Collaborative Research: Towards an understanding of the Holocene paleomagnetic record through new data (Hawaii/North American) and time series/spherical harmonic model comparisons

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

Historical and recent paleomagnetic observations, along with geodynamo modeling studies highlight the importance of non-axisymmetric flux concentrations, not only as an indicator that the mantle has an important influence on the geodynamo, but also that it may act as a potential organizing structure that might control much of the dynamics of the geomagnetic field including paleomagnetic secular variation (PSV). Comparison of specific, well-dated Holocene PSV time series of inclination, declination, and paleointensity at key locations suggest the existence of a relatively simple first order pattern that is most clearly observed over the last four thousand years where the highest quality data are available. Over this time range, the field morphology can be roughly broken into two "modes": The first mode having a dominant flux lobe over North America and the second a dominant flux lobe over Europe. The "North American mode" is consistent with the historically time averaged field. The "European mode" is consistent with the time averaged mid-to-late Holocene field. A new inclination anomaly reconstruction for the NE Pacific region derived from Alaskan, and older Hawaiian and Oregon records, suggests that the influence of this oscillation may extend into the Pacific and continue through the Holocene and possibly beyond. The discovery of such an oscillation would be a significant step toward an understanding of what drives PSV. Unfortunately, available PSV data from North America and the northeast Pacific, because of uncertain chronologies and limited modern relative paleointensity records, are not adequate to fully assess whether the relationship observed persists over longer paleomagnetic time intervals. This three-year study will focus on the North American and northeast Pacific records to improve observational constraints and assess the relationship between data derived PSV time series and continuous spherical harmonic models to inform the interpretation of the PSV record. Data quality, including chronology is a limiting factor in our understanding of the geomagnetic causes of PSV. This will be improved through a synthesis of existing data and radiocarbon dates, and the collection of new cores from classic paleomagnetic sites and other nearby locations with proven sedimentary records, but where modern dating and paleomagnetic practices have yet to be employed. We study the paleomagnetic record for many reasons, with the most fundamental being to understand the past history of Earth's magnetic field. Paleo-geomagnetic observations from rocks, sediments, and archeological artifacts provide fundamental information about geomagnetic field generation process that cannot be obtained from the short historical record. These observations tell us that large amplitude geomagnetic changes in direction and intensity occur over timescales that range from decades to millions of years. Yet our knowledge of the processes and boundary conditions that govern paleo-geomagnetic change are far from complete resulting in significant uncertainty in our understanding of the geomagnetic field and any process controlled by geomagnetic change, from magnetic stratigraphy to space climate. This study is designed to determine if boundary conditions may act as a potential organizing structure that might control much of the dynamics of the geomagnetic field including millennial and centennial scale changes know as paleomagnetic secular variation (PSV). Results will help to differentiate between the contributions of geomagnetic and solar forcing of terrestrial cosmic ray flux and cosmogenic isotope production with practical implications for telecommunications, human health, global ecosystems and climate. The potential linkage between climate change and field morphology is a relatively new topic of research and one that deserves special attention at this time of rapid climate change. Holocene magnetic stratigraphy has a long history, but its usefulness is ultimately limited by how well we know the paleomagnetic record. An understanding of the geomagnetic cause of paleomagnetic change will provide significant new magnetic stratigraphic opportunities. This project will support undergraduate, graduate, and postdoctoral education, providing training in core collection, stratigraphy, paleomagnetic data analysis, environmental magnetic data analysis, geomagnetism, geochronology and paleoclimatology.