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Finding Fresh Water Under the Sea

July 14, 2017

WHOI geophysicist Dan Lizarralde points to a real-time image of the seafloor off Martha’s Vineyard, generated by an EK80 echosounder on the research vessel Neil Armstrong. Lizarralde can use the EK80 to look for gas bubbles—possible evidence of fresh water seeping into the ocean from the sediments below. On a previous cruise to the same area, WHOI geophysicist Rob Evans used another instrument to map areas of fresh water underneath the seabed: controlled source electromagnetic (CSEM) sounding. Because fresh water is a poor conductor of electricity, Evans and colleagues can use CSEM to distinguish it from salt water. (Photo courtesy of Evan Lubofsky, Woods Hole Oceanographic Institution)