scholarly journals On the gravity and geoid effects of glacial isostatic adjustment in Fennoscandia - a short note

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
L. E. Sjöberg
Keyword(s):  
Gravity Field ◽  
Short Note ◽  
Ice Age ◽  
Glacial Isostatic Adjustment ◽  
Land Uplift ◽  
Spectral Window ◽  
Isostatic Adjustment ◽  
Global Correlation ◽  
Band Limited ◽  
Gravity Signal

AbstractMany geoscientists argue that there is a gravity low of 10-30 mGal in Fennoscandia as a remaining fingerprint of the last ice age and load, both vanished about 10 kyr ago. However, the extraction of the gravity signal related with Glacial Isostatic Adjustment (GIA) is complicated by the fact that the total gravity field is caused by many significant density distributions in the Earth. Here we recall a methodology originating with A. Bjerhammar 35 years ago, that emphasizes that the present land uplift phenomenon mainly occurs in the region thatwas covered by the ice cap, and it is highly correlated with the spectral window of degrees 10-22 of the global gravity field, whose lower limit fairly well corresponds to the wavelength that agrees with the size of the region. This implies that, although in principle the GIA is a global phenomenon, the geoid and gravity lows as well as the land upheaval in Fennoscandia are typically regional phenomena that cannot be seen in a global correlation study as it is blurred by many irrelevant gravity signals. It is suggested that a regional multi-regression analysis with a band-limited spectral gravity signal as the observable, a method tested already 2 decades ago, can absorb possible significant disturbing signals, e.g. from topographic and crustal depth variations, and thereby recover the GIA signal.

scholarly journals Glacial isostatic adjustment in the static gravity field of Fennoscandia

2015 ◽  
Vol 120 (1) ◽  
pp. 503-518 ◽  
Author(s):  
B. C. Root ◽  
W. van der Wal ◽  
P. Novák ◽  
J. Ebbing ◽  
L. L. A. Vermeersen
Keyword(s):  
Gravity Field ◽  
Glacial Isostatic Adjustment ◽  
Isostatic Adjustment

scholarly journals The glacial isostatic adjustment signal at present day in northern Europe and the British Isles estimated from geodetic observations and geophysical models

Solid Earth ◽  
2018 ◽  
Vol 9 (3) ◽  
pp. 777-795 ◽  
Author(s):  
Karen M. Simon ◽  
Riccardo E. M. Riva ◽  
Marcel Kleinherenbrink ◽  
Thomas Frederikse
Keyword(s):  
Mass Loss ◽  
Barents Sea ◽  
Joint Inversion ◽  
Vertical Motion ◽  
Ice Age ◽  
Northern Europe ◽  
Glacial Isostatic Adjustment ◽  
British Isles ◽  
Isostatic Adjustment ◽  
Vertical Land Motion

Abstract. The glacial isostatic adjustment (GIA) signal at present day is constrained via the joint inversion of geodetic observations and GIA models for a region encompassing northern Europe, the British Isles, and the Barents Sea. The constraining data are Global Positioning System (GPS) vertical crustal velocities and GRACE (Gravity Recovery and Climate Experiment) gravity data. When the data are inverted with a set of GIA models, the best-fit model for the vertical motion signal has a χ2 value of approximately 1 and a maximum a posteriori uncertainty of 0.3–0.4 mm yr−1. An elastic correction is applied to the vertical land motion rates that accounts for present-day changes to terrestrial hydrology as well as recent mass changes of ice sheets and glaciered regions. Throughout the study area, mass losses from Greenland dominate the elastic vertical signal and combine to give an elastic correction of up to +0.5 mm yr−1 in central Scandinavia. Neglecting to use an elastic correction may thus introduce a small but persistent bias in model predictions of GIA vertical motion even in central Scandinavia where vertical motion is dominated by GIA due to past glaciations. The predicted gravity signal is generally less well-constrained than the vertical signal, in part due to uncertainties associated with the correction for contemporary ice mass loss in Svalbard and the Russian Arctic. The GRACE-derived gravity trend is corrected for present-day ice mass loss using estimates derived from the ICESat and CryoSat missions, although a difference in magnitude between GRACE-inferred and altimetry-inferred regional mass loss rates suggests the possibility of a non-negligible GIA response here either from millennial-scale or Little Ice Age GIA.

scholarly journals Assessment of Earth Gravity Field Models in the Medium to High Frequency Spectrum Based on GRACE and GOCE Dynamic Orbit Analysis

Geosciences ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 441
Author(s):  
Thomas D. Papanikolaou ◽  
Dimitrios Tsoulis
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Real Data ◽  
Present Contribution ◽  
Earth Gravity ◽  
Orbit Analysis ◽  
Band Limited ◽  
Gravity Signal ◽  
The Individual ◽  
Gravity Field Models

An analysis of current static and time-variable gravity field models is presented focusing on the medium to high frequencies of the geopotential as expressed by the spherical harmonic coefficients. A validation scheme of the gravity field models is implemented based on dynamic orbit determination that is applied in a degree-wise cumulative sense of the individual spherical harmonics. The approach is applied to real data of the Gravity Field and Steady-State Ocean Circulation (GOCE) and Gravity Recovery and Climate Experiment (GRACE) satellite missions, as well as to GRACE inter-satellite K-band ranging (KBR) data. Since the proposed scheme aims at capturing gravitational discrepancies, we consider a few deterministic empirical parameters in order to avoid absorbing part of the gravity signal that may be included in the monitored orbit residuals. The present contribution aims at a band-limited analysis for identifying characteristic degree ranges and thresholds of the various GRACE- and GOCE-based gravity field models. The degree range 100–180 is investigated based on the degree-wise cumulative approach. The identified degree thresholds have values of 130 and 160 based on the GRACE KBR data and the GOCE orbit analysis, respectively.

