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Henrik Søiland deploys an Argo float on a cruise with the research vessel Johan Hjort during 15 May - 4 June 2019. Photo: Tor de Lange

A recent freshening and warming of the Norwegian Sea

When the Norwegian Sea is warmer than normal, the water is normally more salty. The last decade has brought something different – water that is warm, but fresh. New research links this to the atmosphere and to less salt from the Atlantic. Kjell Arne Mork explains.  

Argo deployment
Argo floats measure temperature and salinity as they dive to 2000 meters, then rise to the surface and send the data to land via satellite. Photo: Tor de Lange

Written by Kjell Arne Mork at the Bjerknes Centre and the Institute of Marine Research.

Hydrographic changes in the Norwegian Sea are mostly observed as warm/salt or fresh/cold. However, a different story happened recently in the Norwegian Sea. Data from Argo floats revealed that the Norwegian Sea warmed and freshened during 2011–2018.

In a new article, we argue that two different mechanisms caused this: reduced local heat loss to the atmosphere and freshening of inflowing Atlantic Water.

The analysis showed that the air-sea heat fluxes can explain half or even more of the variation in the ocean heat content on time scales exceeding four months. 

We were able to make monthly estimates of the ocean heat and freshwater contents in the Norwegian and Lofoten Basins by using data from Argo floats during 2002-2018. Ten Argo profiles per month, that corresponds to 3-4 Argo floats, in each basin, resolved the seasonal hydrographic variation with reasonable accuracy.

Norwegian Sea circulation
Schematic view of the surface circulation in the Nordic seas, from the new article. 

The number of Argo floats in the Nordic Seas will sustain and be improved through the NorArgo2 project. Read more about them here (in Norwegian).

Where are the Argo floats today? Have a look at the map!

Reference

Mork, K.A., Ø. Skagseth, and H. Søiland, 2019: Recent Warming and Freshening of the Norwegian Sea Observed by Argo Data. J. Climate, 32, 3695–3705, https://doi.org/10.1175/JCLI-D-18-0591.1

This work was supported by AOIP (Atmosphere-Ocean-Ice interactions in Polar and subpolar regions), one of the Bjerknes Centre's strategic projects for 2018–2021.