Archeomagnetic jerks & Unexplained Geomagnetic Field Instability

[Saul]

Geomagnetic researchers have found in the last 10 years that the Earth's geomagnetic field abruptly changes in intensity with the non-dipole portion of the total field suddenly becoming stronger. These abrupt change events are referred to as archeomagnetic jerks, as one analysis method to find the position and intensity of the Earth's magnetic field is to analysis pottery fragments. (Pottery at the time of firing is heated above the Curie point and hence captures the intensity and direction of the Earth's magnetic field when it cools.)

As noted below during the abrupt change event the geomagnetic field appears to move off center from the planet's rotation.

http://adsabs.harvard.edu/abs/2005AGUFMGP44A..02S

Abrupt Shifts in the Position of the North Magnetic Pole From Arctic lake Sediments: Relationship to Archeomagnetic Jerks

Historical observations document ~1100 km change in the position of the North Magnetic Pole (NMP) over the last century. This movement has accelerated over the last few decades to an astonishing 40 km/yr and along with the diminishing intensity of the dipole field has led to speculation of imminent reversal or excursion. Recently it has been shown that movement of the NMP is sensitive to small and rapid variations of the field known as Geomagnetic Jerks (Newitt et al., 2002; Mandea and Dormy 2003). These observations indicate that tracking the migration of the NMP provides a tracer of field variations allowing a more complete understanding of geomagnetic field behavior prior to historical observations. Reconstruction of the late Holocene paleomagnetic record from the Canadian High Arctic has been undertaken using u-channel paleomagnetic measurements from lakes in Ellesmere, Devon, Cornwallis and Bathurst Islands.

At present the most complete records come from Ellesmere Island (Sawtooth Lake, 79°21 N, 83°56 W and Murray Lake, 81°34 N, 69°54 W) as these sediments have excellent magnetic properties, and preserve a strong, stable, single component magnetization. Multiple records have been obtained from each of these lakes and they possesses independent age control based on varve chronologies.

The paleomagetic record from several other lakes support observations from Sawtook and Murray Lakes, although they lack either independent age control or replicate-coring. These data help to establish the characteristics of late Holocene paleomagnetic secular variation (PSV) for the Canadian High Arctic for the last 2600 yrs. Correlations between sediment PSV records and historical observations demonstrate that the geomagnetic record is influenced by the position of the NMP, and that Arctic sediment magnetizations are sensitive to its movement. Over the last 2000 yrs, the PSV record documents at least 3 rapid (< 100 yrs) high amplitude NMP shifts that are much larger than anything observed in the historical record (the last 400 yrs). Abrupt shifts in the position of the NMP by thousands of kilometers appear to closely coincide with the three most recent archeomagnetic "jerks" of Gallet et al., (2003).

http://adsabs.harvard.edu/abs/2009E&PSL.284..179G

Geomagnetic field hemispheric asymmetry and archeomagnetic jerks
We investigate the origin of the so-called archeomagnetic jerks detected in the French archeomagnetic record over the past three millennia. Although only very large-scale global archeomagnetic field models are currently available, we show that the occurrence of archeomagnetic jerks is intimately linked to what we define as “most eccentric” events, i.e., periods of time when a simple description of the geomagnetic field in terms of an eccentric dipole reveals the center of this eccentric dipole to strongly move away from the Earth's center. From the behavior of the much better known historical field, we interpret the evolution of the center of the eccentric dipole as reflecting the production and gathering of flux patches at the core-mantle boundary within preferential hemispheres. Archeomagnetic jerks would thus correspond to episodes of maximum geomagnetic field hemispheric asymmetry. Such “most eccentric” events could also provide an explanation for some of the properties previously reported in the long-term paleomagnetic field.

 

[Saul]

The archeomagnetic jerks are spaced roughly 200 years apart. As the observational papers linked to above note, during an “archeomagnetic jerk” the geomagnetic field abruptly moves off center from the planet’s core. This cyclic event causes the geomagnetic field to be less dipole like.

What is causing the cyclic abrupt changes in the geomagnetic field, the archeomagnetic jerks? Could the cause of the archeomagnetic jerks be the cause of the geomagnetic excursions? (A geomagnetic excursion is a very strong abrupt change to the geomagnetic field that appears to be a stronger version of the archeomagnetic jerk. i.e. The non dipole portion of the geomagnetic field becomes stronger during a geomagnetic excursion.)

As researchers have noted, regions of the planet experience cooling during the archeomagnetic jerk.

