Deep Sea crisis: a country disappears from the Global Digital Map for 38 days

Every time you visit a web page or send an email, data is being sent and received through an intricate cable system that stretches around the globe.

Since the 1850s, we've been laying cables across oceans to become better connected.

Today, there are hundreds of thousands of miles of fiber optic cables constantly transmitting data between nations.

From 36KR

How does the "undersea lifeline" affect the whole world?

The story of Tonga has told the world that the breakage of a single submarine cable can make a country disappear from the digital map.

On January 15, 2022, a loud noise erupted from the seabed in the South Pacific.
An undersea volcano violently erupted, and the shockwaves and tsunamis instantly snapped the only submarine cable connecting Tonga to the outside world.
Nearly 80 kilometers of the cable was broken into several pieces and buried deep under the volcanic ash.
This island nation with a population of about 100,000 instantly "disappeared" from the internet map.

For 38 days, there was a communication blackout.
There were no bank transfers, no international calls, and no internet connection.
A glass fiber with a diameter smaller than an adult's palm determined whether a country was "online or offline."

As the "information arteries" carrying 99% of intercontinental data transmission, although submarine cables are hidden beneath the sea, they are the key communication infrastructure that affects the global digital economy.

There are approximately 500 submarine communication cables globally, with a total length exceeding 1.7 million kilometers, which can circle the Earth's equator more than 40 times.
They are truly the "undersea lifelines." 

However, a ship's anchor dragging across the seabed, a submarine landslide, a regional conflict, or a geopolitical game could all become the "guillotine" to cut off the information flow, and for each country, it could be an unbearable communication disaster.

In the deep - sea battlefield full of intertwined risks, how to protect the undersea lifelines and enhance the resilience of digital infrastructure has become a global proposition that must be jointly answered in this era.

 

The Tonga islands have been cut off from the world since last week's volcanic eruption which damaged a major undersea communications cable that could take weeks to repair.

 
Frequent "Injuries"

The vast ocean creates an illusion of protection for submarine cables.
However, beneath the calm sea surface, cable damage occurs almost every day.
According to data from the International Cable Protection Committee (ICPC) and the International Telecommunication Union (ITU), the number of global submarine communication cable failures ranges from 150 to 200 per year, with an average of about 3 cables needing repair each week.

"Human - induced cable failures account for 70% to 80% of the total.
Fishing trawling and merchant ship anchoring are the main sources of damage." Chen Liang, the deputy general manager and senior engineer of China Submarine Cable Construction Co., Ltd.
(hereinafter referred to as "Cable Company"), told a reporter from IT Times.

There is an under - construction international submarine cable off the coast of Shanghai Lingang.
Due to its long project cycle, it has not been connected to the main system and is not marked on the electronic nautical chart.
When the Sino - British Submarine Cable Company recently participated in the repair, they found that the cable was severely damaged by the anchor of a ten - thousand - ton ship, with multiple fiber optic breaks, making the repair extremely difficult.

A shocking "anchor strike" incident in Europe brought the vulnerability of submarine cables to the public eye.

On Christmas Day in 2024, the Estlink 2 power line and four key communication cables between Finland and Estonia were cut by the dragging anchor of an oil tanker.
The 11 - ton anchor dragged nearly 90 kilometers along the seabed, causing losses of over 70 million euros and interrupting regional power and the internet for several days.

To address this persistent problem, the Cable Company's operation and maintenance team's main daily task is "preventive patrols." Chen Liang introduced that the team uses a remote monitoring system to check in real - time whether there are ships operating in the cable protection area.
Once an abnormality is detected, they immediately dispatch patrol boats along the route to persuade the ships to leave and cooperate with law - enforcement forces such as the coast guard, maritime authorities, and fishery administration for control, forming a complete protection process from monitoring and early warning to on - site disposal.

However, facing the complex global sea conditions, local protection cannot achieve full coverage.
In addition, due to long - term seawater corrosion, ocean current scouring, and the influence of marine organisms, the natural aging risk of submarine cables continues to accumulate, and sudden failures cannot be completely eliminated, posing a hidden danger for large - scale network outages.

This vulnerability is essentially an inevitable result of the over - concentration of internet infrastructure.

Sangita Abdul Chaudhry, a scholar from the University of California, Irvine, told a reporter from IT Times that "Global data centers and submarine cables are highly concentrated in Europe and the United States, and network services are controlled by a few giants.
A single - point failure can easily trigger a chain - reaction paralysis."

Image source: unsplash

Searching for Cables in the Deep Sea

If ship anchoring is a preventable "hidden injury," then the damage caused by extreme natural disasters and deep - water geological disasters is an unpredictable "fatal blow."

CBS News detailed the difficulties in the repair after the Tonga volcanic eruption in a 2022 report: The cable was buried under 30 centimeters of silt and displaced 5 kilometers.
It took the repair ship 20 days to replace a 91 - kilometer - long damaged cable.
Due to the shortage of spare cables, full repair may take 6 to 9 months.

Tongatapu Island, the main island of Tonga, photographed on January 17, 2022. 

Image source: New Zealand Ministry of Defense

On the western coast of the Pacific Ocean, the difficulty of deep - water repair is also astonishing.
In 2016, a submarine landslide occurred in the eastern waters of Taiwan, China.
Submarine cables at a depth of 2000 to 4000 meters were snapped horizontally.
Zhang Zhe, the general manager of the operation department of the Cable Company, recalled that the standard process for cable repair is to salvage the cable, cut off the faulty section, splice the spare cable, and rebury it.
However, the most difficult part is not the splicing but "finding it."

