A research team from the University of Bergen have collected over 100 years of research to observe how ocean heat transport has evolved. The results revealed that The Gulf Stream has increased gradually over the past century.
“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,” commented Lars H. Smedsrud, Professor at UiB and researcher at the Bjerknes Centre for Climate Research.
What is ocean transport?
Ocean heat transport is dependent upon how much water is circulating in and out of an area, and how much warmer the water that is flowing in is compared to the water flowing out.
How does this apply to The Gulf Stream?
Scientists observed that with the surprising volume increase, the total heat transport within The Gulf Stream increased by 30%. 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.
“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,” explained Smedsrud.
Horizontal Circulation is related to the Earth’s rotation; as the planet 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.
What is Meridional Overturning Circulation and why is it important?
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, becoming denser as it 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 temperatures and will somewhat weaken this part of the circulation.
Smedsrud explained: “Global warming could potentially weaken the vertical part of the ocean circulation in the future, the part known as the Atlantic Meridional Overturning Circulation.
“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.”
What does this mean for the future?
Scientists are uncertain regarding how ocean circulation will evolve in the future. However, researchers have noted that the study also reveals a steady loss of sea ice in the Arctic over the last hundred years, which has allowed a 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,” concluded Smedsrud.