ORCID Profile
0000-0002-8125-4752
Current Organisations
University of Leeds
,
University of California, San Diego
,
University of Sydney
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Publisher: Springer Science and Business Media LLC
Date: 18-05-2011
DOI: 10.1038/NATURE10068
Abstract: The Earth's magnetic field is generated by a dynamo in the liquid iron core, which convects in response to cooling of the overlying rocky mantle. The core freezes from the innermost surface outward, growing the solid inner core and releasing light elements that drive compositional convection. Mantle convection extracts heat from the core at a rate that has enormous lateral variations. Here we use geodynamo simulations to show that these variations are transferred to the inner-core boundary and can be large enough to cause heat to flow into the inner core. If this were to occur in the Earth, it would cause localized melting. Melting releases heavy liquid that could form the variable-composition layer suggested by an anomaly in seismic velocity in the 150 kilometres immediately above the inner-core boundary. This provides a very simple explanation of the existence of this layer, which otherwise requires additional assumptions such as locking of the inner core to the mantle, translation from its geopotential centre or convection with temperature equal to the solidus but with composition varying from the outer to the inner core. The predominantly narrow downwellings associated with freezing and broad upwellings associated with melting mean that the area of melting could be quite large despite the average dominance of freezing necessary to keep the dynamo going. Localized melting and freezing also provides a strong mechanism for creating seismic anomalies in the inner core itself, much stronger than the effects of variations in heat flow so far considered.
Publisher: Informa UK Limited
Date: 08-2008
Publisher: Springer Science and Business Media LLC
Date: 03-2008
DOI: 10.1038/452165A
Publisher: Wiley
Date: 27-09-2010
DOI: 10.1002/CPE.1593
Publisher: American Geophysical Union (AGU)
Date: 09-2019
DOI: 10.1029/2019JB017479
Abstract: Most subduction zones have associated long‐wavelength anomalies in the lithospheric magnetic field observed at satellite altitude. We model the 13 subduction zones defined by seismicity and seismic tomography using vertically integrated magnetizations that are increasing, level, or decreasing away from the trench. These mimic end members of a magnetized mantle wedge, a uniform layer, and a magnetized dipping lithospheric slab. They are added to a global model of vertically integrated magnetization based on continental and oceanic geology. We find the dipping slab places the anomaly too close to the trench, while the other two fit the data equally well and use the level model in the main part of the study. Anomalies at the Sunda, Aleutians, Cascadia, Central American, and Kamchatka‐Japan zones are well modeled by uniform magnetization of differing susceptibilities and spatial extents. We show the South American anomaly is weak because the magnetization lies mainly in the null space that produces no external potential magnetic field. There is no anomaly associated with the Ryukyu system, possibly because the present subduction started too recently for magnetization to have formed. The magnetic anomaly stretching down the Baja California peninsula is not present in the prediction because there is no seismicity on which to base a slab geometry, but recent tomography suggests a fossil slab there and we propose historic subduction as the origin of the Baja magnetic anomaly. Finally, we discuss the mineralogical origins of the magnetization and favor serpentinization of the region above the subducted plate.
Publisher: Elsevier BV
Date: 1993
Publisher: Oxford University Press (OUP)
Date: 11-2003
Publisher: Elsevier BV
Date: 06-2007
Publisher: Oxford University Press (OUP)
Date: 09-2000
Publisher: Elsevier BV
Date: 07-1200
Publisher: Springer Science and Business Media LLC
Date: 03-1994
DOI: 10.1038/368051A0
Publisher: Elsevier BV
Date: 08-2002
Publisher: Elsevier BV
Date: 12-1990
Publisher: Oxford University Press (OUP)
Date: 08-2000
Publisher: Wiley
Date: 15-11-2021
Publisher: Wiley
Date: 08-10-2021
Publisher: Springer Science and Business Media LLC
Date: 08-2010
Publisher: Springer Science and Business Media LLC
Date: 11-04-2012
DOI: 10.1038/NATURE11031
Abstract: The Earth acts as a gigantic heat engine driven by the decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing (as the solid inner core grows), and on chemical convection (due to light elements expelled from the liquid on freezing). The power supplied to the geodynamo, measured by the heat flux across the core-mantle boundary (CMB), places constraints on Earth's evolution. Estimates of CMB heat flux depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent experimental and theoretical difficulties. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles--unlike previous estimates, which relied on extrapolations. The mixtures of iron, oxygen, sulphur and silicon are taken from earlier work and fit the seismologically determined core density and inner-core boundary density jump. We find both conductivities to be two to three times higher than estimates in current use. The changes are so large that core thermal histories and power requirements need to be reassessed. New estimates indicate that the adiabatic heat flux is 15 to 16 terawatts at the CMB, higher than present estimates of CMB heat flux based on mantle convection the top of the core must be thermally stratified and any convection in the upper core must be driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted, and future models of mantle evolution will need to incorporate a high CMB heat flux and explain the recent formation of the inner core.
