When electrically charged particles move through a magnetic field an electrical field is developed that is perpendicular to the movement of the particles. This has been known since the pioneering experiments of James Maxwell in the mid-1800s. The same physics dictate that when ions in seawater are advected by ocean currents through the magnetic field of the Earth, an electric field is produced perpendicular to the direction of the water motion. Because seawater is a conductive media, these electric fields "short-out" in the vertical, yielding a single electric field corresponding to the vertically averaged horizontal flow (with a minor vertical weighting effect due to small conductivity changes at different depths). Submarine cables provide a means for measuring these "motionally-induced" voltages in the ocean. Using the voltages induced on the cables, the full-water-column transports across the cable can be estimated.... MORE
Since 1982 cables have been used to measure the transport of the Florida Current between Florida and the Bahamas near 27°N. Geomagnetic data from the San Juan, Puerto Rico, Fredricksburg, Virginia and Stennis, Mississippi magnetic observatories have been used during different segments of this time period to remove the magnetic field fluctuations from the voltage data.
Details of the history of cable measurements in the Florida Current can be found in Larsen, 1992. Most recently, a cable between West Palm Beach, FL and Eight Mile Rock, Grand Bahamas Island has been used. These measurements continued until October 1998, when this cable was retired from telephone service and replaced by a cable between Vero Beach, FL and Eight Mile Rock, Grand Bahamas Island. When the first cable was retired, it was grounded at West Palm Beach with the expectation that voltages could be recorded only at the other end.... MORE