Wind creates waves on the surface of the Gulf of Maine. Photo: Gregory Rec/Portland Press Herald via Getty Images

Researchers have for the first time mapped an aquifer under the ocean, suggesting it and other water systems could be a new source of freshwater supply.

Details: The newly mapped aquifer is located off the East Coast, stretching from near Martha's Vineyard to the waters off Long Island and New Jersey.

The big picture: Millions of people face greater water stress from population growth, groundwater depletion and climate change. While the brackish water described in the study, published in Scientific Reports, would need to be desalinized before consumption, it would not require the energy-intensive process currently undertaken in some countries, such as Israel.

What they did: The researchers used new electromagnetic methods typically employed for mapping offshore oil and gas resources.

  • They deployed receivers to the seafloor to measure the electromagnetic fields below, and also towed a device behind the ship that emitted electromagnetic pulses and recorded the seafloor's responses to them.
  • Because saltwater is a better conductor of electromagnetic waves compared to freshwater, the aquifer showed up as a clear band of low conductance.

What they found: An aquifer system located within porous rock formations extending from the shoreline to about 50 miles off the coast of both survey locations.

  • The researchers note it may extend well beyond the study region, and the aquifer could be one that "rivals the largest onshore aquifers."
  • The aquifer isn't a trapped underground lake that can simply be tapped into like a straw, says lead author Chloe Gustafson, also of Columbia University. Instead, "it's more like a water-soaked sponge," she says.
  • This aquifer spans nearly 220 miles of the Atlantic Coast from end to end, and could hold at least 670 cubic miles of low-salinity groundwater.

The backstory: It's thought the groundwater originated during the end of the last glaciation, some 15,000 to 20,000 years ago, when sea levels were lower and mile-thick ice sheets retreated.

  • The glacial runoff formed offshore deltas, and eventually trapped pockets of water underneath them.
  • In a surprising finding, the researchers say the aquifer is also likely receiving some freshwater from the land via subterranean runoff, which raises the possibility it may be recharged over time.

The scientists had an inkling they would find groundwater in some of these areas based on previous pinprick-like drill holes that had been made to search for oil or study geological history in these locations.

  • Those boreholes had detected water's presence.
  • "It's like the difference between seeing a few pixels of an image (i.e. point drill hole measurements) and trying to infer what the image is, versus looking at a high resolution scan of the whole image...," study co-author Kerry Key of the Lamont-Doherty Earth Observatory at Columbia University told Axios in an email.

Between the lines: A 2012 study found freshwater aquifers likely are present in Outer Continental Shelf regions of every continent. That finding combined with the new results could spur more surveys to search for tappable offshore groundwater reserves.

  • However, like groundwater on land, this water should be treated more like a savings account that can be quickly depleted.
  • Also, because the water lies within porous rocks, the geological consequences of pumping it out would need to be studied.

The bottom line: “The big thing that we want people to know is that this isn’t just an isolated incident off the coast of New Jersey and Martha's Vineyard,” Gustafson says.

While the brackish water contained in such an aquifer would need to be desalinized before consumption, it would not require the energy-intensive desalinization currently undertaken in some countries, such as Israel.

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