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Freshwater Reservoirs Discovered Under the Seabed

New freshwater resources have been found in the most unlikely places. Scientists have discovered vast reservoirs of freshwater submerged beneath the ocean floor, presenting an opportunity to avert an anticipated global water crisis due to increased demand and decreased supply.

In a report that was recently published in the scientific journal, Nature, the scientists estimate that approximately half a million cubic kilometers of low-salinity water lies buried below the seafloor on the continental shelves surrounding many countries around the world.

These freshwater reserves have been found off the coasts of Australia, South Africa, North America and China, and could potentially be used to supplement water supplies of expanding coastal cities in these regions.

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“The volume of this water resource is a hundred times greater than the amount we’ve extracted from the Earth’s sub-surface in the past century since 1900,” says lead author Dr Vincent Post of the National Centre for Groundwater Research and Training (NCGRT) and the School of the Environment at Flinders University. “Knowing about these reserves is great news because this volume of water could sustain some regions for decades.”

Freshwater Aquifers Common In Ocean

While scientist have been aware that freshwater reserves existed beneath the seabed, they initially believed this only occurred on rare occasions under special conditions. However, this research reveals that freshwater as well as brackish aquifers are in fact quite commonly found beneath the seabed. According to Dr Post, these aquifers were formed over the last hundreds of thousands of years, when sea levels tended to be much lower than their present levels and the coastline extended further out to sea. Rainwater that fell to the ground would filter through the soil, filling up the water  table to develop underground aquifers in areas that have since been covered by seawater due to rising sea levels.

“It happened all around the world, and when the sea level rose when ice caps started melting some 20,000 years ago, these areas were covered by the ocean,” explains Dr Post. “Many aquifers were – and are still – protected from seawater by layers of clay and sediment that sit on top of them.”

According to Dr Post, these aquifers are much the same as aquifers found below land, which people all over the world rely on as a source of drinking water, and because they have low salinities, it is entirely feasible for them to be able to provide a source of potable water to surrounding areas. “There are two ways to access this water – build a platform out at sea and drill into the seabed, or drill from the mainland or islands close to the aquifers,” he explains.

These Aquifers Are A Finite Resource

While offshore drilling is typically quite costly, Dr Post notes that this freshwater resource should be considered and assessed in terms of cost, sustainability and environmental impact compared to other water resources such as desalination or building new reservoirs on land.

“Freshwater under the seabed is much less salty than seawater,” Dr Post explains. “This means it can be converted to drinking water with less energy than seawater desalination, and it would also leave us with a lot less hyper-saline water.

“Freshwater on our planet is increasingly under stress and strain so the discovery of significant new stores off the coast is very exciting. It means that more options can be considered to help reduce the impact of droughts and continental water shortages.”

However, while these offshore freshwater sources may offer coastal regions new sources of drinking water to tied them through droughts and other crises, it is important that the seabed is managed effectively to prevent contamination of these resources.

“Sometimes boreholes are drilled into the aquifers for oil and gas exploration or production, or aquifers are targeted for carbon dioxide disposal. These activities can threaten the quality of the water,” cautions Dr Post, who also warns that this source of water is by its very nature non-renewable as they lie buried beneath the seabed and won't be replenished with rainwater until sea levels drop once more, which will not be for a very, very long time.

Journal Reference

Vincent E.A. Post, Jacobus Groen, Henk Kooi, Mark Person, Shemin Ge, W. Mike Edmunds. Offshore fresh groundwater reserves as a global phenomenon. Nature, 2013; 504 (7478): 71 DOI: 10.1038/nature12858
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