When you buy through links on our articles, Future and its syndicate partners may earn a commission.
Researchers are finding out how a huge reservoir of fresh water ended up under the ocean off the east coast. | Credit: Anton Petrus/Getty Images
A giant ‘secret’ reservoir of fresh water off the East Coast that could power a city the size of New York City for 800 years may have formed during the last ice agewhen the region was covered by glaciers, researchers say.
Preliminary analyzes suggest that the reservoir, which lies beneath the sea floor and appears to stretch offshore from New Jersey as far north as Maine, was locked in cold conditions about 20,000 years ago, suggesting it formed during the last ice age due, in part, to thick ice sheets.
Last summer, researchers went on an expedition to follow up on reports from the late 1960s and early 1970s of fresh water beneath the seafloor off the East Coast. “It was really a project and kind of a lifelong dream.” Brandon Duganco-chief scientist of the expedition and professor of geophysics at the Colorado School of Mines, told Live Science.
The research trip, known as Expedition 501it took three months and dredged 13,200 gallons (50,000 liters) of water from beneath the sea floor at three locations near the islands of Nantucket and Martha’s Vineyard. The results are not yet complete, but so far it appears that the reservoir may extend further underground than early reports suggested, meaning it could be even larger than previously thought.
Dugan and his colleagues also think they know what created the reservoir because of the preliminary radiocarbonnoble gases and isotope analysis, he said.
Freshwater in the region was first reported 60 years ago by the US Geological Survey (USGS) during assessments of mineral and energy resources offshore between Florida and Maine. “In a very strange way, they found fresh water in the sediments beneath the ocean,” Dugan said. “In the 1980s, some of the USGS guys came up with ideas about how that fresh water could get there. Then it went quiet for a while — nobody was talking about it.”
In 2003, Dugan et Mark the Personprofessor of hydrology at the New Mexico Institute of Mining and Technology, rediscovered these records and he came up with three ideas about how fresh water can get under the ocean. One way a submarine freshwater reservoir can form is if the sea level is very low for a long period of time and rain seeps into the ground. Then, when sea levels rise again over hundreds of thousands of years, that fresh water gets trapped in the underlying sediment, Dugan said.
A second possibility is that tall mountains near the ocean funnel rainwater directly into the seafloor from their high point, he said. And third—related to the first hypothesis—a reservoir of fresh water can form under the ocean if the ice sheets expand, causing sea levels to fall. Meltwater collects at the bottom of ice sheets as it grinds against bedrock, producing heat. The huge weight of the ice sheet then pushes the water into the ground, trapping it under layers of sediment.
More than two decades later, researchers are finally close to an answer, with preliminary data indicating that most of the fresh water came from glaciers sometime during the last ice age (2.6 million to 11,700 years ago). “We kind of ruled out the big topography for New England because we don’t have big mountains near the coast,” Dugan said. However, “there could be a rain component” mixed into the glacier water, he said. “You can imagine that in front of a glacier they have precipitation, so it’s probably a mixed system.”
Expedition 501 extracted water samples from locations 20 to 30 miles (30 to 50 kilometers) off the coast of Massachusetts. The researchers drilled down to 1,300 feet (400 meters) below the sea floor, which was deep enough to reveal a thick layer of sediment filled with fresh water sitting beneath a layer of salty sediment and an impermeable “seal” of clay and silt.
To extract water samples, researchers drilled the seabed at three locations near Martha’s Vineyard and Nantucket. | Credit: Rainer Lesniewski/Getty Images
“We have a seal at the top [of the fresh water] that keeps the seawater on top of the fresh water below,” Dugan said. That seal is strong enough to separate the two layers now, but it wasn’t strong enough to prevent a glacier from forcing water through it — if that happened. There was enough energy to flush it out with fresh water,” he said.
Salinity measurements showed that the freshness of the water in the reservoir decreases with distance from shore, but remains well below ocean salinity in the areas studied last summer. The drill site closest to Nantucket and Martha’s Vineyard had a salt content of 1 part per 1,000, which is the maximum safe limit for drinking water. Farther out to sea, the salt content was 4 to 5 parts per 1,000, and at the farthest point, the researchers recorded 17 to 18 parts per 1,000 — or about half the ocean’s average salt content.
RELATED STORIES
— The 1.2 billion-year-old groundwater is one of the oldest on Earth
— Scientists discover enormous reservoir hidden in Cascades – more than twice the amount of water in Lake Mead
— Enough fresh water is lost from the continents each year to meet the needs of 280 million people. Here’s how we can combat it.
“The important part was that we collected all the samples we needed to answer our main questions,” Dugan said. “When we finish drilling and remove the equipment, the holes collapse back and seal.”
Now scientists are studying the reservoir in more detail, including any microbes, rare earth elements, pore space — which can help researchers better estimate the size of the reservoir — and the age of the sediments, which will help narrow down when it formed. More definitive results about how and when the reservoir formed are expected in about a month, Dugan said.
“Our goal is to provide an understanding of the system so that if and when someone needs to use it, they have information to start from, rather than recreating information or making an ill-informed choice,” he said.