Publisher: Elsevier BV
Date: 07-2007
Publisher: Informa UK Limited
Date: 2002
Publisher: Oxford University Press (OUP)
Date: 06-1999
Publisher: Elsevier BV
Date: 11-1995
Publisher: No publisher found
Date: 1983
Publisher: Informa UK Limited
Date: 10-2007
Publisher: Oxford University Press (OUP)
Date: 2000
Publisher: Elsevier BV
Date: 1976
Publisher: Elsevier BV
Date: 02-2013
Publisher: Elsevier BV
Date: 08-2008
Publisher: Informa UK Limited
Date: 10-2005
Publisher: Elsevier BV
Date: 12-1995
Publisher: American Geophysical Union (AGU)
Date: 21-03-2013
DOI: 10.1002/GRL.50186
Publisher: Oxford University Press (OUP)
Date: 04-2009
Publisher: Oxford University Press (OUP)
Date: 02-2004
Publisher: Springer Science and Business Media LLC
Date: 1982
DOI: 10.1038/295015B0
Publisher: Elsevier BV
Date: 12-2001
Publisher: Oxford University Press (OUP)
Date: 09-2001
Publisher: Oxford University Press (OUP)
Date: 12-08-2011
Publisher: American Physical Society (APS)
Date: 22-01-2013
Publisher: Elsevier BV
Date: 08-2011
Publisher: Elsevier
Date: 1979
Publisher: Elsevier BV
Date: 03-1994
Publisher: American Association for the Advancement of Science (AAAS)
Date: 12-05-2006
Abstract: Earth's magnetic field has decayed by about 5% per century since measurements began in 1840. Directional measurements predate those of intensity by more than 250 years, and we combined the global model of directions with paleomagnetic intensity measurements to estimate the fall in strength for this earlier period (1590 to 1840 A.D.). We found that magnetic field strength was nearly constant throughout this time, in contrast to the later period. Extrapolating to the core surface showed that the fall in strength originated in patches of reverse magnetic flux in the Southern Hemisphere. These patches were detectable by directional data alone the pre-1840 model showed little or no evidence of them, supporting the conclusion of a steady dipole up to 1840.
Publisher: Informa UK Limited
Date: 12-2004
Publisher: Elsevier BV
Date: 09-2003
Publisher: Oxford University Press (OUP)
Date: 04-1999
Publisher: American Geophysical Union (AGU)
Date: 06-2009
DOI: 10.1029/2009GL037792
Publisher: Elsevier BV
Date: 11-2007
Publisher: Cambridge University Press (CUP)
Date: 10-12-2009
DOI: 10.1017/S0022112009991583
Abstract: We investigate thermally driven convection in a rotating spherical shell subject to inhomogeneous heating on the outer boundary, extending previous results to more rapid rotation rates and larger litudes of the boundary heating. The analysis explores the conditions under which steady flows can be obtained, and the stability of these solutions, for two boundary heating modes: first, when the scale of the boundary heating corresponds to the most unstable mode of the homogeneous problem second, when the scale is larger. In the former case stable steady solutions exhibit a two-layer flow pattern at moderate rotation rates, but at very rapid rotation rates no steady solutions exist. In the latter case, stable steady solutions are always possible, and unstable solutions show convection rolls that cluster into nests that are out of phase with the boundary anomalies and remain trapped for many thermal diffusion times.
Publisher: Oxford University Press (OUP)
Date: 04-2008
Publisher: Elsevier BV
Date: 1
Publisher: Springer Science and Business Media LLC
Date: 12-1990
DOI: 10.1007/BF01902965
Publisher: Elsevier BV
Date: 08-1991
Publisher: Elsevier BV
Date: 05-2014
Publisher: Oxford University Press (OUP)
Date: 14-07-2004
Publisher: American Geophysical Union (AGU)
Date: 05-01-2022
DOI: 10.1029/2021GL095913
Abstract: Mars has a magnetic field originating in its strongly magnetized crust that holds clues to the planet's interior. We apply vector spherical harmonic decomposition to simple candidate magnetic structures to separate the parts responsible for the anomalies from those that remain invisible. A uniform magnetic layer produces no anomalies: spatial variations are essential although secondary magnetization does produce a weak field that might reflect the primordial dynamo field. A hemispheric layer produces anomalies confined to the equator rather than the observed hemispheric difference. A uniformly magnetized crust with variable thickness determined from gravity and topography produces a crustal field with large anomalies at the major impact crater sites that are not observed. These anomalies are not present if the magnetic layer lies deeper than the crater floor. We conclude that decomposing magnetizations in this way is a useful tool in the interpretation of Martian magnetic anomalies.
Publisher: Elsevier BV
Date: 03-1991
Publisher: Oxford University Press (OUP)
Date: 28-09-2011
Publisher: Oxford University Press (OUP)
Date: 09-2008
Publisher: Oxford University Press (OUP)
Date: 06-2004
Publisher: Springer Science and Business Media LLC
Date: 10-1985
DOI: 10.1038/317777A0
Publisher: Elsevier BV
Date: 08-2011
Publisher: Oxford University Press (OUP)
Date: 08-2000
Publisher: Elsevier BV
Date: 12-1983
Publisher: Oxford University Press (OUP)
Date: 11-1999
Publisher: Elsevier BV
Date: 15-07-2006
Publisher: Elsevier BV
Date: 12-1990
Publisher: Springer Science and Business Media LLC
Date: 08-1971
DOI: 10.1038/232548B0
Publisher: Oxford University Press (OUP)
Date: 09-2001
Publisher: Oxford University Press (OUP)
Date: 29-12-2012
DOI: 10.1093/GJI/GGS063
Location: United Kingdom of Great Britain and Northern Ireland
Location: United States of America
No related grants have been discovered for David Gubbins.