The signature of inner-core nucleation on the geodynamo

Landeau, Maylis; Aubert, Julien; Olson, Peter

doi:10.1016/j.epsl.2017.02.004

Cited by 75 publications

(53 citation statements)

References 58 publications

(115 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…There could be little to no abrupt change in dipolar field intensities during the transition from that ancient exsolution dynamo prior to inner core crystallization to the modern dynamo powered by light‐element release due to inner core growth. This is inline that there would also be no change in dipolar field intensity (Landeau et al, ) in the transition from a thermal to a buoyancy‐driven dynamo at the onset of inner‐core nucleation.…”

Section: Exsolution and The Geodynamomentioning

confidence: 61%

Magnesium Partitioning Between Earth's Mantle and Core and its Potential to Drive an Early Exsolution Geodynamo

Badro

Aubert

Hirose

et al. 2018

Geophysical Research Letters

Self Cite

110

View full text Add to dashboard Cite

Magnesium partitioning between metal and silicate was experimentally investigated between 34 and 138 GPa, 3,500 and 5,450 K using laser‐heated diamond anvil cells. The 22 measurements are combined with previously published data (total of 49 measurements) to model magnesium metal‐silicate partitioning using a thermodynamically consistent framework based on the interaction parameter formalism. The observations support the mechanism of MgO dissolution in the metal, ruling out other mechanisms. The magnesium partition coefficient depends on temperature and metal composition, but not on pressure or silicate composition. The equilibrium concentration and the exsolution rate of MgO in Earth's core can therefore be calculated for any P, T, and composition. Using a core thermal evolution model, the buoyancy flux converts to a magnetic field at Earth's surface, with dipole intensities between 40 and 70 μT prior to inner core growth, consistent with the paleomagnetic record going back to the Archean.

show abstract

Section: Exsolution and The Geodynamomentioning

confidence: 61%

Magnesium Partitioning Between Earth's Mantle and Core and its Potential to Drive an Early Exsolution Geodynamo

Badro

Aubert

Hirose

et al. 2018

Geophysical Research Letters

Self Cite

110

View full text Add to dashboard Cite

show abstract

“…Subcritical entrainment could buffer the increase in convective vigor provoked by increased core/mantle heat flow. Speculatively, this negative feedback might help explain why paleointensity measurements seem relatively constant over time (Aubert et al, 2009;Driscoll, 2016;Landeau et al, 2017;Smirnov et al, 2016).…”

Section: Predictions For Mars and Other Planetsmentioning

confidence: 99%

Hydrogenation of the Martian Core by Hydrated Mantle Minerals With Implications for the Early Dynamo

O’Rourke

Shim

2019

JGR Planets

View full text Add to dashboard Cite

Mars lacks an internally generated magnetic field today. Crustal remanent magnetism and meteorites indicate that a dynamo existed after accretion but died roughly four billion years ago. Standard models rely on core/mantle heat flow dropping below the adiabatic limit for thermal convection in the core. However, rapid core cooling after the Noachian is favored instead to produce long‐lived mantle plumes and magmatism at volcanic provinces such as Tharsis and Elysium. Hydrogenation of the core could resolve this apparent contradiction by impeding the dynamo while core/mantle heat flow is superadiabatic. Here we present parameterized models for the rate at which mantle convection delivers hydrogen into the core. Our models suggest that most of the water that the mantle initially contained was effectively lost to the core. We predict that the mantle became increasingly ironrich over time and a stratified layer awaits detection in the uppermost core—analogous to the E′ layer atop Earth's core but likely thicker than alternative sources of stratification in the Martian core such as iron snow. Entraining buoyant, hydrogen‐rich fluid downward in the core subtracts gravitational energy from the total dissipation budget for the dynamo. The calculated fluxes of hydrogen are high enough to potentially reduce the lifetime of the dynamo by several hundred million years or longer relative to conventional model predictions. Future work should address the complicated interactions between the stratified, hydrogen‐rich layer and convection in the underlying core.

