Electric oceans change the magnetic field on Earth

Salty oceans actually have an impact on the Earth's protective magnetic field. It's tiny and hard to measure. But this has now been done with great precision by the European Swarm Satellites. 

It’s small and difficult to detect. But it’s there and scientists can now map the intriguing contribution of the oceans movements to the Earth’s magnetic field very precisely by using measurements from the European Swarm satellites. This provides new insight on the structure and composition of our planet and might be of practical use too.

Oceans might not be thought of as magnetic, but they actually do make a tiny contribution to our planet’s protective magnetic shield. With the help of the three Swarm satellites operated by the European Space Agency (ESA) scientists have now measured this faint field and discovered new features about the electrical nature of the Earth.

“Using the Swarm satellites we have been able to map Earth’s magnetic field much more precisely than ever before. Which in turn also gives us a more precise picture of the oceanic contribution”, said Rune Floberghagen Swarm Mission Manager at ESA.

By far the largest part of Earth’s magnetic field originates from Earth’s deep interior. This field shields us from harmful radiation and charged particles from the Sun bombarding Earth.

It is well known that there is also a small contribution to this shield from movement of seawater through the Earth’s magnetic field. A small electric current is generated when the salty and electrically conducting ocean water is pushed by the tides and hence moves in the main magnetic field. This current induces an even weaker secondary current in Earth’s crust and creates a field which contributes to the Earth’s magnetic field.

But to measure the tiny contribution from the oceans precisely is much harder.

“The magnetic field is constantly changing and including these weak contributions is important for the precise mapping of the upper part of Earth. We are now able to do this for the whole oceanic regions. This information is useful for scientific work, but could also be of practical use in search for oil and gas for example” said Rune Floberhagen.

The new results have just been published by Swarm scientists in the reputed journal Science Advances.

It is not the first time the oceans magnetic contributions have been measured and mapped from space. But this is the first study that uses this information to probe the Earth’s interior.

Thanks to Swarm’s precise measurements along with those from the former CHAMP mission also measuring Earth’s magnetic field scientists have also been able to image the electrical nature of Earth’s upper mantle some 250 km below the ocean floor and gain new knowledge about the interior of the Earth.

Just below the rigid outer part of the earth, the lithosphere, lies the asthenosphere which is hotter and more fluid than the lithosphere. The new research showed a sharp increase in electric conductivity at about 72 km depth. This might be a boundary between the colder lithosphere on top and the hotter asthenosphere beneath.

“These new results are important for understanding plate tectonics, the theory which argues that Earth’s lithosphere consists of rigid plates that glide on the hotter and less rigid asthenosphere that serves as a lubricant, enabling plate motion”, said Alexander Grayver from the Swiss Federal Institute of Technology in Zurich and leading author of the work published in Science Advances.

Facts: The magnetic field of the Earth

Earth’s magnetic field is created mainly by movements of molten iron in the outer core of Earth more than 3,000 km beneath our feet. In addition there are contributions from magnetized rocks in the Earth’s crust and from other sources such as the ocean tides. It’s uncovered since long that the magnetic field originates in different parts of Earth and that each source generates magnetism of different strengths. But it’s still not fully understood exactly how the main part is generated and why it changes and weakens as is the case at the moment.

Full bibliographic information

Satellite tidal magnetic signals constrain oceanic lithosphere-asthenosphere boundary.
Alexander V. Grayver et al.
Science Advances 30 Sep 2016: Vol. 2, no. 9, e1600798. DOI: 10.1126/sciadv.1600798.
Attached files
  • 1: The different sources that contribute to the Earth magnetic field measured by Swarm. The coupling currents or field-aligned currents flow along magnetic field lines between the magnetosphere and ionosphere. Sea tides contribute to creating a field in the Earth's crust which in turn contribute to the general magnetic field aorund the Earth. (Credit: ESA/DTU Space)
  • 2. The Earth's magnetic field and electric currents in and around Earth generate complex forces that have impact on every day life. The field can be thought of as a huge bubble, protecting us from cosmic radiation and charged particles that bombard Earth from solar winds. It's this field that makes a compass point north. (Credit:ESA/ATG medialab)

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