"In long - distance offshore areas, the positioning error of shore - based testing can range from several kilometers to more than ten kilometers," Zhang Zhe explained.
With a depth of thousands of meters and the surging sediment turbidity current, it is almost impossible for the remotely operated vehicle (ROV) to locate the cable.
Operators can only rely on the lifting cable of the surface ship for "blind fishing," and it took more than half a month just to salvage the cable.

This difficulty of "finding the broken cable" in the dark deep sea is not an isolated case.

The repair personnel of the Sino - British Submarine Cable Company also experienced a repair operation after a major earthquake in the Philippine Sea.
The water depth in the affected area was two to three thousand meters.
The strong earthquake triggered a large - scale submarine landslide, and a large amount of earth and rock buried the cable.
The detection equipment could not capture the cable's position at all, and the repair work was once in a desperate situation like "looking for a needle in a haystack." They could only try to recover the cable one kilometer at a time along the pre - determined route.
It took a month to salvage both ends of the broken cable ashore.

"The salvaged cable was completely unrecognizable.
The originally corrosion - resistant outer sheath was eroded by the heavy pressure and turned completely gray - black, indicating that it had been buried and squeezed on the seabed for a long time and under great stress," Zhang Lei, a training instructor of the Sino - British Submarine Cable Company, told a reporter from IT Times.
In the face of extreme natural conditions, one can only proceed steadily and step by step, using the most clumsy but reliable method to regain the deep - sea communication lifeline bit by bit.

Typhoons, huge waves, ocean currents, etc.
may interrupt the operation at any time; it is necessary to coordinate the closure of the shipping lane in densely trafficked areas; after the fishing ban ends, fishing boats go out to sea in large numbers, and the repair window closes...
When a fault occurs at a global data bottleneck, the consequences are even more disastrous.

In 2024, a local conflict occurred in the Red Sea region, damaging four cables.
25% of the telecommunications traffic in West Asia and North Africa was interrupted, and 25% of the data traffic between Asia and Europe was affected.
Due to the conflict area, the repair work was almost impossible to carry out.

"Aging" Crisis

"The most difficult part of submarine cable repair is not the splicing technology, but waiting for ships and waiting for certificates," said Yan Xiang, the president of Zhongshi Technology.
There are only about 60 professional ships globally with the ability to repair in deep - sea areas over 3000 meters, and they are mainly concentrated in developed regions.
Regions such as Africa, Latin America, and the Middle East have almost no independent repair capabilities.
After a fault occurs, they can only "wait in line for repair," and the waiting period can even be as long as several months.

This is also the shortcoming of internet resilience that Chaudhry is worried about: There is no globally balanced protection and repair system.
Once there are concentrated failures in key areas, it will be in a helpless situation.

The maintenance area in Yokohama, Japan, managed by the Sino - British Submarine Cable Company is the area with the densest international submarine cables in China.
Ships from China, Japan, and South Korea take turns on standby, but there are still tense situations where "the cable breaks again right after it is repaired." The high - density fishing operations in international waters keep the repair pressure saturated.

What is even more troublesome is cross - border approval.
"Technology can be standardized, but administrative barriers cannot," Yan Xiang revealed.
In 2024, there was a submarine cable repair that was delayed by layers of approval, taking a total of 947 days, far exceeding the time required for the actual repair of the fault.

The shortage of spare parts also restricts the repair efficiency.
Some of the materials required for submarine cable repair, such as spare cables and splicing boxes, rely on overseas production.
The procurement and transportation cycle can be as long as several months, and sometimes the repair window may be missed.
"Once there are consecutive failures, the spare consumables will be quickly exhausted, and we can only wait," a repairman told a reporter from IT Times.

After a submarine cable breaks, it is a competition of the speed and scheduling of repair resources.
However, the global submarine cable repair ships are quietly entering an "aging crisis." The overall ship age is relatively high, and the construction cycle of new ships is several years.

Image source: Shanghai Telecom

The report "The Future of Submarine Cable Maintenance" jointly released by TeleGeography and Infra - Analytics in 2025 shows that by 2040, the total kilometers of cables deployed in the global ocean will increase by 48% net.
By then, about two - thirds of the global cable maintenance ships will reach the end of their service life.
The remaining half of the fleet will also be close to the 40 - year retirement age.

For the Chinese fleet, "strengthening combat capabilities" is on the agenda.
The "Tianyi Navigator," which was launched on New Year's Day this year and is planned to be officially put into operation in June, is the first large - scale submarine cable engineering ship in China with the ability to construct and repair at a water depth of 5000 meters.
This 18,000 - ton submarine cable ship with unlimited navigation area realizes localization, digitalization, and intelligence, and is equipped with a full - set electric propulsion system and a DP - 2 dynamic positioning system.
"It directly improves the delivery and repair efficiency of the entire submarine cable system,"Chen Liang said.
However, he also admitted that compared with developed countries, Chinese submarine cable enterprises still have a gap in the number of ships and technical accumulation in terms of overall construction capabilities.
Deep - Sea "Offensive and Defensive Battle"

Physical damage tests the hardware resilience of submarine cables, while geopolitical games target the "sovereign resilience" of the global digital network.
Submarine cables have been included in the scope of geopolitical competition.

In August 2025, the US Federal Communications Commission (FCC) passed new regulations, prohibiting the use of equipment and services provided by "foreign adversaries" in submarine cable systems and encouraging the preferential use of trusted technologies from the United States and its allies.
This is the first major and comprehensive revision of submarine cable - related rules since 2001.

In fact, restrictive arrangements for submarine cables have been in place for a long time.
In August 2020, the United States launched the "Clean Network" initiative, listing submarine cables as one of the six key areas to be suppressed.
Since 2021, the United States has repeatedly abused state power, without proper justification, and based solely on subjective speculation and suspicion, taken unreasonable measures to suppress China Telecom, such as revoking the 214 license.
In 2022, Huawei Marine Networks was included in the Entity List.
In 2024, the United States joined with multiple countries to sign the "New York Joint Declaration," requiring the selection of allied contractors for submarine cable components and services.

