A large strip of ocean has cooled in an incredibly short time frame — and scientists don’t know why. Now, this very same strip of water is warming back up to normal temperatures, further baffling researchers.

This strip of water first began to form and cool at the beginning of July. Interestingly, this cooling event also happened after this region experienced the warmest waters seen in about 40 years.

This patch spans between Brazil and the coast of East Africa. This region is otherwise known as the central equatorial Atlantic.

Franz Tuchen, a University of Miami in Florida postdoctoral research associate explained that this event is “really unprecedented.”

Michael McPhaden, a National Oceanic and Atmospheric Administration (NOAA) senior scientist, explained, “We are still scratching our heads as to what’s actually happening.”

“It could be some transient feature that has developed from processes that we don’t quite understand,” McPhaden added.

Between February and March, eastern equatorial Atlantic waters were more than 86 degrees Fahrenheit.

By July, the coolest recorded waters were seen of this event, as temperatures reached 77 degrees Fahrenheit.

An Atlantic Niña is a climate pattern that can result in increased rainfall occurring over areas of the world, such as western Africa. Meanwhile, other areas, such as northeastern Brazil, will see decreased rainfall. An Atlantic Niña hasn’t been seen since 2013.

Usually around July and August, the cooling temperatures of the ocean cause the easterly winds to pick up. On a local scale, the Atlantic Niña affects which parts of the world become wetter and drier.

As a result, Tuchen has said, “The verdict is already quite certain that it’s not gonna be classified as Atlantic Niña.”

Cooler waters off the coast of Africa can suppress the formation of African easterly waves, which can develop into tropical storms or hurricanes later.

In 2013, the last Atlantic Niña caused devastating floods in large areas of Brazil, including Rio de Janeiro.

Dr Tuchen said: “It will be interesting to monitor whether this Atlantic Niña fully develops, and if so, whether it has a dampening effect on hurricane activity as the season progresses.”

The two La Niñas may influence each other directly, but it is challenging to predict how. The Atlantic could be delaying the development of the Pacific La Niña. McPhaden said: “There could be a tug of war between the Pacific trying to cool itself and the Atlantic trying to warm it.”

However, this has left them further stumped, as it doesn’t appear that winds are impacting the waters and cooling them, as is normal. Tuchen explained, “At the moment, we believe that the winds are actually responding to the cooling.”

As a result, McPhaden has said, “There’s something else going on.”

While an Atlantic Niña might provide some cooling for some regions, it may not last long in the face of global warming.

After over a year of record heat on land and at sea due to global warming, this could be a positive change.

Pedro DiNezio at the University of Colorado said: “We are starting to see that the global mean ocean temperatures are going down a bit.”

They have simulated strong heat fluxes in the atmosphere or changes in ocean and wind currents. “From what we see, these are not obvious drivers of this cooling event,” said Tuchen.

“At first blush, this is just a natural variation of the climate system over the equatorial Atlantic,” McPhaden said.

For much of 2023, the equatorial Atlantic saw the highest sea surface temperatures in decades. “It’s the latest episode in a string of events for a climate system that’s gone off the rails for a number of years,” said McPhaden.

“It’s potentially going to be a consequential event,” McPhaden concluded. “We just have to watch and see what happens.”