Monday, January 5, 2026

The quest to chart the sea

From a distance, this map of the ocean looks complete


In truth, knowledge of the seabed remains patchy. As of 2025, little more than one quarter of the seabed has been measured directly.
The remainder is an estimate.
Scientists can infer what the seafloor looks like by studying the sea surface.
Ridges, which exert more of a gravitational pull, pull water towards them, raising the local sea level. Trenches have the reverse effect, creating surface depressions.
These undulations are slight—invisible to the naked eye—but can be detected by satellites.  
 
From The Economist 
 
This map reveals what scientists care about—and what armed forces don’t want to share
 
While these estimates have given scientists a good idea of the underwater landscape, they lack crucial detail.
And the missing “details” can be huge: researchers have found underwater mountains as tall as Mount Fuji lurking in the unmapped zones.

There are many reasons why governments should want to find out what the remaining 73% of the ocean really looks like.
Depth data benefit nearly any marine activity you can think of: modelling climate, building infrastructure, mining the deep sea, managing fisheries and searching for wrecks. On December 30th, Malaysia Airlines will resume its search for Flight MH370, a plane that disappeared with 239 passengers and crew without trace in 2014.
During two previous searches, a significant chunk of the Indian Ocean was mapped.
Despite this, progress on charting the ocean floor—known as bathymetry—has been sluggish.
In 1903, Prince Albert I of Monaco founded the General Bathymetric Chart of the Oceans (GEBCO) to produce a map of the entire seabed, pooling data from governments, NGOs and companies.
But by 2017 the effort had only managed to map 6%. In 2017, to speed things along, GEBCO launched a project called Seabed 2030 in partnership with the Nippon Foundation (Economist Impact, our sister organisation, has collaborated with the non-profit on an initiative against ocean pollution).
As the name suggests, it hoped to have all the seabed mapped by 2030, and although progress is now moving at a decent clip, completion is still a long way off.



Why is it taking so long to map the oceans?
In 2000 the Endeavour space shuttle collected data to produce the first near-global map of Earth’s land surface. It took just 11 days.
But radio waves, which the Endeavour used to measure elevation, can travel only short distances in water.
The same is true for light.
This means that, to take a direct measurement of the seabed—rather than an estimate based on the sea surface—scientists must use slower vehicles for much of the ocean instead.
Most of the data has to be gathered the traditional way: by boat.
Humans have been measuring the seabed from boats for at least 3,000 years, by lowering poles or weighted lines.
But the process became far more efficient once they learned to bounce sound waves off the bottom. Sound, unlike light, travels readily through water.
Leonardo da Vinci was the first to experiment with using sound underwater, but his idea did not catch on until 1912 when, dismayed by the sinking of the Titanic, engineers scrambled to create a device that could detect icebergs.
The resulting echo sounder proved useful for mapping, too.
Instead of taking one measurement at a time with a weighted line, a ship could take a constant series of soundings.


 These discoveries, including seamounts too small to be spotted previously, were made thanks to a remarkable improvement in the resolution of the sea-surface gravity data.
But scientists cannot be certain how many there are, or what those measured with satellite data look like, until they have been properly charted by vessels.
 

Missing pieces

Bathymetric data are expensive to collect. A research vessel can cost $150m-200m and poor countries have often scarcely mapped their local waters because they lack the equipment and expertise. Exceptions are countries with something of interest to others, such as underwater canyons in the Democratic Republic of Congo or trade routes in Djibouti.

Elsewhere, gaps are due to a lack of openness rather than an absence of resources. Seabed 2030 estimates that perhaps another 20% of the ocean has been mapped covertly, but the data have not been disclosed to the public. To encourage governments to be transparent, the organisation has to convince them that what they publish is not going to spill valuable state secrets. At its most detailed, the map contains one depth measurement for a patch of ocean the size of a football pitch—enough to plot the broad contours of mountains but too coarse to reveal infrastructure such as subsea cables.


At that resolution “you could hide quite a large ship in there,” says Kevin Mackay, head of Seabed 2030’s Pacific Ocean Centre.
Yet many countries are reluctant to share their soundings.
Some shallows are deemed too strategically important to provide even coarse bathymetric data. Australia’s navy, for example, won’t share any coastal measurements, presumably because it is wary of Chinese espionage.
In April Australian officials monitored a Chinese ship suspected to be mapping subsea cables surrounding the continent.


Such caution is not universal. New Zealand and—surprisingly—America share data up to their beaches and allow scientists to map within their Exclusive Economic Zone (EEZ), a segment of sea within 200 nautical miles of a country’s shores, without a permit.
In his first term President Donald Trump signed a directive calling for all of America’s EEZ to be mapped.
To complete the total ocean’s sunlit zone—depths up to 200m that are currently the least well mapped—more countries will need to follow their example.

North Korea, unsurprisingly, is among the most secretive countries.
The majority of the soundings in its seas come from old navigational charts submitted by South Korea. The shallow parts of the South China Sea—a much-disputed territory—are also sparsely mapped.
China has the world’s largest navy and certainly has the kit to survey its EEZ, but it has shared data on just 11% of it. India, another naval power, has officially charted a mere 2%.

Sources: Copernicus Marine Environment Monitoring Service; GEBCO; “Global Distribution and Morphology of Small Seamounts”, by J. Gevorgian et al., 2019; International Seabed Authority; marineregions.org; Seabed 2030; World Bank; Yao Yu, University of California San Diego; Yi Chao, Seatrec Corp; The Economist
 
Attitudes are changing.
A decade ago getting bathymetric data was “always a struggle”, says Anne-Cathrin Wölfl, an academic at GEOMAR, a German marine research institute.
Now many are more willing to share.
After years of coaxing, Seabed 2030 has acquired low-resolution data from several oil and gas companies.
It hopes to repeat this success with deep-sea miners, another industry that has been unforthcoming so far.
Just five of the 57 patches contracted for mining in the Clarion-Clipperton Zone, an expanse of seabed in the eastern Pacific dotted with mineral-rich lumps of rock, are on the map.


 
Seabed 2030 thinks that mapping the remaining three quarters of the Earth’s seabed will cost up to $5bn—or take one ship about 200 years.
That could fall to $3bn if uncrewed technology were to be ramped up, says Jamie McMichael-Phillips, the head of Seabed 2030.
His team has high hopes for a fleet of bathymetry-measuring buoys, similar to the 3,500 floats already measuring ocean temperatures.
Seatrec, the company designing the buoys, estimates that a fleet of 2,000 could take 5m soundings a year.
A big number that is just a drop in the ocean: it would cover 0.2% of the 2.1bn roughly equal-sized squares of ocean left to survey in GEBCO’s latest map.
But if they succeed, the buoys could fill in remote parts that few scientists have bothered to investigate, such as the apparently empty abyssal plains.
Their findings might make waves.
 
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