Image source: Shanghai Telecom

This geopolitical "exclusion of China" is most directly reflected in the submarine cable route planning.
Gao Xin (a pseudonym), an insider in the submarine cable industry, told a reporter from IT Times that in the past, the shortest route was preferred for submarine cable laying.
However, affected by geopolitics, foreign submarine cable route planning now deliberately avoids Chinese waters.
For example, the Intra - Asia Marine Cable project from Japan to Singapore deliberately chooses to go south around the eastern part of Taiwan, China, the Philippines, and Borneo, bypassing the "nine - dash line" area in the South China Sea.

"As long as a Chinese telecom operator participates in the investment, or even if the cable only lands in the Chinese mainland or Hong Kong, China, these submarine cable projects face the risk of partners withdrawing due to US regulations," Gao Xin said.
European and American internet giants also tend to "bypass China" when building new systems.
Huawei Marine Networks, which was once powerful, now "doesn't even have the opportunity to bid."

In the view of an analyst, the core purpose of exclusive construction is to build a data corridor for a "values alliance." By controlling the submarine cable routes, landing points, and supply chains, an "independent cable belt" that does not pass through specific regions is created.
This is not only a business competition but also a division of "spheres of influence" in the digital age, ensuring that every node through which data flows is under "trusted" sovereign control.

"In essence, it is to instrumentalize civilian infrastructure to serve the great - power competition," the analyst told a reporter from IT Times.

However, China is not completely passive.
In November 2025, the Southeast Asia - Hainan - Hong Kong (SEA - H2X) international submarine cable project landed in Tseung Kwan O, Hong Kong.
This approximately 6000 - kilometer - long cable, equipped with 8 pairs of main optical fibers, connects Hainan, China, Hong Kong, China, the Philippines, Thailand, and Singapore, breaking the restrictions of geopolitical blockade on China's participation in international submarine cable construction.
Resilience "Firewall"

Facing natural risks, repair shortcomings

 

Links :

• PCMag : The Day the Internet Died: How an Underwater Cable Cut Plunged a Nation Into Digital Darkness 
• Reuters : Undersea cable fault could cut off Tonga from rest of the world for weeks 
• The Guardian : Parts of Tonga without internet after cables damaged and Starlink ordered to cease operations / What lies beneath: the growing threat to the hidden network of cables that power the internet 
• NPR : An undersea cable fault could cut Tonga from the rest of the world for weeks
• BBC : How will Tonga's broken internet cable be mended?  / Tonga volcano: Internet restored five weeks after eruption 

El Niño is here to turn the world’s weather upside down

photo : NOAA satellites

From Wired by Brian Kahn

 

El Niño Is Here to Turn the World’s Weather Upside Down
From a wet winter in the Southwest to fewer Atlantic hurricanes, this is what to expect as a potential super El Niño takes shape. 

THE WAIT IS finally over: El Niño has officially begun.

On Thursday, the National Oceanic and Atmospheric Administration declared that the semiannual climate phenomenon has arrived.
Congratulations if you took the pre-July 1 prediction on Kalshi.

Prediction markets aren’t the only places with a lot riding on El Niño.
The phenomenon—characterized by hotter-than-normal waters in the eastern tropical Pacific—has a huge impact on weather in nearly every corner of the globe.
And with this year’s iteration projected to be among the strongest ever recorded, the impacts are likely to be particularly acute.

There are a handful of ways to measure El Niño, but NOAA’s threshold hinges on temperatures being 1 degree Fahrenheit (0.5 C) above average for a three-month period in a specific part of the Pacific.
(That area is dubbed NINO3.4 if you want to impress and/or bore someone at a party.) The Pacific surpassed that threshold thanks to a rapid upswing in temperatures in record weeks.
But there are other signs of El Niño, including a surge in sea levels of up to 7 inches (18 centimeters) in the eastern tropical Pacific, thanks to winds blowing from the west that cause water to pile up there.

The shift in ocean temperatures in turn influences the atmosphere regionally, which then has knock-on effects on weather around the globe, from increasing the odds of wet weather in the southwestern US to lowering the odds of an active Atlantic hurricane season.
Drought also becomes more likely in places like Indonesia and the Sahel region of Africa.
El Niño also releases extra heat into the atmosphere, warming the already-heating planet even further.
In essence, El Niño is like the engine of a car: Fire it up and the atmosphere gets moving.

NASA’s Sentinel-6 satellite has detected higher sea surface height across parts of the Pacific Ocean, a sign that heat may be building beneath the surface as El Niño 2026 strengthens.

NOAA has confirmed El Niño conditions are underway, but scientists are still watching to see how powerful this event becomes.

 
The key questions now are how strong this year’s edition of El Niño will be and how that will affect its impacts.
The answers appear to be “very” and “quite a bit.” NOAA gives this year’s El Niño a 63 percent chance of exceeding the 3.6-degree F threshold, which would qualify it as a super El Niño.
But climate models are bullish that it could surpass that threshold by a wide margin.
Some have it surpassing 5.4 F, which would make this the strongest El Niño on record.

There have been four other El Niños that have reached the super threshold, and all led to widespread problems around the globe.
To revisit the car analogy, if your average El Niño is like the engine in a Toyota Prius, a super El Niño is more akin to the one in a Ferrari Luce.

