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Laschamp event

The Laschamp event, also known as the Laschamp geomagnetic excursion, was a brief episode of geomagnetic instability that occurred approximately 41,000 years ago during the Last Glacial Period, characterized by a dramatic weakening of Earth's magnetic field to roughly 10% of its modern intensity and a temporary reversal of the magnetic poles.^[1] This excursion was first identified in the 1960s through paleomagnetic analysis of volcanic lava flows from the Laschamp and Olby sites in the Chaîne des Puys region of central France, where reversed magnetic directions were dated to around 40–42 thousand years before present.^[2] Unlike a full geomagnetic reversal, which can span thousands of years, the Laschamp event represented a short-lived deviation from the normal axial dipole field configuration, with the dipole moment dropping near zero and transitional virtual geomagnetic poles (VGPs) clustering over the Americas and forming clockwise loops across the equator.^[3] Global paleomagnetic records from ocean sediments, lake varves, and ice cores confirm the event's timing between approximately 42 and 39 ka, with the core phase of field decay and recovery lasting about 1,800 years at Earth's surface, though core-mantle boundary processes extended to around 5,000 years.^[1]^[3] During this period, the geomagnetic field exhibited multipolar characteristics, including non-dipolar components and a dipole tilt of up to 76°, leading to fully reversed directions in some records, such as southerly declinations and steep positive inclinations observed in Southern Ocean sediments.^[4] Paleointensity proxies, like increased cosmogenic isotopes (e.g., ¹⁰Be and nitrate enhancements up to four times background levels in Antarctic ice cores), indicate heightened cosmic ray penetration due to reduced magnetic shielding, with field minima as low as 0.12 μT in some models.^[5]^[3] The Laschamp event's implications extend to paleoclimatology and geophysics, as the weakened field likely expanded the auroral oval to low latitudes—reaching regions like northern Africa and Australia—and enhanced ultraviolet radiation and atmospheric ionization, potentially influencing climate patterns and early human adaptations during the Aurignacian period.^[1] Global field models, such as LSMOD.2 and GGF100k, reconstruct the excursion as primarily driven by axial dipole collapse without significant non-axial influences, distinguishing it from contemporaries like the Mono Lake excursion at 34.5 ka, which showed shallower inclinations and less reversal.^[3]^[4] Ongoing research continues to refine its chronology and environmental impacts through high-resolution archives, underscoring its role as a key marker for studying geomagnetic variability over Quaternary timescales.^[2]

Discovery and Chronology

Initial Identification

The Laschamp event was first identified in the mid-1960s through paleomagnetic investigations of Quaternary volcanic rocks in the Chaîne des Puys volcanic field near Clermont-Ferrand, central France. In 1967, Norbert Bonhommet and Jacques Babkine reported reversed natural remanent magnetization directions in two lava flows—one at Laschamp (Puy de Laschamp) and another at nearby Olby—based on systematic sampling and measurements that revealed inclinations and declinations far from the expected normal polarity orientation of the contemporary geomagnetic field.^[6] Subsequent analysis by Bonhommet and Jochen Zähringer in 1969 employed potassium-argon (K-Ar) radiometric dating on whole-rock samples from these flows, yielding ages between approximately 8,000 and 20,000 years before present, while confirming the anomalous reverse polarity through detailed rock magnetic studies, including hysteresis and thermomagnetic analyses.^[7] This work established the event's recency within the Brunhes normal chron, ruling out local tectonic remagnetization or self-reversal mechanisms as primary causes.^[7] The initial interpretation framed the Laschamp event as a short-lived geomagnetic polarity transition rather than a full reversal, given the brevity implied by the clustered eruption ages and the lack of widespread stratigraphic evidence for prolonged instability; it was named the "Laschamp geomagnetic polarity event" and distinguished from major reversals like the Brunhes-Matuyama boundary at around 780,000 years ago.^[7] This discovery highlighted geomagnetic excursions—temporary deviations in field direction—as key features of paleomagnetic records, prompting further global searches for similar anomalies.^[8]

