The monitoring of ocean currents is of primary importance for understanding sea water quality, climate change and the global CO2 budget. Currently, global monitoring of ocean currents relies mainly on satellite radar measurements of the dynamic sea surface height. From two years of high precision CHAMP satellite magnetic measurements it has now been found possible to map the magnetic signal of ocean tidal flow. Movement of the highly conductive sea water through the Earth's magnetic field induces electric fields and currents, similar to a dynamo. The electric currents generate secondary magnetic fields which have been identified in the CHAMP satellite data. See:
Science, January 10, 2003, Volume 299, pp. 239-241.
Apart from opening new opportunities in the monitoring of ocean flow, the inclusion of ocean flow magnetic fields in our geomagnetic field modeling will raise the detectability of small scale crustal magnetisation.