The 1982-83 event—the first one in recorded history—caused Lake Mead to overflow, while the 1997-98 version caused what was Indonesia’s worst drought on record.
The most recent iteration in 2023-24 caused Southern Africa's worst drought in 100 years, leading to 61 million people requiring food assistance.
All the heat in the ocean also fries coral reefs, which are already struggling to adapt to the rising temperatures caused by burning fossil fuels.

A new phase of the natural El Niño weather pattern is "on our doorstep", according to UN scientists, boosting temperatures on a planet already under strain from climate change.

The World Meteorological Organization said El Niño is “very likely” to officially begin within the next few months, driving more extreme weather around much of the globe.

Several forecasts from national weather agencies suggest this El Niño could end up as one of the strongest ever recorded, nicknamed by some as a possible “super” or even “Godzilla” event.

 
And really, that’s the other issue at play with what will happen with this year’s El Niño.
The world has never been hotter in human history.
Pile an El Niño on and it’s likely there will be a burst of warming in the pipeline for this year and next.
If I was a betting person, I would definitely take the over on 2026 being among the hottest years on record.

Links :

• GeoGarage blog : Strongest El Niño in a century? What this rare phenomenon ...

Shifting currents

On the bridge of the RRS Discovery, Captain Antonio Gatti scans the horizon for a surfacing RAPID mooring.

NATIONAL OCEANOGRAPHY CENTRE

From Sciences by Paul Voosen  Sarah Crespi, Kevin McLean, Paul Voosen 

 
After decades of warnings, new data suggest the Atlantic’s vital circulation may withstand climate warming better than feared 11 Jun 2026

Off the coast of the Canary Islands—In calm waters here off the northwestern coast of Africa, the crew of the RRS Discovery, a U.K. research ship, was scanning the horizon, waiting for a sentinel to return from the deep.
An acoustic ping had triggered the release of a mooring holding 2 years of precious ocean measurements from its anchor 2000 meters below.
More than 20 minutes had elapsed, and there was still no sign of the bright orange float that would lift the mooring to the surface.
But Ben Moat, the cruise’s chief scientist and an oceanographer at the United Kingdom’s National Oceanography Centre (NOC), wasn’t worried.
He had been here before.

On the bridge, Moat glanced at a black Casio watch attached to his clipboard: 22 minutes.
There was more competition than usual to be the first to spot the float.
Moat, the captain, and the third officer were joined by NOC’s CEO, as well as several members of a U.K. TV news crew.
“Is it still off to port?” Moat asked, peering through binoculars for a mote of orange against a sea of azure.

The crowd on the bridge reflected the importance of the mooring, one of 10 in a vital climate observatory called the RAPID array.
For more than 2 decades, RAPID’s instrument-packed moorings, spaced across the Atlantic Ocean at 26°N between the Bahamas and the Canary Islands, have monitored the changing strength of ocean currents called the Atlantic Meridional Overturning Circulation, or AMOC.
The currents usher tropical waters and heat to the northeastern Atlantic, allowing cabbage palms to flourish in Ireland and keeping Norwegian ports ice-free in winter.
As the waters move north, they cool and become saltier as sea ice forms and rejects brine.
The resulting cold, salty water becomes dense enough to sink to the abyss, carrying heat and carbon dioxide down with it.
The water returns south along the floor of the Atlantic, heading to the Southern Ocean and beyond. 

Climate models have long warned that global warming could weaken “deep-water formation”—the density-driven sinking that is the engine of the AMOC.
The logic is straightforward: As Greenland’s ice sheets melt and sea ice formation declines, North Atlantic waters will freshen.
Combined with warmer sea temperatures, the freshening makes surface waters more buoyant.
The AMOC was thought to have shut down abruptly during past climate warmings, and a handful of researchers now argue such a tipping point could occur this century.
A sputtering AMOC could trigger a sharp cooldown in northwestern Europe, rising seas along the U.S.
east coast, and shifts in tropical rainfall.
“It is a risk that would really have severe impacts,” says Stefan Rahmstorf, a climate scientist at Potsdam University and a prominent voice warning of the threat.

Yet for all the alarming headlines, most climate researchers think the AMOC is more resilient than these worst case scenarios make it seem.
Emerging evidence suggests the AMOC may not have actually collapsed in the warm climates following ice ages.
More detailed climate models suggest it could weaken but not collapse in the current surge of warming.
And studies of the AMOC’s present behavior do not yet show any clear signs of trouble.
They’re also exposing new facets of the circulation that could buffer any eventual weakening.

“The paradigm has been, if we warm and freshen these areas, we’ll get less dense water and AMOC will slow down,” says Susan Lozier, an oceanographer at the Georgia Institute of Technology.
“That paradigm isn’t holding up.”

By retrieving the RAPID moorings and harvesting their data, the cruise to the Canaries in February should sharpen the picture.
Back on the Discovery bridge, 25 minutes after the mooring’s release, experience won the informal competition to spot it.
“There it is,” Moat announced.
The orange float bobbed several hundred meters off the port bow, with a ribbon of smaller yellow floats and instruments trailing behind it.

From a young age, Moat was drawn to the ocean.
He grew up the son of a fisherman in Bridlington, on England’s northeastern coast, and by age 8 was piloting his father and friends to North Sea fishing grounds—standing on a box to see over the bow.
A math whiz, he later studied computational fluid dynamics and joined NOC, where he spent years at sea studying how wind stirs the ocean’s surface.
Conditions were often punishing.
“We were seeking that big bad weather,” he says. 