Age and Duration Estimates

The Laschamp event was initially identified in the 1960s through paleomagnetic analysis of volcanic flows in the Chaîne des Puys, France, with potassium-argon (K-Ar) dating yielding age estimates between 8,000 and 20,000 years before present (BP).^[9] Subsequent refinements using argon-argon (⁴⁰Ar/³⁹Ar) dating on the same Laschamp and Olby lava flows produced a weighted mean age of 40.4 ± 2.0 ka BP, incorporating analytical and decay constant uncertainties.^[10] Modern consensus places the event at approximately 41,000–42,000 years BP, supported by multiple dating techniques including calibrated radiocarbon (¹⁴C), uranium-thorium (U-Th), and ⁴⁰Ar/³⁹Ar methods applied to diverse archives such as lavas, sediments, and speleothems.^[11] High-precision U-Th dating of a speleothem from Crevice Cave, Missouri, identifies the main phase at 41.10 ± 0.35 ka BP, corroborated by annual layer counting that confirms growth bands with ~100-year resolution.^[12] Varve chronology from Lake Suigetsu, Japan, provides a mid-age of 42,050 ± 120 IntCal20 yr BP using a Bayesian model integrated with ¹⁴C calibration from ice cores, enhancing accuracy for this period where geomagnetic field minima affect atmospheric ¹⁴C production.^[11] Estimates for the duration of the Laschamp excursion vary by record type but indicate a rapid polarity flip lasting 250–1,000 years within a broader interval of weakened geomagnetic field intensity extending up to 2,000–2,500 years.^[13] In the Crevice Cave speleothem, the directional excursion's main phase spanned ~700 years, embedded in a total low-intensity period of ~2,550 years from 42.25 to 39.70 ka BP.^[12] High-resolution varve counts at Lake Suigetsu yield a duration of 790 years for the excursion, aligning with sediment records showing paleointensity drops and virtual geomagnetic pole excursions over similar timescales.^[11] Recent global paleomagnetic modeling as of 2025 refines the surface duration of the core excursion phase to approximately 1,800 years within the 42–39 ka interval.^[1] These advancements in dating precision, from early volcanic K-Ar methods to integrated U-Th and ¹⁴C-ice core calibrations, have narrowed uncertainties and established the Laschamp as a benchmark for late Quaternary geomagnetic variability.^[10]

Geomagnetic Characteristics

Field Reversal Dynamics

The Laschamp event involved a gradual weakening of Earth's geomagnetic dipole field, reducing its intensity to approximately 5–10% of modern values over several centuries, prior to a brief reversal in polarity.^[1] This process began around 42 ka, with the dipole moment declining steadily until reaching a critical low, after which the North and South magnetic poles effectively swapped positions for a duration of about 250–1,000 years.^[14] The reversal was not a stable, full geomagnetic inversion but a transient excursion, characterized by unstable field configurations that allowed the dominant dipole to flip temporarily before recovering to the normal polarity.^[11] During the transitional phase of the reversal, the geomagnetic field deviated significantly from a simple dipolar structure, leading to the dominance of non-dipolar components. Virtual geomagnetic poles (VGPs), which represent the apparent position of the magnetic pole based on local paleomagnetic directions, exhibited erratic wandering paths primarily across low-latitude regions.^[11] These paths formed distinct clusters in hemispherically symmetric areas, such as the North Pacific, South Pacific, Southern Indian Ocean, and eastern Africa, with movements occurring at rates of up to half a degree in latitude per year.^[11] This multipolar behavior, involving multiple subcentennial "swings" in field direction, underscored the instability and complexity of the field morphology, as non-axial dipolar sources intermittently overpowered the weakening axial dipole.^[11] A key quantitative indicator of this reversal was the sharp decline in the virtual axial dipole moment (VADM), which dropped below $1 \times 10^{22} \ \mathrm{Am}^2 during the excursion's nadir around 41 ka, compared to modern values of approximately $8 \times 10^{22} \ \mathrm{Am}^2.^[15] This reduction, reaching as low as $0.12 \times 10^{22} \ \mathrm{Am}^2 in some global models, reflected the near-collapse of the axial dipole and the temporary ascent of higher-order spherical harmonics in the field expansion.^[15] The recovery phase saw a gradual restoration of the dipole, with VADM increasing at rates of about $1.6 \times 10^{22} \ \mathrm{Am}^2/ka, highlighting the event's short-lived nature within the broader context of geomagnetic variability.^[14]

Intensity and Polarity Variations

During the Laschamp event, the Earth's geomagnetic field intensity experienced a dramatic global reduction, with estimates varying by record: global sediment models indicate drops to as low as ~2% of present-day values (virtual axial dipole moment minimum of 0.12 × 10^{22} Am²), while cosmogenic isotope and some paleointensity records suggest minima around 19% (1.5 × 10^{22} Am²), compared to the modern value of about 8 × 10^{22} Am².^[15]^[14] This decline was not uniform, exhibiting regional variations; for instance, paleointensity records from the North Atlantic indicate some of the lowest values, approaching near-zero field strengths during the excursion's peak.^[16] Such reductions highlight the event's instability, where the field weakened sufficiently to allow significant penetration of cosmic rays into the atmosphere.^[1] Polarity variations during the Laschamp event were characterized by a brief full reversal of the geomagnetic field, lasting approximately 440 years, during which the magnetic north and south poles effectively swapped positions.^[17] This reversed phase was preceded and followed by periods of partial polarity flips and excursional loops, where paleomagnetic directions oscillated erratically between normal and reversed orientations over timescales of several hundred years.^[2] These instability patterns, observed in multiple sedimentary and volcanic records, indicate a highly dynamic transitional regime rather than a stable reversal, with the full excursion spanning roughly 1,800 years at the surface.^[1] Local volcanic records show paleointensities of 4–5 μT during the reversed phase (about 10% of Holocene values), while global models suggest even lower intensities.^[18] Paleointensity measurements for the Laschamp event have primarily relied on the Thellier-Thellier double-heating method applied to volcanic rocks, which compares the natural remanent magnetization (NRM) with thermoremanent magnetization (TRM) acquired in a laboratory field to estimate ancient field strengths.^[19] In European sites, such as those in the French Chaîne des Puys and Icelandic lavas recording the event, this technique has yielded reliable values averaging 4–5 μT during the reversed phase, representing about 10% of typical Holocene intensities in those regions.^[18] These low estimates, derived from samples with single-domain-like magnetic grains, confirm the field's severe weakening and provide quantitative constraints on the excursion's geomagnetic behavior.^[20]

