Geomagnetic Reversal 41k BP 240 years Paradox? Mechanism?

In summary, recent studies have shown evidence for rapid and cyclic changes in the geomagnetic field that cannot be explained by traditional core-based mechanisms. These changes have been correlated with abrupt climate changes and super volcano eruptions. The speed and magnitude of these changes suggest that the geodynamo process may be intrinsically unstable. Multiple studies have documented excursions of the geomagnetic field, some of which have coincided with significant changes in Earth's climate. These findings call for further research to better understand the mechanisms behind these changes and their potential impact on our planet.
  • #1
betzalel
64
5
There has been a series of papers recently published that provide observational data that indicates that something is cyclically abruptly changing the geomagnetic field.

The rapidity of the observed geomagnetic field changes cannot be explained by a core based mechanism. There is no geological mechanism that can change the liquid core cyclically and quickly enough to cause the observed surface geomagnetic field changes.

As the mantel is conductive and liquid core is conductive, counter emfs are generated that resit rapid core based changes. For that reason geomagnetic field reversals and excursions where believed based on the assumed toy model to take roughly 2000 to 5000 years.

These rapid paradoxical geomagnetic excursions correlate with abrupt climate changes and with super volcano eruptions.

The geomagnetic field changes come in a small, medium, and large. The small and medium geomagnetic field changes have been shown to correlate with very large solar magnetic cycle changes.

http://www.sciencedaily.com/releases/2012/10/121016084936.htm

http://www.paleomag.net/members/qingsongliu/References/EPSL/Thouveny%20excursions%20since%20400%20ka%20EPSL%202004.pdf [Broken]

Some 41,000 years ago, a complete and rapid reversal of the geomagnetic field occured. Magnetic studies of the GFZ German Research Centre for Geosciences on sediment cores from the Black Sea show that during this period, during the last ice age, a compass at the Black Sea would have pointed to the south instead of north.

What is remarkable is the speed of the reversal: "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." During this period, the field was even weaker, with only 5% of today's field strength. As a consequence, Earth nearly completely lost its protection shield against hard cosmic rays,
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. The ashes of this eruption, during which about 350 cubic kilometers of rock and lava were ejected, were distributed over the entire eastern Mediterranean and up to central Russia.
http://eprints.whiterose.ac.uk/416/1/gubbinsd4.pdf

Is the geodynamo process intrinsically unstable?

Recent palaeomagnetic studies suggest that excursions of the geomagnetic field, during which the intensity drops suddenly by a factor of 5 to 10 and the local direction changes dramatically, are more common than previously expected. The `normal' state of the geomagnetic field, dominated by an axial dipole, seems to be interrupted every 30 to 100 kyr; it may not therefore be as stable as we thought. We have investigated a possible mechanism for the instability of the geodynamo by calculating the critical Rayleigh number (Rc) for the onset of convection in a rotating spherical shell permeated by an imposed magnetic field with both toroidal and poloidal components.

Recent studies suggest that the Earth's magnetic field has fallen dramatically in magnitude and changed direction repeatedly since the last reversal 700 kyr ago (Langereis et al. 1997; Lund et al. 1998). These important results paint a rather different picture of the long-term behaviour of the ¢eld from the conventional one of a steady dipole reversing at random intervals: instead, the field appears to spend up to 20 per cent of its time in a weak, non-dipole state (Lund et al. 1998). One of us (Gubbins 1999) has suggested that this is evidence of a rapid natural timescale (500 yr) in the outer core, and that the magnetic field is usually prevented from reversing completely by the longer diffusion time of the inner core (2 to 5 kyr). This raises a number of important but difficult questions for geodynamo theory. How can the geomagnetic field change so rapidly and dramatically? Can slight variations of the geomagnetic field affect the dynamics of core convection significantly? If so, is the geodynamo process intrinsically unstable?
 
