Abstract
Holocene records documenting variations in direction and intensity of the geomagnetic field during the last about seven and a half millennia are presented for Northwest Africa. High resolution paleomagnetic analyses of two marine sediment sequences recovered from around 900 meter water depth on the upper continental slope off Cape Ghir (30°51′N, 10°16′W) were supplemented by magnetic measurements characterizing composition, concentration, grain size and coercivity of the magnetic mineral assemblage. Age control for the high sedimentation rate deposits (∼60 cm/kyr) was established by AMS radiocarbon dates. The natural remanent magnetization (NRM) is very predominantly carried by a fine grained, mostly single domain (titano-)magnetite fraction allowing the reliable definition of stable NRM inclinations and declinations from alternating field demagnetization and principal component analysis. Predictions of the Korte and Constable (2005) geomagnetic field model CALS7K.2 for the study area are in fair agreement with the Holocene directional records for the most parts, yet noticeable differences exist in some intervals. The magnetic mineral inventory of the sediments reveals various climate controlled variations, specifically in concentration and grain size. A very strong impact had the mid-Holocene environmental change from humid to arid conditions on the African continent which also clearly affects relative paleointensity (RPI) estimates based on different remanence normalizers. To overcome this problem the pseudo-Thellier RPI technique has been applied. The results represent the first Holocene record of Earth’s magnetic field intensity variations in the NW Africa region. It displays long term trends similar to those of model predictions, but also conspicuous millennium scale differences.
Similar content being viewed by others
References
Bleil U. and cruise participants, 2004. Report and preliminary results of Meteor Cruise M 58/2. Berichte, 227, Fachbereich Geowissenschaften, Universität Bremen, Bremen, Germany.
Claussen M., Kubatzki C. and Petoukhov V., 2003. Climate change in northern Africa: the past is not the future. Clim. Change, 57, 99–118.
deMenocal P., Ortiz J., Guilderson T., Adkins J., Sarnthein M., Baker L. and Yarusinsky M., 2000. Abrupt onset and termination of the African Humid Period: rapid climate responses to gradual insolation forcing. Quat. Sci. Rev., 19, 347–361.
Gallet Y., Genevey A. and Fluteau F. 2005. Does Earth’s magnetic field variation control centennial climate change? Earth Planet. Sci. Lett., 236, 339–347.
Genevey A., Gallet Y. and Margueron J.-C., 2003. Eight thousand years of geomagnetic field intensity variations in the eastern Mediterranean. J. Geophys. Res., 108, 2228, doi: 10.1029/2001JB001612.
Genevey A. and Gallet Y., 2002. Intensity of the geomagnetic field in western Europe over the past 2000 years: new data from ancient French potteries. J. Geophys. Res., 107, 2285, doi: 10.1029/2001JB000701.
Jackson M., Gruber W., Marvin J. and Banerjee S.K., 1988. Partial anhysteretic remanence and its anisotropy: applications and grainsize-dependence. Geophys. Res. Lett., 15, 440–443.
King J.W., Banerjee S.K. and Marvin J., 1983. A new rock-magnetic approach to selecting sediments for geomagnetic paleointensity studies: application to paleointensity for the last 4000 years. J. Geophys. Res., 88, 5911–5921.
Kirschvink J.L., 1980. The least-squares line and plane and the analysis of palaeomagnetic data. Geophys. J. R. Astron. Soc., 62, 699–718.
Korte M. and Constable C.G., 2005. Continuous geomagnetic field models for the past 7 millennia: 2. CALS7K. Geochem. Geophys. Geosyst., 6, Q02H16, doi: 10.1029/2004GC000801.
Kruiver P.P., Ko Y.S., Dekkers M.J., Langereis C.G. and Laj C., 1999. A pseudo-Thellier relative paleointensity record, and rock magnetic and geochemical parameters in relation to climate during the last 276 kyr in the Azores region. Geophys. J. Int., 136, 757–770.
Kuhlmann H., Freudenthal T., Helmke P. and Meggers H., 2004a. Reconstruction of paleoceanography off NW Africa during the last 40,000 years: influence of local and regional factors on sediment accumulation. Mar. Geol., 207, 209–224.
Kuhlmann H., Meggers H., Freudenthal T. and Wefer G., 2004b. The transition of the monsoonal and the N Atlantic climate system off NW Africa during the Holocene. Geophys. Res. Lett, 31, L22204, doi: 10.1029/2004GL021267.
Levi S. and Banerjee S.K., 1976. On the possibility of obtaining relative paleointensities from lake sediment. Earth Planet. Sci. Lett., 29, 219–226.