Underlying Mechanisms

Proposed Geophysical Causes

The Laschamp event is hypothesized to have been triggered by interactions at the core-mantle boundary (CMB), where anomalous magnetic flux patches play a central role in destabilizing the geomagnetic field. Paleomagnetic reconstructions indicate that inverse flux patches emerged near the equator at the CMB and migrated poleward, leading to a synchronous decay in both dipolar and non-dipolar field components, without the persistent polarity opposition seen in full geomagnetic reversals. Such CMB flux anomalies are thought to arise from heterogeneous heat flow or compositional variations at the boundary, disrupting the stable convection patterns in the outer core.^[21] Numerical models of the geodynamo further support the role of internal instabilities in generating the Laschamp excursion's transient features. Simulations demonstrate that chaotic, turbulent flows in the liquid outer core can produce rapid field variations, including virtual geomagnetic poles wandering to high latitudes and brief polarity flips lasting less than a millennium. These models, spanning magnetic Reynolds numbers from 100 to 700, reveal that low field intensities—similar to those during the Laschamp—allow reversed flux patches to propagate across the core surface, particularly at latitudes below 40°, driving directional changes up to 10° per year at the Earth's surface. Recent high-resolution models (as of 2025) further corroborate these instabilities, emphasizing the role of low-latitude flux patches in driving transient excursions on timescales of centuries.^[22]^[23] Unlike longer-term reversals, these instabilities recover without significant non-dipolar energy dominance, highlighting the excursion as a short-lived dynamo perturbation.^[22] Subtle paleoclimatic influences, tied to orbital forcing and ice sheet dynamics during Marine Isotope Stage 3, may have indirectly modulated core convection through surface loading effects. Growth of northern hemisphere ice sheets, driven by Milankovitch cycles, altered Earth's moment of inertia and induced isostatic adjustments that propagated to the CMB via topographic coupling. These changes could generate tangential velocities at the CMB on the order of 0.03 cm/s—comparable to outer core flows—potentially perturbing convection and amplifying dynamo instabilities over 100-ka glacial timescales. While not the primary driver, such loading effects provide a plausible external modulation to internal geodynamo processes during the Laschamp period.^[24]

Links to Broader Geomagnetic Processes

The Laschamp event exemplifies a geomagnetic excursion, characterized by a transient deviation in the Earth's magnetic field direction without a complete and enduring polarity reversal. Positioned within the Brunhes normal polarity chron, which extends from the present day back to approximately 780,000 years ago, the Laschamp excursion occurred around 41,000 years ago and involved the virtual geomagnetic pole (VGP) shifting more than 45° from the geographic pole before returning to its prior orientation.^[11] This contrasts sharply with full geomagnetic reversals, such as the Matuyama-Brunhes boundary that initiated the Brunhes chron, where the dominant axial dipole polarity inverts permanently for extended periods, often spanning 100,000 years or more, reflecting a fundamental reconfiguration of the geodynamo.^[11] Excursions like Laschamp thus represent aborted or incomplete reversal attempts, with durations typically under 1,000 years and field intensities dropping to 5–10% of modern values before recovery.^[15] In the broader geomagnetic record, the Laschamp event is one of roughly 13 documented excursions within the Brunhes chron over the past 780,000 years, underscoring their relative frequency compared to full reversals.^[25] Comparable events include the Mono Lake excursion at approximately 34,000 years ago, marked by regional field weakening and directional anomalies, and the Norwegian-Greenland Sea excursion around 65,000 years ago, both of which exhibit similar short-term dipole collapses without polarity flips.^[15] These occurrences cluster during intervals of overall low field intensity, suggesting periodic vulnerabilities in the geomagnetic system rather than isolated anomalies, with global paleomagnetic records confirming their recurrence every 50,000–100,000 years on average within the chron.^[25] The Laschamp excursion illuminates critical instability thresholds in the geodynamo, the convective processes in Earth's liquid outer core that sustain the magnetic field, by demonstrating how dipole weakening enables transient dominance of non-axial dipolar components.^[11] Such insights refine numerical models of core dynamics, revealing how flux patches at the core-mantle boundary can trigger field deviations and inform predictions for full reversals, which proceed irregularly but average 200,000–300,000 years apart over the past few million years, with the Brunhes chron representing an unusually stable interval.^[15]^[26] By highlighting recoverable low-energy states of the dipole, the event contributes to understanding the geodynamo's resilience and the precursors to more drastic polarity transitions.^[11]

