Highs, Lows, and Puzzling Intensity Variations of the Earth’s Magnetic Field

Abstract

The Earth’s magnetic field has a pivotal role in the Earth Sciences. Together with seismology, it is the only window into the deep Earth and the Earth’s core. The Earth’s magnetic field protects the Earth against harmful solar radiation, and it protects satellites orbiting the Earth. Without the Earth’s magnetic field, the atmosphere would have been stripped away and life on Earth would not have been possible. Understanding the evolution and behavior of the Earth’s magnetic field is therefore of great importance. In my dissertation I set out to unravel fast and local fluctuations in the direction and strength of the geomagnetic field. The geomagnetic field can be described by a dipole for approximately 70 to 90%; local variations in direction and strength are attributed to higher-order magnetic behavior. To improve our understanding of this higher-order behavior of the Earth’s magnetic field and therefore the evolution of its local variations, high-resolution records of geomagnetic field variations throughout time and space are needed. Our understanding is especially hampered by the lack of high-resolution intensity records. It is relatively straightforward to obtain a magnetic direction of the past state of the Earth’s magnetic field. Obtaining the strength (intensity) of the Earth’s magnetic field is however very challenging. In Chapters 1 & 2, I set out to ease and standardize the interpretation of paleointensity data and I introduce paleointensity.org, an online application for the interpretation of paleointensity data. These standards were used to derive high-quality paleomagnetic records from marine Mediterranean sediment cores and Holocene volcanic lavas from Pico and Reunion islands. The paleosecular variation curve obtained for Pico Island, Azores (Chapter 3), is successfully used to date five recent lavas based on their paleomagnetic information. With the paleosecular variation curves from the Mediterranean sediment cores (Chapter 4), I was able to constrain the extent of the Levantine Iron Age geomagnetic Anomaly (LIAA). The intensity high moves westward in time while diminishing in strength. For the ongoing low field anomaly in the South Atlantic the spatial evolution is challenged by the lack of Southern Hemisphere data. In Chapter 5, I present a secular variation record from La Reunion, located East of the African continent. This record is of great importance to be able to track the South Atlantic Anomaly in time and to constrain its origin. The hypothesis of an emerging South Atlantic Anomaly from a reverse flux patch at the core-mantle boundary East of Africa is precluded by my new paleomagnetic data from Reunion island. I have provided constraints on the spatial and temporal extent of two short-term anomalous features of the Earth’s magnetic field. This brings us closer to unraveling these non-dipolar geomagnetic field features. This enhances our understanding of the physical mechanism driving the geomagnetic field and can shed light on improving our understanding of the geodynamo and the outer core.