show abstract

“…For QPI ≥ 3 a jump in V(A)DM occurs around 1.3 Ga (Figure 13), which was interpreted as a signature of inner core nucleation (ICN) by Biggin et al (2015). The smoothed average then drops back down to normal, pre-jump intensities, which is not predicted from dynamo models of ICN (Aubert et al, 2009;Driscoll, 2016;Landeau et al, 2017). Using an even more stringent criteria of QPI ≥ 4, which includes even less data, does not show a peak around 1.3 Ga (Figure 14).…”

Section: Pint Paleointensity Databasementioning

confidence: 99%

“…There are at least three possible reasons for the lack of a clear paleomagnetic signature of ICN: (1) the paleomagnetic signature of ICN is too small or old to be preserved, (2) the paleointensity record is too sparse, or (3) the signature is obscured by non-GAD fields. Regarding the latter possibility, it has recently been proposed that prior to inner core nucleation around 600 Ma a non-GAD field may have been persistent in the Neoproterozoic as a consequence of the geodynamo being powered only by weak thermal convection at the time (Driscoll, 2016;Landeau et al, 2017). Unfortunately the paleointensity record around this time is sparse, possibly due to a lack of wide spread magmatism, a lack of preservation, inability to recover primary remanence, or low quality criteria.…”

Section: Introductionmentioning

confidence: 99%

Paleomagnetic Biases Inferred From Numerical Dynamos and the Search for Geodynamo Evolution

Driscoll

Wilson

2018

Front. Earth Sci.

View full text Add to dashboard Cite

The paleomagnetic record is central to our understanding of the history of the Earth. The orientation and intensity of magnetic minerals preserved in ancient rocks indicate the geodynamo has been alive since at least the Archean and possibly the Hadean. A paleomagnetic signature of the initial solidification of the inner core, arguably the singular most important event in core history, however, has remained elusive. In pursuit of this signature we investigate the assumption that the field is a geocentric axial dipole (GAD) over long time scales. We study a suite of numerical dynamo simulations from a paleomagnetic perspective to explore how long the field should be time-averaged to obtain stable paleomagnetic pole directions and intensities. We find that running averages over 20 − 40 kyr are needed to obtain stable paleomagnetic poles with α 95 < 10 • , and over 40 − 120 kyr for α 95 < 5 • , depending on the variability of the field. We find that models with higher heat flux and more frequent polarity reversals require longer time averages, and that obtaining stable intensities requires longer time averaging than obtaining stable directions. Running averages of local field intensity and inclination produce reliable estimates of the underlying dipole moment when reversal frequency is low. However, when heat flux and reversal frequency are increased we find that local observations tend to underestimate virtual dipole moment (VDM) by up to 50% and overestimate virtual axial dipole moment (VADM) by up to 150%. A latitudinal dependence is found where VDM underestimates the true dipole moment more at low latitudes, while VADM overestimates the true axial dipole moment more at high latitudes. The cause for these observed intensity biases appears to be a contamination of the time averaged field by non-GAD terms, which grows with reversal frequency. We derive a scaling law connecting reversal frequency and site paleolatitude to paleointensity bias (ratio of observed to the true value). Finally we apply this adjustment to the PINT paleointensity record. These biases produce little change to the overall trend of a relatively flat but scattered intensity over the last 3.5 Ga. A more careful intensity adjustment applied during periods when the reversal frequency is known could reveal previously obscured features in the paleointensity record.

show abstract

The signature of inner-core nucleation on the geodynamo

Cited by 75 publications

References 58 publications

Magnesium Partitioning Between Earth's Mantle and Core and its Potential to Drive an Early Exsolution Geodynamo

Magnesium Partitioning Between Earth's Mantle and Core and its Potential to Drive an Early Exsolution Geodynamo

Hydrogenation of the Martian Core by Hydrated Mantle Minerals With Implications for the Early Dynamo

Paleomagnetic Biases Inferred From Numerical Dynamos and the Search for Geodynamo Evolution

Contact Info

Product

Resources

About