The Holocene Paleomagnetic Record of the Arctic
Like most Arctic phenomena, the geomagnetic field in this region is both poorly understood and critically important to the global system. Historical observations, paleomagnetic data and geodynamo theory all attest to the rather unique properties of the polar geomagnetic field, though a clear understanding has yet to be achieved.
Theory predicts that a different process might drive the geomagnetic field of the polar-regions, because they correspond with the surface expression of a geodynamo region known as the tangent cylinder (± 69.5°) (Fig. 1). The tangent cylinder is defined as the region in the outer core (where the Earth’s magnetic field is generated) where a theoretical cylinder tangent to the solid inner core and parallel to the axis of rotation would separate distinct convective regimes. Flow within the tangent cylinder is thought to be moving as an upwelling polar vortex (Fig. 1) similar to that of a hurricane. Whereas, the main field at mid-latitudes is thought to be generated by down-welling convective structures, that extend through the whole of the fluid outer core. These features are not symmetrically distributed around the solid inner core, but at least historically, are concentrated at fixed locations known as bundles or lobes (See figure in section on North Atlantic). Therefore, the main field appears to be controlled by large scale flux features at about 50°N. How these vary relative to one another may be a main driver of paleomagnetic secular variation (PSV) at mid-latitudes, while the PSV of the Arctic could be distinctly different. However, there is little paleomagnetic evidence to support these concepts.
Our past and current projects in the Arctic have focused on reconstructing the paleo-geomagnetic field to assess the migration of the North Magnetic Pole (Fig. 2) and determine if the geomagnetic field of the region is truly unique. This information will not only provide a better understanding of the geodynamo process that drives the geomagnetic field, but will also serve as a dating tool for other sediment studies and be used to help assess the recent hypothesis that the geomagnetic field plays a role in climate. To further these goals, we are developing an Arctic Paleomagnetic Transect extending from Alaska to Scandinavia. This transect will combine data from new and old core sites (Fig. 2), providing an unprecedented view of the polar paleo-geomagnetic field from a 180° perspective.
Figure 1. Illustration of the Earth’s core and the tangent cylinder.
Figure 2. Reconstruction of the position of the North Magnetic Pole (NMP) from 200 A.D. to present from a number of sources. Yellow dots represent actual historical observations, blue line represents historical model predictions and red dots are the paleo-geomagnetic reconstruction of the NMP from Lower Murray Lake, Ellesmere Island, Nunavut Canada. Site locations, including currently available data, and new core sites where data will be collected as part of this project are listed. These data will result in the development of a Paleomagnetic Transect spanning half the Arctic.