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

2021 ◽  
Author(s):  
C.P. Marsman ◽  
W. Wal ◽  
R.E.M. Riva ◽  
J.T. Freymueller
Keyword(s):  
Little Ice Age ◽  
Ice Age ◽  
Earth Structure ◽  
Glacial Isostatic Adjustment ◽  
Southeast Alaska ◽  
Isostatic Adjustment ◽  
The Impact

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>

scholarly journals Influence of 3D Earth structure on Glacial Isostatic Adjustment in the Russian Arctic

2020 ◽  
Author(s):  
Tanghua Li ◽  
Nicole Khan ◽  
Alisa Baranskaya ◽  
Timothy Shaw ◽  
W Richard Peltier ◽  
...  
Keyword(s):  
Earth Structure ◽  
Glacial Isostatic Adjustment ◽  
Russian Arctic ◽  
Isostatic Adjustment ◽  
3D Earth Structure

scholarly journals Joint inversion estimate of regional glacial isostatic adjustment in Antarctica considering a lateral varying Earth structure (ESA STSE Project REGINA)

2017 ◽  
Vol 211 (3) ◽  
pp. 1534-1553 ◽  
Author(s):  
Ingo Sasgen ◽  
Alba Martín-Español ◽  
Alexander Horvath ◽  
Volker Klemann ◽  
Elizabeth J Petrie ◽  
...  
Keyword(s):  
Joint Inversion ◽  
Earth Structure ◽  
Glacial Isostatic Adjustment ◽  
Isostatic Adjustment

scholarly journals Simulated retreat of Jakobshavn Isbræ since the Little Ice Age controlled by geometry

2018 ◽  
Vol 12 (7) ◽  
pp. 2249-2266 ◽  
Author(s):  
Nadine Steiger ◽  
Kerim H. Nisancioglu ◽  
Henning Åkesson ◽  
Basile de Fleurian ◽  
Faezeh M. Nick
Keyword(s):  
Little Ice Age ◽  
Ice Age ◽  
Climate Forcing ◽  
Relative Role ◽  
Regional Warming ◽  
History Of ◽  
The Impact ◽  
Term Response

Abstract. Rapid retreat of Greenland's marine-terminating glaciers coincides with regional warming trends, which have broadly been used to explain these rapid changes. However, outlet glaciers within similar climate regimes experience widely contrasting retreat patterns, suggesting that the local fjord geometry could be an important additional factor. To assess the relative role of climate and fjord geometry, we use the retreat history of Jakobshavn Isbræ, West Greenland, since the Little Ice Age (LIA) maximum in 1850 as a baseline for the parameterization of a depth- and width-integrated ice flow model. The impact of fjord geometry is isolated by using a linearly increasing climate forcing since the LIA and testing a range of simplified geometries. We find that the total length of retreat is determined by external factors – such as hydrofracturing, submarine melt and buttressing by sea ice – whereas the retreat pattern is governed by the fjord geometry. Narrow and shallow areas provide pinning points and cause delayed but rapid retreat without additional climate warming, after decades of grounding line stability. We suggest that these geometric pinning points may be used to locate potential sites for moraine formation and to predict the long-term response of the glacier. As a consequence, to assess the impact of climate on the retreat history of a glacier, each system has to be analyzed with knowledge of its historic retreat and the local fjord geometry.

Paleoclimatic reconstruction during the Little Ice Age in the Llanganuco basin, Cordillera Blanca (Peru)

2020 ◽  
Author(s):  
Joshua Er Addi Iparraguirre Ayala ◽  
Jose Úbeda Palenque ◽  
Ronald Fernando Concha Niño de Guzmán ◽  
Ramón Pellitero Ondicol ◽  
Francisco Javier De Marcos García-Blanco ◽  
...  
Keyword(s):  
3D Reconstruction ◽  
Air Temperature ◽  
Little Ice Age ◽  
Ice Age ◽  
Lapse Rate ◽  
Ratio Method ◽  
Equilibrium Line Altitude ◽  
Paleoclimatic Reconstruction ◽  
High Resolution Satellite Images ◽  
The Impact

