New Evidence for a West Pacific Anomaly: Paleomagnetic Data from Taveuni, Fiji

The Earth’s magnetic field, generated in the liquid outer core, predominantly behaves as a dipole over time. The processes generating the magnetic field, however, are complex and therefore also generate higher order pole signals. These higher order pole signals can alter the Earth’s magnetic field on a short time scale, even when the dipole signal is strong. A substantial deviation from the current dipole field is the South Atlantic Anomaly (SAA), a large weak spot in the Earth’s magnetic field above South-America. In the SAA’s center, the magnetic field strength is ~22 μT, approximately half of the field strength at the same latitude in Australia.

To better understand the origin and evolution of the SAA, it is essential to develop high-quality geomagnetic models of the Earth’s magnetic field over the past millennia. A major challenge for the current geomagnetic models is the significant data absence from the Southern Hemisphere, where the SAA is located. This lack of data hinders accurate modeling of the SAA’s evolution over time.

Our research aims to increase the amount of data on the Southern Hemisphere, particularly at locations on the same latitude as the current SAA. These locations are chosen based on the observation that the SAA has been moving westward over the past few decades, leading to the hypothesis that this westward movement has been ongoing for a longer period. We are currently working on enhancing the amount of data by adding high-quality full-vector paleomagnetic data from volcanic deposits on Réunion Island, Bali and Fiji.

Here we present the results of our paleomagnetic study of lava flows from Taveuni, Fiji, revealing a remarkable weak magnetic field of approximately 12 μT in flows dated to around 600 years ago. These flows also have a 20-30 degrees deviation in declination and inclination from expected values. Incorporating this new data into the global geomagnetic dataset allows us to refine existing models, leading to the unexpected conclusion that this exceptionally low field intensity cannot be attributed to the South Atlantic Anomaly—located below Africa at the time—but rather points to the presence of another geomagnetic feature: a West Pacific Anomaly.