 

In a brief period of calm, Ben Moat, RAPID’s chief scientist, prepares for a TV news interview in the RRS Discovery’s storage hangar.National Oceanography Centre

The circulation he now studies operates on a very different scale.
For more than a century, oceanographers had pieced together an understanding of the Atlantic’s slow, density-driven churning from shipboard measurements.
In the 1980s, famed climate scientist Wallace Broecker dubbed the system the “great ocean conveyor belt”—a vivid shorthand that stuck.
He also helped popularize the more troubling idea that this conveyor belt could collapse if large pulses of freshwater from melting ice sheets flooded the North Atlantic, disrupting the sinking of dense waters.
Evidence from ice cores and seafloor debris suggested it happened at the end of the last ice age—and perhaps more than once.
Such shutdowns, scientists proposed, could explain abrupt temperature swings seen in paleoclimate records.

Around the same time, climate models began to suggest global warming could also weaken the AMOC, not so much by melting ice, but by warming waters and keeping them buoyant.
But ship-based observations were too sparse to show any change in the AMOC.

So instead of relying on occasional ship surveys, researchers set out to continuously monitor the circulation with moorings spanning the Atlantic.
They settled on a line at 26.5°N—a transect where the overturning signal would stand out against other currents.
Backed by U.K. and U.S. funding agencies, the array was deployed in 2004.

After steaming out from Santa Cruz de Tenerife, Moat and his team got straight to work.
RAPID cruises run each year, alternating between the eastern and western boundaries of the Atlantic.
This one would be brief: Over the course of 1 week, the team would recover four moorings along the continental slope near the Canaries—like the one now bobbing alongside them—and replace them with fresh instruments.

Each mooring is studded with MicroCATs, compact sensors that measure water characteristics including temperature, pressure, and salinity.
They can be fickle, so the team had to calibrate new ones before deploying them.
The team sank the MicroCATs thousands of meters alongside a reference sensor, then retrieved them and compared the readings.
After the Discovery’s crew winched a set back up onto the deck, engineers hustled to remove them like a NASCAR pit crew, readying the winch for another submersion.
Some of the instruments were wonky “and had to be sent back for bad behavior,” said Yvonne Firing, a physical oceanographer at NOC.
But in the end, the team had 37 MicroCATs ready for their 2-year tour of duty, with one good spare ready to step in. 

Fresh from the deep, each MicroCAT instrument is rushed to the lab, where 2 years of data are downloaded. P. Voosen/Science

The sensors do not directly measure the currents, which creep along in many places with the speed of a tortoise, but rather the structure of the ocean itself.
From subtle changes in temperature, pressure, and salinity across the basin, scientists can estimate the “dynamic height” of the ocean—the equivalent of atmospheric pressure.
Just as winds flow from regions of high to low pressure, the tilt of these ocean heights, across the basin, leads to a calculation of flow.
Combined with other measurements, those data yield RAPID’s estimate of the AMOC’s strength.

What the currents lack in velocity they make up in flow rate, which is measured in sverdrups, millions of cubic meters per second.
A sverdrup (Sv) is roughly the combined flow of all the world’s rivers; the Amazon carries about 0.2 Sv.
RAPID measurements show the northward, surface leg of the AMOC, which flows as part of the Gulf Stream in the western Atlantic, transports about 17 Sv.
(The Gulf Stream, which is mostly driven by winds, carries 90 Sv in total.) A similar volume oozes southward above the ocean floor.

That stately flow actually swings wildly year to year, masking any long-term trend, the first RAPID measurements showed.
Swings between apparent decline and recovery have since become a hallmark of AMOC monitoring, and a recurring source of alarm and reassessment.

The Gulf Stream is one of Earth’s strongest ocean currents.

It is resilient to climate change because it is primarily driven by surface winds and the planet's spin.

But the Gulf Stream is one small part of the Atlantic Meridional Overturning Circulation (AMOC), a complex network of currents that may be vulnerable to global warming.

The AMOC redistributes heat across the North Atlantic Ocean, warming northwest Europe.
Surface flows (red) usher tropical heat north before cooling, sinking, and returning south along the sea floor (blue)

The AMOC is powered by a process called deep-water formation, which occurs in the North Atlantic.
Climate change could threaten it, triggering a sharp cooldown in Europe and rising seas along the U.S.
east coast.

Deep-water formation, also known as overturning, is driven by density and salinity changes of North Atlantic waters.

1

Deep-water formation begins when warm surface waters move north, cool, and get saltier from brine expelled as sea ice forms.

2

The resulting cold, salty water is denser and sinks.

3

Cool water returns south along the ocean floor.

4

But global warming, combined with the disappearance of sea ice and ice sheets, could cause waters to warm and freshen.
The resulting surface waters would be more buoyant, potentially disrupting deep-water formation.

 

Scientists rely on sensors suspended along moored lines at a range of depths to monitor the AMOC's strength.
One mooring array in the North Atlantic is called OSNAP.

 

Since 2014, OSNAP moorings have not detected any change in the AMOC’s strength.
Some data suggest that deep water can form farther north in the Arctic, perhaps fortifying the AMOC.

Farther south, at 26.5ºN, the RAPID mooring array has collected more than 20 years of data on the AMOC’s strength.

 

The AMOC’s flows are measured in sverdrups, millions of cubic meters per second—a unit roughly equivalent to the combined flow of all the world’s rivers.

RAPID’s estimates of the AMOC’s strength, adjusted to remove seasonal variations and the effects of wind, show that its flows swing wildly.

Scientists extract a smoothed signal from the noisy data.
Swings between periods of decline and recovery have become a recurring source of alarm and reassessment.

 

Whether climate change is responsible for the slight, gradual weakening of the AMOC is uncertain.

