Paleomagnetic field variability and revised chronostratigraphy of bering sea (IODP ex. 323) deep-sea sediments during MIS 8-10

Abstract

This paper develops three composite paleomagnetic secular variation (PSV) records (directions and relative paleointensity) for MIS 8–10 (243–375 ka) from IODP Ex. 323 Sites 1343, 1344, and 1345 in the Bering Sea. There are 79 inclination features and 74 declination features in each of these records that can be correlated among them. Oxygen isotope records and correlation of our Bering Sea paleointensity records to the oxygen-isotope dated global PISO-1500 paleointensity record provide a detailed chronostratigraphy for our three sites with an uncertainty of ∼±2000 years. There are two excursions recorded reproducibly in our PSV records, the Portuguese Orphan Excursion (286 ± 2 ka) and the Calabrian Ridge Excursion (326 ± 2 ka). Both of these excursions have only short intervals (less than 500 years) of excursional directions. Both excursions have simple open looping of the directions. The Portuguese Orphan excursion has counter-clockwise (CC) looping, while the Calabrian Ridge Excursion has clockwise (C) looping. Statistical study of the PSV after removal of all excursional directions has been carried in overlapping 3-ky and 9-ky intervals. We have identified two distinctive features of the long-term secular variation. First, the ‘normal’ PSV has coherent long-term variability noted by several successive 9-ky inclination or declination averages distinct from overall averages. These persistent >10⁴ ky variations indicate long-term memory in the regional pattern of dynamo activity. Such memory is not consistent with persistent millennial-scale drift of the Earth's magnetic field. Second, PSV angular dispersion (a measure of directional variability) is quite low (∼15°) for ∼75% of the MIS 8–10 time interval. But angular dispersion more than doubles (∼35°) in three short intervals around 265–272 ka, 283–295 ka, and 307–325 ka. The onset and termination of these three high-angular-dispersion intervals occurs fast (∼10³ yrs). These same three high-angular-dispersion intervals also occur almost synchronously in the North Atlantic Ocean (Lund, 2022). These high-angular-dispersion intervals are also intervals in which excursions occur in both regions and are associated with relatively low paleointensity. We think this constitutes a distinctive bimodal pattern to overall pattern to Global secular variation in the Brunhes Chron.