RECONSTRUCTING HOLOCENE PALEOMAGNETIC SECULAR VARIATION FROM THE GULF OF ALASKA

Understanding of dynamic variations of the Holocene geomagnetic field is hampered by a lack of high-quality, high-resolution data from the North Pacific, an area with unique behavior in the historical record. Here we present two well-dated paleomagnetic records from the Gulf of Alaska in jumbo piston cores EW0408-85JC (59.56° N, 144.15° W, 682 m depth) and EW0408-79JC (59.53° N, 141.76° W, 158 m depth). Core 85JC extends back >17 kybp; sedimentation rates vary from an early Holocene low of ~20 cm/kyr, to late glacial values of >500 cm/kyr reflecting ice proximal conditions. Core 79JC extends back >8 kybp, offering an expanded view of the mid-late Holocene with sedimentation rates of >200 cm/kyr. Associated multi- and trigger cores are appended to the jumbo piston cores using magnetic susceptibility, sediment density, and radiocarbon dates, ensuring a continuous record from modern through the late-Holocene. Sedimentary facies and structures were analyzed via CT-scans, and chronologies are constrained by more than 100 foraminiferal radiocarbon dates and inter-core correlations based on stable-isotope data). Natural and laboratory remanent magnetizations were studied by progressive alternating field (AF) demagnetization of u-channel samples. Within the last 8 kybp, both cores preserve a generally strong, stable, well-defined (MAD <5) magnetization. Component inclinations are consistent with historical reconstructions and those expected for a geocentric axial dipole (GAD). Although these records have similar magnetic mineral assemblages, and similar patterns of secular variation, the apparent timing of secular variation features are offset by about 1000 years. The consistently older ages for apparently correlative PSV features in the lower-resolution 85JC can be resolved by assuming a lock-in depth of around 20 cm. Variability in the age of magnetic mineral lock-in relative to the age of sediment has long been a confounding factor in interpreting paleomagnetic records. The high-resolution independent chronologies established for nearby cores with different sediment accumulation rates help to constrain the paleomagnetic transfer function on the Gulf of Alaska margin, and facilitate regional reconstructions of rapid variations in the geomagnetic field.