A global geoid model with imposed plate velocities and partial layering

Čadek, O.; Fleitout, Luce

doi:10.1029/1999jb900150

Cited by 55 publications

(67 citation statements)

References 75 publications

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“…This implies that mantle viscosity is at least 10 22 -10 26 Pa s. This is consistent with the estimates of the viscosity for the lower mantle, 10 22 -10 24 Pa s [King, 1995;Č adek and Fleitout, 1999;Forte and Mitrovica, 2001]. …”

Section: Viscositysupporting

confidence: 86%

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Small‐scale convection in the D″ layer

Solomatov

Moresi

2002

J. Geophys. Res.

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[1] Small-scale convection has been suggested as a possible explanation for seismic heterogeneities in the D 00 layer of the Earth's mantle. Recently developed scaling laws for convection with realistic viscosities allow quantitative assessment of this hypothesis. Large temperature and viscosity contrasts across the thermal boundary layer at the core-mantle boundary suggest that small-scale convection starts at the bottom of the thermal boundary layer and propagates upward before the thermal boundary layer as a whole becomes unstable. The convection boundary is likely to become a chemical boundary as a result of mixing within the convective layer. This implies that the D 00 discontinuity can represent both convective and chemical boundary and that the presence or absence of small-scale convection can be responsible for the observed intermittent nature of the D 00 discontinuity. Most lateral heterogeneities in the D 00 layer are concentrated near the convection boundary, consistent with seismic data. The length scale of lateral temperature variations, the topography of the core-mantle boundary, and the viscosity of the D 00 layer are in agreement with observational constraints. The thickness of the secondary thermal boundary layer formed at the bottom of the convective layer is similar to the thickness of the ultralow-velocity zone. The magnitude of lateral variations in temperature can only marginally be responsible for lateral variations in seismic velocities. Variations in the topography of the convection boundary and chemical heterogeneities are likely to be more important factors. A large seismic velocity drop in the ultralow-velocity zone cannot be explained by thermal effects alone and must be caused by other factors such as partial melting.

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Section: Viscositysupporting

confidence: 86%

“…This is only marginally consistent with the observed seismic velocity variations [Weber, 1993;Lay et al, 1997;Liu et al, 1998;Castle et al, 2000]. Other factors such as chemical heterogeneities and anisotropy can be more important for seismic velocity variations.…”

Section: Lateral Temperature Variationsmentioning

confidence: 44%

Small‐scale convection in the D″ layer

Solomatov

Moresi

2002

J. Geophys. Res.

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“…Our analyses of rebound data from formerly glaciated regions (64) and of deglaciation-induced changes in the dynamic flattening and rotation of the Earth (65)(66)(67) are consistent with the highviscosity results, although these solutions are also ice-model dependent. Inversions of geoid and seismic tomographic data are less sensitive to the choice of ice models (the observed geoid needs corrections for the GIA contribution) and point to an increase in depth-averaged mantle viscosity of one to three orders of magnitude from average upper to lower mantle (68)(69)(70)(71)(72)(73). Likewise, inferences of viscosity from the sinking speed of subducted lithosphere also point to high (3-5) × 10 22 Pa s values for the lower-mantle viscosity (74).…”

