Undersea cables—The thread holding our world together

Posted: October 21, 2024

Email. Cell phone calls. Cloud data. Financial transactions. They all travel over fiber optic cables about the size of garden hoses snaking along the sea floor. Over 95% of data shared internationally travels through a network of about 500 or so undersea cables, which could circle the Earth over 32 times if laid end-to-end.

Satellite communications can’t compete. While speeds vary, data travels at least 5X faster across undersea cables than via satellite. The record for satellite data transmission is 200 gigabits per second, whereas the newest cables transfer data at over 200 terabits per second—fast enough to transmit the entire Library of Congress from Virginia to Spain three times every second.

But, if the image of a garden hose just lying on the ocean floor strikes you as vulnerable, you’re not wrong. About 100-150 undersea cables break every year, threatening the global communications upon which societies and economies are built.

What’s breaking undersea cables?

Most of those 100-150 cable breaks each year result from human accidents. Nets and anchors from fishing boats are responsible for about 40% of them. Natural disturbances—such as earthquakes, landslides, or just wayward rocks—account for around 5%. There’s also a growing problem of intentional tampering for espionage and malicious disruption. It’s largely a myth that shark bites pose any serious threat. While sharks caused four faults on the first undersea fiber optic cable in the 1980s, they haven’t caused any since 2006. 

The risks posed by a broken cable can be tremendous, with the potential for entire countries to be cut off from the rest of the world. The 2011 tsunami in Japan broke seven of its 12 cables—if one more had broken, Japan could have been cut off from the internet.

Moreover, the lifespan of most cables is about 25 years—so many of the cables laid during the dot-com boom are now nearing the end of their lives and need to be either repaired or replaced.

How are companies repairing and replacing undersea cables

Google, Amazon and Meta are laying more and more new cables, but there’s not much financial incentive to repair cables that break. The world relies on a fleet of just 22 cable-repair ships to keep the global economy humming along whenever a cable breaks. Those 22 repair ships are often converted tugs and ferries, some of them pushing 40 years old.

“We’re all happy to spend billions to build new cables, but we’re not really thinking about how we’re going to look after them,” Mike Constable, the former CEO of Huawei Marine Networks, told The Verge. “If you talk to the ship operators, they say it’s not sustainable anymore.”

As with many other industries, the cable repair workforce is also aging and difficult to replace. Working on a cable repair vessel requires working unpredictable schedules far from home.

“One of the biggest problems we have in this industry is attracting new people to it,” said Constable. Of recent graduates:

“They all want to be data scientists and that sort of stuff. But for me, I find this industry fascinating. You’re dealing with the most hostile environment on the planet, eight kilometers deep in the oceans, working with some pretty high technology, traveling all over the world. You’re on the forefront of geopolitics, and it’s critical for the whole way the world operates now.”

Adding to high costs and workforce attrition, the industry is caught in many of the same supply-chain issues bedeviling other industries. With so many resources going into building new cables, it’s difficult to get the supplies to repair existing cables, says researcher Kevin Frazier.

In 1866, the first deep sea telegraph cable repair mission dragged a grapnel hook across the seafloor, 2.5 miles below, hoping to snag the broken cable and haul it aboard a repair ship. The grapnel caught on the first try, but just as the cable was aboard, it fell back into the sea. It took 28 more tries to hook it again. When it finally successfully came on board, the expedition’s leader, Cyrus Field, went to his cabin and wept.

Deep sea cable repair today works much the same way as that first fraught expedition. It’s a time-consuming process of trying to locate cable breaks and then pull up the cable ends with grappling hooks from 6,000 m (20,000 ft) under the sea.

Work is ongoing to outfit fiber optic cables with sensors that can detect and localize strain or temperature changes on cables by measuring how the light travelling through them interacts with acoustic waves caused by mechanical or thermal strain.

Gathering data with undersea cables

Similar technology may put undersea cables to work not just transmitting data, but acting as sensors themselves. Last year, scientists detected a tsunami in Japan by measuring differences in the time it took light to travel through a fiber optic cable as the tsunami distorted its shape. In theory, this technology could turn the fiber optic telecommunications network into a vast global sensor array detecting everything from earthquakes, tsunamis and ocean swells to ship traffic and whale calls. Under land, they can even monitor changes in commercial activity by measuring the vibrations of vehicles and pedestrian traffic.

There are also plans to install additional sensors that measure temperature, pressure, sounds and seismic activity within the repeater cylinders that are positioned at 70 km (45 mi) intervals along cables to boost their signals.

Data from these sensors could give cities like Lisbon a half hour warning before tsunamis strike. They’d also give scientists a more comprehensive picture of the changes in ocean temperatures and currents happening as part of climate change.

As undersea cables grow to be an even more essential part of our industrial information infrastructure, industries and governments may have to coordinate to keep information flowing smoothly.