It’s been about 50 years since researchers first discovered fresh water deep below the ocean floor. But the undersea aquifer off Cape Cod hasn’t been studied until now.
This summer an international team of scientists drilled three test wells over a thousand feet below the ocean floor, south of Nantucket. The goal of Expedition 501 was to tap into an undersea aquifer to learn more about the water trapped there. Scientists hope testing the samples will reveal how old the water is, how salty it is, and what types of microbes are swimming around in it.
Brandon Dugan is a co-chief scientist on the expedition.
“There's lots of samples that have gone to labs all over the world where people are looking at the age of the water,” he said. “There's other samples that have gone to four labs around the world looking at what the biology is doing there.”
Dugan said undersea aquifers like this exist off every continent, but we know very little about them. And countries that experience drinking water shortages are paying close attention.
Mark Person is Hydrology Team Lead for the project. His involvement in this research goes back to 1991, when he began studying the hydrogeology of Nantucket. He said this aquifer was likely formed over 20-thousand years ago, when sea level was 120 meters lower than today, and Nantucket Sound was all dry land.
“It's likely that that water is quite old,” said Person, “that it's beyond 20,000 years old and maybe up to a million years old.”
Those answers will come as the samples are tested. Carbon 14 dating will be able to determine ages between one thousand and fifty thousand years. Crypton 81 can date older water – up to a million years. The age of the water will help determine how it got there, and if it’s connected to the aquifers that supply our drinking water.
Rob Evans is a senior scientist in the department of Geology and Geophysics at Woods Hole Oceanographic Institution. He says that last point is important.
“We need to know really carefully, in some level of detail, how those water bodies connect to our terrestrial system – if they do,” said Evans. “We don’t really even know that.”
About ten years ago Evans helped map the underwater aquifer off Cape Cod using electromagnetic methods that measure how well the seafloor conducts electricity.
“Which is a really good technique for finding areas of freshwater verses salt water, because saltwater conducts electricity really well, fresh water doesn’t,” he explained. “And so, we can use this geophysical technique to map out these areas of buried fresh water in the subsurface.”
That work informed this summer’s drilling.
Dugan, the Exhibition 501co-chief scientist, says most of the samples collected this summer contained brackish water – with salinity somewhere between fresh and seawater.
“We know that we have a significant volume of brackish water,” he said. “We do have documentation of some water that we sampled that was less than one part per thousand salinity, which would qualify as fresh water.”
And he noted, “But there is a lot of water out there that is not seawater, which is pretty exciting.”
Dugan said the bulk of the sample cores are headed to the University of Bremen, in Germany, where an international team of scientists will gather to analyze them in early 2026. After a year, the samples will be available for anyone to examine.
“Our goal is to explain the science and then let other scientists and other citizens use those data for whatever they want as well,” Dugan said.
Hydrologist Mark Person says there is international interest.
“The UN states that by 2030, two-thirds of the population will experience water shortages and they're now embracing unconventional water resources and unconventional aquifers like this. But it's controversial,” he said.
Controversial because there is so much about these systems that is still unknown, including if the aquifers are all ancient water, or if they are being replenished. And controversial because tapping a finite resource, no matter how vast, is not sustainable.
Nonetheless, Person and Dugan believe that this type of water aquifer will be tapped, somewhere, within the next few decades.