Paleomagnetic and Proxy Evidence

Sediment and Lava Records

The Laschamp event was initially identified through paleomagnetic analyses of Quaternary lava flows in the Chaîne des Puys volcanic field near Clermont-Ferrand, France, where several flows exhibit anomalous remanent magnetizations indicative of a brief geomagnetic excursion.^[2] The Laschamp flow itself records a fully reversed polarity with inclinations approaching -60°, while nearby flows like Olby show similar reversed directions at -67.6°, and transitional sites such as Louchadière and Royat display intermediate inclinations between +65° and -60°, capturing the rapid field swing.^[27] These volcanic records, dated to approximately 40-41 ka via 40Ar/39Ar methods, provide snapshot evidence of the event's intensity drop and polarity reversal, with virtual geomagnetic poles (VGPs) scattering across low latitudes, suggesting a non-dipolar field configuration during the excursion.^[28] Comparable volcanic records extend to other regions, including lava flows from Mount Etna in Italy, which preserve transitional directions and low paleointensities consistent with the Laschamp excursion around 41 ka.^[29] These Italian basalts, alongside French examples, demonstrate the global reach of the event's magnetic signature in rapidly cooled volcanic rocks, where thermal remanent magnetization locks in the ambient field at eruption, minimizing post-emplacement alteration.^[3] Sediment cores from marine environments offer continuous records of the Laschamp event, revealing progressive directional changes and paleointensity variations. In the North Atlantic, Ocean Drilling Program (ODP) Sites 1061 and 1062 yield high-resolution paleomagnetic data showing inclination swings from +60° to -60° over a few centuries, accompanied by a paleointensity low to less than 10% of normal values at ~41 ka.^[2] Similarly, southeastern Black Sea sediment sequences from multiple cores document the full excursion with declination shifts up to 180° and inclination reversals, tied to a paleointensity minimum via relative paleointensity proxies like normalized natural remanent magnetization.^[17] These archives, with sedimentation rates of 20-30 cm/ky, enable detailed tracking of the event's duration and asymmetry. Recent paleomagnetic records from sediments in the Drake Passage, southern high latitudes, confirm the Laschamp excursion's occurrence around 41 ka, revealing multipolar field behavior with significant inclination swings and paleointensity reductions to near zero, supporting a global non-dipolar configuration during the event.^[4] Reliability of sediment records can be challenged by magnetic overprinting from later diagenetic processes, such as greigite formation in anoxic environments, but alternating field demagnetization effectively isolates the primary detrital remanent magnetization in many cases.^[30] Volcanic records, being less prone to such alterations, serve as anchors for correlating sediment data, confirming the event's timing around 41 ka across hemispheres.^[31]

Isotopic and Cosmogenic Indicators

One of the primary isotopic indicators of the Laschamp event is the pronounced spike in beryllium-10 (¹⁰Be) concentrations observed in Greenland ice cores, such as the Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice Core Project (GRIP), which reflects an enhanced flux of cosmic rays due to the geomagnetic field's temporary weakening. These records show a characteristic double peak in ¹⁰Be flux around 41 ka, with concentrations reaching up to twice the background levels, directly correlating with the period of low dipole moment during the excursion. Similar ¹⁰Be enhancements have been documented in sediment traps from ocean environments, where the nuclide's deposition serves as a proxy for atmospheric production rates that inversely scale with geomagnetic shielding efficiency. This cosmogenic signal aligns temporally with paleomagnetic records, confirming the event's duration and intensity. Carbon-14 (¹⁴C) production also exhibits a significant peak during the Laschamp event, as evidenced by Δ¹⁴C anomalies in annually resolved tree-ring chronologies and coral records, reaching up to +100‰ relative to pre-event baselines around 41 ka. These excursions arise from increased cosmic ray bombardment of atmospheric nitrogen, leading to elevated ¹⁴C formation when the geomagnetic field offers reduced protection, with the anomaly persisting for several millennia post-event due to carbon cycle dynamics. Tree rings from northern hemisphere sites and coral samples from the tropics provide high-precision timelines for this signal, demonstrating a rapid rise and gradual decline in atmospheric ¹⁴C levels that corroborates the field's dipole low to approximately 5-10% of modern strength. Additional cosmogenic nuclides, such as chlorine-36 (³⁶Cl) in Greenland ice cores and ¹⁰Be in ocean sediments, further quantify the Laschamp event's impact on production rates, which were elevated by factors of 2-3 compared to stable periods, inversely proportional to the diminished geomagnetic field intensity. The ³⁶Cl flux in the GRIP core displays a prominent peak at approximately 40-41 ka, attributed to the same cosmic ray modulation, while authigenic ¹⁰Be in marine sediments from mid-latitude sites records comparable enhancements, offering a global perspective on the event's spatial uniformity. These tracers collectively indicate a transient but profound reduction in Earth's magnetic shielding, with production rates scaling roughly as the inverse square of the dipole moment.