(

GRAPHIC) M. Hersher and N. Burgess/Science; (DATA) Map sensors: Darren Rayner/National Oceanography Centre; Map arrows: AMOC flows are a simplified approximation developed in consultation with Susan Lozier; Chart: G. D. McCarthy et al., Geophysical Research Letters, 52, e2025GL115055 (2025)

Gerard McCarthy remembers well the first time he saw an AMOC decline.
It was 2011, and McCarthy, now a climate scientist at Maynooth University, had just joined the RAPID team.
His first task was calculating AMOC’s strength.
Beginning in 2009, it plunged.
“Everyone was like, ‘The new guy made a mistake,’” he recalls.
Others checked the numbers.
The drop held.
“We all realized that something dramatic had happened.”

What happened was not caused by climate change, but rather the weather.
That winter, unusual swings in air pressure weakened the jet stream and shifted wind patterns, disrupting the AMOC’s flow.
The decline likely contributed to a frigid European winter in 2009 and, by leaving more heat in tropical basins, also led to an active Atlantic hurricane season the following summer.

A permanently crippled AMOC would lead to bigger problems.
In the U.K., it could blunt rising temperatures, partially offsetting global warming.
Farther north, however, Scandinavia would sit “in the bull’s eye,” says Marius Årthun, a physical oceanographer at the University of Bergen: Temperatures could plunge, even as the planet warms, and sea ice could creep south from the Arctic.
Across northwestern Europe, storm tracks could shift and rainfall could falter.

The impacts would ripple far beyond Europe.
If the AMOC’s flows weaken, sea levels on the U.S. east coast could rise by up to 30 centimeters, says Denis Volkov, an oceanographer at the U.S.
National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Laboratory.
Globally, tropical rain belts might shift south, weakening the Asian monsoon and rainfall over the Amazon.
And if the AMOC’s currents stop sequestering heat and carbon dioxide into the ocean’s deep waters, overall planetary warming could rise by an extra 0.2°C. 

Freshwater melt from the Greenland Ice Sheet may pose less of a threat than scientists once feared to deep-water formation, which drives the Atlantic Meridional Overturning Circulation. 

Paul Souders/Getty Images

To some scientists, those dire scenarios can be a distraction.
“It is taking our attention from impacts of climate change that we are sure are happening,” says Fiamma Straneo, an oceanographer at Harvard University.
But even a weakening AMOC could have consequences, like the cold European winter McCarthy remembers.
The question is just how weak it might get.

The RAPID array isn’t alone in searching for clues.
High in the North Atlantic is a second array of moorings, called the Overturning in the Subpolar North Atlantic Program (OSNAP), spanning the ocean from Newfoundland to Greenland to Scotland.
Funded since 2014 by the U.S.
National Science Foundation (NSF) along with international partners, OSNAP was sold on the idea that its location would give a better view of the deep-water formation that drives the AMOC.
Its first 10 years of data, expected to be published soon, will show a slight increase in the AMOC’s strength—but can’t yet say much about the effect of climate change, says Lozier, its longtime leader.

Comparing RAPID and OSNAP has already led to some puzzles.
Scientists expected AMOC changes would be apparent throughout the entire circulation, so any speedup or slowdown would register at both arrays.
“We had somewhat naïve expectations,” Lozier says.
In fact there’s little coherence in the system—when one part of the AMOC weakens, another might kick up, or not respond at all.
It seems the AMOC is not a single conveyor belt, but a belt of belts, each part operating semiautonomously.
Straneo wants to ditch the conveyor belt analogy entirely.
“It has hindered our ability to imagine how these systems might evolve,” she says.

 

 

Encrusted with barnacles after 2 years in the abyss, a float reappears (first image) as it lifts a mooring to the surface.
Marine organisms cover other parts of the moorings (second image).
P.
Voosen/Science

OSNAP has changed the picture in other ways, including by showing that overturning occurs not so much in the Labrador Sea, as models suggested, as it does farther north, in the Irminger and Iceland basins.
Additional data suggest deep-water formation is migrating even farther north, into the Arctic Ocean, following the retreat of sea ice, Årthun says.
“You’re expanding the reach of this cooling machine.” The northward migration could make the AMOC more resilient to warming, although the Arctic areas in which these cold, salty waters can form is not infinite, he says.
“How long can the compensation last? That’s the natural question to ask.”

OSNAP also acts as a sentinel for the AMOC’s response to injections of freshwater.
There are signs that, for the past 2 decades, the Beaufort Gyre, a loop of current in the Arctic Ocean, has been trapping freshwater from Arctic rivers, fat with thaw from permafrost.
This freshwater now seems to be migrating south into the Atlantic, a potential threat to deep-water formation, Straneo says.
But she notes that such a freshwater invasion has happened before, most famously during the “great saline anomaly” of the late 1960s, only to be flushed out of the system several years later.

Other omens come from sea surface temperature measurements, particularly those showing a “warming hole” in the subpolar Atlantic, where the ocean has cooled despite global warming.
Rahmstorf and others have argued the hole is the result of a weakened AMOC ushering less heat northward.
In 2023, Peter and Susanne Ditlevsen, sibling researchers at the University of Copenhagen, went further, reporting variability in this record that they said suggested the AMOC was nearing a tipping point within the next few decades.

Many researchers argue these warnings rest on shaky ground.
Sea surface temperatures, they note, are strongly shaped by the atmosphere and may not reliably track the AMOC.
Others found that the statistical indicators used by the Ditlevsens tend to point to AMOC collapse regardless of the underlying data.

Even so, hints of change are mounting.
In February, a study led by René van Westen, an oceanographer at Utrecht University (UU), suggested the Gulf Stream has shifted north in recent decades—a potential sign of AMOC weakness.
That’s because a weak AMOC would shrink the subpolar gyre—a broad circulation of currents south of Greenland—allowing the Gulf Stream to drift north.
With each piece of evidence, “you can quibble that it’s not AMOC,” Rahmstorf says.
“But when you have all this evidence pointing in the same direction, then it starts to become robust.”

