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Earth’s magnetic field is generated by turbulent motion in its fluid outer core. Although the bulk of the outer core is vigorously convecting and well mixed, some seismic, geomagnetic and geodynamic evidence suggests that a global stably stratified layer exists at the top of Earth’s core. Such a layer would strongly influence thermal, chemical and momentum exchange across the core–mantle boundary and thus have important implications for the dynamics and evolution of the core. Here we argue that the relevant scenario is not global stratification, but rather regional stratification arising solely from the lateral variations in heat flux at the core–mantle boundary. Using our extensive suite of numerical simulations of the dynamics of the fluid core with het- erogeneous core–mantle boundary heat flux, we predict that thermal regional inversion layers extend hundreds of kilometres into the core under anomalously hot regions of the lowermost mantle. Although the majority of the outermost core remains actively convecting, sufficiently large and strong regional inversion layers produce a one-dimensional temperature profile that mimics a globally stratified layer below the core–mantle boundary—an apparent thermal stratification despite the average heat flux across the core–mantle boundary being strongly superadiabatic.
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Multidisciplinary Constraints on the Thermal‐Chemical Boundary Between Earth's Core and Mantle
Abstract Heat flux from the core to the mantle provides driving energy for mantle convection thus powering plate tectonics, and contributes a significant fraction of the geothermal heat budget. Indirect estimates of core‐mantle boundary heat flow are typically based on petrological evidence of mantle temperature, interpretations of temperatures indicated by seismic travel times, experimental measurements of mineral melting points, physical mantle convection models, or physical core convection models. However, previous estimates have not consistently integrated these lines of evidence. In this work, an interdisciplinary analysis is applied to co‐constrain core‐mantle boundary heat flow and test the thermal boundary layer (TBL) theory. The concurrence of TBL models, energy balance to support geomagnetism, seismology, and review of petrologic evidence for historic mantle temperatures supportsQCMB∼15 TW, with all except geomagnetism supporting as high as ∼20 TW. These values provide a tighter constraint on core heat flux relative to previous work. Our work describes the seismic properties consistent with a TBL, and supports a long‐lived basal mantle molten layer through much of Earth's history.
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- PAR ID:
- 10374385
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 23
- Issue:
- 3
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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