25 - Late Pleistocene Geomagnetics
The catalyst for some fairly catastrophic events.
The previous post concluded that several extremely large Miyake Events (MEs) almost certainly hit Earth during the 14,000+ years the ice sheets were melting, and that these extremely energetic events very likely caused severe Outer Core heating, geomagnetic field disruptions, an large increase in Earth’s geothermal heat flux and volcanism, a strengthening of the the Atlantic Meridional Overturning Circulation (AMOC), and vigorous glacial melting. This post examines the relationship between the ME occurrences and the geomagnetic field variations using the integrated geomagnetic-geothermal-temperature (IGGT) model.
MEs often cause magnetic excursions
A previous post demonstrated that the 1859 Carrington event - a large Solar Particle Event (SPE) - very likely caused a geomagnetic excursion. A geomagnetic excursion is defined as a significant and relatively rapid change to the the Earth’s magnetic field. Some of humankind’s earliest scientific observations suggest the 993 AD ME very likely caused such an excursion: Chinese scientists observed an increase in magnetic declination from -15° in 900 to 15° in 1100[1], and so documented a North Magnetic Pole shift from Asia to North America. This declination shift is also very apparent in the Paris paleomagnetic declination data[2] as well as CALS7K.2 declination animations. Gallet et al.[2] also recognized:
a remarkable coincidence between sharp cusps in geomagnetic field direction and intensity maxima […; around] AD 800. These sharp changes may constitute a new feature of geomagnetic secular variation (‘archaeomagnetic jerks’) with time characteristics intermediate between ‘geomagnetic jerks’ and ‘magnetic excursions’.
Similarly, Channell et al.[2] recognized a geomagnetic excursion around ~13 ka that concurs with similarly timed MEs (see figures below), the Laschamps excursion concurs with a huge increase in cosmogenic10Be (below), and the excursion around ~11 ka (below) roughly concurs with the very large SPE around 11.1 ka[11].
Late Pleistocene Geomagnetic variations
A reconstruction of the geomagnetic field between 14 - 10 ka [3] demonstrates that it was very weak around 13 ka, 11 ka, and 10 ka. The geomagnetic dipolar moment - a measure of intensity - had over ~5-6 millennia decreased from a local high of ~14 1022 A.m2 at 18 ka[4] to these local lows[3] of ~5 1022 A.m2.
Connecting the Late Pleistocene / Early Holocene Miyake Events (MEs) identified in the previous post to individual geomagnetic perturbations is tempting, but the age uncertainty of both is too large to make a credible attempt. The paleogeomagnetic record shows numerous “sharp cusps” that could plausibly be assigned to interpreted MEs. e.g. around 13 ka.
Bølling-Allerød and Younger Dryas ME activity
Around 13.5 ka the geomagnetic field started to gradually weaken, possibly due to a very large ME around the same time (previous post), progressively allowing more Galactic Cosmic Rays (GCRs) to penetrate further into Earth’s atmosphere, thereby gradually increasing the atmospheric 14C. The abrupt 14C increase that started around 13 ka however cannot be explained by geomagnetic field variations.
From an analysis of Cariaco Basin sediment cores LaViolette[5] concluded there was strong evidence for a series of MEs around the end of the Bølling-Allerød (BA) / start of the Younger Dryas (YD) that were very likely very large solar particle events (SPEs):
Varve chronology dates [the SPEs] at 12,973 ± 10, 12,904 ± 10, 12,837 ± 10, and 12,639 ± 10 cal yrs BP. It is worth noting that they are spaced from one another by multiples of the Hale solar cycle period of 22.2 ± 2 years, that is, by 69 ± 9, 67 ± 9, and 198 ± 9 years, or three and nine Hale cycles (~67 years and ~200 years).
Alternatively, a ~100-year long, high-intensity GCR event, modulated by the heliomagnetic field, could also have plausibly caused a single, drawn-out 14C increase between ~13.0 and ~12.9 ka.
Note that a significant effort is required to accurately calibrate varve chronology to 14C and ice core chronology, and that the process often results in a significant shift of dates by multiple decennia. For example, a recent study[7] re-dated the Laacher See volcanic eruption to from 12,900 BP[6] to 13,006 ± 9 BP, which resulted in a shift in the chronology of European varved lakes relative to the Greenland ice core record, and suggested a shift of the onset of the YD to 12,807 ± 12 BP.