Environmental and Biological Impacts

Radiation and Atmospheric Effects

During the Laschamp event, the Earth's geomagnetic field intensity dropped to approximately 5-10% of its present-day value, severely compromising its shielding against galactic cosmic rays (GCRs). This modulation failure allowed a greater influx of GCRs into the atmosphere, increasing the cosmic ray flux by a factor of roughly 2, as indicated by elevated production rates of cosmogenic isotopes like ¹⁰Be preserved in Greenland ice cores and marine sediments.^[32] Proxy evidence from these isotopes confirms sharp spikes in atmospheric radiation exposure during the excursion.^[32] The heightened GCR penetration intensified atmospheric ionization, particularly in the stratosphere, leading to enhanced production of nitrogen oxides (NOₓ) via reactions between cosmic ray-induced electrons and ambient N₂ and O₂ molecules. These NOₓ compounds acted as catalysts in ozone-destroying cycles, resulting in modeled global stratospheric ozone reductions of 1-2% above 20 km altitude and up to 5% near the northern hemispheric tropopause.^[33] Such changes were driven by simulations incorporating the weakened field conditions and GCR ionization rates from the CRAC:CRII model.^[33] The field's collapse and nondipolar configuration further enabled solar wind particles to access lower latitudes, dramatically expanding the auroral ovals. Auroral displays, typically confined to polar regions, shifted equatorward, becoming visible across middle and low latitudes in both hemispheres; in the Southern Hemisphere, they extended as far as eastern Australia and New Zealand around 41 ka. This global redistribution of auroral activity stemmed from a rapid dipole tilt exceeding 70° and an enlarged open-field polar cap. Recent modeling as of 2025 indicates that this wandering of the auroral oval, combined with reduced cutoff rigidities, amplified cosmic radiation effects, including modest ozone depletion and increased UVR exposure.^[1]

Implications for Ecosystems and Human Ancestors

The weakened geomagnetic field during the Laschamp event, reaching approximately 5-10% of its modern intensity, resulted in a substantial increase in incoming cosmic rays and ultraviolet radiation (UVR) at Earth's surface, elevating radiation exposure risks for prehistoric ecosystems. Modeling indicates that UVR flux may have increased by 10–20% compared to present levels due to associated ozone depletion, leading to elevated rates of DNA damage through the formation of cyclobutane pyrimidine dimers and other photoproducts that impair cellular replication and transcription.^[34]^[35] This heightened radiation could have contributed to increased mutation rates and oxidative stress in organisms, potentially exacerbating vulnerabilities in populations already stressed by environmental changes, though direct causation remains debated.^[34] In the context of early human evolution, the Laschamp event temporally overlaps with the decline and extinction of Neanderthals around 41–39 thousand years ago (ka) and the migration of anatomically modern Homo sapiens into Eurasia around 40 ka. Neanderthals, with potentially greater sensitivity to UVR due to differences in the aryl hydrocarbon receptor (AhR) pathway compared to modern humans, may have faced compounded health risks from elevated DNA damage and cancer incidence, contributing to their demise alongside competition and climatic pressures. Meanwhile, the event coincided with a surge in cave art production across Europe and Indonesia, possibly inspired by intensified auroral displays visible at lower latitudes due to the expanded auroral oval, prompting increased sheltering and cultural expression among surviving human groups.^[34]^[36]^[1] Ecosystem disruptions during the Laschamp event likely imposed stress on megafaunal populations, particularly in Australia and Eurasia, where environmental shifts amplified radiation effects. In Australia, approximately 14 of 16 large marsupial and reptilian genera became extinct around 40 ka, with increased UVR potentially hindering reproductive success and foraging behaviors in open habitats, though primary drivers such as climate variability and human arrival are also contested. In Eurasia, similar pressures may have affected herbivore communities, altering vegetation dynamics and contributing to trophic cascades, but evidence suggests radiation acted as a secondary factor rather than the sole cause of these declines.^[34]^[36]

