Measurement of the degree of smoothing in sediment paleomagnetic secular variation records: an example from late Quaternary deep-sea sediments of the Bermuda Rise, western North Atlantic Ocean

Abstract

Replicate paleomagnetic secular variation (PSV) records for the last 15,000 yr have been recovered from two deep-sea sediment gravity cores on the Bermuda Rise, western North Atlantic Ocean. The records have been correlated using several different parameters and dated by correlation to a nearby piston core which has a high-resolution 14C chronology. The PSV records are systematically subdued with respect to the expected local magnetic field variability during the Holocene, when sedimentation rates were about 10 cm/kyr. During the Late Pleistocene, when sedimentation rates were a factor of 2–3 higher, the PSV variability was significantly larger. We attribute this to smoothing of the PSV records by a depositional/post-depositional remanence (DRM/PDRM) acquisition process with a 10–20 cm lock-in interval. The degree of PSV smoothing was evaluated by comparing the VGP angular dispersion and vector spectral content of the Bermuda Rise cores with high-resolution PSV records from North America and Great Britain. These results suggest a 50% reduction in the DRM/PDRM recording of vector variability during the Holocene on the Bermuda Rise, with most of the PSV reduction occurring for features of less than 2000 yr in duration. We can reproduce the subdued PSV pattern with a mathematical model that simulates the site DRM/PDRM remanence acquisition process. Finally, the replicate gravity cores document that PSV records may be reproducible on a local scale, even though they only retain a low-pass filtered record of true magnetic field variability.