First humans in Tasmania must have seen spectacular auroras

 Drilling a 270,000-year old core from a Tasmanian lake has provided the first Australian record of a major global event where the Earth's magnetic field 'switched '- and the opportunity to establish a precedent for developing new paleomagnetic dating tools for Australian archaeology and paleosciences.

"This is the first study of this kind in Australia since pioneering studies in the 1980s," said author Dr Agathe Lisé-Provonost, a McKenzie Fellow from the School of Earth Sciences at the University of Melbourne.

"Just two lakes in north-east Australia previously provided such "full-vector" record, where both the past directions and the past intensity of the Earth magnetic field are obtained from the same cores."

Published in the journal Quaternary Geochronology, Chronostratigraphy of a 270-ka sediment record from Lake Selina, Tasmania: Combining radiometric, geomagnetic and climatic dating, details how drilling into the 5.5 metre long Lake Selina core established that 41,000 years ago, people in Tasmania must have seen spectacular auroras when the Earth's magnetic field flipped, and for a few thousand years, north was south and south was north.

"During the geomagnetic 'excursion', the strength of the Earth's magnetic field almost vanished," said DrLisé-Provonost.

"This would lead to a big increase in cosmic and solar particles bombarding our planet because the magnetic field normally acts like a shield.

"We don't know when the next geomagnetic excursion will happen, but if one was to occur today, satellites would be rendered useless, smartphone navigation apps would fail, and there would be major disruptions of power distribution systems."

Research leading to that discovery got underway in 2014 when the author travelled to a small sub-alpine lake in western Tasmania with a team led by Associate Professor Michael-Shawn Fletcher, where a makeshift floating platform rigged to two inflatable rafts was used to drill down into the sediment.

With the core containing a climate, vegetation, and paleomagnetic record of the area, the team looked to first accurately date its layers finding evidence of the ecosystem changes that occurred as Tasmanian Aboriginals arrived 43,000 years ago and managed the land over thousands of years. Abrupt changes that occurred since the arrival of Europeans 200 years ago are also evidenced.

"Magnetic particles are eroded from rocks, making their way to a lake by wind or water, and settle down on the lake bottom," said Dr Lisé-Provonost.

"The magnetic particles act like tiny compass needles, aligning with the Earth's magnetic field. As these particles accumulate and become buried, they become locked in place, leaving a history of the Earth's magnetic field. The deeper we drill, the further back in time we go."

It's hoped the research will lead the way for more studies of the past geomagnetic field behavior from Australian lakes and other geological materials such as lava flows, cave deposits and fired archaeological artefacts, for developing new paleomagnetic dating tools and improving models of the Earth's magnetic field to, one day, maybe predict the next geomagnetic excursion.

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Winter monsoons became stronger during geomagnetic reversal

New evidence suggests that high-energy particles from space known as galactic cosmic rays affect the Earth's climate by increasing cloud cover, causing an "umbrella effect."

When galactic cosmic rays increased during the Earth's last geomagnetic reversal transition 780,000 years ago, the umbrella effect of low-cloud cover led to high atmospheric pressure in Siberia, causing the East Asian winter monsoon to become stronger. This is evidence that galactic cosmic rays influence changes in the Earth's climate. The findings were made by a research team led by Professor Masayuki Hyodo (Research Center for Inland Seas, Kobe University) and published on June 28 in the online edition of Scientific Reports.

The Svensmark Effect is a hypothesis that galactic cosmic rays induce low cloud formation and influence the Earth's climate. Tests based on recent meteorological observation data only show minute changes in the amounts of galactic cosmic rays and cloud cover, making it hard to prove this theory. However, during the last geomagnetic reversal transition, when the amount of galactic cosmic rays increased dramatically, there was also a large increase in cloud cover, so it should be possible to detect the impact of cosmic rays on climate at a higher sensitivity.

In the Chinese Loess Plateau, just south of the Gobi Desert near the border of Mongolia, dust has been transported for 2.6 million years to form loess layers -- sediment created by the accumulation of wind-blown silt -- that can reach up to 200 meters in thickness. If the wind gets stronger, the coarse particles are carried further, and larger amounts are transported. Focusing on this phenomenon, the research team proposed that winter monsoons became stronger under the umbrella effect of increased cloud cover during the geomagnetic reversal. They investigated changes in particle size and accumulation speed of loess layer dust in two Loess Plateau locations.

In both locations, for about 5000 years during the geomagnetic reversal 780,000 years ago, they discovered evidence of stronger winter monsoons: particles became coarser, and accumulation speeds were up to > 3 times faster. These strong winter monsoons coincide with the period during the geomagnetic reversal when the Earth's magnetic strength fell to less than ¼, and galactic cosmic rays increased by over 50%. This suggests that the increase in cosmic rays was accompanied by an increase in low-cloud cover, the umbrella effect of the clouds cooled the continent, and Siberian high atmospheric pressure became stronger. Added to other phenomena during the geomagnetic reversal -- evidence of an annual average temperature drop of 2-3 degrees Celsius, and an increase in annual temperature ranges from the sediment in Osaka Bay -- this new discovery about winter monsoons provides further proof that the climate changes are caused by the cloud umbrella effect.

Read more at Science Daily