Freshwater Reserve Bigger Than Rhode Island Discovered Deep Beneath the Sea

Geologists have announced a rare discovery—a large body of freshwater near Canterbury, New Zealand, that scientists say could offer a brand new supply of water to areas exposed to regular drought.

Researchers describe the newly-discovered offshore freshened groundwater (OFG) system in the journal Nature Communications, after 3D mapping revealed the complex shape of the underwater water body.

"We know of about 30 offshore freshened groundwater systems around the world, but the information we have on these is extremely limited because it predominantly derives from incidental discoveries in scientific or petroleum wells," lead author Aaron Micallef, Geosciences at the University of Malta, told Newsweek. "Our study was the first one to map one in 3D"

In terms of size, the OFG is at least 37 by 44 miles (60 by 70 kilomteres), making it 1,628 miles squared (4,200 kilometers squared) and larger than the state of Rhode Island. But this is just what has been mapped so far and it is likely larger than that, said Micallef.

Micallef's survey shows the OFG between Timaru and Ashburton extends 37 miles (60 kilometers) from the coastline. It is also one of the shallowest OFGs we know of at just 66 feet (20 meters) below the seafloor.

OFGs are important to understand for several reasons. They may provide an archive a past environmental change, Micallef explained, giving one example. But perhaps the biggest motivation for understanding these systems are their potential to be used as a water source.

A combination of growing populations and regular dry spells—brought by climate change—are putting an increased strain on New Zealand's water resources. At the same time, the quality of these resources are declining. Groundwater supplies are becoming increasingly polluted as well as over-exploited.

OFGs like these could provide a buffer and alternative water system in periods of intense droughts like this year's record-breaking dry spell in Auckland. These extreme weather events are only expected to become more common with climate change. According to National Institute of Water and Atmospheric Research (NIWA), parts of the country including Canterbury could spend between 5 and 10 percent more of the year in drought by 2050.

"One of the most important aspects of this study is the improved understanding it offers to water management," Dr. Joshu Mountjoy, a marine geologist at the National Institute of Water and Atmospheric Research (NIWA) in New Zealand, said in a statement. "If you're going to manage the groundwater on shore and near the coast, you need to understand what the downstream limits are."

Next, the team hope to collect samples to understand the system better.

"At the moment we have used remote techniques, modelling and geophysics," said Mountjoy. "We really need to go out there and ground-truth our findings and we are investigating options for that."

Christchurch New Zealand
Stock photo over looking Lyttleton harbour, Christchurch, New Zealand. Geologists have discovered a large body of freshwater larger than Rhode Island in New Zealand. 7Michael/iStock