Lund S.P. and Schwartz M., 1999. Environmental factors affecting geomagnetic field paleointensity estimates from sediments. In: B. A. Maher and R. Thompson (Eds.), Quaternary Climates, Environments and Magnetism. Cambridge University Press, Cambridge, U.K., 324–351.
Maher B.A., 1988. Magnetic properties of some synthetic sub-micron magnetites. Geophys. J., 94, 83–96.
Neuer S. and cruise participants, 2000. Report and preliminary results of Meteor Cruise M45/5. Berichte, 163, Fachbereich Geowissenschaften, Universität Bremen, Bremen, Germany.
Nachasova I.E. and Burakov K.S., 2000. The geomagnetic field intensity in Central Asia from 6000 to 3000 B.C. Izv.-Phys. Solid Earth, 36, 358–363.
Petermann H. and Bleil U., 1993. Detection of live magnetotactic bacteria in South Atlantic deep-sea sediments. Earth Planet. Sci. Lett., 117, 223–228.
Robinson S.G., Sahota J.T.S. and Oldfield F., 2000. Early diagenesis in North Atlantic abyssal plain sediments characterized by rock-magnetic and geochemical indices. Mar. Geol., 163, 77–107.
Sagnotti L, Budillon F., Dinarès-Turell J., Iorio M., and Macri P., 2005. Evidence for a variable paleomagnetic lock-in depth in the Holocene sequence from the Salerno Gulf (Italy): Implications for “high-resolution” paleomagnetic dating. Geochem. Geophys. Geosyst., 6, Q11013, doi: 10.1029/2005GC001043.
Snowball I. and Sandgren P., 2004. Geomagnetic field intensity changes in Sweden between 9000 and 450 cal BP: extending the record of “archaeomagnetic jerks” by means of lake sediments and the pseudo-Thellier technique. Earth Planet. Sci. Lett., 227, 361–376.
Snowball I., Zillén L., Saarinen A., Ojala A. and Sandgren P., 2007. FENNOSTACK and FENNORPIS: Varve dated Holocene palaeomagnetic secular variation and relative palaeointensity stacks for Fennoscandia. Earth Planet. Sci. Lett., 55, 106–116.
Stoner J.S., Channell J.E.T. and Hillaire-Marcel C., 1996. The magnetic signature of rapidly deposited detrital layers from the deep Labrador Sea: relationship to North Atlantic Heinrich layers. Paleoceanography, 11, 309–325.
St-Onge G., Stoner J.S. and Hillaire-Marcel C., 2003. Holocene paleomagnetic records from the St. Lawrence Estuary, eastern Canada: centennial-to millennial-scale geomagnetic modulation of cosmogenic isotopes. Earth Planet. Sci. Lett., 209, 113–130.
Stuiver M., Reimer P.J., Bard E., Beck J.W., Burr G.S., Hughen K.A., Kromer B., McCormac G., van der Plicht J. and Spurk M., 1998. INTERCAL98 rardiocarbon age calibration, 24,000-0 cal BP. Radiocarbon, 40, 1041–1083.
Tauxe L., 1993. Sedimentary records of relative paleointensity of the geomagnetic field: theory and practice. Rev. Geophys., 31, 319–354.
Tauxe L., Pick T. and Kok Y.S., 1995. Relative paleointensity in sediments: a pseudo-Thellier approach. Geophys. Res. Lett., 22, 2885–2888.
Thouveny N. and Williamson D., 1988. Palaeomagnetic study of the Holocene and Upper Pleistocene sediments from Lake Barombi Mbo, Cameroun: first results. Phys. Earth Planet. Inter., 52, 193–206.
Valet J.-P., 2003. Time variations in geomagnetic intensity. Rev. Geophys., 41, 1004, doi: 10.1029/2001RG000104.
Watkins S.J. and Maher B.A., 2003. Magnetic characterisation of present-day deep-sea sediments and sources in the North Atlantic. Earth Planet. Sci. Lett., 214, 379–394.
Weaver P.P.E., Wynn R.B., Kenyon N.H. and Evans J., 2000. Continental margin sedimentation, with special reference to the north-east Atlantic margin. Sedimentology, 47, 239–256.
Yang S., Odah H. and Shaw J., 2000. Variations in the geomagnetic dipole moment over the last 12 000 years. Geophys. J. Int., 140, 158–162.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Bleil, U., Dillon, M. Holocene Earth’s magnetic field variations recorded in marine sediments of the NW African continental margin. Stud Geophys Geod 52, 133–155 (2008). https://doi.org/10.1007/s11200-008-0010-6
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11200-008-0010-6