Some climate modeling backs him up.
Research led by van Westen and UU oceanographer Henk Dijkstra has recently suggested a collapse will begin when the buoyancy of surface waters in the North Atlantic turns positive.
Climate models, even if they don’t show AMOC collapse, tend to predict changes in temperature, salinity, and other factors that would flip the buoyancy to positive by 2063.
Van Westen thinks a slow, centurylong collapse could begin then.
“We say it tips at 2.5°C,” he says.
“There’s quite a substantial risk.”

Yet such outcomes often require freshwater inputs far beyond what Greenland is expected to deliver.
New climate model runs that capture more realistic melt from the Greenland Ice Sheet are less dire.
In two preprints posted online in the past year—one led by Chuncheng Guo, a climate scientist at the Danish Meteorological Institute (DMI), the other led by Oliver Mehling, an ocean modeler at UU—researchers created multiple simulations where carbon emissions continued until 2250 and temperatures rose by up to 7°C.
In both studies the AMOC weakened, losing about 40% of its strength.
But it never collapsed.
Both studies also suggest the weakening is reversible, says Marion Devilliers, a DMI climate modeler.
Once emissions stop, she says, the “AMOC comes back.” 

In a third, even more sophisticated simulation, that resilience persisted even in the face of catastrophic warming.
This modeling effort, presented in February at the Ocean Sciences Meeting, found that even if atmospheric carbon dioxide levels quadrupled, driving extreme warming, the AMOC would decline by 40% after 20 or so years—but once again, it would rebound.
The result seemed to reflect the high resolution of the model, which could resolve currents flowing through narrow straits in the North Atlantic better than earlier models.
When a low-resolution version of the model simulated the same conditions, the AMOC simply collapsed.

The past, too, is proving more complicated than once thought.
Evidence from past ice ages seemed to suggest the AMOC switched off entirely when massive pulses of freshwater from the melting of the North American ice sheet poured into the Atlantic.
But new work, also presented at Ocean Sciences, suggests the AMOC may not have collapsed at all during these periods.
Using marine cores collected off the U.S. east coast, David Thornalley, a paleoceanographer at University College London, and colleagues measured differences in the grain size of sediments to calculate the AMOC’s ancient flows.
They found that even at the end of the last ice age—seen as a likely moment for an AMOC shutdown—the Atlantic circulation didn’t change much.
If anything, Thornalley says, “it may have been stronger.”

Yet even if the classic scenario of AMOC collapse doesn’t hold up, there is still reason to worry.
In work also presented at Ocean Sciences, Thornalley and his colleagues analyzed marine cores from a time some 400,000 years ago, when the climate was slightly warmer than today’s and Greenland experienced strong melt.
Those cores show the AMOC weakened by 30%, cooling the North Atlantic region by up to 7°C.
“This is the poster child for where we might be heading,” Thornalley says.

RAPID aims to provide an early warning.
After the first mooring floated to the surface near the Discovery, Moat and the crew set about recovering it.
Captain Antonio Gatti carefully approached the chain of floats, bringing it to the ship’s starboard with a kind of parallel parking maneuver.
Precision was essential—a wrong approach could entangle the propellers in hundreds of meters of line.

With grappling hooks, the crew snared the tangled-up mooring and dragged the mess to the ship’s aft, where it was winched aboard.
Neon red crabs and alien-looking snails festooned the mooring, and the MicroCATs were slick with algae and seaweed.
After an inspection, they were sent off to the instrument bay, where 2 years of data would be immediately downloaded.

The work was no easier on the ship’s final day at the array.
In rising swells, the crew set out to recover one last mooring and a seafloor lander from 3000 meters down.
The lander came up cleanly.
The mooring did not, and the crew faced another tangle.
On deck, technicians methodically cut through the snarls with knives.
“It’s a right mess,” said John Hopley, an engineer overseeing the work.

Piece by piece, they freed the line and retrieved the instruments.
By afternoon, a replacement mooring had vanished serenely into the depths.
The ship would soon be turning back to shore.
Was Moat, visibly tired, also relieved? Not yet, he said.
“When I step off the ship.”

Tenerife and the other Canary Islands shielded the RRS Discovery from swells.

National Oceanography Centre

The new AMOC calculations from the recovered data won’t be released until September.
But the circulation is beginning to reveal a pattern.
Late last decade, it surged, erasing the decline RAPID initially measured.
In the past few years, however, the readings have slipped again, suggesting an overall decline of nearly 2 Sv since 2004.
Some of that drop appears in the cold deep waters flowing south in the western Atlantic, though it has been partially offset by strengthening southward currents near the Canaries.
Meanwhile, strong warming in the western Atlantic has caused some northward flows to slow, though not the Gulf Stream.

This weakening is consistent with model predictions, but it is not yet statistically significant, nor clearly tied to global warming, Moat says.
Another decade of measurements is needed to make such a call.
By then, the array may be able to rule out the most extreme scenarios of imminent collapse this century, Moat and others reported in a study published last year in Geophysical Research Letters.
For now, Moat is wary of terms such as collapse and shutdown.
“Shutdown,” he says, “is not meaningless, but it’s not a good term.”

RAPID’s U.K. funding is secure until 2029, but OSNAP’s funding ends in January 2027, and hopes are dwindling that NSF will renew it.
Just last week, NSF said it would remove several OSNAP moorings in the Irminger Sea as part of cuts to the agency’s wider Ocean Observatories Initiative.

Efforts are underway to get the measurements more cheaply.
This month, the RAPID team is testing an experimental mooring off the Bahamas that can transmit its data to ships or autonomous submersibles.
Others are exploring whether satellite altimetry, which measures subtle sea-surface topography, combined with autonomous Argo floats can reproduce RAPID measurements.
And NOC is investigating whether subsea telecom cables could double as sensors.
“Eventually, we would move away from the heavy engineering of moorings,” Moat says.

