What are subsea cables, and what happens when one gets cut?

There’s virtually a 100 per cent chance that the text message you just sent, the show you streamed on Netflix last night, and your Christmas online purchases were all facilitated by subsea cables.

Subsea communications cables might be one of the most underrated yet most important parts of the global economy – but they are also among the most vulnerable and open to disruption.

The cables are about as thick as garden hoses, and their filaments are about the diameter of a human hair. They lie deep on the ocean floor and carry an estimated 98 per cent of international data transfers. They transmit more than $US10 trillion ($15.6 trillion) in financial transactions daily, and they are vital to the functioning of the global economy.

Australia was forced to finance the Coral Sea Cable, connecting Port Moresby, Honiara and Sydney, to block China's Huawei from building it.Credit: DFAT

Amid an ongoing global digital transformation and explosion in data usage, especially since the COVID-19 pandemic, the number of subsea cables has skyrocketed over the past decade, growing from 130 in 2010 to more than 600 today.

There are about 1.5 million kilometres of cables globally, but a single cable being severed or damaged can cause chaos, including widespread outages, disruptions to payments systems and flights, and even business closures.

What are subsea cables?

Submarine cable networks are critical infrastructure. They carry nearly all the world’s public internet and private network data traffic, facilitating global economic and financial activity as well as government and military communications and operations.

Modern submarine cables rely on fibre-optic technology and are far more efficient than satellites, which handle only a small fraction of global data transmission. Lasers on one end of the cable fire at extremely rapid rates down thin glass fibres to receptors at the other end of the cable. These glass fibres are wrapped in layers of plastic, and sometimes steel wire, for protection.

Australia has a long history with the technology: the nation’s first subsea cable, connecting Darwin to Indonesia about 150 years ago, was used to transmit Morse code. It was followed by the Commonwealth Pacific Cable System, or COMPAC, a telephone cable connecting Sydney to Canada via New Zealand in the 1960s, and then TASMAN2, Australia’s first fibre-optic cable that connected to New Zealand from 1992. Fifteen known international cables manage 99 per cent of Australia’s data traffic.

Almost no subsea cables are owned and operated by governments. Australian telco giant Telstra is Asia’s largest subsea cable provider, while Google and Huawei have invested in dozens of cables globally.

The cables are vital but are also highly vulnerable to a range of risks, from shark attacks and weather damage to subterfuge.

Why are they in the news?

Finnish authorities recently seized a Russia-linked ship that is suspected to have damaged an undersea cable between Finland and Estonia, dubbed Estlink-2, as well as four telecom cables.

The alleged attack is being described as potential “hybrid warfare”, which refers to the use of unconventional methods – including the damaging of critical infrastructure – to create instability.

Finnish Prime Minister Petteri Orpo at a press conference in Helsinki on December 26, as police investigate the electricity transmission between Finland and Estonia through the Estlink 2 connection, which was cut on Christmas Day.Credit: AP

Closer to home, a major new project was announced in November to deliver two new subsea cables between Australian mainland capital cities and Christmas Island. The project, dubbed Australia Connect, is being delivered by a consortium of Google Cloud, NEXTDC, SUBCO, Vocus, state and local governments. It will link Australia to the rest of the Asia-Pacific region and the US.

What happens when a subsea cable gets cut or damaged?

Ruptures can be caused by ageing infrastructure, weather, accidents – and acts of suspected sabotage. The biggest threats to subsea cables are not from shark attacks or weather events, but from human activities, according to research that found that anchors and fishing account for more than three-quarters of known cable faults.

In areas served by several cables, traffic can usually be quickly rerouted. In other instances, however, entire nations can be cut off from global data, and might have to rely instead on satellites for connectivity.

The average repair time for a subsea cable is two weeks, which can blow out during extreme weather events or geopolitical conflict. There are about 70 cable ships globally, with a third of those set up for repairs, according to data from Australian think tank ASPI.

What is Australia doing about those risks?

Redundancy – being able to rely on other cables or satellites – is a crucial part of network resilience, and more cables are constantly being built globally to help minimise impact to connectivity. The federal government recently announced it would spend $18 million over four years on a new body – The Cable Connectivity and Resilience Centre – to protect cables throughout the Indo-Pacific region.

The UN technology agency has also created a new body specifically to boost protection for the cables after the litany of recent high-profile failures and outages.

“It’s definitely not just a technical issue, but an issue that can affect our economies and our societies ... And this critical infrastructure is vulnerable to disruptions,” Tomas Lamanauskas, deputy head of the UN’s telecoms arm, the International Telecommunication Union, told reporters.

About 200 cable failures were reported in 2023, according to UN data, with roughly 80 per cent of cable disruptions thought to be caused by natural hazards or human accidents.

Streaming services such as Netflix rely on subsea cables for data transmission.Credit: Bloomberg

Meanwhile, a recent report from ASPI made five key recommendations for Australia to become more attractive as a subsea cable hub, including that the Australian government better support and strengthen regional repair and maintenance capabilities, and engage more closely with industry.

“Australia’s subsea cable resilience is generally good,” ASPI technical specialist Jocelinn Kang said. “This is because of several factors, including that multiple cables land at different geographic locations and offer a degree of redundancy and resilience. Another is that Australia enforces legislation to protect cables in the shallow waters as they make landfall, designating certain areas as cable protection zones.”

Another report, from the Australian Human Rights Commission, recommended that commercial subsea cable diversification be prioritised and that the government ramp up investment in subsea cable repair and supply capabilities.

Where do the US tech giants fit in?

Google, Meta, Microsoft and Amazon have an increasing influence on the subsea cable industry, which hasn’t yet been seriously considered, according to ASPI. They are already widely referred to as “hyperscalers” for their growing scale and control over the cable systems.

“These hyperscalers account for the majority of total submarine cable capacity usage, with that share continuing to grow,” ASPI’s Kang said. “This means that an increasing portion of the world’s data is under the stewardship of only a few entities, making the availability of that data highly dependent on their seamless operation.

“Such a concentration creates a digital supply-chain dependency risk, where potential disruptions could lead to widespread consequences. Additionally, as their bandwidth needs to increase, hyperscalers are transitioning from being primary customers of network capacity to owning and operating subcable systems.”

Kang warned that if the tech giants continue to control the world’s subsea cables, it would heighten the risk of a single point of failure. She said the shift in power dynamics means governments –including Australia’s – must engage more directly with the tech giants to get the best balance between commercial interests and safeguarding national interests.

“The impact of hyperscalers on the global subcable ecosystem is undeniable, and their influence is reshaping both the physical and digital landscapes of global connectivity,” she said.

The Business Briefing newsletter delivers major stories, exclusive coverage and expert opinion. Sign up to get it every weekday morning.