Other researchers have noted the stronger abrupt cooling events Heinrich events and the Danssgaard Oescherger events (warming following by cooling) are also concurrent with magnetic field changes.

Curiously some researchers are appealing to abrupt climate events being the cause of geomagnetic excursions.

Some researchers have appeal to a chaotic knife edge planetary climate system. Following that paradigm the planet’s climate can abruptly change from one state to another as it amplifies small forcing changes.

Continuing on that line of reasoning – An abrupt change in the climate occurs as a small planetary temperature change is amplify by the planet’s positive feedback - other researchers have hypothesized that an abrupt change in climate can cause an abrupt increase in volcanism in both hemispheres in addition to causing abrupt changes to the geomagnetic field. (The abrupt increase in volcanism is concurrent with the strongest geomagnetic field changes.)

That line of reasoning is not supported by the observational evidence. The roughly 200 year spaced archeomagnetic jerks do not lag the planetary zones of cooling (the zones of cooling are spatially aligned with the regions of the planet where the geomagnetic field changes occur) that are observed when they occur.

Likewise the magnetic excursion that is concurrent with the Younger Dryas cooling does not lag the cooling. It should be noted that roughly 60% of the Younger Dryas cooling occurred in 10 years.

It should be noted that Uranus and Neptune also have magnetic fields that are for some odd reason off set from the center of the planet's core. The point is the axis of rotation of Uranus and Neptune is highly tilted towards the sun.

The Earth's geomagnetic field changes correlate with the timing of its axis changes (When the Earth is more tilted the geomagnetic field is stronger). Also curiously the geomagnetic field's intensity is greater when the eccentricity of the Earth's orbit is greater. (I will provide a link that shows the geomagnetic field's intensity changes on a 100 kyr basis and the geomagnetic field's intensity correlates with the glacial/interglacial cycle.)http://cat.inist.fr/?aModele=afficheN&cpsidt=14797100

http://www.ias.ac.in/currsci/apr252003/1105.pdf

The effect of changes in the Earth’s moment of inertia during glaciation on geomagnetic polarity excursions and reversals: Implications for Quaternary chronology

Geomagnetic polarity reversals and excursions in the Quaternary correlate well with interglacial-to-glacial transitions and glacial maxima. It is suggested that this relationship results from interactions between the Earth’s mantle and core that accompany decreases in the Earth’s moment of inertia during ice accumulation, which weaken the geomagnetic field in order to try to counter the decrease in differential rotation between the mantle and inner core that is being forced. In the Late Pleistocene, geomagnetic excursions directly correlate with brief phases of rapid ice growth that accompany falls in global sea-level, notably during the Younger Dryas stage, Dansgaard– Oeschger interstadials 5 and 10 that precede the rapid melting events during Heinrich events H3 and H4, and during the transitions between oxygen isotope stages 5c-5b, and 5e-5d. It is proposed that similar relationships between instabilities in climate and the geomagnetic field also typefied the Middle Pleistocene.

As a result of the transfer of some of the mass of the oceans into polar ice sheets, the climate instabilities that initiate these rapid ice accumulations redistribute angular momentum and rotational kinetic energy between the Earth’s mantle and inner core. These changes weaken the Earth’s magnetic field, facilitating geomagnetic excursions and also causing enhanced production of cosmogenic nuclides, including 14C. The subsequent phases of rapid ice melting, Heinrich events, reverse this effect: strengthening the field. This explanation, of forcing of geomagnetic excursions by climate instabilities, provides a natural explanation for why, during the Middle-Late Pleistocene, excursions have been numerous but none has developed into a polarity reversal: the characteristic duration of the climate instabilities is too short.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC404046/

Bipolar correlation of volcanism with millennial climate change

Analyzing data from our optical dust logger, we find that volcanic ash layers from the Siple Dome (Antarctica) borehole are simultaneous (with >99% rejection of the null hypothesis) with the onset of millennium-timescale cooling recorded at Greenland Ice Sheet Project 2 (GISP2; Greenland). These data are the best evidence yet for a causal connection between volcanism and millennial climate change and lead to possibilities of a direct causal relationship.

Evidence has been accumulating for decades that volcanic eruptions can perturb climate and possibly affect it on long timescales and that volcanism may respond to climate change. If rapid climate change can induce volcanism, this result could be further evidence of a southern-lead North–South climate asynchrony.

