Extreme heat wave in the ocean can cause mass death

21 June, 2023

It is warmer than usual in the North Sea and the North Atlantic. It could be about one of the worst marine heat waves ever. If the temperatures stay the same, it can mean mass death for fish, algae, seaweed and mussels.

-It is very serious, says oceanographer Ola Kalén.

The surface temperature in the North Atlantic and in the North Sea, particularly off the north-east coast of England and the west of Ireland, is in some places four to five degrees above normal for this time of year. There, the ongoing marine heat wave has been classified as category four on a five-point scale, meaning extreme, by the US weather agency NOAA.

-Extreme is the least you can say. It could be one of the worst marine heat waves ever, says Ola Kalén, oceanographer at SMHI, to TT.

There are also higher than normal temperatures for the season in a large area of the North Atlantic, from the coast of West Africa all the way up to the North Sea.

-It is a special situation and very serious. The biggest reason is global warming, says Kalén.

“Unfortunate Combination”

But climate change is not the only cause of the heat wave in the North Atlantic and North Sea. There are a variety of theories as to what other factors have contributed to the unusually high levels recorded in recent months.

-It is an unfortunate combination of primarily climate warming and then human causes but also natural climate variations that have been stacked on top of each other, says Kalén.

-But it’s hard to answer exactly which processes have contributed because we haven’t seen how this end yet. A thorough analysis is needed, perhaps only after the El Niño situation is over.

The large-scale weather phenomenon El Niño made its official entry into the tropical Pacific on June 8. It has a major impact on the weather in the area and will in the long run also give the global average temperature a boost.

-It is uncertain how much it contributes to what is happening around the UK right now, but globally it is already having a strong impact. But we are in the initial phase of El Niño and the effects are gradually spreading from the tropical Pacific, says Kalén.

Threatens ecosystems

Marine heat waves, i.e. prolonged periods of extremely high surface water temperatures, can damage ecosystems in the sea. Harmful algal blooms have already occurred in the North Sea. But if the high temperatures in the water off the British coast persist throughout the summer, the situation could become really serious for animals and plants.

-It is most difficult for those that cannot move, for example seaweed and mussels. The extreme heat has cascading effects, if there is less phytoplankton, there is less food for fish and it spreads further up the food web, says Kalén.

Really strong heat waves can lead to mass deaths of fish but also of seabirds. They simply starve to death when there is increased competition for food.

“Warning Bells”

-Many curves relating to the state of the oceans have looked strange during the year, according to Kalén.

In April, a record was set for the average temperature of the surface waters of the world’s oceans, and there is also a very low extent of sea ice in Antarctica for this time of year.

-There are many curves that look strange and unusual. We are seeing many extreme events in the climate system right now, says Kalén.

-It is important for everyone to realize that the only thing we can do to try to reduce this is to reduce emissions as quickly as possible. There are clear warning bells, if we do nothing about this the situation will worsen and soon.

El Niño and La Niña are phases of the El Niño-Southern Oscillation (ENSO) weather cycle. El Niño warms the surface water in the eastern parts of the Pacific Ocean while La Niña cools it.
El Niño returns on average every two to seven years and usually lasts nine to twelve months. The climax often occurs around Christmas, hence the name El Niño (the boy).
El Niño is associated with increased heat, drought or precipitation. It is mainly countries in the Pacific Ocean that are affected, above all in Oceania, Indonesia and South America, but also parts of North America and more distant areas across Asia and Africa.
The opposite condition, La Niña, has a cooling effect on the Earth’s climate.
Earlier in 2023, a multi-year episode of La Niña ended. And at the beginning of June, the agency NOAA announced that El Niño had officially entered the Pacific Ocean.
Sources: WMO, SMHI, NOAA

Text: Sofia Eriksson/TT
Photo: Peter Morrison/AP/TT

Related articles

The Baltic Sea is becoming a hot water bath. It affects the fish more than we might understand. It is a slow process that can be difficult to see. But there is one place where, for a relatively short period of time, scientists have been able to see just that – what happens to the fish when the sea gets warmer. Right next to Forsmark’s nuclear power plant in northern Uppland….
Reportage: Lena Scherman
Photo:Elin Jenjila Franzén, Alexandre Gobatti
UW-Photo: Kimmo Hagman, Robert Westerberg
Drone:Robert Westerberg
Editing: Apollonia Meleouni
The world’s coral reefs are in trouble. As the oceans get warmer, corals are stressed and eventually die. Coral scientist Tessa Hempson calls corals the “canary in the coal mine”. The little bird that used to be placed far down the mine shafts, because when it died you knew the oxygen in the mine would soon run out. A whistleblower who suffers long before we humans do. …
Reportage: Johan Candert
Photo: Johan Candert, Göran Ehlmé, Leif Eiranson
How are we affected by the oceans getting warmer?…
Text: Fanny Jönsson
Photo: TT News Agency
Scroll to Top