Collaborative Research: Archeomagnetism of southern Africa and dynamo modeling: Testing the hypothesis of South Atlantic Anomaly-Large Low Shear Velocity Province Agency

University Of Rochester, Rochester NY

Investigators

Abstract

Earth’s dipole magnetic field has been rapidly decreasing in strength, by ∼9% over the past 160 years, with the decline linked to a broad swath of low field intensity in the Southern Hemisphere known as the South Atlantic Anomaly. When extrapolated to Earth’s deep interior, to the boundary between the liquid core and overlying solid mantle, this weak surface field appears as prominent patches of reversed polarity beneath South Africa and Patagonia. This pattern, together with the rapidly decreasing field strength, has led to hotly debated speculation that Earth is in the early stages of a geomagnetic polarity reversal. Principal limitations in this debate have been a lack of data for the last 1500 years from key regions in the Southern Hemisphere and theoretical understanding of deep Earth controls on magnetic fields. To address these limitations, this project will refine the archeomagnetic record of the southern Hemisphere, develop numerical simulations to explore the affect the deep Earth has on magnetic fields, and integrate these two components to explore whether the unusual mantle beneath South Africa and Patagonia (the African Low Shear Velocity Province) places a first-order control on the character of the South Atlantic Anomaly. This project will foster international collaboration with archeologists from South Africa, Botswana, and Zimbabwe, develop a revised geodynamo code that will be made available to the community, and support of graduate and undergraduate students who will receive a broad training in the field, experimental rock and paleomagnetism, and geophysical modeling. This project will support a collaborative study that will bring together workers in disparate disciplines and subdisciplines to further refine the archeomagnetic record and more directly test the efficacy of Low Shear Velocity Province control on the character of the geomagnetic field. Specifically, the research team will: (i) conduct field studies including field surveys and collection materials with the goal of refining the Iron Age archeomagnetic record with potential application to both deep Earth and to archeological problems; (ii) conduct rock magnetic, analytical microscopy, and paleomagnetic analyses and processing of field magnetic survey data to define ambient magnetic fields of the collection sites, magnetic carriers in the collected archeological artifacts, and ancient recordings of direction and intensity with the goal of testing primary hypothesis of the proposed work; and (iii) use numerical dynamo simulations to investigate whether the African Large Low Shear Velocity Province can locally defect core flow, drive the magnetic Reynolds number toward unity, favoring magnetic diffusion and flux expulsion, and thus place first-order controls on geomagnetic observations made at Earth’s surface. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.