The exact ages of the volcanic, varve, ice core and SPEs/GCR events are therefore still a matter of debate, although their occurrence several decades before the start of the YD is not. The geothermal increase that caused the Laacher See eruption pre-dates the onset of the YD by ~200 years, and can therefore be ruled out as the cause of the YD cooling[7]. This geothermal increase was very likely due to the increased Outer Core energy absorption and heating caused by Earth-incident SPEs/GCR pulses around ~13.5 - 13 ka. Also note the Cariaco Basin data show 14C increases/MEs at 14.5+ ka (14.8 ka ME?) and around 11 ka[5].
Late Pleistocene IGGT reconstruction
A reconstruction of the Late Pleistocene variations according to the IGGT model indicates that around 32 ka Earth’s Orbital Inclination was at a maximum. Roughly 1/8 glacial cycle period (12.5 ka) before this maximum the geomagnetic field strength became minimal (Laschamps excursion) at a time when the Outer Core reached a temperature minimum, resulting in a progressively stronger geomagnetic field between 41 ka - 18 ka[4]. An enormous spike of cosmogenic 10Be around ~41 ka can be attributed to the weak geomagnetic field strength, a huge ME, or - very likely - a combination of both occurring around then.
The large ME around the start of the Oldest Dryas (18.5 ka) very likely significantly warmed the Outer Core, as its power was very likely numerous orders of magnitude larger than what could be transmitted as geothermal heat to surface via the Mantle. The ME and the increasing solar wind strength (decreasing Orbital Inclination) therefore caused a progressively hotter Outer Core, a weakening geomagnetic field, and an increase in Earth’s geothermal gradient and volcanism, e.g. Mt St Helens “Cougar Stage”. Another huge ME around 14.8 ka caused similar events, including the renewed volcanism along the mid-Atlantic ridge that resulted in the large retreat of the North Atlantic sea ice cover that heralded the start of the Bølling-Allerød, as well as increased the strength of the AMOC.
Very large SPEs/ME’s around 14.0, 13.5 and 13.0 ka renewed mid-Atlantic ridge volcanic activity and intermittently caused North Atlantic sea ice cover retreat.
Revisiting Abu Hureyra - Lightning
A previous post documented that Epipaleolithic Abu Hureyra very likely suffered an intense lightning strike around 11,070± 40 14C BP, or ~13,000 cal BP, an age that similarly pre-dates the start of the YD and roughly concurs with the intense MEs/large GCR event mentioned above, suggesting a possible link between "catastrophically large” lightning strikes and intenser space particle radiation.
Lightning is a natural electrostatic discharge through the atmosphere between two electrically charged regions. These highly-energetic discharges of up to 7 GJ[8] can locally increase temperatures by up to 25,000 °C, and pressures by up to 7 GPa, which in turn causes a shock wave and thunder.
According to Science:
the phenomenon of lightning remains a scientific enigma.
so linking intense space particle events to intense lightning strikes is highly speculative, although some studies have linked[9] galactic cosmic ray ionisation to lightning on other planets with convecting atmospheres.
GCRs and large SPEs are the main sources of ionization in the Earth’s stratosphere and troposphere. Particularly intense particle events can cause ionized atmospheric O2 and N2 to emit light of varying color, often noticeable at high latitudes as Auroras. Particularly intense events, such as the Carrington event, can overwhelm the geomagnetic field, and cause atmospheric ionization and Auroral displays in the tropics. Therefore, around 13 ka a weak geomagnetic field combined with a very intense ME would have almost certainly caused intense atmospheric ionization above Abu Hureyra, though whether this would have caused intense lightning strikes remains speculative. The mainly positively charged space radiation particles would on average have almost certainly penetrated much deeper into Earth’s atmosphere, and could plausibly have delivered a positive charge to the top of tropospheric clouds, thereby causing “positive” lightning.
An average bolt of negative lightning carries an electric current of 30 kA, and transfers 15 C of electric charge and 1 GJ of energy, while the average positive flash can produce peak currents up to 400 kA and charges of several hundred coulombs, and could therefore have plausibly caused “catastrophic” damage to the Abu Hureyra settlement.
