us to fabricate and ship the sea chest to the dock in Sweden where it was to be installed. The University of Bergen (UiB) covered the yard costs, and thanks to Prof. Hilding Sundqvist at the University of Stockholm the Wallenberg Foundation provided the funds for the GPS system. A decade later Prof. Corinna Schrum at the UiB and Dr. Henrik Søiland secured the funding to buy a 75 kHz ADCP enabling us to profile currents to ~700 m depths. Mr. Pierre Jaccard at the UiB took charge of the operations. Profs. Martin Mork and Harald Svendsen (UiB) arranged for the institutional support. Later, my associate Mrs. Sandra Fontana took over the processing and prepared the final QC’d copy of all data. It is thanks to their efforts and contributions that the Nuka Arctica program could happen.
Several comprehensive studies emerged from this cooperative effort:
Chafik, L., T. Rossby and C. Schrum (2014). On the spatial structure and temporal variability of poleward transport between Scotland and Greenland. J. Geophys. Res. doi:10.1002/2013JC009287
This paper elucidates in detail the zonal structure of currents and eddy kinetic energy near 60°N, the eastbound zonal section of the Nuka Arctica. It shows the main flow of the North Atlantic Current in the Iceland Basin as well as the northbound flow along the European continental slope.
Chafik, L. and T. Rossby (2019). Volume, heat, and freshwater divergences in the subpolar North Atlantic suggest the Nordic Seas as key to the state of the meridional overturning circulation. Geophys. Res. Lett.,46, https://doi.org/10.1029/2019GL082110
This study shows that with directly measured currents it is possible to not only obtain quantitative estimates of volume, heat, and fresh water fluxes, but also of their divergences. It concludes that the major heat losses associated with the AMOC take place in the Nordic Seas, not in the subpolar North Atlantic.
Childers, K. H., C. N. Flagg, T. Rossby, and C. Schrum (2015). Directly Measured Currents and Estimated Transport Pathways of Atlantic Water between 59.5oN and the Iceland-Faroes-Scotland Ridge. Tellus A, 67,28067 http://dx.doi.org/10.3402/tellus.v67.28067
This study uses all east- and westbound transits to map out upper ocean transport in the Iceland Basin. It confirms what is generally known but not always recognized, namely that all warm North Atlantic Current water entering the Nordic Seas flows north in the Iceland Basin and not through Rockall Trough (Slope Current notwithstanding).
Knutsen, Ø., H. Svendsen, S. Østerhus, T. Rossby and B. Hansen (2005). Direct measurements of the mean flow and eddy kinetic energy structure of the upper ocean circulation in the NE Atlantic. Geophys. Res. Lett.,32. L14604, doi:10.1029/2005GL023615
This study discovers that the Irminger Current along the western slope of the Reykjanes Ridge has two distinct velocity maxima. See also the Chafik et al. (2014) paper listed above.
Rossby, T., G. Reverdin, L. Chafik, and H. Søiland (2017). A direct estimate of poleward volume, heat, and freshwater fluxes at 59.5°N between Greenland and Scotland, J. Geophys. Res., 122, doi:10.1002/2017JC012835.
This study is modelled after and expands upon an earlier paper by Sarafanov and spans all seasons.
Vindenes, H., K. A. Orvik, H. Søiland, and H. Wehde (2018). Analysis of tidal currents in the North Sea from shipboard acoustic Doppler current profiler data. Cont. Shelf Res., 162, 1-12
The title says it all. This is an impressive piece of work.
We rightly think of ocean observation as an expensive activity. We are further challenged by the small horizontal scale of the most energetic scales of motion in the ocean. Satellites see ocean surface action in fabulous detail but not the water column. To go deep the traditional approach has been to deploy current meter moorings and while these resolve fast time scales their cost limits how many can be deployed. This is where programs like the Nuka Arctica can help, not replace, but help. They miss the fast time scales but can capture the horizontal and vertical structure of currents (ADCP) in great detail, they can profile temperature (XBT), record surface salinity, and profile ‘biomass’ as expressed in acoustic backscatter. All with the modest investment of single instruments operating 24/7 for as long as the vessel remains in operation.
Nothing whatsoever has been done with the backscatter data. Look at the May 7 and May 9, 2024 posts of backscatter in the Iceland Basin showing the diurnal cycle of zooplankton and myctophids and whatever else. Note the striking difference between summer and winter patterns. While the ADCP acoustics have not been calibrated to estimate backscatter strength, it is a safe bet that the gain remains constant over time. This opens up the possibility to study spatial and seasonal variations in backscatter across the entire subpolar North Atantic - perhaps even relating these to currents and eddy activity? Surely there is much here to be explored?!