Geomagnetic intensity and inclination variations at Hawaii for the past 98kyr from core SOH-4 (Big Island): a new study and a comparison with existing contemporary data

Làj, C.; Kissel, Catherine; Scao, Vincent; Beer, J.; Thomas, Donald M.; Guillou, Hervé; Muscheler, Raimund; Wagner, G.

doi:10.1016/s0031-9201(01)00291-6

Cited by 59 publications

(42 citation statements)

References 47 publications

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“…While at most sites the field intensity drops to about 10-20% of the pre-transitional values close to the dipole minimum, in some regions like the Pacific relatively large intensities are retained. This IMOLEe prediction is consistent with independent paleomagnetic observations in Hawaii (Laj et al 2002) although the ages for the paleomagnetic data are not well constrained. According to IMOLEe, lowest intensities are observed 2 kyr M prior to the Laschamp excursion in Hawaii.…”

Section: Implications Of Paleomagnetic Observations Of Excursionssupporting

confidence: 79%

Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations

2010

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Recent advances in the study of geomagnetic field reversals are reviewed. These include studies of the transitional field during the last geomagnetic reversal and the last geomagnetic excursion based on paleomagnetic observations, and analysis of reversals in self-consistent 3D numerical dynamo simulations. Field models inferred from observations estimate reversal duration in the range of 1-10 kyr (depending on site location). The transitional fields during both the Matuyama/Brunhes reversal and the Laschamp excursion are characterized by low-latitude reversed flux formation and subsequent poleward migration. During both events the dipole as well as the non-dipole field energies decrease. However, while the non-dipole energy dominates the dipole energy for a period of 2 kyr in the reversal, the non-dipole energy merely exceeds the dipole energy for a very brief period during the excursion. Numerical dynamo simulations show that stronger convection, slower rotation, and lower electrical conductivity provide more favorable conditions for reversals. A nondimensional number that depends on the typical length scale of the flow and represents the relative importance of inertial effects, termed the local Rossby number, seems to determine whether a dynamo will reverse or not. Stable polarity periods in numerical dynamos may last about 1 Myr, whereas reversals may last about 10 kyr. Numerical dynamo reversals often involve prolonged dipole collapse followed by shorter directional instability of the dipole axis, with advective processes governing the field variation. Magnetic upwellings from the equatorial inner-core boundary that produce reversed flux patches at low-latitudes of the core-mantle boundary could be significant in triggering reversals. Inferences from the observational and modeling sides are compared. We summarize with an outlook on some open questions and future prospects.H. Amit ( )

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Section: Implications Of Paleomagnetic Observations Of Excursionssupporting

confidence: 79%

Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations

2010

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“…As shown in Fig. 3, the strength of the geomagnetic field seems to be relatively weak over the entire period between 20 and 70 ka (Mankinen and Champion, 1993;Laj and Kissel, 1999;Laj et al, 2002;Teanby et al, 2002 (Roperch et al, 1988;Mochizuki et al, 2006). These paleointensity data suggest that the reduction of the dipole field is characteristic for the excursions.…”

Section: Comparison With Other Excursional Datamentioning

confidence: 86%

Further K-Ar dating and paleomagnetic study of the Auckland geomagnetic excursions

et al. 2007

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Three different excursional paleomagnetic directions were reported from eight volcanoes of the Auckland volcanic field in New Zealand: north-down (ND) directions obtained from five volcanoes, west-up (WU) from two volcanoes, and south-up (SU) from one volcano. K-Ar ages have been reported for two of these volcanoes: 27±5 (1σ ) ka for the Wiri volcano of the ND group and 55±5 ka for the Hampton Park volcano of the WU group. In the present study, we have carried out further K-Ar age determinations on three other volcanoes and obtained reliable ages for two of them: 30±5 ka for the Puketutu volcano of the ND group and 50±6 ka for the McLennan Hills volcano of the SU group. The age of Puketutu agrees well with that of Wiri, and these two ages give a weighted mean age of 29±3 (1σ ) ka for the ND group. The age of the ND group is distinguishable from those of the SU and WU groups at the 2σ level, confirming that excursions occurred at two different times separated by a few tens of thousands of years. The age of the SU group is indistinguishable from that of the WU group, and a weighted mean age of 53±4 ka can be calculated for this combined group (SU-WU group). The age of the ND group and that of the SU-WU group are distinguishable from the latest age estimate of the Laschamp excursion. Overall, these age data from volcanic rocks show that at least three excursions occurred between approximately 30 and 60 ka. These three excursions are likely to be confined in the weak dipole interval of 20-70 ka, and all of these excursions yield particularly low virtual dipole moments (VDMs) of 2×10 22 A m 2 or less. Since it is suggested that the larger virtual geomagnetic pole (VGP) deviations from the geographic pole are related to the lower VDMs, the excursional fields possibly have resulted from a significantly reduced dipole field and comparable non-dipole components.

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“…data from volcanic rocks shows quite oscillatory nature of paleointensity in the time range of 40-100 ka, and recent review was given by Laj et al (2002) with many new data from a Hawaii drilled core. Hence the value of ASD from this study for the time span of 20-90 ka which is also typical for the last 5 my is not surprising.…”

Section: Discussionmentioning

confidence: 99%

Paleomagnetism of the late Quaternary Ontake Volcano, Japan: directions, intensities, and excursions

Tanaka

Kobayashi

2014

Earth Planet Sp

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Study of paleosecular variation was carried out to mostly andesite lavas from the late Quaternary Ontake Volcano which have detailed stratigraphy and accurate radiometric ages. Among 42 sites, some of the results from lava successions were combined due to possible equivalent ages, remaining 35 sites. After excluding two low latitude VGPs, angular dispersion of 15.6• was obtained for a period which is accurately confined between 20 ka and 90 ka. The obtained angular dispersion is not different from the typical value for the last 5 my, and this is not surprising if we consider that the global paleointensity was not necessarily low and rather oscillatory during the period of 40-100 ka which precedes the global low in 20-40 ka. Two low latitude VGPs from 48 ka lava (41.9• N, 196.2• E) and 80 ka lava (15.9• N, 183.3• E) indicate existence of excursions in Japan during the latest Pleistocene. Preliminary paleointensity experiments indicate that the 80 ka excursion is accompanied by a low paleointensity of about 5 μT while the 48 ka one is not. These two excursions are probably related to those reported previously not only from the Ontake Volcano and its proximity but also from other several sites in Japan, although they were not conclusive. The 48 ka excursion probably correlates to the Laschamp excursion. This is consistent with the fact that the VGP position from the 48 ka lava comes to the central Pacific region, similar to those from the Laschamp excursion found in New Zealand. Possible correlation of the 80 ka excursion is the one from Norwegian-Greenland Sea and Arctic Ocean, which are stratigraphically between the Laschamp and the Blake excursions.

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Geomagnetic intensity and inclination variations at Hawaii for the past 98kyr from core SOH-4 (Big Island): a new study and a comparison with existing contemporary data

Cited by 59 publications

References 47 publications

Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations

Polarity Reversals from Paleomagnetic Observations and Numerical Dynamo Simulations

Further K-Ar dating and paleomagnetic study of the Auckland geomagnetic excursions

Paleomagnetism of the late Quaternary Ontake Volcano, Japan: directions, intensities, and excursions

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