Section: Discussionmentioning

confidence: 99%

Sea level and global ice volumes from the Last Glacial Maximum to the Holocene

Lambeck

Rouby

Purcell

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

1,937

1,613

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The major cause of sea-level change during ice ages is the exchange of water between ice and ocean and the planet's dynamic response to the changing surface load. Inversion of ∼1,000 observations for the past 35,000 y from localities far from former ice margins has provided new constraints on the fluctuation of ice volume in this interval. Key results are: (i) a rapid final fall in global sea level of ∼40 m in <2,000 y at the onset of the glacial maximum ∼30,000 y before present (30 ka BP); (ii) a slow fall to −134 m from 29 to 21 ka BP with a maximum grounded ice volume of ∼52 × 10 6 km 3 greater than today; (iii) after an initial short duration rapid rise and a short interval of near-constant sea level, the main phase of deglaciation occurred from ∼16.5 ka BP to ∼8.2 ka BP at an average rate of rise of 12 m·ka −1 punctuated by periods of greater, particularly at 14.5-14.0 ka BP at ≥40 mm·y −1 (MWP-1A), and lesser, from 12.5 to 11.5 ka BP (Younger Dryas), rates; (iv) no evidence for a global MWP-1B event at ∼11.3 ka BP; and (v) a progressive decrease in the rate of rise from 8.2 ka to ∼2.5 ka BP, after which ocean volumes remained nearly constant until the renewed sea-level rise at 100-150 y ago, with no evidence of oscillations exceeding ∼15-20 cm in time intervals ≥200 y from 6 to 0.15 ka BP.he understanding of the change in ocean volume during glacial cycles is pertinent to several areas of earth science: for estimating the volume of ice and its geographic distribution through time (1); for calibrating isotopic proxy indicators of ocean volume change (2, 3); for estimating vertical rates of land movement from geological data (4); for examining the response of reef development to changing sea level (5); and for reconstructing paleo topographies to test models of human and other migrations (6). Estimates of variations in global sea level come from direct observational evidence of past sea levels relative to present and less directly from temporal variations in the oxygen isotopic signal of ocean sediments (7). Both yield modeldependent estimates. The first requires assumptions about processes that govern how past sea levels are recorded in the coastal geology or geomorphology as well as about the tectonic, isostatic, and oceanographic contributions to sea level change. The second requires assumptions about the source of the isotopic or chemical signatures of marine sediments and about the relative importance of growth or decay of the ice sheets, of changes in ocean and atmospheric temperatures, or from local or regional factors that control the extent and time scales of mixing within ocean basins.Both approaches are important and complementary. The direct observational evidence is restricted to time intervals or climatic and tectonic settings that favor preservation of the records through otherwise successive overprinting events. As a result, the records become increasingly fragmentary backward in time. The isotopic evidence, in contrast, being recorded in deep-water carbonate marine sediments, extends further...

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“…We have assumed that the physical conditions at the surface can be approximated by free slip and we have neglected the surface forces which may result from the mineral changes at the boundary between the upper and lower mantle.Čadek and Fleitout [37] have recently demonstrated that the free slip may not be appropriate for the top mantle boundary and that the non-uniqueness of the inversion can be significantly reduced if the observed plate velocities are imposed at the base of the lithosphere. The long-wavelength forces acting at the 660-km discontinuity and hampering the mass exchange between the upper and lower mantle have been discussed by several authors [38,39].…”

Section: Limitations Of Inversionmentioning

confidence: 99%

Radial profiles of temperature and viscosity in the Earth's mantle inferred from the geoid and lateral seismic structure

Čadek¹,

Berg²

1998

Earth and Planetary Science Letters

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In the framework of dynamical modelling of the geoid, we have estimated basic features of the radial profile of temperature in the mantle. The applied parameterization of the geotherm directly characterizes thermal boundary layers and values of the thermal gradient in the upper and lower mantle. In the inverse modelling scheme these parameters are related to the observables (geoid and seismic structure of the mantle) through the viscosity profile which is parameterized as an exponential function of pressure and temperature. We have tested ¾10 4 model geotherms. For each of them we have found proper rheological parameters by fitting the geoid with the aid of a genetic algorithm. The geotherms which best fit the geoid show a significant increase of temperature (¾600-800ºC) close to the 660-km discontinuity. The value of the thermal gradient in the mid-mantle is found to be sub-adiabatic. Both a narrow thermal core-mantle boundary layer and a broad region with a superadiabatic regime can produce a satisfactory fit of the geoid. The corresponding viscosity profiles show similarities to previously presented models, in particular in the viscosity maximum occurring in the deep lower mantle. The best-fitting model predicts the values of activation volume V Ł and energy E Ł which are in a good agreement with the data from mineral physics, except for V Ł in the lower mantle which is found somewhat lower than the estimate based on melting temperature analysis. An interesting feature of the viscosity profiles is a local decrease of viscosity somewhere between 500 and 1000 km depth which results from the steep increase of temperature in the vicinity of the 660-km discontinuity.

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A global geoid model with imposed plate velocities and partial layering

Cited by 55 publications

References 75 publications

Small‐scale convection in the D″ layer

Small‐scale convection in the D″ layer

Sea level and global ice volumes from the Last Glacial Maximum to the Holocene

Radial profiles of temperature and viscosity in the Earth's mantle inferred from the geoid and lateral seismic structure

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