It’s common knowledge that the Earth has a magnetic field. It protects us from outer space particles that could be detrimental to life on earth. But now scientists have also found that the Earth’s oceans have a magnetic field of their own. Indeed, this oceanic magnetic field is 100 times weaker than that of the earth’s crust and 20,000 times weaker than the global magnetic field.
The oceans of the Earth, because they contain salt, conduct electricity. When this salt water moves in the Earth’s magnetic field, it is then traversed by a small electric current, as stipulated by Faraday’s law.
This “mobile” electric current –extremely weak — in turn generates a magnetic field. The latter is very weak, 20,000 times weaker than the global magnetic field induced by the movements of liquid iron within the nucleus, which attracts the needles of compasses. Nonetheless, it is still measurable.
The constellation of European satellites Swarm has made it possible to draw the finest map ever made to date of this magnetic field. It was unveiled Tuesday at the annual conference of the European Union of Geosciences, held in Vienna, Austria. In it is shown a periodic variation of the field’s intensity, with a reversal of its polarity, which coincides with the lunar cycles, ie every 12.5 hours.
“We used Swarm to measure the tidal magnetic signal from the ocean surface to the ocean floor, giving us a complete picture of how the oceans flow, at all depths, which is new, “says Nils Olsen from the Technical University of Denmark. “As oceans absorb the heat contained in the atmosphere, tracking the way this energy is redistributed and stored in the ocean, especially at depth, is very important for better understanding climate change.”
The satellite trio of the European Space Agency has also produced the most accurate map to date of magnetism induced by the magnetic rocks of the Earth’s crust and upper mantle. This field is 200 times more intense than that induced by the oceans, but 100 times less than the global field that protects our planet from solar winds. Without this magnetic protection, our atmosphere would have been long blown by the continuous flow of charged particles that bombard everyday.
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