Although the Earth maintains a remarkably constant temperature, climate fluctuations have been identified on many timescales. On the 10^3-year scale, poorly understood Dansgaard– Oeschger (DO) events (1, 2), extremely rapid coolings warmings and subsequent cold warmperiods, are best exhibited during the last glacial period [20,000–110,000 years before the present or 20–110 thousand years ago (ka)] but may extend with reduced amplitude into the Holocene (3) (the comparatively stable, warm, last 11 ka). Proposed causal mechanisms involve harmonics of Milankovitch (orbital) forcing, thermohaline circulation, internal ocean–atmosphere oscillations, solar forcing, and even long-period tidal resonances in the motions of the Earth and Moon. Recent work suggests that the fluctuations resemble those of a system possessing threshold instability. Rapid transitions between states are exhibited in many climate models, including those of oceanic circulation, atmospheric energy balance, and atmospheric regime change.

 

[Saul]

This is the third paper by the same researchers that validates their assertion that the geomagnetic field's maximum intensity periods correlates with the period when the Earth's orbit around the sun is most eccentric.

Comment:
No one has explained why the geomagnetic field is strongest when the Earth's orbit about the sun is most eccentric. (Check out figure 11 in their paper.)

http://www.terrapub.co.jp/journals/EPS/pdf/2007/5907/59070785.pdf

A relative paleointensity record of the geomagnetic field since 1.6 Ma from the North Pacific

A spectral analysis on the NGC65/KR0310-PC1 paleointensity record shows a power at the ∼100 kyr eccentricity period. The relative paleointensity and magnetic properties of NGC65/KR0310- PC1 were compared with those of MD982185 from the western equatorial Pacific (Yamazaki and Oda, 2002, 2005). The two sites belong to different oceanographic regimes. Coherent variations in the relative paleointensity despite incoherent changes in the magnetic properties suggest that rock-magnetic contamination to the relative paleointensity is small, if any, and the ∼100 kyr period in the relative paleointensity records would reflect the geomagnetic field behavior.Fig. 11. Comparison of relative paleointensity records: NGC65/KR0310 -PC1 from the central North Pacific (red), MD982185 from the western equatorial Pacific (Yamazaki and Oda, 2002, 2005) (blue), and the Sint-2000 stack of Valet et al. (2005) (gray).

 

[Saul]

This is a summary of the voyager data that shows the magnetic field of both Uranus and Neptune are not in alignment with the rotational axis of the planets and is off set from the planet's core.

The New Solar System, 4th Edition by J. Beatth, C. Peterson, A Chaikin

As Voyager approached Uranus in January 1986, we wondered if our experiences with symmetric magnetic environments of Earth, Jupiter, and Saturn would be true for a planet that is quite literally spinning on its side. (My comment in relationship to Uranus’ orbit about the sun.)

An empirical relationship that relates angular momentum and magnetic moments, the “Bode’s law” of planetary magnetism, suggested that the magnetic moment of Uranus would be about one-tenth of Saturn.

We knew that the rotational axis of Uranus would lie, in early 1986, within 8 degrees of the planet-Sun line. If Uranus’s magnetic and rotational axis were nearly parallel, as is the case for other magnetized planets, (my comment in planets in the solar system), one pole would be pointed almost directly at the Sun and the a very unusual magnetospheric shape would be expected.

The planet’s magnetic moment is nearly the same strength as that predicted, but orientation is very different from our expectations. Uranus’ magnetic axis is tilted at huge 59 degrees from Uranus’s rotational axis and offset from the planet’s center.

Figure 18
The magnetic fields of Uranus and Neptune are remarkably – and unexpectedly – alike. The large offset from centre means that the field strength … It also means that the fields source cannot lie in the cores but rather must in a turbulent liquid mantle where dynamo driving convection can be substained.

 

[LudusRex]

I find these findings intriguing and significant. The Earth's geomagnetic field is a complex and dynamic system, and understanding its behavior is crucial for many aspects of our daily lives, such as navigation and communication. The discovery of archeomagnetic jerks, sudden changes in the intensity and position of the geomagnetic field, adds to our understanding of this system and raises new questions about its underlying mechanisms. The use of pottery fragments as a tool for studying these jerks is a creative and innovative approach, and the results from the Canadian High Arctic lakes provide valuable insights into the behavior of the geomagnetic field over the past few millennia. The correlation between the archeomagnetic jerks and the movement of the North Magnetic Pole is particularly interesting, and the suggestion that these jerks are linked to periods of maximum geomagnetic field hemispheric asymmetry is a significant contribution to our understanding of the Earth's magnetic field. Further research in this area will undoubtedly shed more light on these phenomena and enhance our understanding of the Earth's geomagnetic field.