Thermal core‐mantle interactions and time‐averaged paleomagnetic field

Recent studies of historical geomagnetic secular variation and lower mantle seismic velocity suggest the Earth's magnetic field is controlled by lateral variations in mantle temperature. In this paper the average expected magnetic field pattern is compared with the time‐averaged field obtained from paleomagnetic pole positions from the last 5 m.y. The historical record suggests that the time‐averaged inclination anomalies are negative (“far‐sided”) in the Atlantic region north of 30°S and the west Pacific and positive in the South Atlantic, extreme North and South Pacific, and east Pacific. The pole positions give positive inclination anomalies in the South Atlantic and extreme North Pacific, and negative anomalies elsewhere, in agreement with the theory except for the east Pacific. This suggests that the historical record is not long enough to give an accurate picture of long term secular change in the eastern Pacific but that elsewhere the time‐averaged field of paleomagnetism is predicted satisfactorily. The preponderance of “far sidedness” in the paleomagnetic record is a consequence of the present distribution of temperature at the base of the mantle rather than a fundamental property of the geodynamo, and it may therefore change on the long time scale of mantle convection. In the historical record declinations average to negative values in the Atlantic hemisphere and positive values in the Pacific which, if typical of longer‐term behavior, could explain the preponderance of positive declinations for reversed polarity, which are mainly in the Atlantic hemisphere.