The coldness of the sea in a warmer climate. What is happening?

The coldness of the sea in a warmer climate.  What is happening?
  • Helen Asbjørnsen

    University of Bergen and Perkins Climate Research Center

  • Marius Arthon

    University of Bergen and Bjerknes Climate Research Center

While the world is gradually warming, marine areas south of Greenland have been surprisingly cold in recent years, write Helen Asbjørnsen and Marius Arthon. Photo by Senja.

At the same time that the world is gradually warming, the temperature in the Norwegian Sea has not been much colder in more than 20 years. What is happening?

Knowledge is Aftenposten’s commitment to research and science, with researchers and professionals from all over the country contributing articles.

In icy Siberia, the temperature often appears below -50 ° C in winter. Fortunately, we are escaping this bitter cold here in Norway. The Gulf Stream, and the northern branches of the Gulf Stream, ensure the smooth transfer of hot water from the south. Then the westerly winds carry warm, moist sea air inland. This is how ocean currents and ocean temperatures affect our climate.

While the world is gradually warming, the marine areas south of Greenland have been surprisingly cold in recent years. This area was given a horror movie-like name in English “The Cold Point” and alarmed climate scientists.

During the same period, temperatures in the Norwegian Sea were as cool as they were in the late 1990s. Is it a sign of the weakening of the Gulf Stream?

Not only Gulf Stream

The Gulf Stream transports large amounts of hot, salty water from the Gulf of Mexico north to the Atlantic Ocean. This water makes up large parts of what drains into the Norwegian Sea – but an important component is missing. Portions of the water originally come from the Arctic and circulate as part of the “semi-polar vortex” before flowing into the Norwegian Sea from the south. Compared to Gulf Stream water, this water is cold and fresh.

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Hot and cold water mix well before they reach the Norwegian Sea. This makes it difficult to determine the source of the water, based on direct observations.

So we created a model sea where we tracked 10 million hypothetical water molecules that were released at the inlet of the Norwegian Sea in time. The experience highlights the major routes to the waters of the North Atlantic and how they have changed in recent decades.

The map shows how cold water from the sub-polar vortex (blue arrow) and hot water from the subtropical vortex and Gulf Stream (red arrow) mix together in the North Atlantic and are pushed by southwesterly winds into the Norwegian Sea (white arrow), and north toward the North Pole (arrow). Little). Both ecosystems along the Norwegian coast and the icy edge of the Barents Sea are sensitive to changes in sea temperature.

Cold water from the North Pole

our research It shows that two-thirds of the water flowing into the Norwegian Sea comes from the Gulf Stream, while one-third comes from the Arctic. Changes in this mixing ratio affect the temperature in the Norwegian Sea. If more water comes from the North Pole, the temperature drops.

The “sub-polar front” is the boundary between the cold water from the subpolar vortex and the warm water from the Gulf Stream.

Our research shows that changes in the position of the sub-polar front are also an important source of changes in temperature and salinity at the entrance to the Norwegian Sea.

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Since 2010, the polar front has been eastward than usual. Thus, more cold fresh water enters the Norwegian Sea.

Thus, the cooling of the Norwegian Sea in recent years can be partially explained by the shift in oceanic currents in the North Atlantic.

Surface temperatures in the North Atlantic. Hot water from the Gulf of Mexico is carried north by the Gulf Stream and cooled on the way to the Norwegian Sea. Color ranges from dark red (warm) to light violet (cool).

Stable Gulf Stream

We haven’t found any indication that the Gulf Stream’s hot water flow has weakened in recent decades – quite the contrary. The measurements are shown along the Norwegian coast rather There is no indication that the Gulf Stream is weakening.

On the other hand, models and climate projections for the future indicate a possible weakening of ocean circulation in the North Atlantic.

There is still one important thing to consider: If the Gulf Stream weakens in the future, regardless of the water carried north, it will be much warmer than before.

Thus the amount of heat transferred northward will increase.

In other words, you don’t have to worry about a new ice age entering right away.

  • Helen Asbjørnsen is a researcher in the Department of Geophysics, University of Bergen and the Perkins Center for Climate Research.

  • Marius Arthon is a researcher in the Department of Geophysics, University of Bergen and the Bjerknes Center for Climate Research.

Dalila Awolowo

Dalila Awolowo

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