scholarly journals Post-Glacial Land Uplift Rate in Fennoscandia and Laurentia Determined by GRACE Data

2019 ◽  
Author(s):  
Mehdi S. Shafiei Joud ◽  
Lars Erik Sjöberg ◽  
Mohammad Bagherbandi
Keyword(s):  
Gravity Field ◽  
Signal To Noise Ratio ◽  
Principal Component ◽  
Complete Agreement ◽  
Uplift Rate ◽  
Mathematical Methods ◽  
Land Uplift ◽  
Forward Models ◽  
Isostatic Adjustment ◽  
Grace Data

The mantle mass flow interconnected with the process of Glacial Isostatic Adjustment (GIA) and the reformation of the Earth’s crust constantly perturbs the observed gravity field towards a hypothetic isostatic state. We analyse the temporal changes of the gravity field from the GRACE data, using different mathematical and/or statistical methods to detect the GIA amidst other gravity signals. A number of gravimetric post-glacial land uplift rate (LUR) modelling methods are investigated and compared with the data from a total number of 515 GPS stations and preferred GIA forward models in Fennoscandia and North America. We investigate three mathematical methods, namely regression, principal component, and independent component analysis (ICA) to extracting the GIA signal from the GRACE monthly geoid heights. We use some regularization techniques to exploit the GRACE monthly data to their maximum spatial resolution and to increase the Signal to Noise Ratio of their short wavelengths. Near the centres of the study areas the gravimetric LUR model using the fast-ICA algorithm of Hyvärinen and Oja (2000) is shown to be in a complete agreement with the GPS data and the predictions of the GIA forward models, and for the whole areas, subject to epeirogeny movement of the two regions, their discrepancies reach to the extrema at -1.8 and +3.3, and -4.5 and +7.5 mm/a, respectively. We show that the largest discrepancies between the gravimetric model using the ICA method and the GIA forward model, occur for the sub-regions likely collocated with strong ice mass change signals.

The impact of a 3-D Earth structure on glacial isostatic adjustment following the Little Ice Age in Southeast Alaska

2021 ◽  
Author(s):  
Celine Marsman ◽  
Wouter van der Wal ◽  
Riccardo Riva ◽  
Jeffrey Freymueller
Keyword(s):  
Upper Mantle ◽  
Little Ice Age ◽  
Seismic Velocity ◽  
Scaling Factor ◽  
Ice Age ◽  
Earth Structure ◽  
Glacial Isostatic Adjustment ◽  
Southeast Alaska ◽  
Isostatic Adjustment ◽  
Mantle Viscosity

<p>In Southeast Alaska, extreme uplift rates are primarily caused by glacial isostatic adjustment (GIA), as a result of ice load changes from the Little Ice Age to the present combined with a low viscosity asthenosphere. Current GIA models adopt a one-dimensional (1-D) stratified Earth structure. However, the actual (3-D) structure is more complex due to the presence of a subduction zone and the transition from a continental to an oceanic plate. A simplified 1-D Earth structure may not be an accurate representation in this region and therefore affect the GIA predictions. In this study we will investigate the effect of 3-D variations in the shallow upper mantle viscosity on GIA in Southeast Alaska. In addition, investigation of 3-D variations also gives new insight into the most suitable 1-D viscosity profile.</p><p>We test a number of models using the finite element software ABAQUS. We use shear wave tomography and mineral physics to constrain the shallow upper mantle viscosity structure. We investigate the contribution of thermal effects on seismic velocity anomalies in the upper mantle using an adjustable scaling factor, which determines what fraction of the seismic velocity variations are due to temperature changes, as opposed to non-thermal causes. We search for the combination of the scaling factor and background viscosity that best fits the GPS data. Results show that relatively small lateral variations improve the fit with a best fit background viscosity of 5.0×10<sup>19</sup> Pa s, resulting in viscosities at ~80 km depth that range from 1.8×10<sup>19</sup> to 4.5×10<sup>19</sup> Pa s.</p>

Leveraging non-traditional evidence for glacial isostatic adjustment to constrain past ice sheets

2021 ◽  
Author(s):  
Tamara Pico
Keyword(s):  
Sea Level ◽  
Current Knowledge ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Age ◽  
Small Scale ◽  
Glacial Isostatic Adjustment ◽  
Continental Scale ◽  
Isostatic Adjustment ◽  
Ice Stream

<p>Although understanding the response of ice sheets to a changing climate is a pressing issue of this century, our current knowledge of past ice-sheet changes remains limited by data sparsity. I explore approaches that leverage non-traditional datasets to constrain past ice sheet and sea-level change over the last glacial cycle. For example, I consider the potential to use past landscapes to infer crustal deformation induced by ice sheet loading. Over the ice-age, glacial isostatic adjustment produces rates of uplift comparable to some of the fastest tectonic uplift rates (~10 mm/yr) in regions hundreds of kilometers away from the maximum ice sheet extent. Additionally, I show it is possible to gain insight into longer-term continental scale ice sheet deglacial histories using small-scale ice stream dynamics. Using records for a rapid retreat of the Amundsen Gulf Ice Stream, located on the northwest Laurentide Ice Sheet, along with observations of the Bering Strait flooding as sea-level indicators, I fingerprint the timing and location of North American saddle deglaciation.</p>

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