Thermochemical models of outer core convection with heterogeneous core-mantle boundary heat flux

Souvik Naskar; Jonathan E. Mound; Christopher J. Davies; Andrew T. Clarke

doi:10.46298/jsedi.17084

Article

Thermochemical models of outer core convection with heterogeneous core-mantle boundary heat flux

Souvik Naskar

⁽¹⁾, Jonathan E. Mound

⁽¹⁾, Christopher J. Davies

⁽¹⁾, Andrew T. Clarke

⁽¹⁾

(1) University of Leeds

Download article

Open on arXiv

Submitted on

December 11, 2025

Accepted on

May 9, 2026

Published on

May 15, 2026

Last modified on

June 5, 2026

Volume 2

DOI

10.46298/jsedi.17084

License

Attribution 4.0 International (CC BY 4.0)

Indicators

169

Views

Downloads

Thermochemical models of outer core convection with heterogeneous core-mantle boundary heat flux

Souvik Naskar

⁽¹⁾, Jonathan E. Mound

⁽¹⁾, Christopher J. Davies

⁽¹⁾, Andrew T. Clarke

⁽¹⁾

(1) University of Leeds

Abstract

Convection in Earth's outer core is driven by the release of heat and light elements at the inner core boundary. A key question is whether these buoyancy sources drive convection throughout the core, or whether a stable layer exists just below the core-mantle boundary (CMB). Recent simulations incorporating CMB heat flux heterogeneities propose locally stable ``regional inversion lenses'' (RILs) rather than a global layer, allowing stable and unstable regions to coexist. However, these simulations combine thermal and compositional anomalies, ignoring differences in diffusivities and boundary conditions. Here we simulate thermal, chemical, and thermochemical convection at Ekman number $E=10^{-5}$, with thermal and chemical flux Rayleigh numbers $\widetilde{Ra}_T=30-4000$ and $\widetilde{Ra}_ξ=30-100000$, and Prandtl numbers $Pr_T=1$ and $Pr_ξ=10$. Purely chemical simulations accumulate light elements below the CMB, forming locally stable regions near the poles or global layers, depending on $\widetilde{Ra}_ξ$. These chemically stratified regions persist in thermochemical simulations even when thermal forcing is destabilising. Introducing heterogeneous CMB heat flux produces thermally stratified RILs even with strongly destabilising compositional buoyancy. Our simulations reveal a diverse range of locations, properties, and morphologies of stable regions depending on $\widetilde{Ra}_T$ and $\widetilde{Ra}_ξ$, they can have a seismically detectable thickness and strength and might also have a signature in geomagnetic observations. Submitted to Journal of Studies of Earths Deep Interior

Keywords

Earth and Planetary Astrophysics
Geophysics

Linked publications - datasets - software

Based on data
https://doi.org/10.5285/74c2ed9d-6ab4-4d24-863d-5991afbe84ce

References

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DOI : 10.1016/j.pepi.2010.02.011
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Thermochemical models of outer core convection with heterogeneous core-mantle boundary heat flux

Souvik Naskar

⁽¹⁾, Jonathan E. Mound

⁽¹⁾, Christopher J. Davies

⁽¹⁾, Andrew T. Clarke

⁽¹⁾

(1) University of Leeds

Download article

Open on arXiv

Submitted on

December 11, 2025

Accepted on

May 9, 2026

Published on

May 15, 2026

Last modified on

June 5, 2026

Volume 2

DOI

10.46298/jsedi.17084

License

Attribution 4.0 International (CC BY 4.0)

Indicators

169

Views

Downloads

Thermochemical models of outer core convection with heterogeneous core-mantle boundary heat flux

