Unravelling Geomagnetic Anomalies: Tracing the South Atlantic Anomaly through time and space

Abstract

Our planet is surrounded by a magnetic field, acting like a huge shield against harmful solar and cosmic radiation that, if it would not be deflected by the Earth’s magnetic field, may damage the atmosphere and disrupt communication systems. The Earth’s magnetic field can be described with a direction and a strength, and both are constantly changing through time. By using archaeological materials, volcanic rocks or sediments one can determine the past field value at that location at a specific moment in time. Currently, the Earth’s magnetic field is characterised by a region of weak field strength above South America, named the South Atlantic Anomaly (SAA). This low intensity anomaly is one of the most intriguing features of today’s geomagnetic field. In this thesis, I first focus on studying the reliability of volcanic rocks as paleomagnetic recorders. Data from Mt. Etna reveal that a topographically rough and strongly magnetised volcanic terrain may generate local magnetic anomalies, for which I advise to take samples distributed over a large area. I then study the past behaviour of the SAA using new paleomagnetic data from three locations: the Revillagigedo Archipelago (Mexico), La Réunion and the island of Bali (Indonesia). The data helps to reduce the gap in the global paleomagnetic data distribution, and provide new constraints on the evolution of geomagnetic field anomalies. Paleosecular variation curves constructed for La Réunion and Bali suggest two possible scenarios for the origin and development of the South Atlantic Anomaly.