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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. B5, 2244, doi:10.1029/2001JB001390, 2003

A ∼580 kyr paleomagnetic record from the sub-Antarctic South Atlantic (Ocean Drilling Program Site 1089)

J. S. Stoner

Department of Geology, University of California, Davis, California, USA


J. E. T. Channell

Department of Geological Sciences, University of Florida, Gainesville, Florida, USA


D. A. Hodell

Department of Geological Sciences, University of Florida, Gainesville, Florida, USA


C. D. Charles

Scripps Institution of Oceanography, La Jolla, California, USA


Abstract

We report geomagnetic directional paleosecular variation, relative paleointensity proxies and oxygen isotope data from the upper 88 m composite depth (mcd) at South Atlantic Ocean Drilling Program (ODP) Site 1089 (40°56.2′S, 9°53.64′E, 4620 m water depth). The age model is provided by high-resolution oxygen isotope stratigraphy, augmented by radiocarbon dates from the upper 8 mcd of nearby piston core RC11-83. Mean sedimentation rates at Site 1089 are in the range of 15 to 20 cm/kyr. Two intervals during the Brunhes Chron, at ∼29.6 mcd (∼190 ka) and at ∼48 mcd (∼335 ka), have component magnetization directions with positive (reverse polarity) inclination; however, the excursional directions are heavily overprinted by the postexcursional field. Magnetite is the dominant carrier of magnetic remanence, and occurs in the pseudosingle-domain (PSD) grain size. An additional higher-coercivity magnetic carrier, characterized by low unblocking temperatures (<350°C), is assumed to be authigenic pyrrhotite. A decrease in magnetization intensity down core is mirrored by a reduction in pore water sulfate, indicating diagenetic reduction of magnetite. Despite down-core changes in magnetic mineralogy, normalized intensity records from Site 1089 are comparable with high-resolution paleointensity records from the North Atlantic (e.g., ODP Sites 983 and 984). Sediment properties and sedimentation patterns within the Cape (Site 1089) and Iceland (Sites 983 and 984) Basins are distinctly different at both millennial and orbital timescales and therefore preclude lithologic variability from being the source of this correlation. Variations in normalized intensity from Site 1089 therefore appear to reflect changes in global-scale geomagnetic field intensity.

Received 27 September 2001; accepted 13 November 2002; published 14 May 2003.

Index Terms: 1512 Geomagnetism and Paleomagnetism: Environmental magnetism; 1513 Geomagnetism and Paleomagnetism: Geomagnetic excursions; 1520 Geomagnetism and Paleomagnetism: Magnetostratigraphy; 1521 Geomagnetism and Paleomagnetism: Paleointensity; 1522 Geomagnetism and Paleomagnetism: Paleomagnetic secular variation.

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Citation: Stoner, J. S., J. E. T. Channell, D. A. Hodell, and C. D. Charles (2003), A ∼580 kyr paleomagnetic record from the sub-Antarctic South Atlantic (Ocean Drilling Program Site 1089), J. Geophys. Res., 108(B5), 2244, doi:10.1029/2001JB001390.