Credit: Kerry Key
In a new survey of the sub-seabed off the Northeast coast of the United States, a discovery has been made by scientists: gigantic aquifer relatively fresh water is trapped in porous sediments lying under salt ocean. This seems to be the greatest form of formation still found in the world. The aquifer extends from the coast from Massachusetts to New Jersey at least, extending longer or less out about 50 miles to the edge of the continental shelf. If found on the surface, it would create a lake covering approximately 15,000 square miles. The study suggests that such aquifers are likely to lie away from many other coasts around the world, and may provide much needed water for arid areas that are in danger of becoming extinct.
The researchers employed innovative measurements of electromagnetic waves to map the water, which remained invisible to other technologies. "We knew there was fresh water there in remote locations, but we didn't know what the geometry was," said leading author Chloe Gustafson, a PhD candidate at Lamont-Doherty Earth Observatory of Columbia University. "It could be an important resource in other parts of the world." The study is featured this week in the magazine Science Reports.
The first tips of the aquifer came in the 1970s, when offshore companies drilled for oil, but sometimes they hit fresh water. The drill holes are only pipes in the seabed, and scientists discussed whether the water deposits were one or more remote pockets. Starting around 20 years ago, the Kerry Key study, now a geophysicist Lamont-Doherty, helped oil companies develop techniques to use the electromagnetic imaging of the seabed to seek oil. Later, Key decided to explore whether some form of technology could also be used to acquire freshwater deposits. In 2015, he and Rob L. Evans spent 10 days from Woods Hole Oceanographic Institution on Lamont-Doherty research vessel, Marcus G. Langseth, measuring New Jersey and Martha Viney Island in Massachusetts, where drilled holes were dispersed. fresh sediment filled with water.
They fell receptors to the seabed to measure electromagnetic fields below, and the contribution of natural disturbances such as solar winds and lightning strikes. An apparatus drawn behind the ship also removed artificial electromagnetic pulses and recorded the same type of reactions from the flask. Both methods work in a simple way: salt water is better water than the fresh water, so the fresh water stood out as a low transport band. Analyzes showed that the deposits are not dispersed; they are more continuous or smaller, starting at the shore and extending outside the shallow continental shelf – in some cases, up to 75 miles. Mainly, they start at about 600 feet below the seabed, and bottom up at about 1200 feet.
Consistency of data from the two study areas enabled researchers to understand that freshwater sediments are continuously spreading not only New Jersey and much of Massachusetts, but intermediate coasts of Rhode Island, Connecticut and New York. They consider that the region has at least 670 cubic miles of fresh water. If future research shows that the aquifer will extend further north and south, the great Ogallala aquifer, which provides vital groundwater for eight states of Great Plains, from South Dakota to Texas, could be extended.
The water under the seabed was probably found in two different ways, tell the researchers. Approximately 15,000 to 20,000 years ago, towards the end of the final glacial age, much of the world's water was locked in a thousand deep ice; in North America, it extended through the one now in northern New Jersey, Long Island and the coast of New England. Sea levels were much lower, reflecting much of the underwater continental shelf in the United States. When the ice melted, huge rivers were deposited on top of the shelf, and fresh water was then caught in scattered pockets. Later, sea levels rose. To date, the common explanation for any fresh water obtained under the ocean has been the capture of this “fossil” water.
However, the researchers say that the new results show that the aquifer is being fed by modern ground run-off from the ground. As water flows from rainfall and water bodies through sediment on the shore, it is likely that it is deposited at sea at the rising and falling tidal pressure, Key said. He compared this with someone who was pushing up and down on a sponge to draw water from the sponge. In addition, the aquifer is generally steeper close to the shore, and the water is sooner outwards, suggesting that it gradually mixes with ocean water over time. In terrestrial freshwater freshwater, less than 1 part per thousand of the salt is usually found, which is the value obtained under the sea close to the land. By the time the aquifer reaches its outer edges, it rises to 15 parts per mile. (35 seawater per thousand is the typical sea water).
Withdrawal of water from the outer parts of the aquifer, it would be to desalination for the most useful, but the cost would be much less than the processing of sea water, Key said. "We probably don't need to do that in this region, but if we can show that there is a great aquifer in other regions, it may be a resource" in places like southern California, Australia, the Mideast or Africa. Sahara, he said. Its group hopes to expand its surveys.
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