Scientists Drill and Sample Massive 'Secret' Freshwater Aquifer Beneath Cape Cod Seafloor
Expedition 501 recovered thousands of samples this summer from a buried freshwater system that may extend from New Jersey to Maine
Scientists aboard a summer research expedition have directly tapped and sampled a large, previously hidden body of fresh water beneath the ocean floor off Cape Cod, a discovery researchers say could expand the palette of supplies available as global freshwater demand grows.
Expedition 501 extracted thousands of samples from pore fluids and cores drilled beneath the salty seafloor and found fresh groundwater in sediments that geologists say were exposed land during the last deglaciation. Scientists on the mission describe the reservoir as part of a massive aquifer system they now think stretches from New Jersey northward as far as Maine.
The work this summer followed an incidental discovery nearly 50 years ago, when a U.S. government research vessel prospecting for minerals and hydrocarbons punctured the seafloor and encountered drops of fresh water beneath salt water. The recent expedition — described by organizers as a first-of-its-kind global research effort to systematically investigate shallow continental-shelf aquifers — returned to the region to drill, map and sample the sediments directly.
"We need to look for every possibility we have to find more water for society," said Brandon Dugan, a geophysicist and hydrologist at the Colorado School of Mines and co-chief scientist of the expedition. The team conducted drilling operations from a liftboat platform and reported collecting thousands of samples that will be analyzed to determine chemistry, volume and the age of the stored water.
The freshwater reservoirs under continental shelves form when rising seas drowned landscapes that were once exposed and connected to terrestrial groundwater systems. As glaciers melted and sea level rose at the end of the last ice age, river networks and groundwater systems became submerged, trapping relatively fresh water within sediment layers now under the ocean.
Scientists say similar "sub-seafloor" freshwater bodies have been identified beneath shallow seas around the world. Those deposits are of interest because perennial surface and groundwater supplies are under increasing pressure from population growth, development and climate change, and because coastal aquifers in many regions are becoming saline.
Researchers caution that the existence of the water does not immediately translate into a ready source for public supply. Key unknowns remain about how much water is present, how fast it can be replenished, its vulnerability to mixing with seawater, and the technical, environmental and legal issues involved in extracting it.
Expedition scientists plan laboratory analyses of the samples to measure salinity, dissolved solids and isotopic signatures that indicate the age and origin of the water. Those measurements will help determine whether the deposits are fossil water — trapped and largely nonrenewable on human timescales — or part of a system that exchanges with continental groundwater and could be replenished.
Efforts to tap submerged aquifers would also face engineering challenges. Drilling through marine sediments and pumping fresh water without drawing in salt water requires specialized well designs and careful management to avoid saline intrusion. Environmental assessments would be needed to evaluate potential impacts on marine ecosystems, sediment stability and coastal hydrology.
The findings add to a growing body of research showing that continental shelves can host substantial freshwater stores. Scientists involved in the Cape Cod work said the next steps include refined geophysical mapping to better delineate the subsurface extent of the aquifer, more targeted drilling to constrain volume estimates, and collaborative studies with coastal managers and policy makers to assess feasibility.
The research team described the Cape Cod region work as a demonstration of methods and the value of revisiting long-standing, anomalous data with modern tools and targeted sampling. As analysis continues, the scientific community and resource managers will weigh whether and how submerged freshwater resources could play a role in addressing local and regional water needs amid mounting supply pressures.