Searching for fresh water beneath the ocean floor

In the 1960s, scientists analyzing marine data stumbled upon a surprising discovery: vast reservoirs of fresh or “freshened” water sitting beneath the ocean floor. For decades, the existence of these offshore aquifers remained an intriguing, unexplored anomaly. How did the water get there, and how long has it been there?

An ambitious international exploration co-led by Brandon Dugan, professor and associate department head of geophysics at Mines, is finally bringing those answers to the surface. After completing a landmark offshore drilling phase in summer 2025, the team is closer than ever to unlocking the mysteries of these hidden sub-seafloor water systems.

The project

The initiative, known as Expedition 501 “New England Shelf Hydrogeology,” is a groundbreaking collaboration between the International Ocean Drilling Programme (IODP3) and the U.S. National Science Foundation (NSF). Its primary goal is to investigate the hydrogeology of the New England Shelf, a region offshore from Massachusetts where preliminary surveys suggested the presence of significant freshwater reserves, and understand this offshore aquifer system.

The key priority for researchers is to gain more knowledge about the origin of freshened groundwater in offshore aquifers so that they can confirm or dismiss the existing hypotheses. For example, current hypotheses are that the water could have charged the aquifers at a time when sea-level was 100 meters lower than it is today, or perhaps it was generated under an ice sheet or pro-glacial lake during a glacial period such as existed approximately 450,000 and approximately 20,000 years ago.

“To date, we know very little about the dynamics of these shoreline-crossing groundwater systems and the age of the water in these systems, and even less about their influence on cycling of nutrients and trace elements and their isotopes,” said Karen Johannesson, a professor of geochemistry at the University of Massachusetts Boston and co-lead on the project.

The expedition launched in May 2025 aboard a specialized platform, the liftboat L/B Robert, equipped with a small drilling rig. Over the course of 74 days, the team executed a complex operation to recover water and sediment samples from depths of up to 550 meters below the seafloor.

By the time the offshore phrase wrapped up in August 2025, the mission had exceeded expectations. The team successfully collected 718 cores totaling nearly 872 meters of material from three distinct locations. The expedition also conducted groundwater pumping tests—a first for scientific ocean drilling—which allowed researchers to capture water samples directly from sandy aquifers and clayey aquitards.

”We set out with lofty goals to understand the origin and age of this offshore freshened groundwater system through sampling of sediment and water in a difficult drilling environment consisting of sand and mud. With great teamwork among the science team, the technical staff and the drilling crew, we managed to get great samples including through multiple groundwater pumping tests,” Dugan said. “Those tests were critical to the expedition and a first for scientific ocean drilling. And we did it! Now we have the samples for the science team to really dive into the data and understand the system, which will be helpful for understanding other offshore freshened groundwater systems around the world.”

The research team

The project is a large global undertaking, involving 41 science team members from 13 nations, including Australia, China, France, Germany, India, Italy, Japan, the Netherlands, Portugal, Sweden, Switzerland,
the United Kingdom and the United States. Dugan leads this group, serving as co-chief scientist alongside Johannesson.

With the offshore operations complete, the scientists will reconvene in early 2026 at the Bremen Core Repository at the University of Bremen in Germany to split, sample and analyze the sediment cores and water collected during the summer voyage. The collected cores will also be archived and made accessible for further scientific research after a one year-moratorium period. All expedition data will be open access in the IODP³ MSP data portal in PANGAEA, and resulting outcomes will be published.

The impact

Seventy percent of the Earth’s surface is covered with water, but water also flows beneath its surface. Most coastal communities rely on traditional onshore aquifers for freshwater, however, in many locations worldwide onshore aquifers may have an offshore component where freshened water exists under the ocean floor. The findings from the expedition could be critical for coastal communities worldwide. With strain on traditional freshwater sources, offshore aquifers could represent a vital new supply.

The team believes that the data acquired will help to better understand the processes that lead to the emplacement of freshwater lenses in offshore coastal plain sediments and why this freshened water is present. The findings will be relevant for the hydrogeology of the New England Shelf and for multiple similar settings elsewhere around the world.

The research is essential for a better understanding of the biogeochemical and elemental cycles in the continental shelf environment and will support a focus on the protection and sustainable management of offshore freshwater systems.

“It is exciting to use established scientific ocean drilling approaches with modern data analyses to provide direct tests of our hypotheses,” Dugan said. “Overall, this work offshore New England will help us better understand offshore freshened groundwater around the world.”