Fossil tree shows consequences of magnetic pole reversal | Polarjournal
From the magnetic pole in the Arctic, the Earth’s magnetic field lines stretch across the entire globe. Numerous animals orient themselves at these lines in their long migrations in a way that has not yet been adequately explained. Our navigation systems and compasses are also aligned with the magnetic pole. Graphic: NOAA NCEI / CIRES

The magnetic poles in the northern and southern hemispheres are the points where the earth’s magnetic field lines converge. They are those poles that are not fixed points on the map, but shift throughout history. From geological investigations it has been known for a long time that the charge of the poles reverses itself thereby also again and again. But now, for the first time, an international research team has discovered the consequences for life and climate on Earth. And what they found sounds like a Hollywood disaster movie.

Massive auroras, then electrical storms and significantly increased cosmic rays that hit the Earth and all living things with full force, that’s how researchers Alan Cooper of the South Australian Museum, and Chris Turney of the University of New South Wales, imagine conditions on Earth nearly 42,000 years ago. This situation was caused by a temporary collapse of the Earth’s magnetic field, an event that the researchers refer to in their work as the “Adams Transitional Geomagnetic Event” or “Adams Event” for short. This collapse was caused by a reversal of the magnetic poles (also known as the Laschamps Excursion). This event had been known for some time, but not its impact on the climate and life on Earth. The two researchers investigated this in cooperation with various other scientists, including researchers from ETH Zurich, the Davos Physical & Meteorological Observatory, the Zurich University of Applied Sciences, and the Swiss Federal Laboratories for Materials Science and Technology. The results of the work was published in the latest issue of the journal Science.

Thanks to the discovery of a 60-ton, 40,000-year-old kauri tree native to northern New Zealand, the researchers were able to show the massive changes through dendrochronological analysis and comparison with other sources. Picture: Muriel Bendel /Wiki Commons, small: RNZ-News

“The Kauri trees are like the Rosetta Stone”.

Professor Adam Cooper, lead author

As is often the case in research, chance also played a major role in these results: during excavations for a power station in New Zealand, workers came across a fossil kauri tree. The 60-ton colossus was very well preserved by the swamp into which it had fallen. Kauri trees are native to the north of New Zealand and are the largest trees there. They are durable and were once considered an excellent building material. The discovered tree was estimated by the researchers to be around 40,000 years old and offered them a glimpse into a time span of around 1,700 years, which included the time of the Laschamps Excursion. With the help of radicarbon measurements on that tree and other tree stumps, the researchers were able to precisely determine the changes in the atmosphere and, by comparing them with other sources, also establish a time sequence and the effects. “The kauri trees are like the Rosetta Stone,” explains Adam Cooper. “They help us connect the records of environmental change that have been discovered in caves, ice cores and peat bogs around the world.”

At first, the weakening probably resulted in increased auroral activity, which led to true fireworks in the night sky 42,000 years ago. However, with the collapse of the Earth’s magnetic field, violent electromagnetic storms are likely to have resulted. Picture: Michael Wenger

The Laschamps Excursion was already known from geological investigations. This was more of a prelude as the earth’s magnetic field weakened there. This process can also be observed today. Over the past 170 years, our magnetic field has weakened by about 9 percent. 42,000 years ago, it was another 28 percent less than today, as the researchers write in their paper. The Adams Event (named after sci-fi author Douglas Adams) happened at the beginning of the Laschamps Excursion and was, according to the two main authors, something like the end of the world. This is because the reversal at the magnetic poles in the Arctic and Antarctic caused the Earth’s protective shield, the Earth’s magnetic field, to fail almost completely. Cosmic radiation could hit the earth unchecked and the UV radiation of the sun too. Only the fact that, coincidentally, solar activity was at a minimum at the same time prevented the Earth from being properly barbecued. Nevertheless, the effects on animals and plants were probably striking and Turney and Cooper think that this could also explain, for example, the disappearance of the megafauna of Australia and of the Neanderthals. The growth of the gigantic ice sheets on the North American continent could also be linked to the Adams event. This also shows the great influence on the climate of Earth 42’000 years ago.

Currently, the magnetic north pole is moving towards Siberia. Yet the pace has increased massively over the past 50 years. Some researchers see this as an imminent reversal of the polarity of the poles. What this might mean is now shown by the work of Cooper and Turney.

The researchers warn in their paper that such an event could also be imminent now. This is because, in addition to the weakening of the Earth’s magnetic field, the shift of the magnetic pole in the Arctic has also accelerated massively. For some scientists, including the two lead authors, this is an indication that a reversal of the Earth’s magnetic field, such as last occurred 42,000 years ago, is imminent. But the situation of today is quite different from that time. “Our atmosphere is already filled with carbon at levels never seen by humanity before,” says Chris Turney. “A magnetic pole reversal or extreme change in Sun activity would be unprecedented climate change accelerants. We urgently need to get carbon emissions down before such a random event happens again.”

The video (English) shows how the kauri trees contributed to the results of the two researchers. Video: UNSW Sydney

Dr Michael Wenger, PolarJournal

Link to study: Cooper et al, Science 371, 811-818 (2021), DOI: 10.1126/science.abb8677

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