RELATIVE PALEOINTENSITY OF THE GEOMAGNETIC-FIELD OVER THE LAST 200,000 YEARS FROM ODP SITES 883 AND 884, NORTH PACIFIC-OCEAN

Ocean Drilling Program Sites 883 and 884 were cored as part of a three -site depth transect down the slopes of Detroit Seamount in the North Pacific Ocean. Continuous mineral magnetic and paleomagnetic measureme nts were made using u-channel samples for sediments that span the last 200 kyr. Thermomagnetic and high-field hysteresis data indicate that the magnetic mineralogy of the clay-rich sediments at the two sites is dominated by pseudo-single domain magnetite in a narrow range of grai n sizes and concentrations, thereby meeting established criteria for r elative paleointensity studies. The natural remanent magnetization (NR M) has been normalized using the anhysteretic remanent magnetization ( ARM) and the low field magnetic susceptibility (chi). The NRM/ARM and NRM/chi records are nearly identical for both cores. Furthermore, coev al horizons in the two cores can be correlated by matching > 100 magne tic susceptibility features over the 15 m length of both cores. Cohere nce function analysis indicates that the records are not significantly affected by local environmental conditions, These factors suggest tha t the large-scale Variations in normalized remanence are most likely d ue to geomagnetic paleointensity fluctuations. Dating constraints are provided by a delta(18)O stratigraphy from Site 883. Our North Pacific paleointensity Versus age curve is similar to a published record from the western Caroline basin and a recently proposed global paleointens ity curve. Offsets (up to 10 kyr) in the timing of paleointensity feat ures between our composite North Pacific record and the global curve m ay result from imprecisions in the dating of our record. Nevertheless, the correspondence between the paleointensity records suggests that, in suitable sediments, paleointensity of the geomagnetic field can giv e a globally coherent, dominantly dipolar, signal. (C) 1997 Elsevier S cience B.V.