Modeling the paleosecular variation of the geomagnetic field over the last 3000 years. Anomalies, spikes and core-surface flows

• Autores: Pablo Rivera Perez
• Directores de la Tesis: María Luisa Osete López (dir. tes.), Francisco Javier Pavón Carrasco (dir. tes.)
• Lectura: En la Universidad Complutense de Madrid ( España ) en 2025
• Idioma: inglés
• Títulos paralelos:
  • Modelado de la variación paleosecula del campo geomagnético para los últimos 3000 años. Anomalías, spikes y flujos en la superficie del nucleo
• Tribunal Calificador de la Tesis: Juan José Ledo Fernández (presid.), Fátima Martín Hernández (secret.), Anita di Chiara (voc.), Sanja Panovska (voc.), Juan José Villalaín Santamaría (voc.)
• Programa de doctorado: Programa de Doctorado en Física por la Universidad Complutense de Madrid
• Menciones:
  • Internacional
• Calificación: Sobresaliente Cum Laude
• Enlaces
  • Tesis en acceso abierto en: Docta Complutense
• Resumen

  • The main Earth's magnetic field (or main geomagnetic field) has its origin in the Earth''s outer core. It is a crucial characteristic of our planet that plays a fundamental role in the Earth's evolution and the development of life. However, many aspects of its origin and evolution remain unknown. For a better understanding of the geomagnetic field, it is necessary to obtain information about the past field to explore its behavior during the Earth's history in different timescales. The discipline of archeomagnetism can provide indirect measurement of the past geomagnetic field, therefore, archeomagnetic databases, characterized by independent dating and broad spatial and temporal distributions, are key for reconstructing the pattern of the past geomagnetic field. The constant updating of the archeomagnetic databases allows us to study the behavior of geomagnetic field, especially during the Holocene (last 12 kyr).

    The Earth's magnetic field can be approximated to a tilted dipole during periods of stable polarity. However, anomalies with values different from the expected dipolar field have been recorded during the past millennia. For instance, the most important present-day anomaly is the South Atlantic Anomaly (SAA), where the field intensity is about 35% lower than expected for that region. As we go back on time, the Levantine Iron Age Anomaly (LIAA) is characterized by exceptionally high intensities during the first millennium BCE in the Levantine region. Recent archeomagnetic data have provided more precise constraints on the LIAA, which seems to be highly localized in space and has been classified as a "geomagnetic spike".

    In this PhD Thesis, we analyze the LIAA from three different approaches. First, we develop a monopole equivalent source to model the non-axial radial field of the LIAA and the SAA, comparing the results from two different paleoreconstructions. This representation allows us to show some potential relationship between these anomalous features and the lower mantle heterogeneities. Second, we model the LIAA with a "spike" function that better fits the high archeointensity data in the Mediterranean region. This allows us to distinguish three main maxima (950 BCE, 750 BCE, 500 BCE) and the spherical harmonics analysis of this function gives a better definition of the LIAA's spatial extension. Finally, we study different assumptions to overcome the non-unicity problem of the core-surface velocity flow inversion from geomagnetic models. For present-day field this issue is more explored, however, in this PhD Thesis we attempt its application to a paleomagnetic global reconstruction. We develop and compare five different core-flow models, spanning every 25 yr for the last 3300 yr, using purely toroidal and tangentially geostrophic regularizations. From this perspective, we analyze the long term westward-eastward pattern of the paleosecular variation (PSV) during the last 3000 yr but also the core-flow dynamics in the period and region that characterized the LIAA. Our results suggest a potential contribution of down-upwelling flow to the growth and decay of radial patches at the core-mantle boundary, responsible for surface high intensities recorded by LIAA. Additionally, core-flow models help us to better constrain the duration of the LIAA and reveal a notable change in the flow dynamics around 600 BCE.