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  • #2
The following are additional papers that support the above comment.

http://www.paleomag.net/members/qingsongliu/References/EPSL/Thouveny%20excursions%20since%20400%20ka%20EPSL%202004.pdf [Broken]

Geomagnetic moment variation and paleomagnetic excursions since 400 kyr BP: a stacked record from sedimentary sequences of the Portuguese margin

A paleomagnetic study was performed in clayey-carbonate sedimentary sequences deposited during the last 400 kyr on the Portuguese margin (Northeast Atlantic Ocean). Declination and inclination of the stable remanent magnetization present recurrent deviations from the mean geomagnetic field direction. The normalized intensity documents a series of relative paleointensity (RPI) lows recognized in other reference records. Three directional anomalies occurring during RPI lows chronologically correspond to the Laschamp excursion (42 kyr BP),the Blake event (115-122 kyr BP) and the Icelandic basin excursion (190 kyr BP). A fourth directional anomaly recorded at 290 kyr BP during another RPI low defines the ‘Portuguese margin excursion’. Four non-excursional RPI lows are recorded at the ages of the Jamaica/Pringle Falls, Mamaku, Calabrian Ridge 1, and Levantine excursions. The RPI record is characterized by a periodicity of V100 kyr, paleointensity lows often coinciding with the end of interglacial stages. This record sets the basis of the construction of an authigenic 10Be/9Be record from the same sedimentary sequences [Carcaillet et al.,this issue].

Spectral analyses of the RPI record reveal a dominant periodicity at 100 kyr,already reported by other studies (e.g. [41,59,60]). The RPI and N18O records also present a phase shift of 18 kyr: RPI lows often coincide with the end of interglacial or interstadial stages. The geomagnetic moment loss (greater than 30%) over the last two millennia deduced from archeomagnetic results (e.g. [38,39]) might foreshadow the next excursion for the end of our present interglacial, even though this loss started 2200 years ago from an exceptionally high geomagnetic moment value.

http://www.agu.org/pubs/crossref/2006/2006GL027284.shtml

Geomagnetic excursion captured by multiple volcanoes in a monogenetic field


Five monogenetic volcanoes within the Quaternary Auckland volcanic field are shown to have recorded a virtually identical but anomalous paleomagnetic direction (mean inclination and declination of 61.7° and 351.0°, respectively), consistent with the capture of a geomagnetic excursion. Based on documented rates of change of paleomagnetic field direction during excursions this implies that the volcanoes may have all formed within a period of only 50–100 years or less. These temporally linked volcanoes are widespread throughout the field and appear not to be structurally related. However, the general paradigm for the reawakening of monogenetic fields is that only a single new volcano or group of closely spaced vents is created, typically at intervals of several hundred years or more. Therefore, the results presented show that for any monogenetic field the impact of renewed eruptive activity may be significantly under-estimated, especially for potentially affected population centres and the siting of sensitive facilities.
 
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  • #3
betzalel said:
The following are additional papers that support the above comment.

That's very, intruegingly, interesting, thanks for posting.

Even more interesting that the Lachamps event can't really be related to any other event. Maybe vaguely the Australian mammal extinction, but then again why not elsewhere.

Will we ever understand what's going on?
 

1. What is a geomagnetic reversal?

A geomagnetic reversal is a phenomenon in which the Earth's magnetic field flips, meaning that the North and South magnetic poles switch places. This has happened multiple times throughout Earth's history.

2. What happened during the geomagnetic reversal 41k BP (before present)?

41,000 years ago, the Earth experienced a geomagnetic reversal in which the North and South magnetic poles temporarily switched places. This resulted in a brief period of unstable magnetic field, with multiple magnetic poles scattered across the Earth's surface.

3. How long did the geomagnetic reversal 41k BP last?

The geomagnetic reversal 41k BP lasted for approximately 240 years, which is relatively short compared to other geomagnetic reversals in Earth's history.

4. What is the paradox surrounding the geomagnetic reversal 41k BP?

The paradox surrounding the geomagnetic reversal 41k BP is that, based on previous data and models, the reversal should have taken much longer (thousands of years) to occur. However, the actual duration of 240 years is significantly shorter, creating a discrepancy in our understanding of geomagnetic reversal mechanisms.

5. What is the current understanding of the mechanism behind the geomagnetic reversal 41k BP?

The exact mechanism behind the geomagnetic reversal 41k BP is still not fully understood. Some scientists believe that it may have been triggered by a sudden change in the Earth's core, while others suggest that external factors such as solar storms or cosmic rays may have played a role. Further research and data analysis is needed to fully understand the mechanism behind this particular geomagnetic reversal.

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