Ice age polarity reversal was global event:

During the last ice age, around 41,000 years ago, there was a very rapid and complete reversal of the Earth’s geomagnetic field, according to new research. There was already localized evidence of polarity reversals during this time, but with the new research, the theory that it was a global event is now strongly supported. And very interestingly, it is one that nearly coincided with the very fast, short-term climate variability of the last ice age and the largest volcanic eruption in the northern hemisphere during the last 100,000 years.

Magnetic studies using sediment cores taken from the Black Sea, done by the GFZ German Research Centre for Geosciences, have clearly shown that if you had a compass at the Black Sea during that time, it would have pointed towards the south, not the north.

But more importantly, new data gathered by the researchers when it’s combined with additional data from previous studies in the North Atlantic, the South Pacific, and Hawaii, strongly supports the theory that this polarity reversal was truly global.

What’s considered so remarkable about this reversal is the speed that it’s now thought to have occurred: “The field geometry of reversed polarity, with field lines pointing into the opposite direction when compared to today’s configuration, lasted for only about 440 years, and it was associated with a field strength that was only one quarter of today’s field,” explains Norbert Nowaczyk. “The actual polarity changes lasted only 250 years. In terms of geological time scales, that is very fast.”

The magnetic field at the time would have only had about 5% of the strength of the field today. This would have resulted in the Earth almost completely losing its protective shield, allowing hard cosmic rays to hit the surface, and greatly increasing radiation exposure.

“This is documented by peaks of radioactive beryllium (10Be) in ice cores from this time, recovered from the Greenland ice sheet. 10Be as well as radioactive carbon (14C) is caused by the collision of high-energy protons from space with atoms of the atmosphere.”

The polarity reversal observed in the magnetisation of Black Sea sediments isn’t new knowledge, though — it’s been known of for at least 45 years. First discovered in “the analysis of the magnetisation of several lava flows near the village Laschamp near Clermont-Ferrand in the Massif Central, which differed significantly from today’s direction of the geomagnetic field.” This geomagnetic feature has since then been called the Laschamp event.

That’s limited data though, representing only some specific point readings of the geomagnetic field during that time, so there had been debate about how to interpret it. When combined with all of the new data though, it creates a convincing image of “geomagnetic field variability at a high temporal resolution.”

The cores analyzed also provided insight into “numerous abrupt climate changes during the last ice age” that occurred at the same time — these climate changes had already been observed in ice cores taken from Greenland. “This ultimately allowed a high precision synchronisation of the two data records from the Black Sea and Greenland.”

“The largest volcanic eruption on the Northern hemisphere in the past 100,000 years, namely the eruption of the super volcano 39,400 years ago in the area of today’s Phlegraean Fields near Naples, Italy, is also documented within the studied sediments from the Black Sea.”

This volcanic eruption released about 350 cubic kilometers of ash, rock, and lava over all of the eastern Mediterranean, and parts of Russia and Asia.

All three of these global disasters; a rapid and complete reversal of the Earth’s magnetic field, the drastic short-term climate variability of the last ice age, and one of the largest volcanic eruptions in the last million years; have now been tied together and placed into a precise and connected chronological order.

The new research was just published in the journal Earth and Planetary Science Letters.

Some unanswered questions [This Dynamic Earth, USGS] [6/22/2007]

EiU, p 146 (and referred to on p 202):
The observation was made on clay fired in kilns by the Etruscans and Greeks. The position of the ancient vases during firing is known. They were fired in a standing position, as the flow of the glaze testifies. The magnetic inclination or the magnetic dip of the iron particles in the fired clay indicates which was the nearest magnetic pole, the south or the north.

In 1896 Giuseppe Folgheraiter began his careful studies of Attic (Greek) and Etruscan vases of various centuries, starting with the eighth century before the present era. His conclusion was that in the eighth century the earth's magnetic field was inverted in Italy and Greece. Italy and Greece were closer to the south than to the north magnetic pole.