Ongoing Research and Implications

Key Historical Studies

The discovery of the Laschamp event began in the 1960s with paleomagnetic investigations of volcanic flows in the Chaîne des Puys region of France's Massif Central. Norbert Bonhommet and Jochen Zähringer identified anomalous reversed polarity directions in samples from the Laschamp and nearby Olby lava flows, marking the first recognition of a short-lived deviation from the normal geomagnetic field orientation. Their study, involving over 150 sampling sites across more than 50 volcanic units, demonstrated that these directions were not due to local tectonic disturbances but indicated a global geomagnetic instability, initially interpreted as a brief polarity reversal.^[37] This work established the Laschamp as a key example of a geomagnetic excursion, distinct from full reversals like the Brunhes-Matuyama boundary. In the 1970s, efforts focused on refining the age and nature of the event to distinguish it from a true reversal. Early potassium-argon (K-Ar) dating by Bonhommet and Zähringer suggested an age between 20,000 and 8,000 years before present (BP), but this range was inconsistent with emerging global records. Pierre-Yves Gillot and colleagues advanced dating techniques in 1979, applying unspiked K-Ar methods to the Laschamp and Olby flows, yielding ages of 43 ± 5 ka for the Laschamp flow and 50 ± 7.5 ka for Olby; these estimates were later refined using 40Ar/39Ar dating to approximately 40.4 ± 1.0 ka, confirming the event's timing around 41 ka.^[38]^[39] These refinements confirmed the event's brevity—lasting less than 1,000 years—and classified it definitively as an excursion rather than a prolonged polarity switch, providing a chronological anchor for correlating paleomagnetic anomalies worldwide.^[40] During the 1980s and 1990s, sediment core analyses expanded the Laschamp record beyond volcanic terrains, emphasizing its global synchroneity through marine paleomagnetic proxies. Researchers like Norbert R. Nowaczyk shifted focus to deep-sea and lake sediments, where continuous deposition allowed higher-resolution sampling. In a seminal 1997 study, Nowaczyk and Martin Antonow examined four sediment cores from the Greenland Sea, identifying the Laschamp excursion through pronounced dips in relative paleointensity and full vector reversals in inclination and declination, spanning approximately 40 cm of sediment thickness.^[41] This work, combined with contemporaneous analyses from the Indian Ocean and North Atlantic, demonstrated that the excursion occurred simultaneously across hemispheres, with consistent timing around 41 ka, ruling out regional biases in the lava-based records.^[16] The early 2000s saw cosmogenic isotope studies integrate with paleomagnetism to corroborate the Laschamp's age and intensity via independent production proxies. Grant M. Raisbeck and Françoise Yiou pioneered the use of beryllium-10 (¹⁰Be) measurements in polar ice cores, detecting a sharp production peak corresponding to enhanced cosmic ray flux during the geomagnetic low.^[42] Their analyses of Greenland and Antarctic ice, building on prior ¹⁰Be data, aligned the peak precisely at 41 ka, matching sediment and lava chronologies and quantifying the field's dipole moment drop to about 5-10% of modern values.^[43] This linkage solidified the Laschamp's ~41 ka age as a robust tie-point for synchronizing paleoclimate and geomagnetic records, highlighting methodological evolution from direct rock magnetism to isotope-based flux modeling.^[44]

Modern Interpretations and Future Directions

Recent studies since 2010 have refined understandings of the Laschamp event's broader implications, particularly its potential environmental and societal effects. A 2021 analysis by Cooper et al. synthesized geological and archaeological data to propose that the geomagnetic excursion triggered a global environmental crisis around 42,000 years ago, including ozone layer depletion and increased ultraviolet radiation, which may have influenced human behavioral adaptations such as cave usage and the development of symbolic art in prehistoric populations.^[36] This interpretation links the weakened magnetic field to atmospheric changes that exacerbated climate variability during the event. A 2024 study by Clizzie and Constable indicates significant disruptions in core surface flows during the Laschamp excursion, with a reversal from eastward to westward zonal drift, suggesting a major reorganization of convective patterns in Earth's outer core that contributed to the field's instability.^[45] Ongoing debates center on the precise spatial extent of the Laschamp event and its climatic ramifications. While paleomagnetic records confirm its global nature, with field reversals observed across multiple continents, some researchers question the uniformity of intensity reductions, proposing regional variations in non-dipole components that could have led to heterogeneous shielding from cosmic rays.^[15] The 2021 proposal by Cooper et al. has been influential but contentious, with critics arguing that the evidence for direct causal links to ozone depletion, enhanced UV radiation, and specific human adaptations remains speculative and requires further substantiation.^[46] Furthermore, connections to climate teleconnections remain contentious; elevated atmospheric ¹⁴C production due to reduced geomagnetic shielding is well-documented, potentially influencing carbon cycle dynamics and regional cooling through ion-induced cloud formation, though causal links to broader glacial-interglacial shifts require further validation.^[47] In 2025, Mukhopadhyay et al. reconstructed the global auroral oval and space environment during the Laschamp, demonstrating its wandering and expansion to low latitudes such as northern Africa and Australia due to diminished magnetic shielding, with implications for heightened cosmic ray influx and atmospheric ionization.^[1] A November 2024 study further refined definitions and categorizations of geomagnetic excursions and reversals, classifying the Laschamp as featuring pronounced directional changes with brief reversed polarity intervals.^[48] Additionally, a 2024 project sonified the transitional magnetic field variations based on paleomagnetic data, providing an auditory representation to aid public understanding of the event's dynamics.^[49] Future research directions emphasize enhanced data resolution and predictive modeling to better anticipate excursion recurrence. High-resolution drilling projects in polar regions, such as Antarctic ice cores and Arctic sediments, aim to capture finer temporal details of field variations and associated cosmogenic isotope spikes, improving chronologies beyond current limitations.^[50] Complementing this, AI-driven geodynamo models are emerging to simulate excursion precursors by analyzing time-series data from historical field reversals, offering potential forecasts of recurrence intervals on millennial timescales.^[51] These approaches promise to integrate empirical records with numerical simulations for more robust predictions of geomagnetic stability.

