High-resolution inclination records from Sites U1418 and U1419 in the Gulf of Alaska (IODP Expedition 341)

International Ocean Drilling Program (IODP) Expedition 341 in the Gulf of Alaska recovered a 112-meter-long sedimentary record from the continental slope at Site U1419. At this site, an exceptionally expanded late Pleistocene sequence (sedimentation rates >100 cm/kyr) combined with a high-resolution radiocarbon chronology (Walczak et al., 2020), provide an opportunity to study Paleomagnetic Secular Variations (PSV) on centennial to millennial timescales over the past ~43,000 years.
Natural and laboratory-induced magnetic remanence were measured on u-channels using the stepwise AF demagnetization procedure. In addition to continuous magnetic susceptibility measurements, hysteresis parameters were obtained on 95 discrete samples, and IRM acquisition curves on 9 discrete samples to obtain additional information on the magnetic mineralogy of the sediment. Due to the influence of lithology, magnetic mineralogy, depositional and post-depositional processes, Site U1419 is not suitable for paleointensity studies. However, with removal of intervals influenced by the environmental signal and/or coring deformation, the high sedimentation rates at this site have helped to preserve a reliable record of inclination. Because of signal to noise issues, inclination as measured after the 20 mT AF demagnetization step provides the most accurate estimate. This is demonstrated by comparing the U1419 inclination to a stack of the shipboard inclination at Site U1418 on a new age model developed from 19 radiocarbon dates on U1418 and 18 magnetic susceptibility-based tie-points to site survey core EW0408-87JC (Praetorius et al., 2015). This independently replicated inclination record verifies centennial to millennial scale variations in the Gulf of Alaska that can now be compared with other northeast Pacific and western North American records to begin deciphering geomagnetic variability and provide a new stratigraphic correlation tool for 15 and 30 cal kyr BP interval in this region.