As descendants of polar explorer Ernest Shackleton last week trekked to the South Pole to commemorate the 100th anniversary of his unsuccessful bid for the pole, a New Zealand contingent was celebrating a scientifically more important anniversary.
On January 16th, 1909, three of Shackleton’s men successfully made it to the South Magnetic Pole – the point on the planet where the Earth’s geomagnetic field lines are pointed directly vertical upwards. The location of the South Magnetic Pole wanders and is different today to the spot Shackleton’s men reached.
To commemorate the expedition, Neville Jordan, the president of the Royal Society and Nigel Watson of the Antarctic Heritage Trust, visited Shackleton‘s hut, during which they collected samples as part of a conservation effort to preserve the hut.
Jordan and Antarctic historian Baden Norris talks to Noelle McCarthy about the journey by Shackleton’s men to the South Magnetic Pole and why it was more significant to science than the later trip to the physical pole.
Listen to a Radio Live interview with Palaeomagnetist Gary Wilson of the University of Otago as he explains the frequent reversal of the magnetic poles.
Log-in to download a backgrounder on the South Magnetic Pole put together by the Antarctic Heritage Trust and to download high-resolution images of Shackleton’s hut.
University of Otago’s Gary Wilson explains the frequent reversal in polarity of the Earth’s magnetic field:
“In terms of why the earth’s field reverses that is still elusive – as is what the origin of the field is. What we do know very accurately is the pattern or expression of the field at the earth’s surface and that has been recorded for the last few hundred million years as new ocean crust is made at the spreading ridges of the major oceans.
“Studies of sediment cores have, however, added a bit more resolution to the story and in particular relatively recent developments give a bit more picture of the intensity of the field and show that it has varied from nothing to somewhat stronger than today and that field reversals coincide with times of low field intensity but low field intensity is more common, suggesting that the magnetic field has two relatively stable states – normal (as today) and reversed (opposite) and that when the field reduced to nothing it appears to have equal chance to grow in either direction (Pretty speculative, I’m afraid).
“As for the origin of the field (on a global scale) what we are able to do is build a model, which explains the field
we see at the surface of the earth. A simple bar magnet at the centre of the earth would explain about 90% of the field. The remaining 10% is explained by various other less dominant components. Of course one has to be careful applying all this as a navigational tool as magnetic rocks or materials are distributed throughout the earth’s crust and can cause local perturbations.
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