References

[1]
Wandering of the auroral oval 41,000 years ago | Science Advances
Apr 16, 2025 · The Laschamps excursion persisted for roughly 1800 years at the Earth's surface, and a deeper investigation into the core-mantle boundary across ...
[2]
High-resolution record of the Laschamp geomagnetic excursion at ...
We present here high-resolution palaeomagnetic records of the Laschamp excursion obtained from two Ocean Drilling Program (ODP) Sites, 1061 and 1062 on the ...
[3]
Robust Characteristics of the Laschamp and Mono Lake ... - Frontiers
All models suggest that the excursion process during the Laschamp is mainly governed by axial dipole decay and recovery, without a significant influence from ...<|control11|><|separator|>
[4]
The Mono Lake and Laschamps Geomagnetic Excursions Recorded ...
Jan 4, 2025 · During the Laschamps excursion even a slight field recovery can be observed during the reversed phase of the field vector. Both excursions in ...Missing: sources | Show results with:sources
[5]
The Laschamp geomagnetic excursion featured in nitrate record ...
Jan 28, 2016 · The Laschamp excursion was highlighted in different natural archives from both hemispheres as a dramatic paleointensity drop in lava flows and ...
[6]
Self-reversal of natural remanent magnetisation in the Olby ... - Nature
Mar 27, 1980 · In 1967 Bonhommet and Babkine1 reported reversed magnetisation directions in two lavas at Laschamp and Olby (Chaîne des Puys, Auvergne, France).
[7]
[PDF] A review of the discovery of the Laschamp excursion in the Chaîne ...
Bonhommet and Babkine (1967) discovered reversed paleomagnetic directions in the Olby and Laschamp flows. First dated between 20 and 8 ka BP (Bonhommet and ...
[8]
Origin and age of the directions recorded during the Laschamp ...
Aug 6, 2025 · The low geomagnetic field of the Laschamp event, which was first discovered in a lava flow of the Massif Central, France (Bonhommet and ...
[9]
On the age of the Laschamp geomagnetic excursion
### Summary of Abstract and Key Findings on Age of Laschamp Excursion and Dating Methods
[10]
Intermittent non-axial dipolar-field dominance of twin Laschamp ...
Apr 4, 2022 · Here we report a palaeomagnetic record from the varved sediments of Lake Suigetsu, central Japan, which reveals fine structures in the Laschamp Excursion.
[11]
[PDF] Age of the Laschamp excursion determined by U-Th dating of a ...
Jan 4, 2016 · ABSTRACT. The Laschamp geomagnetic excursion was the first short-lived polarity event recognized and described in the paleomagnetic record, ...Missing: papers | Show results with:papers
[12]
https://www.repository.cam.ac.uk/bitstreams/50e5f8f9-25c1-413c-9563-185263b05631/download
[13]
Cosmogenic 10Be production records reveal dynamics of ...
Nov 15, 2020 · Cosmogenic 10Be production records reveal dynamics of geomagnetic dipole moment (GDM) over the Laschamp excursion (20–60 ka). Author links open ...
[14]
Global Evolution and Dynamics of the Geomagnetic Field in the 15 ...
Nov 30, 2021 · For example, for the Laschamps excursion globally distributed sediment records gave an average duration of 1,300 years (Panovska, Constable, & ...
[15]
Deep‐sea sediment records of the Laschamp geomagnetic field ...
Apr 2, 2005 · [5] The Laschamp Excursion was first observed by Bonhommet and Babkine [1967], based on a paleomagnetic study of Quaternary lava flows from the ...
[16]
Dynamics of the Laschamp geomagnetic excursion from Black Sea ...
Oct 15, 2012 · Recorded field reversals of the Laschamp excursion, lasting only an estimated ∼250 yr, are characterized by low relative paleointensities (5% ...<|control11|><|separator|>
[17]
Paleointensity of the Earth's magnetic field recorded by two Late ...
Feb 10, 1991 · ... paleointensity experiments which were performed with the Thellier method. Samples with minimum overprint, composed by single-domain or ...
[18]
[PDF] The Laschamp geomagnetic field excursion recorded in ... - HAL
Apr 13, 2011 · This is a PDF file of an unedited manuscript that has been accepted for publication. ... Laschamp excursion (≈40 ka) (Bonhommet and Babkine, 1967) ...
[19]
Paleointensity of the Earth's magnetic field and K‐Ar dating of the ...
This low value and previous results of the Laschamp excursion from France and Iceland confirm that the Earth's magnetic field was in an intermediate state ...
[20]
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/GL016i010p01189
[21]
https://doi.org/10.1016/j.epsl.2008.11.028
[22]
[PDF] Ice Ages and Geomagnetic Reversals
Since polarity reversals can occur several times in 1 Ma, there must be other phenomena which cause the short time scale variations in topographic coupling.
[23]
Eccentricity-paced geomagnetic field and monsoon rainfall ... - PNAS
