Huge water reservoir under the seabed

Sour water aquifers off the US east coast could be one of the largest in the world

Off the northeastern coast of the US, a huge freshwater repository is hidden under the seabed, as geologists have discovered. © Liran Sokolovski / iStock
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Surprising find: Geologists have discovered one of the largest groundwater reservoirs in the world - off the eastern coast of the US - under the ocean floor of the Atlantic Ocean. The aquifer extends up to 90 kilometers into the sea and is at least 350 kilometers wide. It is estimated that this undersea water reservoir contains at least 2, 800 cubic kilometers of fresh water - more than Lake Victoria. Similar aquifers could lie undetected before other coasts, the researchers suspect.

Drinking water is a scarce commodity - especially where it rains little. Because many groundwater reservoirs are already overused, others are already at shallow depths brackish or salty. Pesticides, fertilizers and chemicals are also increasingly contributing to the loss of clean water resources. In addition, researchers estimate that most groundwater supplies are thousands of years old. Only six percent of the world's aquifers regenerate relatively quickly and regularly.

The yellow-hatched area shows the likely extent of the newly discovered aquifer. © Gustafson et al./ Scientific Reports, CC-by-sa 4.0

Fresh water under the seabed

However, as it turns out, unrecognized drinking water reservoirs could be concealed unexpectedly: off the coast of the continents. The first evidence of this was found in the 1970s, when scientists discovered exploratory drilling off the US east coast of Søwasser instead of Erd l. "We knew there were some seepage down there, but we did not know the scale or the distribution, " says first author Chloe Gustafson of Columbia University in New York.

To find out more about this seepage under the seabed, Gustafson and her colleagues have now mapped the shelf area off New Jersey and Massachusetts with electromagnetic measurements. "These methods record the electrical conductivity, which in the offshore sediments is determined by the porosity and salinity of the pore water, " explain the researchers. Subterranean sanitary deposits therefore appear in the measured data as less conductive layers.

More fresh water than in the largest reservoirs on land

The surprising result: beneath the ocean floor of the Northwest Atlantic, there are not only isolated sewer inclusions, but an extensive reservoir. This extends from the coast at least 90 kilometers far out into the sea and forms below 180 meters depth a layer of about 200 meters thick. "The aquifer spans from the coast of New Jersey to Martha's Vineyard, and most likely will extend far beyond our study area, " the researchers said. display

The scientists estimate that the total aquifer could contain at least 2, 800 cubic kilometers of water - more than the volume of Lake Victoria in Africa. "If we consider the potential extent of this aquifer beyond our coverage area, there could be more groundwater below this part of the Atlantic continental shelf than in the largest groundwater reservoirs on land, " say Gustafson and your team.

At least part of the water probably flows from the coast into the aquifer. Af Gustafson et al./ Scientific Reports, CC-by-sa 4.0

Stream from the coast and Ice Age relic

Measurements have shown that the water in this submarine reservoir contains almost less than one tenth of salt it is almost pure fresh water. Off the coast, the aquifer water is a bit saltier. With a salt content of less than 15 per thousand, however, its salinity is still well below that of normal seawater with around 35 per thousand. The researchers suspect that at least part of this water flows underground from the coast below the seabed.

However, another part of this subsea sewer could be of much older origin: at the peak of the last ice age, some 20, 000 years ago, the Laurentide Ice Sheet covered much of North America, reaching to the present day flooded areas of the continental shelf beyond. As the glaciers melted and sea levels rose, parts of the meltwater were trapped in sinks and remained underneath the seabed, as the researchers explain.

Submarine aquifers elsewhere too?

The newly discovered aquifer under the seabed may not be an isolated case: Gustafson and her team suspect that such freshwater reservoirs could also hide from other coasts. "If we can prove that such large aquifers exist in other regions, such as California, Australia, the Middle East or the South of Africa, these reservoirs could be a valuable resource, " says Gustafson's colleague Kerry Key. (Scientific Reports, 2019; doi: 10.1038 / s41598-019-44611-7)

Source: Earth Institute at Columbia University

- Nadja Podbregar