From undiscovered trenches to the Bermuda Triangle, the world’s oceans are full of unsolved mysteries.
But one of the strangest questions is why much of the Atlantic Ocean is suddenly cooling at record speed.
Through March, the central Atlantic experienced its warmest weather since 1982, with highs of 30° (86°F).
However, after this, a dramatic temperature swing occurred, with surface water temperatures dropping below 25°C (72°F). Scientists still do not know what caused this.
Michael McPhaden of the National Oceanic and Atmospheric Administration (NOAA) said Living science: ‘We still wonder what is actually happening.’
Scientists are baffled as to why a large portion of the Atlantic Ocean (pictured) suddenly began cooling at an unprecedented rate
Scientists are currently intensively monitoring the strip of water that extends several degrees on either side of the equator between Brazil and the coast of East Africa.
Not only is it unusual that this region, the central equatorial Atlantic, is cooling, but it is the speed at which the change is occurring that is unusual.
Each year the temperature in the central equatorial Atlantic changes. The warmest periods are in March and April, after which it cools down until summer.
However, from June onwards, surface water temperatures dropped at an unprecedented rate.
In mid-June, temperatures in this region were 0.5–1.0°C (0.9–1.8°F) colder than average for this time of year.
In June, a large area of the central equatorial Atlantic Ocean unexpectedly reached temperatures well below average for this time of year, with no apparent cause.
Water temperatures are now starting to rise back to normal levels, but scientists still don’t understand what is causing this sudden cooling.
Dr McPhaden says: ‘It could be a temporary phenomenon that has arisen due to processes we don’t fully understand yet.’
In general, the cooler waters of the Atlantic Ocean in summer are associated with stronger trade winds blowing across the equator.
These strong winds blow warmer surface water away and cause colder, deeper ocean water to rise to the surface. This process is called equatorial upwelling.
In a normal year (pictured), strong winds above the equator blow away warm surface water and cause colder water to well up from below (illustrated in purple)
What makes this year so unusual is that the winds over the cold area (pictured) are actually weaker than normal, a condition normally associated with warmer temperatures.
However, winds in the rapidly cooling area were weaker than normal this year, usually a sign of warmer waters on the way.
There were some strong gusts of wind in early May which may have started the cooling process, but Dr McPhaden points out that the wind ‘did not increase as much as the temperature dropped.’
According to Dr. McPhaden, human-induced climate change cannot be ruled out as the cause, but it is unlikely to be the cause.
“At first glance, this is just a natural variation in the climate system over the equatorial Atlantic Ocean,” said Dr. McPhaden.
A deviation of half a degree on either side of the average may not seem like much cause for concern, but scientists are keeping a close eye on this part of the ocean.
The reason for this is that the continued cooling in the central equatorial Pacific could be a sign that an Atlantic Niña is coming.
The abnormally rapid cooling followed the warmest weather since 1982, when temperatures rose to 30°C.
The concern is that this cooling could evolve into an Atlantic Niña event, which is defined by three months of colder than average temperatures
Like their more famous cousins the Pacific El Niño and La Niña, the Atlantic Niña/Niño are the intense peaks and valleys of ocean warming and cooling.
If water temperatures remain below average for three months, that is enough to speak of an Atlantic Niña. That has not happened since 2013.
This is a concern because Atlantic Niña events can have far-reaching effects on nearby weather systems.
In a recent blog postNOAA scientist Dr. Franz Tuchen wrote: “Less rainfall over the Sahel region, more rainfall over the Gulf of Guinea, and seasonal shifts of the rainy season in northeastern South America have all been attributed to Atlantic Niño events.”
The 2024 Atlantic hurricane season is forecast to be ‘exceptional’ as officials have estimated there could be as many as 13 tropical cyclones. However, an Atlantic Niña could reduce the severity of the season
Exceptionally cold Atlantic temperatures in 2012 and 2013 were followed by devastating floods in Brazil. Pictured: Flooded streets in Rio de Janeiro
In 2012, Brazil experienced severe drought in the northeast and flooding in the Amazon, combined with unusually cold water from the Atlantic Ocean.
In 2013, an Atlantic Niña occurred, which also led to devastating flooding in large parts of Brazil, including Rio de Janeiro.
Research published that year from Brazil’s National Institute for Space Research has found that a disruption of an Atlantic Niña was the likely cause.
On the positive side, warm Atlantic Niño events increase the likelihood of strong hurricanes developing near Cape Verde.
If this cooling lasts long enough to trigger a full-blown Atlantic Niña, the colder waters could potentially limit the increased hurricane activity forecast this year.
Dr Tuchen says: ‘It will be interesting to see whether this Atlantic Niña fully develops and, if so, whether it has a dampening effect on hurricane activity as the season progresses.’