Uncertainties of Glacial Isostatic Adjustment Model Predictions in North America Associated With 3D Structure

Li, Tanghua; Wu, Patrick; Wang, Hansheng; Steffen, Holger; Khan, Nicole S.; Engelhart, Simon E.; Vacchi, Matteo; Shaw, Timothy A.; Peltier, W. R.; Horton, Benjamin P.

doi:10.1029/2020gl087944

Cited by 30 publications

(46 citation statements)

References 49 publications

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“…GIA models with a 1-D viscosity in North America match results from laterally averaged 3-D models reasonably well (Geruo et al, 2013). Moreover, the effect of 3-D viscosity on predictions around Hudson Bay is limited (Li et al, 2020). Therefore, it is expected that the 1-D Earth model employed in our model produces reasonably accurate results.…”

Section: Gia Modelsmentioning

confidence: 63%

Long-wavelength gravity field constraint on the lower mantle viscosity in North America

Reusen

Root

Szwillus

et al. 2020

Preprint

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The long-wavelength negative gravity anomaly over Hudson Bay coincides with the area depressed by the Laurentide Ice Sheet during the Last Glacial Maximum, suggesting that it is, at least partly, caused by glacial isostatic adjustment (GIA). Additional contributions to the static gravity field stem from surface dynamic topography, core-mantle boundary (CMB) topography, and density anomalies in the subsurface. Previous estimates of the contribution of GIA to the gravity anomaly range from 25% to more than 80%. However, these estimates did not include uncertainties in all components that contribute to the gravity field. In this study, we develop a forward model for the gravity anomaly based on density models and dynamic models, investigating uncertainty in all components. We derive lithospheric densities from equilibrium constraints but extend the concept of lithospheric isostasy to a force balance that includes the dynamic models. The largest uncertainty in the predicted gravity anomaly is due to the lower mantle viscosity, uncertainties in the ice history, the crustal model, the lithosphere-asthenosphere boundary, and the conversion from seismic velocities to density have a smaller effect. A preference for lower mantle viscosities >10 22 Pa s is found, in which case at least 60% of the observed long-wavelength gravity anomaly can be attributed to GIA. This lower bound on the lower mantle viscosity has implications for inferences based on models for mantle convection and GIA.Plain Language Summary About 26,000 years ago, vast parts of North America and Northern Europe were covered by ice sheets. These glaciations depressed the ground, which is rebounding ever since the ice sheets started melting. The rate of this rebound depends on the structure of the earth below it. In this paper, we obtain more insight into the structure of the earth. To do so, we use the gravitational field since we can observe small deviations in this field very precisely. Over Hudson Bay, we observe such a deviation. The observed gravity anomaly over Hudson Bay closely resembles the area previously covered by ice. One possible explanation for this anomaly is therefore the incomplete rebound of the land. To test this, we include the effects of previous glaciations and mantle flow in a model of the crust and the lithosphere. We vary the viscosities of the upper and lower mantle, which are important parameters when modeling glacial rebound and mantle flow. The best match is found for a stiff lower mantle, implying that at least 200 m of land uplift remains and that a minimum of 60% of this anomaly can be attributed to the depression caused by past glaciations.

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Section: Gia Modelsmentioning

confidence: 63%

Long-wavelength gravity field constraint on the lower mantle viscosity in North America

Reusen

Root

Szwillus

et al. 2020

Preprint

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“…We certainly do not expect a perfect fit from these GIA models, especially since lateral mantle viscosity variation is typically not considered in global GIA models. The sharp change in residual velocities near the forebulge suggests that lateral viscosity variations may have to be considered to account for localized GIA response (e.g., Latychev et al, 2005; Li et al, 2020). Compared to the original velocity field's variance of 0.64 mm 2 /yr 2 , the variances of the residual fields after correction are ICE‐5G = 1.08 mm 2 /yr 2 , ICE‐6G_D = 0.51 mm 2 /yr 2 , and Caron = 1.13 mm 2 /yr 2 .…”

Section: Resultsmentioning

confidence: 99%

Present‐Day Crustal Vertical Velocity Field for the Contiguous United States

2020

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The study of vertical crustal motion in the contiguous United States (CONUS) has traditionally focused on the high-amplitude deformation caused by glacial isostatic adjustment. To better understand more subtle vertical crustal motion resulting from other geophysical processes, we take advantage of the ongoing expansion of continuous Global Positioning System (GPS) networks, whose geodetic observations provide ever-increasing accuracy and spatial resolution of surface deformation. Using position data for 2,782 GPS stations operating between 2007 and 2017, we produce a new vertical crustal velocity field for the CONUS region. We estimate our own station velocities to ensure consistent treatment of time series outliers, noise, and offsets, and we use adaptive smoothing and interpolation to account for spatially varying station density. Our velocity field reveals spatially coherent vertical features that are representative of regional tectonics, hydrologic, and anthropogenic processes. By removing the effects of modeled glacial isostatic adjustment and hydrologic loading estimated from Gravity Recovery and Climate Experiment (GRACE) data, we reduce the variance in our velocity field by 36% and show residuals potentially due to geocenter motion and underlying tectonics.

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“…In some parts of the analysis, we include the ICE‐6G_D GIA model of Peltier et al (2018), since large discrepancies between the

{VLM}_{m o d e l}^{C M}

and

{VLM}_{G N S S}^{C M}

can be explained by the choice of GIA model. Recent study using an ensemble of simulations with 3‐D‐Earth rheologies (Li et al, 2020), seems to favor the results GIA‐rates of Peltier et al (2018).…”

Section: Methodsmentioning

confidence: 91%

Vertical Land Motion From Present‐Day Deglaciation in the Wider Arctic

Ludwigsen

Khan

Andersen

et al. 2020

Geophysical Research Letters

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Vertical land motion (VLM) from past and ongoing glacial changes can amplify or mitigate ongoing relative sea level change. We present a high-resolution VLM model for the wider Arctic, that includes both present-day ice loading (PDIL) and glacial isostatic adjustment (GIA). The study shows that the nonlinear elastic uplift from PDIL is significant (0.5-1 mm yr −1) in most of the wider Arctic and exceeds GIA at 15 of 54 Arctic GNSS sites, including sites in nonglaciated areas of the North Sea region and the east coast of North America. Thereby the sea level change from PDIL (1.85 mm yr −1) is significantly mitigated from VLM caused by PDIL. The combined VLM model was consistent with measured VLM at 85% of the GNSS sites (R = 0.77) and outperformed a GIA-only model (R = 0.64). Deviations from GNSS-measured VLM can be attributed to local circumstances causing VLM.

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Uncertainties of Glacial Isostatic Adjustment Model Predictions in North America Associated With 3D Structure

Cited by 30 publications

References 49 publications

Long-wavelength gravity field constraint on the lower mantle viscosity in North America

Long-wavelength gravity field constraint on the lower mantle viscosity in North America

Present‐Day Crustal Vertical Velocity Field for the Contiguous United States

Vertical Land Motion From Present‐Day Deglaciation in the Wider Arctic

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