A North Pacific View of Holocene Paleomagnetic Secular Variation
Abstract
Recent observations indicate that the paleomagnetic field displays variance on sub-millennial and even sub-centennial time scales, based on reproducible data from high-resolution sedimentary and archeomagnetic records. However, the majority of these observations are concentrated in the Atlantic sector of the Northern Hemisphere, while the under-sampled Pacific is thought to have subdued geomagnetic variability. Here we present new paleomagnetic data and radiocarbon dates from the Gulf of Alaska that contribute to new regional data collection efforts that should allow us to begin addressing geomagnetic regionality. Two 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), with their associated multi- and trigger cores, provide well-dated sedimentary paleomagnetic secular variation (PSV) records from the modern through the late-Holocene. Chronologies for these cores are tightly constrained by foraminiferal radiocarbon dates and inter-core correlations, supported by stable-isotope data. Core 85JC extends back >17 kybp, however high-quality magnetic data are limited to ~10 kybp, where sedimentation rates averaged ~80 cm/kyr. Core 79JC extends back to ~8 kybp with sedimentation rates averaging ~200 cm/kyr, offering an expanded view of the mid-late Holocene. Sedimentary facies and structures were analyzed via CT-scans, X-ray density and grain-size analysis. 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 strong, stable, relatively well-defined (MAD <5°) magnetization. Component inclinations are consistent with historical reconstructions and those expected for a geocentric axial dipole (GAD). The consistently older ages (~1000 yrs) of apparently correlative PSV features in 85JC relative to 79JC implies that the lower-resolution 85JC magnetization was acquired at depth (~20 cm) below the sediment-water interface. Conversely, 79JC’s age of magnetization is assumed to be approximately synchronous with sediment deposition because of its extremely high accumulation rates. Therefore, the chronology of the 79JC PSV record is used as our best estimate for the timing of geomagnetic change. On this independent chronology, PSV is consistent with other high-latitude North American records in intensity, and agrees reasonably well with the intensities and inclinations predicted for the Gulf of Alaska over the last 3 ky by the latest geomagnetic models. Furthermore, there are noteworthy similarities with the European archeointensity records, with overall agreement in broad morphology, but distinct differences at millennial scales.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMGP23A0781D
- Keywords:
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- 1521 GEOMAGNETISM AND PALEOMAGNETISM / Paleointensity;
- 1522 GEOMAGNETISM AND PALEOMAGNETISM / Paleomagnetic secular variation