Fresh water under the sea

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Under the seabed, scientists discovered a huge reservoir of drinking water near New Zealand. The underwater field is 250 meters wide and extends 60 kilometers into the sea. It stores up to 200 cubic kilometers of fresh water, seismic measurements and conductivity surveys. Therefore, this reservoir can be a valuable source of drinking water for one of New Zealand’s driest terrain. Fresh water in many regions is a scarce good. Many reservoirs and groundwater reservoirs are depleted, and harmful substances and saltwater impurities make the water unusable in some places. However, a few years ago, studies found that there are other reservoirs of freshwater on the Earth – seabed deposits. Such aquifers have already been identified by scientists near the American east coast, as well as off the coast of Suriname and Jakarta.

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Another underwater reservoir of fresh water has now been discovered by Aaron Micallef of the University of Malta and his colleagues in front of the South Island of New Zealand. The first proof of its existence was provided by the International Ocean Discovery Program (IODP), in which certain layers showed surprisingly low salt content.

To continue the study, scientists systematically studied the area in front of Canterbury Bay. They used the results of seismic measurements and conductivity surveys.

Analyzes have shown that beneath the surface of the shallow continental shelf in Canterbury Bay is a stretched reservoir of fresh water. “Drinking water is precipitated just 20 meters below the seabed, making it one of the smallest reservoirs in the world,” explained Mikafle. “It stretches 60 kilometers into the ocean and is up to 250 meters wide.”

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Changes in the coastal zone with freshwater reservoirs from the ice age to the present. Image: MARCAN Project.

More detailed measurements revealed that this underwater tank consists of a wedge-shaped main part and two smaller tanks. The quality of the water contained in it is close to drinking water, but farther from the shore, the water becomes more salty.

“In total, this water tank holds up to 200 cubic kilometers of water,” said Mikafle. So this field is slightly larger than the aquifer off the coast of New England, and almost half as large as the one found near New Jersey. “Our measurements revealed a large and fresh water body, as might be expected from wells and simulations,” the scientist said. “This source could potentially provide drinking water to one of New Zealand’s driest regions.”

But how did drinking water get under the seabed? Geochemical analyzes of the cores have shown that part of this reservoir is formed by rainwater flowing over the country. The water seeps into the groundwater and falls through the water layers to the seabed. Part of this water is still being replenished through precipitation.

However, most of the reserves of this freshwater deposit have been here since the Ice Age, scientists said. At that time, sea level was over 100 meters lower than it is today, so part of the continental shelf was visible as land. When it was raining, the water leaked underground and filled the water layers. Then they were covered with clay and sediment, which was later protected by the seawater.

According to Mikalaf and his colleagues, the combination of methods they used can be used to find hidden sources of drinking water off the coast. “The new approach we have developed can be surprisingly detailed in freshwater systems beyond land,” explained co-author Marion Jegen of the GEOMAR Helmholtz Center for Ocean Research.

Scientists suggest that data on the presence and volume of such water reservoirs, which were made earlier, will need to be lifted. “So far, the amount of groundwater recovered from the continental horizons since 1900” has been estimated at 100,000 cubic kilometers, 100 times more than scientists say.

But these estimates are based largely on findings from passive continental borders and well data. Systematic mapping of offshore shelf areas may reveal even more such fresh water reservoirs.

Source:  zbruc



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