Evidence for postglacial signatures in gravity gradients: A clue in lower mantle viscosity

Métivier, Laurent; Greff-Lefftz, M.; Pajot-Métivier, Gwendoline; Fleitout, Luce; Rouby, Hélène

doi:10.1016/j.epsl.2016.07.034

Cited by 14 publications

(26 citation statements)

References 45 publications

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“…Originally, the ANU GIA model makes use of various viscosity profiles, one for each specific GIA region. Because we need global GIA deformation, and because the selection of a viscosity profile is still a subject of debate (e.g., Lambeck et al, 2014;Métivier et al, 2016), we recalculated the global Earth response to the ANU ice history using five different viscosity profiles, independently of the region concerned (models denoted hereafter ANU-V1 to ANU-V5). These profiles, in practice, reflect the mantle behavior under different types of crust (continental, oceanic, margins, etc.)…”

Section: Determinations Of Solid Earth Figure Changes With Realistic mentioning

confidence: 99%

ITRF2014, Earth Figure Changes, and Geocenter Velocity: Implications for GIA and Recent Ice Melting

et al. 2020

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Using a selection of Global Navigation Satellite System vertical velocities from the latest solution of the International Terrestrial Reference Frame (ITRF) ITRF2014, we calculate the degree‐1 and degree‐2 spherical harmonics coefficients (SHC) of the solid Earth figure changes at different dates, with realistic errors that take into account the inhomogeneity of the network. We find that the SHC are globally close to zero except the zonal coefficients, which show values notably larger than those derived from different glacial isostatic adjustment (GIA) models and which have tended to increase during the time span of observations. We show that these differences are most probably due to global recent ice melting (RIM). Assuming elastic RIM deformation, we then investigate the Earth's geocenter velocity and the geoid oblateness time evolution (J2‐rate) derived from our SHC estimations. The obtained geocenter velocity reaches 0.9 ± 0.5 mm/year in 2013 with a z‐component of 0.8 ± 0.4 mm/year, which is slightly larger than previous estimations. We compare our J2‐rate estimations with observations. Our estimations show a similar acceleration in J2 after 2000. However, our estimates are notably larger than the observations. This indicates either that the J2‐rate due to GIA processes is lower than expected (as proposed by Nakada et al., 2015, 2016) or that the deformation induced by RIM is not purely elastic, or both. Finally, we show that viscous relaxation or phase transitions in the mantle transition zone may only partly explain this discrepancy. This raises the question of the accuracy of current mass estimations of RIM and GIA models.

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Section: Determinations Of Solid Earth Figure Changes With Realistic mentioning

confidence: 99%

ITRF2014, Earth Figure Changes, and Geocenter Velocity: Implications for GIA and Recent Ice Melting

et al. 2020

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“…One of the principle drivers of solid Earth deformation is GIA, and across regions that are currently ice-free, GRACE data (and measurements of the static gravity field by the 'Gravity field and steady-state Ocean Circulation Explorer', GOCE) have been used to quantify the magnitude and spatial pattern of the local GIA signal (e.g. Tamisiea et al, 2007;Hill et al, 2010;Metivier et al, 2016), past ice thickness 415 (Root et al, 2015), and local viscosity structure (Paulson et al, 2007a). However, in areas where an ice sheet is still present variations in the local gravity field will reflect the solid Earth response to both past and present ice mass change, as well as contemporary changes to the mass of the ice sheet itself (Wahr et al, 2000).…”

Section: Gravity Datamentioning

confidence: 99%

Glacial Isostatic Adjustment modelling: historical perspectives, recent advances, and future directions

Whitehouse¹

2018

Preprint

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Abstract. Glacial Isostatic Adjustment (GIA) describes the response of the solid Earth, the gravitational field, and 5 consequently the oceans to the growth and decay of the global ice sheets. It is a process that takes place relatively rapidly, triggering 100 m-scale changes in sea level and solid Earth deformation over just a few tens of thousands of years. Indeed, the first-order effects of GIA could already be quantified several hundred years ago without reliance on precise measurement techniques and scientists have been developing a unifying theory for the observations for over 200 years. Progress towards this goal required a number of significant breakthroughs to be made, including the recognition that ice sheets were once 10 more extensive, the solid Earth changes shape over time, and gravity plays a central role in determining the pattern of sealevel change. This article describes in detail the historical development of the field of GIA and an overview of the processes involved. Significant recent progress has been made as concepts associated with GIA have begun to be incorporated into parallel fields of research; these advances are discussed, along with the role that GIA is likely to play in addressing outstanding research questions within the field of Earth system modelling. 15

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“…Confirming their meaning from comparisons to modeled anomalies and seismic tomography models, this is how broadscale north‐south elongated gradient anomalies following a circum‐Pacific belt of ancient plate boundaries have been related to subducted slabs in the lower mantle (Panet et al, ). This is also how gradients oscillations near boundaries of the expected past location of the Laurentide ice sheet have been associated with a residual glacial isostatic adjustment signal in the Earth's static gravity field (Métivier et al, ).…”

Section: Application To Different Types Of Mass Sourcesmentioning

confidence: 98%

An Analysis of Gravitational Gradients in Rotated Frames and Their Relation to Oriented Mass Sources

Panet

2018

JGR Solid Earth

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Many mass sources within the Earth and its fluid envelopes show elongated geometries, aligning with the orientations of plate boundaries and plate motions, coastlines, rivers, and drainage basins for instance. To enhance their identification and separation in global or regional gravity observations and models, a dedicated method based on gravitational gradients analysis is presented here. This approach provides a detailed description of the geographic pattern of the gravity variations, which are accurately mapped thanks to the regular spatial coverage of high‐accuracy satellite data and arise from lateral density changes within the planet. First, gravity gradients are defined at different spatial scales in spherical frames, which are rotated along the radial axis according to the orientation of the source. The sensitivity of these gradients to the mass distribution inside a spherical Earth is described and analytical expressions relating the source to the observable are introduced. Then, the gravity gradients responses at different spatial scales to flat, elementary mass sources located at the surface and at increasing depth are studied. Specifically, the paper investigates how a source width and orientation can be determined, for localized and oscillatory mass anomalies with different width‐to‐length aspect ratios. This theoretical case study aims at providing a basis for the analysis of more complex mass structures, when applying the presented method to static or time‐varying satellite gravity field models. It may help deciphering the nature of the gravity sources by the detection of meaningful geometries and orientations in the gravity field.

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Evidence for postglacial signatures in gravity gradients: A clue in lower mantle viscosity

Cited by 14 publications

References 45 publications

ITRF2014, Earth Figure Changes, and Geocenter Velocity: Implications for GIA and Recent Ice Melting

ITRF2014, Earth Figure Changes, and Geocenter Velocity: Implications for GIA and Recent Ice Melting

Glacial Isostatic Adjustment modelling: historical perspectives, recent advances, and future directions

An Analysis of Gravitational Gradients in Rotated Frames and Their Relation to Oriented Mass Sources

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