Palaeomagnetic evidence for the persistence or recurrence of geomagnetic main field anomalies in the South Atlantic

Shah, Jay; Koppers, Anthony A. P.; Leitner, Marko; Leonhardt, Roman; Muxworthy, Adrian R.; Heunemann, C.; Bachtadse, V.; Ashley, Jack; Matzka, Jürgen

doi:10.1016/j.epsl.2016.02.039

Cited by 23 publications

(20 citation statements)

References 43 publications

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“…For example, ignoring the existence of multiple surface minima might lead to discontinuous tracking of the absolute minimum. In addition, attempts to identify the SAA using regional archeointensity time-series (Tarduno et al 2015;Shah et al 2016) might erroneously ignore the existence of additional minima. Nevertheless such local timeseries may be useful in detecting shallow surface minima that are otherwise non-detectable in strongly regularized global field models.…”

Section: Discussion a N D C O N C L U S I O N Smentioning

confidence: 99%

“…In addition, based on archeological materials from Africa and South America, it was argued that rapid local temporal geomagnetic field variations in these regions are attributed to the SAA time evolution (e.g. Hartmann et al 2010Hartmann et al , 2011Tarduno et al 2015;Poletti et al 2016;Shah et al 2016;Hare et al 2018;Trindade et al 2018). Accordingly, the SAA may be locked to the South Atlantic at the surface, perhaps alternating between Africa and South America.…”

Section: Introductionmentioning

confidence: 99%

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Preferred locations of weak surface field in numerical dynamos with heterogeneous core–mantle boundary heat flux: consequences for the South Atlantic Anomaly

Terra-Nova

Amit

Choblet

2019

Geophysical Journal International

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S U M M A R YThe present-day geomagnetic field is characterized by a region of weak surface intensity, the socalled South Atlantic Anomaly (SAA). We identify the locations of surface intensity minima in modern, historical and archeomagnetic field models. We then investigate whether lower mantle thermal heterogeneity may explain the location of the SAA. We run numerical dynamos with heterogeneous core-mantle boundary (CMB) heat flux inferred from a lowermost mantle tomography model, varying dynamo internal control parameters as well as the amplitude of the CMB heat flux heterogeneity. Histograms of the longitude and latitude of surface intensity minima show the persistence of different locations. We find two preferred longitudes of surface intensity minima, one close to the present SAA minimum longitude. In contrast, in the dynamo models and in the archeomagnetic field models the surface intensity minima are often close to the equator, whereas the present-day SAA is at mid-latitudes. We demonstrate that the determining ingredients in dynamo models to reproduce the SAA latitude are related to north-south asymmetries of reversed and normal geomagnetic flux on the CMB. The imposed heterogeneous heat flux leads to more convective and magnetic activities in the Northern Hemisphere. Large time-average upwelling structure below the South Atlantic in the dynamo models correlates well with the present-day SAA region. Scaling laws analysis indicates that the persistence of surface minima longitudes is favored by slow rotation, strong convection and large heat flux heterogeneity. Furthermore, increasing mantle control yields two preferred longitudes and southern surface minima, the latter indicating that the present-day southern location of the SAA is mantle controlled. However, the rareness of mid-latitude minima in dynamo models and archeomagnetic field models leads us to speculate that the SAA midlatitude value at present is possibly unusual.

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Section: Discussion a N D C O N C L U S I O N Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Preferred locations of weak surface field in numerical dynamos with heterogeneous core–mantle boundary heat flux: consequences for the South Atlantic Anomaly

Terra-Nova

Amit

Choblet

2019

Geophysical Journal International

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“…1) suggest that the SAA is a recurrent feature (11,12). Subsequent analyses of Pleistocene basalts support this recurrence (13). Moreover, a hypothesis (11) based on the Limpopo data posits that the recurrence reflects a kind of top-down influence on the geodynamo.…”

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confidence: 94%

Subterranean clues to the future of our planetary magnetic shield

Tarduno

2018

Proc. Natl. Acad. Sci. U.S.A.

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“…I also combined the northern and southern hemisphere data, because the southern hemisphere data is very limited both spatially and temporally for the last 5 Myr. For example, for a 10 • bin size, several of the southern hemisphere bins have no data, and others have only one dataset covering narrow time periods, e.g., data from Tristan da Cunha (Shah et al, 2016) is the single data set in the −30 to −40 • bin and covers a time period of <50 kyr. After folding and binning at 10 • steps, the 80-90 • bin has no data, but the next least populated bin, the 0-10 • bin, has eight points.…”

Section: Comparison Of Current Ggp Models With the Latitudinal Palaeomentioning

confidence: 99%

Considerations for Latitudinal Time-Averaged-Field Palaeointensity Analysis of the Last Five Million Years

Muxworthy

2017

Front. Earth Sci.

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Central to palaeomagnetism and geophysics is the assumption that the time-averaged geomagnetic field is approximated by a geocentric-axial-dipole (GAD). In this paper, it is demonstrated through the use of a simple cap model that due to secular variation the time-averaged palaeointensity record will always have a smaller latitudinal dependency than a true GAD field. However, the simple cap model does not fully explain the behavior of the palaeointensity database (averaged over 0-5 Ma) especially at high-latitudes. To investigate this dependency I use a Giant Gaussian Processes (GGP) model to estimate the contribution of permanent non-dipole features and determine their statistical significance. It was found that an axial quadrupole term between −5 and −10% of the GAD field combined with octupole term ∼ −15% of the GAD field, best explained palaeointensity latitudinal behavior. In particular, the octupole term with a sign opposite to that of the GAD, is required to describe the palaeointensity behavior at high latitudes, i.e., >60 • .

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Palaeomagnetic evidence for the persistence or recurrence of geomagnetic main field anomalies in the South Atlantic

Abstract: 13We present a dataset of a full-vector palaeomagnetic study of Late Pleistocene lavas from the island 14

Cited by 23 publications

References 43 publications

Preferred locations of weak surface field in numerical dynamos with heterogeneous core–mantle boundary heat flux: consequences for the South Atlantic Anomaly

Preferred locations of weak surface field in numerical dynamos with heterogeneous core–mantle boundary heat flux: consequences for the South Atlantic Anomaly

Subterranean clues to the future of our planetary magnetic shield

Considerations for Latitudinal Time-Averaged-Field Palaeointensity Analysis of the Last Five Million Years

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