The north magnetic pole shifts constantly, in loops up to 80 kilometers (50 miles) wide each day.
The recorded location of the pole is really an average of its daily treks, which are driven by fluctuations in solar radiation.
The pole is currently at about 80º north latitude and 104º west longitude, in the Canadian territory of Nunavut.
Importance of the Pole
Pinpointing the precise location of the north magnetic pole is important for navigation: As you move closer to the pole, the direction north indicated by your compass becomes less accurate.
The pole also plays a role in the Northern Lights, which form when solar radiation bounces across the magnetic field in the upper atmosphere. As the north magnetic pole drifts, it will take the Northern Lights with it.
But for scientists, studying the field provides a tantalizing glimpse into the fiery center of the Earth.
The planet's outer core of molten iron spins constantly, acting as a giant dynamo, or electromagnet.
This energy interacts with the rocky mantle of the Earth, which is also shifting, resulting in a complex, ever-changing magnetic field.
"We're close to having a much better understanding on how the field fluxes," Stoner said.
The first readings of the north magnetic pole date to 1831, when Sir John Ross and his ship searching for the Northwest Passage became ice-bound.
To pass the time he sent out a team with a compass to take readings, and the team soon found a dipolean area with compass readings pointing both north and southin what is now Nunavut. It was the north magnetic pole.
While historical readings date back almost two centuries, Stoner's team wanted to take a deeper look into the past.
They went to the Arctic and pulled 4.5-meter-long (15-foot-long) cores of mud and clay from the bottom of frigid lakes.
Each year, snowmelt deposits a layer of silt at the bottom of the lakes, which is then covered with a layer of clay. "There are these distinct couplets every year," Stoner said. "It's a lot like counting rings in a tree."
Back at his laboratory at Oregon State University, Stoner and his team sliced the cores into thin sections.
They then ran each section through an instrument that reads tiny magnetic particles in the silt to reveal both the direction and intensity of the magnetic field.
Each section comprises five to ten layers, or five to ten year's worth of magnetic readings.
"We can't get down to the yearly scale yet," Stoner said, "but that's getting to be a pretty tight resolution."
In contrast, similar techniques used to measure magnetism in rock have yielded much coarser resolutions of thousands to tens of thousands of years.
Besides recording the movement of the pole, the silt cores also show a recent drop in the strength of the magnetic field, Stoner said, a phenomenon that often accompanies north-south reversals.
But research by French scientists published in 2003 suggests that such "jerks" in the magnetic fieldabrupt shifts in intensity and directionoccur often, not just during reversals.
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