Meanwhile, climate scientists are still struggling to describe the AMOC’s future.
At a U.K. workshop this month titled “Collapse of the Atlantic Ocean circulation: Can it? Has it? Will it?” researchers debated the evidence.
A broader assessment, commissioned by the European Union and modeled on United Nations climate reports, is now underway.
Most agree the media-stoked drama of collapse has outpaced the evidence.
“People may be inclined to be more inflammatory,” says Eleanor Frajka-Williams, a physical oceanographer at the University of Hamburg who previously led RAPID.
But that risks oversimplifying a system that resists easy narratives.
“There’s a reason we don’t have a unified simple theory for the AMOC,” she adds.
“It doesn’t exist.”

Aboard the Discovery, the crew continued to plumb the currents.
Recovered MicroCATs were lowered back into the water to verify their measurements, another set of checks in a project built on patience and repetition.
Between shifts came dart games in the bar, sunrises at breakfast, and the rare clear night when the clouds parted and the sky opened wide.
Beneath it, the ship motored on in the darkness, a small point on a vast, moving ocean that still hid its secrets.

Is cold-water swimming good for you, really?

Cold water swimming has been linked to a range of health benefits – potentially improving brain fog, energy levels and chronic pain, according to researchers.

In this BBC episode of Health Decoded, science journalist Melissa Hogenboom uncovers emerging research that suggests how cold water swimming could help with mental health disorders such as anxiety and depression. 

 

From FT by Hannah Coates

 

Yes

 

Whether in the sea, a lake, river or lido, cold-water swimming – immersing yourself in water typically between 10 and 15°C – has become a popular way to support wellbeing.

Venturing into cold water can act as a controlled stressor.

The body responds instantly: skin temperature drops, heart rate and blood pressure rise, and blood vessels constrict to preserve heat in the core.
At the same time, stress hormones such as cortisol and norepinephrine are released, explains Dr Mark Harper, author of Chill: The Cold Water Swim Cure.

 

With repeated exposure, this brief stress can train the body to become more resilient – a phenomenon known as hormesis.
“The body dampens its stress response, reducing chronic inflammation and insulin resistance,” says Harper.
It also activates brown fat, which helps regulate temperature and metabolism, thereby increasing energy expenditure, adds scientist Dr Susanna Søberg.

It’s the mental-health benefits, however, that many swimmers rave about.
While the initial cold-water-shock response briefly increases inflammation, studies suggest stress levels drop significantly around 12 hours later.
Nutritional therapist Hannah Lawton says this may be due to stimulation of the vagus nerve, supporting parasympathetic (“rest and digest”) activity and the release of mood-regulating neurotransmitters such as serotonin and dopamine, helping to ease stress and anxiety. 

 

Despite common misconceptions, cold-water swimming is reportedly as beneficial for women as it is for men, with some evidence suggesting it may help regulate body temperature during perimenopause and alleviate endometriosis symptoms.
There could also be added benefits from being outdoors and swimming socially.
Water below 20°C is optimal.
“Start swimming in summer, when it’s above 15°C,” recommends Dr Harper.
He also advises to always swim with others.
“Don’t try to control your breathing, and enter the water gradually to allow the body to adapt,” says Dr Heather Massey, associate professor in extreme environments and physiology at University of Portsmouth.
Just a couple of minutes is enough to begin with, while building up to five can boost alertness, focus and energy.

 

No

 

Evidence is still mixed on whether the benefits of cold-water swimming come from the cold water itself or from surrounding factors such as being in nature, overcoming a challenge and social connection.
“We know that some people even experience improvements just by being close to water,” says Dr Massey.
“There is debate over what the magic ingredient is.”

 

There are also important safety considerations.
Each year, hundreds of deaths are linked to cold water, meaning it’s an activity that should be approached with care.
Diving is not generally advised: when the face and body are exposed to cold simultaneously, the body can enter autonomic conflict – a state in which the sympathetic and parasympathetic nervous systems are activated simultaneously, explains Dr Massey.

“It sends competing signals to the heart to speed up and slow down at once,” she says.
This can trigger serious cardiac arrhythmias and, in rare cases, be fatal.
Instead, “get your body in and, once your breathing is under control, that’s when you can put your face in”, advises Dr Harper.
Those with high blood pressure, heart conditions or underlying health issues should consult a GP before taking part.
Warming up quickly afterwards is also key to reducing risk and avoiding hypothermia, Lawton notes.

Many begin cold-water swimming without proper guidance or progression, says Dr Søberg.
It’s important to seek qualified instruction – in the UK, for example, through Royal Life Saving Society UK or Swim England-accredited coaches with open-water safety training, although qualifications vary based on the kind of water.

“It’s important to listen to your body and never start when you’re feeling exhausted, run down or depleted,” she advises.
Experts also caution against hyperventilation-style breathing techniques popularised by figures such as Wim Hof, instead favouring slow, steady breaths.

Not everyone will enjoy the cold.
Those with Raynaud’s or other circulatory conditions – as well as pregnant women – should check with their healthcare provider before trying it.
The good news is that even minimal exposure can be beneficial.
According to Dr Harper, simply dunking your face in a sink of icy water can instantly lower stress levels.

Spectacular video of an osprey rising from the ocean after catching a barracuda

Spectacular video of an osprey rising from the ocean after catching a barracuda.

📽: Mark Smith Photographypic.twitter.com/LhYshPqsFF

— Wonder of Science (@wonderofscience) April 30, 2026

Mark Smith Photography