Have the temperature and direction of the Gulf Stream changed?

Yes, the temperature and speed are changing.

To understand it well we need to contextualize.

The Gulf Stream is part of a system of Atlantic currents called

Southern Atlantic Overturning Circulation.

(AMOC) and that it is composed of superficial and deep currents.

The surface waters of the southern hemisphere are transported through the tropics, where they heat up, reach the Caribbean, leave the east coast of the United States, cross the Atlantic and rise to the Norwegian Sea.

The Gulf Stream is only one part of this system, it leaves the Gulf of Mexico, runs more or less parallel to the coast of the United States, and then becomes the North Atlantic Current.

This entire system reaches the subpolar Atlantic, there it cools down and as they are very saline waters they sink and return as deep currents to the south.

That is why it is called

overturning circulation

, because it is a current that brings water from the southern hemisphere to the north and then returns to the south.

The importance of these currents, in addition to transporting water, is that they also move a lot of energy in the form of heat.

The latest studies show that this entire system of currents has slowed down by 15% since the middle of the 20th century.

The consequence of this slowdown is an accumulation of warm water in mid / low latitudes and a decrease in the entry of warm water in the north.

The Gulf Stream has increased its temperature, while in the subpolar Atlantic there is an area that has cooled down quite a bit.

They call it the cold region of the North Atlantic.

That region receives the icebergs and meltwater that come from the Arctic and as the thaw is increasing, that area is getting colder and colder.

As the meltwater has lower salinity, there is less subsidence of water, with which less deep water is formed in that region and that is the cause of the slowdown of the entire system.

When we look at the past we see that all these processes have occurred before and on a much larger scale when the ice ages occurred.

Then there was the same slowdown that we are seeing now but much more pronounced.

At that time, the formation of deep waters in the subpolar Atlantic was much smaller than the current one, so the movement of the entire current system was much slower.

We know that there are areas where salinity is increasing in the Atlantic

To know all these things we use various tools.

We use satellites and buoys to measure in situ changes in temperature, current speed and even salinity.

Thanks to these measurements we know that there are areas where salinity is increasing in the Atlantic.

For example, throughout the tropical and subtropical region, this is where the greatest evaporation occurs and as the water moves less, it gains salinity.

And to study the past we use sediment cores that are samples from the seabed.

In them we can analyze different indicators.

One of those used to evaluate the slowdown of the AMOC is the analysis of the grain size of the sediment.

With this, the speed of deep currents is inferred.

Other ways to see how this entire circulatory system has been changing is to observe what was happening on the surface.

For example, in the region of the Labrador Sea, which is the most sensitive to all these changes, many studies have been done with foraminifera and particles carried by icebergs that arrived in the area.

The water temperature is higher when the current is more active, when the water is colder, the AMOC is weaker

Foraminifera fossils are very useful because in addition to indicating the temperature of the water, they can also indicate the salinity.

Foraminifera are planktonic microorganisms with a calcium carbonate shell.

Their shells were made up of different concentrations of elements depending on the temperature and salinity of the water in which they lived.

Comparing the data that we obtain from the analysis of these fossils with what is seen now, we can reconstruct times of greater cooling or times with warmer and saline water.

The water temperature is higher when the current is more active, when the water is colder, the AMOC is weaker.

This current slowdown has many consequences.

Changing the water temperature in some of the most important fishing grounds is going to have consequences on our economy and food.

And another consequence may be changes at the atmospheric level.

Studies show some conflicting data, but overall, all this warming in the Gulf Stream area is seen to produce more intense hurricanes due to increased evaporation.

It also influences winter storms, the fact that the Gulf Stream is warmer makes it much more nourishing, so they will also be stronger.

And when those storms collide with cold Arctic air masses, very heavy snowfall occurs.

All changes in currents affect our daily life in some way because they change the atmospheric system, and the conditions in the fishing areas.

Montserrat Alonso García

is a professor at the University of Salamanca and investigates climate changes in the North Atlantic and the Indian Ocean in the last three million years.

Question sent via email by John Doney, PhD

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