Apr 17, 2023 · The 10BeGM flux (a proxy for geomagnetic field-induced 10Be production rate) reveals 13 consecutive geomagnetic excursions in the Brunhes chron, ...
[24]
[PDF] Reversals & Excursions:
Nov 11, 2019 · The most recent reversal, the. Matuyama-Brunhes transition was at 0.78 Ma. • Reversals form an important part of the geological time scale.
[25]
[PDF] Origin and age of the directions recorded during the Laschamp ...
Compilation of the Virtual Geomagnetic Poles (VGPs) published so far from volcanic lava flows linked to the Laschamp event (Bonhommet and Zähringer, 1969; ...
[26]
Origin and age of the directions recorded during the Laschamp ...
Jul 30, 2007 · Bonhommet and Zähringer (1969) rapidly discovered other flows from the same area with directions significantly away from the axial dipole. The ...
[27]
Mono Lake or Laschamp geomagnetic event recorded from lava ...
The flow am2 (excursional unit) gives an average palaeointensity (using two results) of 24.0 μT, corresponding to a VDM of 3.4 × 1022 A m2. The two normal flows ...
[28]
Records of the Laschamps geomagnetic polarity excursion from ...
Oct 23, 2020 · In this paper, we discuss palaeomagnetic records obtained from greigite-affected sediment cores that were recovered from two different water ...
[29]
Synchronizing volcanic, sedimentary, and ice core records of Earth's ...
Aug 7, 2019 · ... value of 2.46 × 1022 Am2 occurring during the Laschamp excursion (39). These six lavas yield 40Ar/39Ar ages ranging from 786 ± 5 to 781 ± 6 ...
[30]
https://academic.oup.com/gji/article/224/2/1079/5936340
[31]
https://www.science.org/doi/10.1126/sciadv.aaw4621
[32]
The Role of Geomagnetic Field Intensity in Late Quaternary ...
May 29, 2019 · The geomagnetic field influenced evolution of large long-lived mammals through exposure to UVR at times of low field strength.
[33]
A global environmental crisis 42,000 years ago | Science
Feb 19, 2021 · Studies of Greenland ice cores have failed to reveal marked impacts in high-latitude paleoclimate associated with Laschamps (5, 6), and this ...
[34]
A review of the discovery of the Laschamp excursion in ... - NASA ADS
Bonhommet and Babkine (1967) discovered reversed paleomagnetic directions in the Olby and Laschamp flows. First dated between 20 and 8 ka BP (Bonhommet and ...Missing: original | Show results with:original
[35]
Age of the Laschamp paleomagnetic excursion revisited
The reverse paleomagnetism of the lava flows of Laschamp and Olby, already discovered by Bonhommet and Babkine, is confirmed. ... Paris. (1966). BonhommetN ...
[36]
[PDF] 5.10 Geomagnetic Excursions - Elsevier
Bonhommet and. Babkine (1967) discovered this excursion and named it after the Puy de Laschamp, in the French. Chaîne des Puys (Massif Central, France). The ...
[37]
High-resolution magnetostratigraphy of four sediment cores from
According to Nowaczyk & Baumann (1992), sampling for magnetostratigraphic and rock magnetic analysis was carried out using cubic plastic boxes (volume=6.2 cm3) ...
[38]
Enhanced cosmic‐ray production of 10Be coincident with the Mono ...
Mar 1, 1995 · Enhanced cosmic-ray production of 10Be coincident with the Mono Lake and Laschamp Geomagnetic Excursions ... Raisbeck, G. M., 10Be deposition at ...
[39]
Laschamp Excursion at Mono Lake? - ScienceDirect.com
However, cosmogenic 10Be or 36Cl peaks attributed to the ∼28 14C ka Mono Lake excursion have also been reported in some ice cores [21], [22] and sedimentary ...
[40]
Amplitude and timing of the Laschamp geomagnetic dipole low from ...
Nov 8, 2012 · The first dating by Bonhommet and Zahringer [1969] using K/Ar methods performed on whole rock led to an age determination between 8 and 20 ka.Missing: original | Show results with:original
[41]
Changes in zonal core flow during the Laschamp geomagnetic ...
During the Laschamp excursion, we find an eastward-to-westward transition in drift direction (see figure) suggesting a reorganization in core surface flow.Missing: simulations disruptions
[42]
Midlatitude cooling caused by geomagnetic field minimum during ...
Jan 7, 2013 · The CR–cloud connection suggests that variations in geomagnetic field intensity could change climate through modulation of CR flux.Midlatitude Cooling Caused... · Results And Discussion · Paleomagnetic Measurements
[43]
Connecting the Greenland ice-core and U∕Th timescales via ... - CP
We use cosmogenic radionuclides ( 10 Be, 36 Cl, 14 C) to link Greenland ice-core records to U∕Th-dated speleothems, quantify offsets between the two timescales.
[44]
Can machine learning reveal precursors of reversals of the ...
We investigate if machine learning (ML) techniques can reliably identify precursors of reversals based on time-series of the axial magnetic dipole field.