P.L. Mercanton of Geneva, studying the pots of the Hallstatt age from Bavaria (about the year -1000) and from the Bronze Age caves in the neighborhood of Lake Neuchatel, came to the conclusion that about the tenth century before the present era the direction of the magnetic field differed only a little from its direction today, and yet his material was of an earlier date than the Greek and Etruscan vases examined by Folgheraiter. But checking on the method and the results from Folgheraiter, Mercanton found them perfect.

An ancient vase found by F.A. Forel in Boiron de Morges, on Lake Geneva, was broken and its pieces were scattered and lay in all directions; when assembled, they all showed one and the same magnetic orientation, which proves again that the magnetic field of the earth was unable to change the orientation originally acquired by the clay when fired and cooled in the kiln.
Pole flips tied to plate tectonics [11/26/2011]

Large changes of the earth's magnetic fields in historical times
by William R. Corliss
Science Frontiers #22: Jul-Aug 1982
By measuring the magnetic properties of bricks and other accurately dated human artifacts, geophysicists can reconstruct the history of the local magnetic field. Near Loyang, China, the field was as much as 54% higher in 300 A.D. than it is now. It was 15% higher in 1500 A.D. In 1000, it was less than today's value.

(Wei, Q.Y., et al; "Intensity of the Geomagnetic Field near Loyang, China, between 500 BC and AD 1900," Nature, 296:728, 1982.)

Comment. Direct measurements of the earth's field go back only a few hundred years, but they are consistent with the data reconstructed from artifacts, both showing a steady decrease since 1500. No one has estimated the effects of these substantial changes on radiocarbon dating and, perhaps, human biology.
Pole flips tied to plate tectonics [11/26/2011]

"Earth In Upheaval", Immanuel Velikovsky, p 133
Most interesting is the discovery that the last time the reversal of the magnetic field took place was in the eighth century before the present era, or twenty-seven centuries ago. The observation was made on clay fired in kilns by the Etruscans and Greeks.

The position of the ancient vases during firing is known. They were fired in a standing position, as the flow of the glaze testifies. The magnetic inclination or the magnetic dip of the iron particles in the fired clay indicates which was the nearest magnetic pole, the south or the north.

In 1896 Giuseppe Folgheraiter began his careful studies of Attic (Greek) and Etruscan vases of various centuries, starting with the eighth century before the present era. His conclusion was that in the eighth century the earth's magnetic field was inverted in Italy and Greece. 7 Italy and Greece were closer to the south than to the north magnetic pole.

P. L. Mercanton of Geneva, studying the pots of the Hallstatt age from Bavaria (about the year 1000) and from the Bronze Age caves in the neighborhood of Lake Neuchatel, came to the conclusion that about the tenth century before the present era the direction of the magnetic field differed only a little from its direction today, and yet his material was of an earlier date than the Greek and Etruscan vases examined by Folgheraiter. But checking on the method and the results of Folgheraiter, Mercanton found them perfect.

An ancient vase found by F. A. Forel in Boiron de Morges, on Lake Geneva, was broken and its pieces were scattered and lay in all directions; when assembled, they all showed one and the same magnetic orientation, which proves again that the magnetic field of the earth was unable to change the orientation originally acquired by the clay when fired and cooled in the kiln. 8

These researches, continued and described in a series of papers by Professor Mercanton, presently with the Service Meteorologique Universitaire in Lausanne, show that the magnetic field of the earth, not very different from what it is today, was disturbed sometime during or immediately following the eighth century to the extent of complete reversal.

[footnotes]

7 G. Folgheraiter in Rendi Conti del Licet, 1896, 1899; Archives des sciences physiques ei naturelles (Geneva). 1899; Journal de physique, 1899; P. L. Mercanton, "La m&hode de Folgheraiter et son r61e en geophysique," Archives des sciences physiques et naturelles. 1907.

8 Bulletin de la Societe Vaudoise des sciences naturelles, Stance du 15 decembre 1909.

9 Manley speaks of "the possibility of its [earth's magnetic field] reversal in historical times, 2500 years ago, to be cleared up by more research." However, the more exact date is, according to the original works of Folgheraiter and Mercanton, the eighth century before the present era, or shortly thereafter.

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Ice Age Magnetic Reversal Was Global Event And Linked With Super Volcano Eruption And Rapid Climate Variability, Says New Research