Drilling off Cape Cod has revealed vast submarine aquifers that could transform the future of freshwater supply and change the world. It was a true “eureka moment” for IODP Expedition 501, which includes the participation of Portuguese geologist Davide Gamboa, researcher at CESAM/DGEO.
In 1976, during a search for oil and gas off the US East Coast, a team of scientists encountered something far more unexpected than hydrocarbons. Beneath the salty waters of the Atlantic, freshwater trickled from the sediment cores they were retrieving. At the time, no one knew how to interpret it. Was it merely an isolated anomaly, or a clue pointing to something much greater?
Half a century later, the mystery has returned with renewed significance. This summer, the international team of scientists on Expedition 501, aboard a drilling vessel off Cape Cod, recovered thousands of litres of freshwater from deep within the marine subsurface. Their findings may have confirmed the existence of one of the largest hidden aquifers on the planet, extending over a distance comparable to that between Porto and Faro.
“This is one of the last places anyone would expect to find freshwater on Earth,” said Brandon Dugan, geophysicist and hydrologist at the Colorado School of Mines, and one of the expedition leaders, in an interview with the Associated Press.
It is estimated that the volume of water within this submarine aquifer could supply a city the size of New York for centuries. The discovery raises the possibility that, in the future, we may drill for drinking water on the seafloor in much the same way as we do today for oil and gas.
A hidden reservoir beneath the waves
The ocean covers 70% of our planet, yet what lies beneath its floor remains largely unknown — for obvious reasons.
For some time, scientists have suspected that coastal aquifers on land extend offshore, trapping freshwater — or “brackish” water — that infiltrated thousands of years ago. Until now, however, no systematic drilling of the seabed had been undertaken to test this hypothesis, notes ZME Science.
Expedition 501 was launched with this very goal. Between May and July 2025, researchers used the Liftboat Robert — a platform normally deployed in the offshore oil industry — to drill sediments off the coast of Massachusetts.
At nearly 400 metres below the seafloor, deeper than initially anticipated, they discovered water with salinity levels as low as 1 part per thousand — comparable to many terrestrial freshwater sources.
“Four parts per thousand was our eureka moment,” said Dugan.
“So far, we know very little about the dynamics of these aquifer systems that cross the coastal interface, about the age of the water they contain, and even less about how they influence the cycling of nutrients, trace elements and their isotopes,” explained environmental geochemist Karen Johannesson, researcher at the University of Massachusetts and co-chief scientist of the expedition, in a statement released in May.
The challenge is immense. The United Nations has warned that, by 2030, global demand for freshwater may exceed supply by 40%.
Currently, high-performance computing systems — such as those powering artificial intelligence platforms — consume billions of litres of water for server cooling, a pressure that is expected to grow with the ongoing AI boom.
Meanwhile, rising sea levels are salinising coastal aquifers. And cities such as Cape Town and Jakarta have already come close to the so-called “Day Zero” — the nightmare scenario of turning on the tap and finding no water.
Scientists are now asking whether submarine aquifers might become emergency reserves for increasingly water-stressed societies. Preliminary estimates suggest that the aquifer discovered could supply New York for hundreds of years — and similar deposits may exist off the coasts of Africa, Europe, Asia and elsewhere.
Promise and risk
Before considering how to channel this ancient water to land, researchers must first address crucial questions: Where did it come from? Some hypotheses point to glacial meltwater around 450,000 years ago. Others suggest rainwater infiltration during periods of lower sea level. If the water is “young”, the aquifers may still be recharging and renewable. If it is “old”, the supply would be finite. Determining its age is therefore essential for assessing the viability and long-term impacts of exploiting such resources.
There are also biological concerns. “This is a completely new environment, never before studied,” said biologist Jocelyne DiRuggiero of Johns Hopkins University in an interview with AP. She cautions that the water could contain harmful minerals or microorganisms — although similar processes are what form the potable aquifers we already use on land.
These new results stem from the offshore phase of Expedition 501, where sediment and water samples were collected for preliminary analysis. In six months’ time, the onshore phase will follow, bringing the full scientific team together in Bremen, Germany, for further analyses and the first peer-reviewed publications.
Original news source: ZAP.AEIOU, 13 September 2025