In 2015 we conducted a pilot study of large-scale electromagnetic (EM) surveying of offshore groundwater at locations off New Jersey and Martha’s Vineyard. EM methods remotely measure bulk electrical conductivity, which is strongly a function of groundwater salinity. The large conductivity contrast between sediments containing resistive freshwater and conductive seawater makes offshore aquifers good targets for EM methods. Using equipment designed and built by Scripps Institution of Oceanography, we recorded seafloor magnetotelluric (MT) and controlled-source EM (CSEM) data using 10 receivers deployed at 10 to 20 km spacing. We augmented that with continuous CSEM data recorded by an array of four receivers surface-towed 0.6 to 1.4 km behind the transmitter antenna.
Submarine ground water contained in continental shelves may be a significant global phenomenon, yet little is known about the distribution of these fresh and brackish water bodies. As freshwater resources diminish onshore, characterizing these submarine hydrologic systems will be necessary in understanding the sustainability of coastal freshwater as a resource. Off the US Atlantic coast, a scattering of boreholes has revealed low salinity groundwater, but the limited data do not provide enough information to meaningfully characterize the aquifers.
Rob Evans (Woods Hole Oceanographic Institution)
Funding Source: NSF Award 1458392
Check out these images of the project and the HD drone video of the survey in action: