Global Geomagnetic Field Evolution From 900 to 700 ka Including the Matuyama‐Brunhes Reversal

Mahgoub, Ahmed Nasser; Korte, Monika; Panovska, Sanja

doi:10.1029/2023jb026593

Cited by 3 publications

(4 citation statements)

References 106 publications

(176 reference statements)

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“…where the window length is w = t 1 t 0 . Reversal trends for six events are computed from PADM2M (group A), together with a second estimate for the Matuyama-Bruhnes reversal (group B) from model GFFMB (Mahgoub et al, 2023).…”

Section: Trends Into Excursions and Reversalsmentioning

confidence: 99%

“…The paleomagnetic models are obtained from the EarthRef Digital Archive (Constable, 2016;Mahgoub, 2023;Panovska, 2018Panovska, , 2021Zeigler, 2011). The stochastic model and analysis tools are available from Zenodo (Buffett, 2024).…”

Section: Data Availability Statementmentioning

confidence: 99%

“…Setting x = 0 at the time of the reversal, t = t 1 , gives a trend

b=\frac{x\left({t}_{0}\right)}{w}

where the window length is w = t 1 − t 0 . Reversal trends for six events are computed from PADM2M (group A), together with a second estimate for the Matuyama‐Bruhnes reversal (group B) from model GFFMB (Mahgoub et al., 2023).…”

Section: Trends Into Excursions and Reversalsmentioning

confidence: 99%

“…Trends from these two models are important because they reveal distinctive changes in the trend variance when the duration exceeds the dipole decay time (see below). Transient trends for six reversals are computed from PADM2M; a second estimate for the Matuyama‐Bruhnes reversal is computed from the GGFMB model (Mahgoub et al., 2023).…”

Section: Introductionmentioning

confidence: 99%

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Excursions, Reversals, and Secular Variation: Different Expressions of a Common Mechanism?

Buffett

2024

Geochem Geophys Geosyst

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Fluctuations in the geomagnetic field occur over a broad range of timescales. Short‐period fluctuations are called secular variation, whereas excursions and reversals are viewed as anomalous transient events. An open question is whether distinct mechanisms are required to account for these different forms of variability. Clues are sought in trends b of the axial dipole moment from six time‐dependent geomagnetic field models. Variability in b has a well‐defined dependence on the time interval (or window) for the trend. The variance of b reveals a simple relationship to trends during excursions and reversals. This connection hints at a link between reversals, excursions and secular variation. Stochastic models exhibit a similar behavior in response to random fluctuations in dipole generation. We find that excursions, reversals and secular variation can be distinguished on the basis of trend durations rather than differences in the underlying physical process. While this analysis does not rule out distinct physical mechanisms, the paleomagnetic observations suggest that such distinctions are not required.

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Section: Trends Into Excursions and Reversalsmentioning

confidence: 99%

Section: Data Availability Statementmentioning

confidence: 99%

“…Setting x = 0 at the time of the reversal, t = t 1 , gives a trend

b=\frac{x\left({t}_{0}\right)}{w}

Section: Trends Into Excursions and Reversalsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Excursions, Reversals, and Secular Variation: Different Expressions of a Common Mechanism?

Buffett

2024

Geochem Geophys Geosyst

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Weather at the core: defining and categorizing geomagnetic excursions and reversals

Constable,

Morzfeld

2024

Geophysical Journal International

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Summary Paleomagnetic records provide us with information about the extreme geomagnetic events known as excursions and reversals, but the sparsity of available data limits detailed knowledge of the process and timing. To date there are no agreed on criteria for categorizing such events in terms of severity or longevity. In an analogy to categorizing storms in weather systems, we invoke the magnitude of the global (modified) paleosecular variation index $P_{i_D}$ to define the severity of the magnetic field state, ranging in level from 0 to 3, and defined by instantaneous values of $P_{i_D}$ with level 0 being normal ($P_{i_D}<0.5$) to extreme ($P_{i_D}\ge 15$). We denote the time of entry to an excursional (or reversal) event by when $P_{i_D}$ first exceeds 0.5, and evaluate its duration by the time at which $P_{i_D}$ first returns below its median value, termed the end of event threshold. We categorize each excursional event according to the peak level of $P_{i_D}$ during the entire event, with a range from Category-1 (Cat-1) to Cat-3. We explore an extended numerical dynamo simulation containing more than 1200 events and find that Cat-1 events are the most frequent (72%), but only rarely lead to actual field reversals where the axial dipole, $g_1^0$, has reversed sign at the end of the event. Cat-2 account for about 20% of events, with 34% of those leading to actual reversals, while Cat-3 events arise about 8% of the time but are more likely to produce reversals (43%). Higher category events take as much as 10 times longer than Cat-1 events. Two paleomagnetic field models separately cover the Laschamp excursion and Matuyama-Brunhes (M-B) reversal which are Cat-2 events with respective durations of 3.6 and 27.4 ky. It seems likely that Cat-2 may be an underestimate for M-B due to limitations in the paleomagnetic records. Our overall results suggest no distinction between excursions and reversals other than a reversal having the ending polarity state opposite to that at the start.

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Robustness of characteristics of the Matuyama-Brunhes geomagnetic field reversal found in global models

Mahgoub,

Korte,

Panovska

et al. 2024

Front. Earth Sci.

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Paleomagnetic data enables the global reconstruction of the geomagnetic field, allowing the investigation of significant events like polarity reversals and excursions. When compared to prior polarity reversals, the most recent one, the Matuyama-Brunhes (MB), is the best recorded reversal in terms of number of available paleomagnetic data. Nevertheless, several of these data have poor age control, and they are not distributed equally worldwide. Few global models have been presented for the MB; the most recent is the GGFMB (Global Geomagnetic Field Model for the MB reversal). Limitations imposed by input data and subjective assumptions about the data that are made in modelling restrict the resolution and reliability of these models. This study presents a suite of eight additional global models that reconstruct the magnetic field during the interval 700–900 ka ago, including the MB reversal and Kamikatsura (KKT) excursion. Through model comparisons, the robustness of the models in resolving MB reversal characteristics is assessed. The majority of models indicate that the reversal was mainly driven by the axial dipole field contribution gradually decreasing, while non-dipole parts slightly increased. At the core-mantle boundary, two high-latitude reverse flux patches appear at the beginning of the reversal, and it seems like a few precursors in the form of regionally seen transitional field occurred, related to variations in the decaying dipole moment. The main global polarity change occurred close to 778 ka, with the axial dipole quickly strengthening in the opposite direction in the following, completing the full polarity transition. All the models confirm the previously reported asymmetry of slow dipole decay and fast recovery, and indicate that the dipole moment was clearly lower in the late Matuyama than the early Brunhes. The whole reversal process occurred on average between 800 and 770 ka, with a duration of approximately 30 kyr. Out of four apparent excursions discovered in some of the models between 900 and 800 ka, the KKT excursion (890–884 ka), can be confirmed as a robust magnetic field feature. Additional, well dated paleomagnetic records in particular from the southern hemisphere are required to confirm several details suggested by the models that should only be interpreted with caution so far.

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Global Geomagnetic Field Evolution From 900 to 700 ka Including the Matuyama‐Brunhes Reversal

Cited by 3 publications

References 106 publications

Excursions, Reversals, and Secular Variation: Different Expressions of a Common Mechanism?

Excursions, Reversals, and Secular Variation: Different Expressions of a Common Mechanism?

Weather at the core: defining and categorizing geomagnetic excursions and reversals

Robustness of characteristics of the Matuyama-Brunhes geomagnetic field reversal found in global models

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