Geomagnetic dipole strength and reversal rate over the past two million years

Independent records of relative magnetic palaeointensity from sediment cores in different areas of the world can be stacked together to extract the evolution of the geomagnetic dipole moment and thus provide information regarding the processes governing the geodynamo. So far, this procedure has been limited to the past 800,000 years (800 kyr; ref. 3), which does not include any geomagnetic reversals. Here we present a composite curve that shows the evolution of the dipole moment during the past two million years. This reconstruction is in good agreement with the absolute dipole moments derived from volcanic lavas, which were used for calibration. We show that, at least during this period, the time-averaged field was higher during periods without reversals but the amplitude of the short-term oscillations remained the same. As a consequence, few intervals of very low intensity, and thus fewer instabilities, are expected during periods with a strong average dipole moment, whereas more excursions and reversals are expected during periods of weak field intensity. We also observe that the axial dipole begins to decay 60–80 kyr before reversals, but rebuilds itself in the opposite direction in only a few thousand years.

[1]  Elisabeth Schnepp,et al.  IAGA paleointensity database: distribution and quality of the data set , 2004 .

[2]  N. Opdyke,et al.  Palaeomagnetic field intensity variation recorded in a Brunhes epoch deep-sea sediment core , 1977, Nature.

[3]  J. Valet.  Time variations in geomagnetic intensity , 2003 .

[4]  Jean-Pierre Valet,et al.  Global changes in intensity of the Earth's magnetic field during the past 800 kyr , 1999, Nature.

[5]  A. Roberts,et al.  A 2.14-Myr astronomically tuned record of relative geomagnetic paleointensity from the western Philippine Sea , 2003 .

[6]  P. Gillot,et al.  Link between excursions and paleointensity inferred from abnormal field directions recorded at La Palma around 600 ka , 1999 .

[7]  M. Suter,et al.  A 200 kyr record of cosmogenic radionuclide production rate and geomagnetic field intensity from 10Be in globally stacked deep-sea sediments , 1997 .

[8]  L. Meynadier,et al.  Post-depositional realignment of magnetic grains and asymmetrical saw-tooth patterns of magnetization intensity , 1996 .

[9]  Philippe Gaillot,et al.  Wavelet analysis of relative geomagnetic paleointensity at ODP Site 983 , 2000 .

[10]  C. Laj,et al.  Relative geomagnetic field intensity and reversals for the last 1.8 My from a central equatorial Pacific Core , 1996 .

[11]  L. Meynadier,et al.  Geomagnetic field intensity and reversals during the past four million years , 1993, Nature.

[12]  J. Valet,et al.  Relative variations in geomagnetic intensity from sedimentary records: the past 200 , 1996 .

[13]  R. Parker,et al.  Analysis of 11 Myr of geomagnetic intensity variation , 1998 .

[14]  C. Richter,et al.  Paleointensity record from Pleistocene sediments (1.4-0 Ma) off the California margin , 1999 .

[15]  P. Gillot,et al.  The age and duration of the Matuyama–Brunhes transition from new K–Ar data from La Palma (Canary Islands) and revisited 40Ar/39Ar ages , 2003 .

[16]  A. Mazaud.  ‘Sawtooth’ variation in magnetic intensity profiles and delayed acquisition of magnetization in deep sea cores , 1996 .

[17]  R. Parker,et al.  Assessing the dipolar signal in stacked paleointensity records using a statistical error model and geodynamo simulations , 2004 .

[18]  J. Channell,et al.  Effects of variable sedimentation rates and age errors on the resolution of sedimentary paleointensity records , 2002 .

[19]  R. Parker,et al.  Geomagnetic intensity variations over the past 780 kyr obtained from near-seafloor magnetic anomalies , 2000, Nature.

[20]  J. Channell,et al.  Geomagnetic palaeointensities and astrochronological ages for the Matuyama–Brunhes boundary and the boundaries of the Jaramillo Subchron: palaeomagnetic and oxygen isotope records from ODP Site 983 , 2000, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[21]  G. Acton,et al.  A sedimentary paleomagnetic record of the Matuyama chron from the Western Antarctic margin (ODP Site 1101) , 2001 .

[22]  J. Valet,et al.  A comparison of relative paleointensity records of the Matuyama Chron for the period 0.75 1.25 Ma , 2006 .

[23]  D. Kent,et al.  A detailed chronology of the Australasian impact event, the Brunhes-Matuyama geomagnetic polarity reversal, and global climate change , 1992 .

[24]  A. Roberts,et al.  Relative geomagnetic paleointensity from the Jaramillo Subchron to the Matuyama/Brunhes boundary as recorded in a Mediterranean piston core , 2002 .

[25]  L. Meynadier,et al.  Relative paleointensity across the last geomagnetic reversal from sediments of the Atlantic, Indian and Pacific oceans , 1994 .

[26]  N. Shackleton,et al.  Asymmetrical saw-tooth pattern of the geomagnetic field intensity from equatorial sediments in the Pacific and Indian Oceans , 1994 .

[27]  Beer,et al.  Geomagnetic modulation of the 36Cl flux in the GRIP ice core, greenland , 1998, Science.

[28]  D. Schneider,et al.  A high-resolution marine sedimentary record of geomagnetic intensity during the Brunhes Chron , 1996 .

[29]  J. Beer,et al.  North Atlantic palaeointensity stack since 75ka (NAPIS–75) and the duration of the Laschamp event , 2000, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[30]  K. Verosub,et al.  Magnetostratigraphy and relative palaeointensity of late Neogene sediments at ODP Leg 167 Site 1010 off Baja California , 1999 .

[31]  L. Tauxe,et al.  A relative geomagnetic paleointensity stack from Ontong‐Java Plateau sediments for the Matuyama , 1999 .

[32]  J. Dyment,et al.  A geomagnetic record over the last 3.5 million years from deep-tow magnetic anomaly profiles across the Central Indian Ridge , 2001 .

[33]  M. Frank.  Comparison of cosmogenic radionuclide production and geomagnetic field intensity over the last 200 000 years , 2000, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.