Nearly all of Earth’s freshwater--some 97 percent--consists of groundwater. Yet surprisingly little is known about the movement of all that water. In particular, no one has carefully measured how much of it enters the sea. Willard Moore, a geochemist at the University of South Carolina in Columbia, has addressed that oversight. He has found that more groundwater reaches the oceans than anyone suspected.
Most groundwater nestles in underground pores in rock layers that may be thousands of feet thick. This water leaks into the sea primarily in two ways: either as coastal springs bubbling directly into the sea or by a process called tidal pumping. At high tide, salt water, which is denser than freshwater, washes into groundwater-saturated sediments on the continental shelf; when the tide ebbs, the brackish seawater and groundwater mixture is sucked into the ocean. New groundwater then flows into the sediment and is pumped out with ...