Souvik Naskar

⁽¹⁾, Jonathan E. Mound

⁽¹⁾, Christopher J. Davies

⁽¹⁾, Andrew T. Clarke

⁽¹⁾

(1) University of Leeds

Abstract

Keywords

Earth and Planetary Astrophysics
Geophysics

Linked publications - datasets - software

Based on data
https://doi.org/10.5285/74c2ed9d-6ab4-4d24-863d-5991afbe84ce

References

Alexandrakis, C., & Eaton, D. W. (2010). Precise seismic-wave velocity atop Earth’s core: No evidence for outer-core stratification. Physics of the Earth and Planetary Interiors, 180(1–2), 59–65. https://doi.org/10.1016/j.pepi.2010.02.011
DOI : 10.1016/j.pepi.2010.02.011
Amit, H. (2014). Can downwelling at the top of the Earth’s core be detected in the geomagnetic secular variation? Phys. Earth Planet. Inter. 229, 110–121. doi: 10.1016/j.pepi.2014.01.012.
Aubert, J. (2005). Steady zonal flows in spherical shell dynamos. J. Fluid Mech., 542, 53–67. https://doi.org/10.1017/s0022112005006129
DOI : 10.1017/S0022112005006129
Aubert, J. (2025). Rapid geomagnetic variations and stable stratification at the top of Earth’s core. Phys. Earth Planet. Inter. 362, 107335. doi: 10.1016/j.pepi.2025.107335.
Bouffard, M., M. Landeau, and A. Goument (2020). Convec- tive Erosion of a Primordial Stratification Atop Earth’s Core. Geophys. Res. Lett. 47.14, e2020GL087109. doi: 10.1029/2020GL087109.
Bouffard, M., G. Choblet, S. Labrosse, and J. Wicht (2019). Chemical Convection and Stratification in the Earth’s Outer Core. Front. Earth Sci. 7. doi: 10.3389/feart.2019.00099.
Breuer, M., A. Manglik, J. Wicht, T. Trümper, H. Harder, and U. Hansen (2010). Thermochemically driven convection in a rotating spherical shell. Geophys. J. Int. 183 (1), 150–162. doi: 10.1111/j.1365-246X.2010.04722.x.
Brodholt, J. and J. Badro (2017). Composition of the low seis- mic velocity E layer at the top of Earth’s core. Geophys. Res. Lett. 44 (16), 8303–8310. doi: 10.1002/2017GL074261.
Buffett, B. (2014). Geomagnetic fluctuations reveal stable stratification at the top of the Earth’s core. Nature, 507(7493), 484–487. https://doi.org/10.1038/nature13122
DOI : 10.1038/nature13122
Buffett, B. A., & Seagle, C. T. (2010). Stratification of the top of the core due to chemical interactions with the mantle. Journal of Geophysical Research: Solid Earth, 115(B4). https://doi.org/10.1029/2009jb006751
DOI : 10.1029/2009JB006751
Calkins, M. A., Orvedahl, R. J., & Featherstone, N. A. (2021). Large-scale balances and asymptotic scaling behaviour in spherical dynamos. Geophysical Journal International, 227(2), 1228–1245. https://doi.org/10.1093/gji/ggab274
DOI : 10.1093/gji/ggab274
Christensen, U. R. (2006). A deep dynamo generating Mer- cury’s magnetic field. Nature 444.7122, 1056–1058. doi: 10.1038/nature05342.
Christensen, U. (2018). Geodynamo models with a stable layer and heterogeneous heat flow at the top of the core. Geophys. J. Int., 215(2), 1338–1351. https://doi.org/10.1093/gji/ggy352
DOI : 10.1093/gji/ggy352
Davies, C. J., D. Gubbins, and P. K. Jimack (2011). Scalability of pseudospectral methods for geodynamo simulations. Concurr. Comput. Pract. Exp. 23.1, 38–56. doi: 10.1002/cpe. 1593.
Davies, C. J. (2015). Cooling history of Earth’s core with high thermal conductivity. Phys. Earth Planet. Inter. 247. Transport Properties of the Earth’s Core, 65–79. doi: 10.1016/j. pepi.2015.03.007.
Davies, C. J. and S. Greenwood (2023). Dynamics in Earth’s Core Arising from Thermo-Chemical Interactions with the Mantle. Core-Mantle Co-Evolution. American Geophysical Union (AGU). Chap. 12, pp. 219–258. doi: 10 . 1002 / 9781119526919.ch12.
Gastine, T., J. Aubert, and A. Fournier (2020). Dynamo-based limit to the extent of a stable layer atop Earth’s core. Geophys. J. Int. 222.2, 1433–1448. doi: 10.1093/gji/ggaa250.
Greenwood, S., C. J. Davies, and J. E. Mound (2021). On the evolution of thermally stratified layers at the top of Earth’s core. Phys. Earth Planet. Inter. 318, 106763. doi: 10.1016/j. pepi.2021.106763.
