Enormous freshwater reservoir discovered off the East Coast may be 20,000 years old and big enough to supply NYC for 800 years

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A huge “secret” freshwater reservoir off the East Coast may have been formed in the 10th century AD and could have supplied a city the size of New York City for 800 years. the last ice ageWhen the area was covered by glaciers, researchers say.

Preliminary analysis shows that the reservoir, which lies beneath the ocean floor and appears to stretch from offshore New Jersey to Maine, was locked in cold conditions about 20,000 years ago, suggesting it formed during the last glacial period, in part because of thick ice sheets.

Last summer, researchers conducted an expedition to track reports of fresh water beneath the seafloor along the East Coast in the late 1960s and early 1970s. “This is a pretty big project and a lifelong dream of mine,” Brandon Duganthe expedition’s co-chief scientist and a professor of geophysics at the Colorado School of Mines told Live Science.

This research voyage is called Expedition 501Over the course of three months, 13,200 gallons (50,000 liters) of water were dredged from beneath the ocean floor at three locations near Nantucket and Martha’s Vineyard. The results are not yet final, but so far it appears the reservoir may extend further underground than early reports suggested, meaning it could be larger than previously thought.

Duggan and his colleagues also believe they know how the reservoirs formed through preliminary research. radiocarbonnoble gas and isotope analysis, he said.

Freshwater conditions in the area were first reported 60 years ago by the U.S. Geological Survey (USGS) during an offshore mineral and energy resource assessment between Florida and Maine. “They found fresh water in the seafloor sediments in a very peculiar way,” Dugan said. “In the 1980s, some people at the U.S. Geological Survey came up with the idea of ​​how to get fresh water there. And then it went quiet for a while — no one was talking about it.”

In 2003, Dugan and Mark PersonA professor of hydrology at the New Mexico School of Mines and Technology rediscovered the records and Came up with three ideas How fresh water ends up on the ocean floor. One way undersea freshwater reservoirs form is when sea levels remain very low for long periods of time and rainfall seeps into the ground. Then, when sea levels rise again over hundreds of thousands of years, the fresh water becomes trapped in the sediments below, Dugan said.

The second possibility, he said, is that mountains close to the ocean direct rainwater from high-altitude points directly to the seafloor. Third, and related to the first hypothesis, if ice sheets expand, causing sea levels to fall, freshwater reservoirs will form on the seafloor. Meltwater collects at the base of the ice sheet because it rubs against bedrock, generating heat. The immense weight of the ice sheet then pushes the water underground, trapping it beneath layers of sediment.

More than two decades later, researchers are finally getting closer to an answer, with preliminary data suggesting that much of the freshwater came from glaciers sometime during the last Ice Age (2.6 million to 11,700 years ago). “We kind of excluded the big terrain in New England because we don’t have big mountains near the coast,” Dugan said. However, he said “there may be a rainfall component” to the glacier water. “You can imagine that there’s rainfall in front of the glacier, so it’s probably a mixed system.”

Expedition 501 took water samples from sites 20 to 30 miles (30 to 50 kilometers) off the Massachusetts coast. The researchers drilled down to 1,300 feet (400 meters) below the seafloor, deep enough to reveal a thick layer of sediment filled with fresh water, underneath a layer of salty sediment and an impermeable “seal” of clay and silt.

“We have a seal on the top [of the fresh water] Dugan said. Now, this seal is strong enough to separate the two layers, but it’s not strong enough to stop the glacier from forcing water through it – if that’s what happens. “No matter where the water is, it doesn’t matter if there’s a seal. There’s enough energy to flush it with fresh water,” he said.

Salinity measurements show that the freshness of the water in the reservoir decreases with distance from the coast, but in the area studied last summer it was still much lower than ocean salinity. The nearest drilling sites to Nantucket and Martha’s Vineyard have salt levels of 1 part per 1,000, the maximum safe limit for drinking water. Further offshore, the salt content was 4 to 5 parts per thousand, while at the farthest sites the researchers recorded 17 to 18 parts per thousand, about half the average ocean salt content.

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“It’s important that we collect all the samples we need to address the main questions,” Dugan said. “When we finish drilling and pull the equipment out, the hole collapses and seals itself.”

Now, scientists are studying the reservoir in more detail, including microorganisms, rare earth elements, pore space (which can help researchers better estimate the size of the reservoir), and the age of the sediment (which will help narrow down when it was formed). Dugan said clearer results on how and when the reservoir formed are expected in about a month.

“Our goal is to provide an understanding of the system so that when someone needs to use it, they have the information to start, rather than recreating information or making uninformed choices,” he said.