Offshore fresh groundwater reserves as a global phenomenon

The flow of terrestrial groundwater to the sea is an important natural component of the hydrological cycle. This process, however, does not explain the large volumes of low-salinity groundwater that are found below continental shelves. There is mounting evidence for the global occurrence of offshore fresh and brackish groundwater reserves. The potential use of these non-renewable reserves as a freshwater resource provides a clear incentive for future research. But the scope for continental shelf hydrogeology is broader and is is envisaged that it can contribute to the advancement of other scientific disciplines, in particular sedimentology and marine geochemistry. A new article in Nature by Vincent E.A. Post, Jacobus Groen, Henk Kooi, Mark Person, Shemin Ge and W. Mike Edmunds. 

2013.12.09 Post»The existence of vast freshwater reserves trapped beneath the ocean floor could sustain future generations as current sources dwindle. Lead author Vincent Post, from Australia’s Flinders University, said that an estimated 500,000 cubic kilometres (120,000 cubic miles) of low-salinity water had been found buried beneath the seabed on continental shelves off Australia, China, North America and South Africa.

“The volume of this water resource is a hundred times greater than the amount we have extracted from the Earth’s sub-surface in the past century since 1900”, said Vincent Post. His team’s findings were drawn from a review of seafloor water studies done for scientific or oil and gas exploration purposes. “By combining all this information we have demonstrated that the freshwater below the seafloor is a common finding, and not some anomaly that only occurs under very special circumstances”, he said. The deposits were formed over hundreds of thousands of years in the past, when the sea level was much lower and areas now under the ocean were exposed to rainfall which was absorbed into the underlying water table. When the polar icecaps started melting about 20,000 years ago these coastlines disappeared under water, but their aquifers remain intact — protected by layers of clay and sediment. Post said the deposits were comparable with the bore basins currently relied upon by much of the world for drinking water and would cost much less than seawater to desalinate. Drilling for the water would be expensive, and Post said great care would have to be taken not to contaminate the aquifers. He warned that they were a precious resource which should be used carefully, as once gone, they will not be replenished until the sea level drops again, which is not likely to happen for a very long time.«