Core samples from a seabed drill carried out in May as part of IODP's Expedition 501 have verified the presence of a vast reservoir of freshwater under the U.S continental shelf offshore New England, USA.
The freshwater pockets sit 200m below the seafloor, trapped inside layers of 1000-year-old sediment. Scientists estimate there is 1300km3 of "offshore freshened groundwater" between New Jersey and Maine. To put this into perspective, New York City's annual freshwater need is about 1.5km3.
Working as part of the international project, geoscientists from the University of Leicester in the UK and University of Bremen, Germany, analysed the sediment cores form the drill during January and February 2026, documenting for the first time "a freshened water system beneath the ocean floor".
Scientists have thought these offshore systems existed for decades, but they have remained virtually unexplored until now.
Professor Sarah Davies, Professor of Sedimentology and lead of the IODP group at the University of Leicester, said: "Expedition 501 has been innovative from the outset, introducing new tools, new methods, and new collaborations across the ocean drilling community. The onshore operations continue that momentum, and the cores are already revealing an exciting story."
Further analyses by the science team will help find out where and especially when the water became established.
Rebecca Robinson from the Graduate School of Oceanography, University of Rhode Island, USA said the cores contain sediment with a wide range of composition and ages. "It was surprising to see sediment, not rocks, throughout the section. The sediment has not yet transformed into rock – I did not expect to see that, and it will be an interesting component of our future work."
The findings are expected to inform better understanding of offshore freshened groundwater systems off the coast of New England and shed light on similar hidden water aquifers around the world. Many coastal communities depend on land-based aquifers for their freshwater supply.
The cores were retrieved during offshore operations between May and August 2025, using a specially adapted lifeboat, the Montco Offshore-owned 185ft jack-up L/B Robert (above) which was equipped with a small drilling rig. This was used to access the sediments below the ocean floor at up to three locations on the New England Shelf. The three primary sites were drilled in water depths ranging from 40m to 50m and with total penetration depths around 550m.
