Scientists have made a surprising discovery in a new study of the Northeast Coast of the US: a gigantic aquifer of relatively fresh water trapped in porous sediments that lie beneath the salty ocean. It seems to be the largest such formation in the world. The aquifer extends from the shore at least from Massachusetts to New Jersey and stretches more or less continuously for about 80 kilometers to the edge of the continental shelf. If found on the surface, it would create a lake covering about 15,000 square miles. The study suggests that such aquifers are likely to be located off many other shores in the world, providing much-needed water to arid areas that are now in danger of spilling.
The researchers used innovative measurements of electromagnetic waves to map the water, which remained invisible to other technologies. "We knew there were fresh water down there in places, but we did not know the size or the geometry," said lead author Chloe Gustafson, Ph.D. Candidate at the Lamont-Doherty Earth Observatory of Columbia University. "It could turn out to be an important resource in other parts of the world." The study appears this week in the journal Scientific Reports .
The first indications of the aquifer came in the 1970s, when companies drilled oil offshore, but sometimes encountered freshwater. Wells are just pinholes in the seabed, and scientists discussed whether the water resources were just isolated pockets or something larger. About 20 years ago, study co-author Kerry Key, now geophysicist at Lamont-Doherty, helped oil companies develop techniques for underwater electromagnetic imaging in the search for oil. More recently, Key decided to see if any form of technology could be used to find freshwater deposits. In 2015, he and Rob L. Evans of the Woods Hole Oceanographic Institution spent 10 days on the Lamont-Doherty research vessel Marcus G. Langseth, taking measurements in southern New Jersey and Massachusetts Island Martha's Vineyard where scattered holes had encountered newly harvested holes. water rich sediments.
Dropping receivers to the ocean floor to measure the electromagnetic fields underneath and the extent of natural disturbances such as solar winds and lightning strikes. A device pulled behind the ship also emitted artificial electromagnetic impulses and recorded the same reactions from the ground. Both methods work in a simple way: salt water conducts electromagnetic waves better than fresh water, so freshwater stands out as a low-conductivity band. Analyzes showed that the deposits are not scattered. They are more or less continuous and start at the coast and extend far beyond the flat continental shelf – in some cases up to 120 km. For the most part, they begin about 600 feet below the seabed and land on a bottom of about 1,200 feet.
The consistency of data from both study areas allowed researchers to conclude with a high degree of certainty that freshwater sediments cover not only New Jersey and much of Massachusetts, but also the intervening shores of Rhode Island, Connecticut, and New Jersey include York. They estimate that the region contains at least 670 cubic miles of fresh water. If future research reveals that the aquifer extends further north and south, it could compete with the large Ogallala aquifer, which supplies eight Great Plains states from South Dakota to Texas with vital groundwater.
The water is probably in two cases under the seabed passes different species, say the researchers. Between 15,000 and 20,000 years ago, towards the end of the last Ice Age, much of the world's water was trapped in kilometer-long ice. In North America, it stretched across what is now north of New Jersey, Long Island and the New England coast. The sea level was much lower, exposing much of today's US underwater shelf. As the ice melted, sediments formed huge river deltas on the shelf, and fresh water was trapped there in scattered pockets. Later, the sea level rose. So far, trapping such "fossil" water has been the common explanation for any freshwater found under the ocean.
According to new findings, however, the aquifer is also fed by modern underground drains from the sea land. As water from precipitation and waters seeps ashore through sediments, it is likely to be pumped seaward by rising and falling tidal pressure, Key said. He compared this to a person who pressed on a sponge to suck water from the sides of the sponge. In addition, the aquifer near the coast is usually the freshest and saline the farther you are from it. Terrestrial freshwater normally contains less than 1 part per thousand salt, and this is about the value found under water near land. When the aquifer reaches its outer edges, it rises to 15 per thousand. (Typical seawater is 35 per thousand.)
If water were taken from the outer parts of the aquifer, it would have to be desalted for most uses, but the costs would be much lower than when treating seawater, Key said. "We probably do not need to do that in this region, but if we can show that there are large aquifers in other regions that may be a resource," he said. His group hopes to expand the polls.
Scientists discover ancient seawater from the last ice age
Chloe Gustafson et al., Aquifer Systems, which extend well off the coast of the US Atlantic Scientific Reports (2019). DOI: 10.1038 / s41598-019-44611-7
Scientists map giant underwater freshwater aquifer off the northeastern US (2019, June 21)
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