On mantle-induced heat flow variations at the inner core boundary

Abstract

Seismic shear wave velocity variations in the Earth’s lower mantle have led to the inference that fluid motion in the core can be controlled by the mantle. Non-axisymmetric features of the observed geomagnetic field as well as fields produced in dynamo calculations support this viewpoint. However, it is not well-understood how the mantle-modified flow pattern can affect heat flow as far down as the inner core surface. In this paper we study the possible effect of lower-mantle variations on the heat flux distribution at the Earth’s inner core boundary (ICB). As the lateral variation at the core–mantle boundary (CMB) is increased in a geodynamo model, strong narrow downwelling jets are produced which impinge on the lower boundary, giving rise to regions of intense cooling separated by broad regions where warm fluid can rise relatively slowly. Significant heat flow into the inner core, which might lead to melting beneath Africa and the Pacific, is more likely to occur in a partially locked solution rather than a quasi-stationary, tightly locked solution. We also report a dynamo solution where the computed maximum heat flux variation at the core–mantle boundary is one order of magnitude higher than the mean flux. Although this regime does not have heat flowing into the inner core, varying the magnitude of the CMB anomaly can potentially make the heat flux negative over a large area of the inner core surface.