What do Earth's magnetic fields tell us about warming oceans?

Originating in our planet's core and ballooning out into space, the Earth's magnetic field has long kept humans safe from charged particles and deadly radiation, and it turns out it might also know a thing or two about our future well being. By tracking deviations in the field as it passes through the ocean, scientists say it is possible to gauge the temperature changes in the sea, helping to fill in important detail about how our planet is responding to global warming.

Much of the warmth we are adding to the Earth system is absorbed by the ocean – as much as 90 percent according to Tim Boyer, a scientist at the National Oceanic and Atmospheric Administration's National Centers for Environmental Information. Rising temperatures in the sea can have all sorts of consequences for the life within, such as coral bleaching, but tracking how much we are cranking up the heat isn't all that straightforward.

Currently, scientists track ocean temperatures through ship measurements, a global network of drifting monitoring stations called Argo floats, and even tagged, free-roaming seals. Even so, the picture of temperature changes in this huge environment is far from complete.

"Even with the massive effort with the Argo floats, we still don't have as much coverage of the ocean as we would really like in order to lower the uncertainties," says Boyer. "If you're able to measure global ocean heat content directly and completely from satellites, that would be fantastic."

Such an approach may well be possible, thanks to a combination of geophysical features and some clever thinking on part of scientists at NASA's Goddard Space Flight Center.

The concept begins with the fact that seawater conducts electricity. This means that as it moves around the ocean, it actually sways the magnetic field lines running from the Earth's core out into space. And because the conductivity of the water is influenced by its temperature, scientists believe it is possible to use satellite data to monitor these fluctuations and pin down how much the ocean might be warming.

The scientists are presenting a proof-of-concept study at the American Geophysical Union in San Francisco this week, demonstrating that with some computer modeling, temperature measurements can be drawn from these shifting magnetic signals. The technique is still in its early stages, however, with the researchers keen to iron out some sizable kinks in the modeling, such as identifying fluctuations caused by other ocean movements like eddies. But with further refinement, the researchers hope that the technique can come to offer a way to track global ocean temperatures across all depths.

"Even with the massive effort with the Argo floats, we still don't have as much coverage of the ocean as we would really like in order to lower the uncertainties," Boyer said. "If you're able to measure global ocean heat content directly and completely from satellites, that would be fantastic."

The animation below offers a brief overview of the approach.

Source: NASA / Video: NASA's Goddard Space Flight Center/Matthew Radcliff