Gubbins, D., C. Thomson, and K. Whaler (1982). Stable regions in the Earth’s liquid core. Geophys. J. Int. 68.1, 241– 251. doi: 10.1111/j.1365-246X.1982.tb06972.x.
Gubbins, D. (2001). The Rayleigh number for convection in the Earth’s core. Phys. Earth Planet. Inter. 128.1. Dynamics and Magnetic Fields of the Earth’s and Planetary Interiors, 3–12. doi: 10.1016/S0031-9201(01)00273-4.
Gubbins, D. (2007). Geomagnetic constraints on stratification at the top of Earth’s core. Earth. Planet. Sci. Lett. 59 (7), 661– 664. doi: 10.1186/BF03352728.
Guervilly, C. (2022). Fingering Convection in the Stably Stratified Layers of Planetary Cores. J. Geophys. Res. Planets 127.11, e2022JE007350. doi: 10.1029/2022JE007350.
Helffrich, G. and S. Kaneshima (2010). Outer-core compositional stratification from observed core wave speed profiles. Nature 468.7325, 807–810. doi: 10.1038/nature09636.
Huguet, L., H. Amit, and T. Alboussière (2018). Geomagnetic Dipole Changes and Upwelling/Downwelling at the Top of the Earth’s Core. Front. Earth Sci. 6, 170. doi: 10.3389/ feart.2018.00170.
Irving, J. C., S. Cottaar, and V. Lekić (2018). Seismically determined elastic parameters for Earth’s outer core. Sci. Adv. 4.6, eaar2538. doi: 10.1126/sciadv.aar2538.
Jones, C. A. (2000). Convection–driven geodynamo models. Philos. T. Roy. Soc. London A 358, 873–897. doi: 10.1098/ rsta.2000.0565.
Kaneshima, S. (2018). Array analyses of SmKS waves and the stratification of Earth’s outermost core. Phys. Earth Planet. Inter. 276, 234–246. doi: 10.1016/j.pepi.2017.03.006.
Kaplan, E. J., N. Schaeffer, J. Vidal, and P. Cardin (2017). Subcritical Thermal Convection of Liquid Metals in a Rapidly Rotating Sphere. Phys. Rev. Lett. 119 (9), 094501. doi: 10. 1103/PhysRevLett.119.094501.
Kono, M. and P. H. Roberts (2001). Definition of the Rayleigh number for geodynamo simulation. Phys. Earth Planet. Inter. 128.1-4, 13–24. doi: 10.1016/S0031-9201(01)00274-6.
Kunnen, R. P. J. (2021). The geostrophic regime of rapidly rotating turbulent convection. J. Turbul. 22.4-5, 267–296. doi: 10.1016/S0031-9201(02)00016-X.
Kutzner, C. and U. R. Christensen (2002). From stable dipolar towards reversing numerical dynamos. Phys. Earth Planet. Inter. 131.1, 29–45. doi: 10.1016/S0031-9201(02)00016-X.
Labrosse, S. (2015). Thermal evolution of the core with a high thermal conductivity. Phys. Earth Planet. Inter. 247. Trans- port Properties of the Earth’s Core, 36–55. doi: 10.1016/j. pepi.2015.02.002.
Labrosse, S., J.-P. Poirier, and J.-L. Le Mouël (1997). On cooling of the Earth’s core. Phys. Earth Planet. Inter. 99.1-2, 1– 17. doi: 10.1016/S0031-9201(96)03207-4.
Landeau, M., P. Olson, R. Deguen, and B. H. Hirsh (2016). Core merging and stratification following giant impact. Nat. Geosci. 9.10, 786–789. doi: 10.1038/ngeo2808.
Lesur, V., Whaler, K., & Wardinski, I. (2015). Are geomagnetic data consistent with stably stratified flow at the core–mantle boundary? Geophys. J. Int., 201(2), 929–946. https://doi.org/10.1093/gji/ggv031
DOI : 10.1093/gji/ggv031
Lister, J. R. and B. A. Buffett (1995). The strength and efficiency of thermal and compositional convection in the geodynamo. Phys. Earth Planet. Inter. 91.1. Study of the Earth’s Deep Interior, 17–30. doi: 10.1016/0031-9201(95) 03042-U.
Long, R. S., J. E. Mound, C. J. Davies, and S. M. Tobias (2020). Scaling behaviour in spherical shell rotating convection with fixed-flux thermal boundary conditions. J. Fluid Mech. 889, A7. doi: 10.1017/jfm.2020.67.
Ma, X. and H. Tkalčić (2024). Seismic low-velocity equatorial torus in the Earth’s outer core: Evidence from the late–coda correlation wavefield. Sci. Adv. 10.35, eadn5562. doi: 10.1126/sciadv.adn5562.
Masters, T. G., S. Johnson, G. Laske, and H. Bolton (1996). A shear-velocity model of the mantle. Philos. T. Roy. Soc. London A 354.1711, 1385–1411. doi: 10 . 1098 / rsta . 1996 . 0054.
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