Reconstructing reversal frequencies: constraints on core-mantle boundary heat flow evolution

Abstract

The core-mantle boundary heat flow controls the geodynamo and in particular the occurrence of geomagnetic reversals. Unfortunately, the present-day and past core-mantle boundary heat flow are poorly constrained. In this work, a series of numerical dynamo models put constraints on the core-mantle boundary heat flow evolution for the past 270 Myr by comparing the reversal frequencies from those models with observations. A benchmark is performed to ensure the correct installation of the code used to run the simulations. The present-day reversal frequency of ≈4 Myr^-1 is reproduced to find a dynamo model representative of the current geodynamo state. By varying the Rayleigh number RaQ, an initial dynamo model with RaQ = 1,26×10^-4 yielded a frequency of 3.85 Myr^-1. Geodynamo evolution is modelled by applying estimates of secular changes in geodynamo control parameters to the initial model. Several scenarios for the evolution of the core-mantle heat flow were imposed, which are validated by comparing computed reversal frequencies with the reversal record. Heat flow evolution scenarios from mantle convection reconstructions and a linear decrease of heat flow with time were employed. It was found that secular changes in the heat flow have been in the order of 1% and not more than 7.5% compared to the time-average heat flow. Moreover, the results indicate that the core-mantle boundary heat flow has decreased linearly with time, from roughly 18 to 15 TW over the past 270 Myr.