Geomagnetic poles over the past 10,000 years

Ohno, Masao; Hamano, Yozo

doi:10.1029/92gl01576

Cited by 81 publications

(52 citation statements)

References 18 publications

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“…The behaviour of the geomagnetic poles over the past 2 and 10 kyr has been studied twice previously (Merrill and McElhinny, 1983;Ohno and Hamano, 1992). The results from these studies agree well, but our results for 7 kyr are quite different for much of the time.…”

Section: Geomagnetic Polessupporting

confidence: 76%

“…To minimise this problem, VGP results from different locations are averaged, but available data are hardly well-distributed over the whole Earth. Ohno and Hamano (1992) already state that their results mainly reflect the geomagnetic variation in northern hemisphere middle to high latitudes, where most of the data come from. Our analysis confirms a westward movement of the dipole axis for the recent 400 yr and a strong eastward swing before, but prior to AD 800 the CALS7K.2 model suggests that there is no predominant westward trend as suggested by the VGPs, but rather more variability in longitudinal movement.…”

Section: Geomagnetic Polesmentioning

confidence: 99%

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Magnetic poles and dipole tilt variation over the past decades to millennia

Korte

Mandéa

2008

Earth Planet Sp

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Due to the strong dipolar character of the geomagnetic field the shielding effect against cosmic and solar ray particles is weakest in the polar regions. We here present a comprehensive study of the evolution of magnetic and geomagnetic pole locations and the Earth's magnetic core field in both polar regions over the past few years to millennia. North and south magnetic poles change independently according to the asymmetric complexity of the field in the two hemispheres, and the changes are not correlated to variations of the dipole axis. The recent, strong acceleration of the north magnetic pole motion appears to be linked to a reverse flux patch at the coremantle boundary, and an increasing deceleration of the pole over the next years seems likely. Over the whole studied period of 7000 years two periods of comparatively high velocity of the north magnetic pole are observed at 4500 BC and 1300 BC, based on the presently available data and models. Geographic latitudes and longitudes of magnetic and geomagnetic poles based on the studied geomagnetic field models are available together with animations of the poles and polar field behaviour from our webpage http://www.gfz-potsdam.de/geomagneticfield/poles.

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Section: Geomagnetic Polessupporting

confidence: 76%

Section: Geomagnetic Polesmentioning

confidence: 99%

Magnetic poles and dipole tilt variation over the past decades to millennia

Korte

Mandéa

2008

Earth Planet Sp

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“…This is dependent upon the cosmic ray flux, which has varied spatially and temporally in association with variations in the geomagnetic field intensity and atmospheric pressure throughout the Quaternary (Lal, 1991;Gosse and Phillips, 2001). Specifically, it is well documented from many independent proxy records that the Earth's geomagnetic field strength fluctuated considerably throughout the Quaternary (Ohno and Hamano, 1992;Guyodo and Valet, 1999;Yang et al, 2000). There is currently much debate regarding the appropriate scaling models and geomagnetic corrections for TCN production to calculate TCN ages (e.g.…”

Section: Timing Of Glaciationmentioning

confidence: 99%

Quaternary glaciation of the Himalayan–Tibetan orogen

Owen

Caffee

Finkel

et al. 2008

J Quaternary Science

210

143

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Glacial geological evidence from throughout the Himalayan-Tibetan orogen is examined to determine the timing and extent of late Quaternary glaciation in this region and its relation to similar changes on a global scale. The evidence summarised here supports the existence of expanded ice caps and extensive valley glacier systems throughout the region during the late Quaternary. However, it cannot yet be determined whether the timing of the extent of maximum glaciation was synchronous throughout the entire region or whether the response was more varied. The lack of organic material needed for radiocarbon dating has hindered past progress in glacial reconstruction; however, application of optically stimulated luminescence and terrestrial cosmogenic radionuclide methods has recently expanded the number of chronologies throughout the region. Limits to the precision and accuracy available with these methods and, more importantly, geological uncertainty imposed by processes of moraine formation and alteration both conspire to limit the time resolution on which correlations can be made to Milankovitch timescales (several ka). In order to put all studies on a common scale, well-dated sites have been re-evaluated and all the published terrestrial cosmogenic nuclide ages for moraine boulders and glacially eroded surfaces in the Himalayan-Tibetan orogen have been recalculated. Locally detailed studies indicate that there are considerable variations in the extent of glaciation from one region to the next during a glaciation. Glaciers throughout monsoon-influenced Tibet, the Himalaya and the Transhimalaya are likely synchronous both with climate change resulting from oscillations in the South Asian monsoon and with Northern Hemisphere cooling cycles. In contrast, glaciers in Pamir in the far western regions of the Himalayan-Tibet orogen advanced asynchronously relative to the other regions that are monsooninfluenced regions and appear to be mainly in phase with the Northern Hemisphere cooling cycles. Broad patterns of local and regional variability based on equilibrium-line altitudes have yet to be fully assessed, but have the potential to help define changes in climatic gradients over time.

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“…At the latitude of our site, the variations in the geomagnetic field, as well as the pole position, produce changes in the production rate. These changes can be expressed in terms of an equivalent change in geomagnetic latitude and can be evaluated using the data from Ohno and Hamano [1992], McElhinny and Senanayake [1982], and the Sint-800 record of Guyodo and Valet [1999]. The ages were calculated with the Stone [2000] latitude and altitude correction factors using software developed at Lawrence Livermore National Laboratory (D. L. Farber, personal communication, 2002).…”

Section: Appendix B: Sampling and Cosmogenic Datingmentioning

confidence: 99%

Irregular earthquake cycle along the southern Tianshan front, Aksu area, China

et al. 2005

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[1] A long deformation record ($16.5 ka) showing nonsteady earthquake recurrence is established for the Aksu thrust (Tianshan, China) on the basis of cosmogenic 10 Be dating of faulted surfaces. Topographic leveling across the Aksu fault scarp indicates up to $10 m uplift across a moraine abandoned $16.5 ka and similar uplift of $6 m across two inset surfaces yielding ages of $12.5 and $5 ka. Successively smaller uplifts of terraces younger than 5 ka indicate that three or more major earthquakes occurred during this period. These data show that the Aksu thrust fault was quiet for at least 7500 years and active in the last $5000 years and probably in the interval 16.5-12.5 ka. The seismic cycle along the Aksu thrust fault over the last $16,500 years was thus strongly irregular showing long quiescence and clustering, which is a challenge for paleoseismology and hazard assessment. This irregularity also makes it more difficult to estimate long-term shortening rates. Nevertheless, we are able to constrain a minimum total shortening rate (>7 mm/yr) across the southern Tianshan front for the last 12,500 years that is about a third of the total geodetic rate for the western Tianshan ($20 mm/yr).

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Geomagnetic poles over the past 10,000 years

Cited by 81 publications

References 18 publications

Magnetic poles and dipole tilt variation over the past decades to millennia

Magnetic poles and dipole tilt variation over the past decades to millennia

Quaternary glaciation of the Himalayan–Tibetan orogen

Irregular earthquake cycle along the southern Tianshan front, Aksu area, China

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