The Gulf Stream has increased steadily over the last century

The heat transport into the Nordic Seas has increased steadily in volume and temperature over the last century, according to recent study.

Together with colleagues, Lars H. Smedsrud, professor at UiB and researcher at the Bjerknes Centre for Climate Research, have examined 100 years of research results to see how the ocean transport has evolved.

-It was surprising to find such consistent results that show a steady increase, which entails that the Gulf Stream’s extension into the Nordic Seas has strengthened, researcher Lars H. Smedsrud says.

Surprising volume increase
With the surprising volume increase, the total heat transport has increased with 30 percent. Smedsrud and his team have examined changes in relation to ice melting in the Arctic, glacier melting on Greenland and CO2 uptake from the atmosphere.
Many of the researchers, including Smedsrud,  are actively taking part in the ongoing Nansen Legacy project that focuses on the Northern Barents Sea were many of the largest observed changes have occurred over the last 100 years.

–  While we have expected an increase in temperature, there is nothing about global warming that would suggest an increase in volume transport. But the increase is consistent with both stronger winds and declining sea ice covers. In addition, we see an increase in the vertical and horizontal ocean circulation in the Nordic Seas and the Arctic.

Ocean circulation might weaken in the future
Smedsrud explains that global warming could potentially weaken the vertical part of the ocean circulation in the future, the part known as the Atlantic Meridional Overturning Circulation (AMOC).

– This would affect the Gulf Stream system, but many observations indicate that the horizontal part will stay unaffected, due to declining sea ice covers and increased heat loss to the atmosphere.  

How the ocean circulation will evolve in the future, is still uncertain. However, the study also shows a steady loss of sea ice in the Arctic over the last hundred years, which has allowed stronger uptake of CO2 from the atmosphere.  

–  During the winter the sea ice isolates the warm ocean from the cold air. With melting sea ice, the heat transfer to the air increases. The air gets warmer, the winters get milder. This is directly connected to the increased ocean heat transport, Smedsrud explains.

Smedrud bilde

Schematic overview of the relationship between the warm Atlantic water inflow across the Greenland-Scotland Ridge and its influence on (1) Nordic Seas heat loss, (2) deep and dense water outflow, (3) CO2 uptake, (4) Greenland melting, and (5) Arctic sea ice cover. The vertical red arrow illustrates the large cooling in the Nordic Seas, and the orange arrow the smaller cooling in the Polar Sea. Graphic by Marlo Garnsworthy/Icebird Studio.

Definitions:

  • The ocean heat transport depends on how much water is circulating in and out of an area, and how much warmer the water flowing in is compared to the water flowing out.
  • Meridional Overturning Circulation is the part of the ocean circulation that flows northwards in the surface and southwards as deep water. The water flowing northwards cools gradually, becomes denser and sinks. When this water sinks, it brings along oxygen-rich water which is important for the organism living there. Less dense water will be formed in the future because of increased ocean temperature and will somewhat weaken this part of the circulation.
  • Horizontal Circulation: Because the earth rotates, warm water flowing northwards will always occur on the eastern side along the Norwegian coast. Cold, dense water flowing southwards in the surface, will always occur on the western side, along Greenland and Canada. This means there can be a large horizontal circulation without any Meridional Overturning Circulation. Increased supply of freshwater due to rainfall and melting glaciers might increase this part of the circulation in the future.

 

Reference: 


Nordic Seas Heat Loss, Atlantic Inflow, and Arctic Sea Ice Cover Over the Last Century
Lars H Smedsrud;Morven Muilwijk;Ailin Brakstad;Erica Madonna;Siv K Lauvset;Clemens Spensberger;Andreas Born;Tor Eldevik;Helge Drange;Emil Jeansson;Camille Li;Are Olsen;Øystein Skagseth;Donald A Slater;Fiamma Straneo;Kjetil Våge;Marius Årthun
ISSN: 8755-1209 , 1944-9208; DOI: 10.1029/2020RG000725
Reviews of geophysics. , 2022, Vol.60(1)