Environmental factors as complicating influences in the recovery of quantitative geomagnetic‐field paleointensity estimates from sediments

We have recently recovered replicate records of the Earth's magnetic-field (relative) paleointensity for 12-71,000 years BP from marine sediments of the western North Atlantic Ocean. Our records are remarkably similar to two other recently published relative paleointensity records from marine and lacustrine sediments in Europe. This suggests to us that, even over this wide region, sediments may serve as reasonable, correlatable recorders of fluctuations in the strength of the Earth's magnetic field. If this is true, then similar records from around the globe could eventually provide valuable information about the deep-Earth processes which create the field. We note, however, that our intensity record is significantly correlated with the down-core ratio of magnetic susceptibility (χ) to anhysteretic remanent magnetism (ARM). This ratio is a measure of the relative grain size of magnetite (the primary magnetic mineral in these sediments), and as such is a sediment magnetic property which is controlled only by the local depositional environment (and indirectly by global climate). We are concerned that the European records may be similarly biased by climatic or other environmental factors, possibly synchronous with ours. We caution that extreme care must be taken to understand and remove any such magnetic influences from sediment relative paleointensity records before they are used as quantitative estimators of the past intensity of the Earth's magnetic field.

[1]  S. Lund.  A comparison of Holocene paleomagnetic secular variation records from North America , 1996 .

[2]  A. Roberts,et al.  Normalised natural remanent magnetisation intensity during the last 240 000 years in piston cores from the central North Atlantic Ocean: geomagnetic field intensity or environmental signal? , 1995 .

[3]  Lisa Tauxe,et al.  Sedimentary records of relative paleointensity of the geomagnetic field: Theory and practice , 1993 .

[4]  K. Creer,et al.  Geomagnetic moment variations in the last 70,000 years, impact on production of cosmogenic isotopes , 1993 .

[5]  F. Guichard,et al.  Paleointensity of the geomagnetic field during the last 80,000 years , 1992 .

[6]  C. Laj,et al.  Geomagnetic field control of 14C production over the last 80 Ky: Implications for the radiocarbon time-scale , 1991 .

[7]  T. Johnson,et al.  Fluctuations in deep western North Atlantic circulation on the Blake Outer Ridge during the last deglaciation , 1991 .

[8]  S. Lund.  Paleomagnetic secular variation , 1989 .

[9]  T. Johnson,et al.  Pleistocene fluctuations in the western boundary undercurrent on the Blake Outer Ridge , 1988 .

[10]  P. Roperch,et al.  Paleointensity of the earth's magnetic field during the Laschamp excursion and its geomagnetic implications , 1988 .

[11]  N. Thouveny.  Variations of the relative palaeointensity of the geomagnetic field in western Europe in the interval 25-10 kyr BP as deduced from analyses of lake sediments , 1987 .

[12]  J. Jouzel,et al.  Evidence for two intervals of enhanced 10Be deposition in Antarctic ice during the last glacial period , 1987, Nature.

[13]  J. King,et al.  A new rock‐magnetic approach to selecting sediments for geomagnetic paleointensity studies: Application to paleointensity for the last 4000 years , 1983 .

[14]  J. King,et al.  A comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials: Some results from lake sediments , 1982 .

[15]  G. Turner,et al.  Lake sediment record of the geomagnetic secular variation in Britain during Holocene times , 1981 .

[16]  J. King,et al.  A rapid method for magnetic granulometry with applications to environmental studies , 1981 .

[17]  Subir K. Banerjee,et al.  On the possibility of obtaining relative paleointensities from lake sediments , 1976 .