Core surface flow and geomagnetic field changes on millennial timescales

One of the most prominent changes in Earth’s magnetic field over the past two centuries is the growth of the South Atlantic Anomaly (SAA)—a region of significantly weakened field intensity. Recent studies have suggested that weak field anomalies such as the SAA are recurrent features of the geomagnetic field, preferentially occurring around certain longitudes and generally drifting westward. These observations have sparked hypotheses linking the weak field anomalies to heat-flux heterogeneities at the core-mantle boundary and/or an eccentric planetary-scale gyre as observed in modern core surface flow reconstructions. To further investigate the underlying mechanisms, we generate core surface flow models that are compatible with the observed geomagnetic field changes. Several recent studies have made use statistics derived from geodynamo simulations to provide physically motivated priors on the core surface flow. Here, we adapt these methods to infer possible core flow solutions spanning the past 9000 years, constrained by archaeomagnetic and sedimentary palaeomagnetic data. Synthetic data are used to explore the extent to which archaeo-/palaeomagnetic observations can recover large-scale core flow variations. The integrated core-field and core-flow modelling approach is then applied to real-world data and the results are discussed within the context of recurrent weak field anomalies.