Revisiting Abu Hureyra - Cosmic Dust
The Abu Hureyra post also mentioned:
Another possible source of the elevated [metal] concentrations is cosmic dust. The geomagnetic field strength was very low around cal 13,000 BP, so was no longer efficiently repelling positive cosmic dust ions (such as Cr3+, Ni2+, etc.). A low geomagnetic field strength would also partially collapse the Van Allen belts, the region in the Earth’s magnetosphere where cosmic ions are trapped, resulting in an increase in cosmic ion deposition. Cosmic dust is chemically indistinguishable from meteoric/comet material.
Recent studies[10] support the hypothesis that cosmic dust fluxes onto Earth’s surface, mainly noticeable as native metal particle spikes in sediments, increase when the geomagnetic field is weak. These sediment layers - up to 1 m - are generally thicker than the thin “YDB” enriched layer, so a more probable cause is that heavy metals accumulated in the flora and fauna that lived near the Euphrates and were enriched in the ashes of the “YDB” lightning-caused fire.
Summary
There is very good evidence that several “catastrophic” events such as the Laacher See volcanism, numerous large Miyake Events / 1 prolonged Galactic Cosmic Ray event, and a severe lightning strike at Abu Huyreyra pre-dated the start of the Younger Dryas Northern Hemisphere cooling event by several decennia, and were therefore not its cause. There is significant evidence that severe Miyake Events caused Outer Core warming, geothermal heat increases, and geomagnetic excursions.
References
[1] Smith, P. & Needham, J., 1967, Magnetic Declination in Mediaeval China. Nature 214, 1213–1214 https://doi.org/10.1038/2141213b0
[2] Gallet, Y. et al., 2003, On possible occurrence of 'archaeomagnetic jerks' in the geomagnetic field over the past three millennia. Earth and Planetary Science Letters, 214, 237-242, doi:10.1016/S0012-821X(03)00362-5.
[3] Pavón-Carrasco, F.J., Osete, M.L., Torta, J.M., De Santis, A., 2014, A geomagnetic field model for the Holocene based on archaeomagnetic and lava flow data, Earth and Planetary Science Letters, 388, 98-109, //doi.org/10.1016/j.epsl.2013.11.046.
[4] Channell, J. , Vigliotti, L., 2019, The Role of Geomagnetic Field Intensity in Late Quaternary Evolution of Humans and Large Mammals. Reviews of Geophysics, 57, 709–738, doi:10.1029/2018RG000629.
[5] LaViolette, P. A., 2011, Evidence for a solar flare cause of the Pleistocene mass extinction, Radiocarbon 53, p 303-323.
[6] Schmincke, H.; Park, C.; Harms, E., 1999, Evolution and environmental impacts of the eruption of Laacher See Volcano (Germany) 12,900 a BP. Quaternary International, 61, 61–72. doi:10.1016/S1040-6182(99)00017-8.
[7] Reinig, et al., 2021, Precise date for the Laacher See eruption synchronizes the Younger Dryas. Nature 595, 66–69 (2021). https://doi.org/10.1038/s41586-021-03608-x
[8] Maggio, C. et al., 2009, Estimations of charge transferred and energy released by lightning flashes, J. Geophys. Res.,114, D14203, doi:10.1029/2008JD011506.
[9] Aplin, K. et al., 2020, Atmospheric Electricity at the Ice Giants. Space Sci Rev 216, 26. https://doi.org/10.1007/s11214-020-00647-0
[10] Kurazhkovskii, A. et al., 2023, Correspondence between Cosmic-Dust-Enriched Sediment Horizons and Geomagnetic Field Excursions. Geomagn. Aeron. 63, 811–817 https://doi.org/10.1134/S0016793223600698
[11] Paleari, C. et al., 2022, Cosmogenic radionuclides reveal an extreme solar particle storm near a solar minimum 9125 years BP. Nat Commun 13, 214, https://doi.org/10.1038/s41467-021-27891-4
[12] Ménabréaz, L. at al., 2011, The Laschamp geomagnetic dipole low expressed as a cosmogenic 10Be atmospheric overproduction at ~41ka, Earth and Planetary Science Letters, 312, 305-317, https://doi.org/10.1016/j.epsl.2011.10.037.