<p>The Equilibrium Line Altitude (ELA, m) is a good indicator for the impact of climate change on tropical glaciers , because it varies in time and space depending on changes in temperature and/or precipitation.The estimation of the ELA and paleoELA using the Area x Altitude Balance Ratio method (AABR; Osmaston, 2005) requires knowing the surface and hypsometry of glaciers or paleoglaciers (Benn et al. 2005) and the Balance Ratio (BR) correct (Rea, 2009).</p><p>In the Llanganuco basin (~ 9°3´S; 77°37´W) there are very well preserved moraines near the current glaciers front. These deposits provide information to reconstruct the extent of paleoglaciers since the Little Ice Age (LIA) and deduce some paleo-climatic variables.</p><p>The goal of this work has been to reconstruct the paleotemperature (°C) during LIA, deduced from the difference between ELA AABR<sub>2016</sub> and paleoELA AABR<sub>LIA</sub>.</p><p>The paleoclimatic reconstruction was carried out in 6 phases: Phase 1) Development of a detailed geomorphological map (scale 1/10,000), in order to  identify glacial landforms (advance moraines and polished rocks) which, due to their geomorphological context, can be considered of LIA, so palaeoglaciers can be delimited. Current glacial extension was done using dry season, high resolution satellite images. Phase 2) Glacial bedrock Reconstruction from glacier surface following the GLABTOP methodology (Linsbauer et al 2009). Phase 3) 3D reconstruction of paleoglacial surface using GLARE tool, based on bed topography and flow lines for each defined paleoglacial (Pellitero et al., 2016). As perfect plasticity model does not reflect the tension generated by the side walls of the valley, form factors were calculated based on the glacier thickness, lateral moraines and the geometry of the valley following the equation proposed by Nye (1952), adjusting the thicknesses generated in the paleoglacial front. Phase 4) Calculation of BR in a reference glacier (Artesonraju; 8° 56’S; 77º38’W), near to the study area, using the product BR = b • z • s, where BR= Balance Ratio; b= mass balance measured in fieldwork 2004-2014 (m); z= average altitude (meters) and s= surface (m<sup>2</sup>) of each altitude band of the glacier (with intervals of 100 m altitude). A value BR = 2.3 was estimated. Phase 5) Automatic reconstruction of the ELA  AABR<sub>2016 </sub>and paleoELA AABR<sub>LIA</sub> using ELA Calculation tool (Pellitero et al. 2015) after 3D reconstruction of the glacial and paleoglacial surface in phases 2 and 3. Phase 6) Estimation of paleotemperature during LIA by solving the equation of Porter et al. (1995): ∆T (°C)= ∆ELA • ATLR, where ∆T= air temperature depression (ºC); ∆ELA = variation of ELA AABR 2016-LIA and ATLR = Air Temperature Lapse Rate, using the average global value of the Earth (0.0065 °C/m), considered valid for tropics.</p><p>The results obtained were: ELA AABR<sub>2016</sub>= 5260m, paleoELA AABR<sub>LIA</sub>= 5084m, and ∆T = 1.1 °C. The reconstruction of air paleotemperature is consistent with different studies that have estimated values between 1–2 °C colder than the present, with intense rainfall (Matthews & Briffa, 2005; Malone et al., 2015).</p>

Using magnetotelluric and seismic geophysical observations to infer viscosity for Glacial Isostatic Adjustment calculations

2020 ◽  
Author(s):  
Florence Ramirez ◽  
Kate Selway ◽  
Clinton Conrad
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Water Content ◽  
Seismic Attenuation ◽  
Conversion Process ◽  
Glacial Isostatic Adjustment ◽  
Partial Melt ◽  
Isostatic Adjustment ◽  
Mantle Viscosity ◽  
The Impact

<p>A physical property that is important for understanding the geodynamics of Earth’s lithosphere and asthenosphere is the effective viscosity <em>η<sub>eff</sub></em> (the ratio of stress and strain rate). This is particularly important for accurate Glacial Isostatic Adjustment (GIA) calculations, which are increasingly crucial for estimating ice loss and sea level rise from the Greenland and Antarctic ice sheets. Mantle viscosity cannot be measured directly, but can be inferred from strain rate, for example as observed by ground uplift following deglaciation or a seismic event. Empirically, mantle strain rate is mainly controlled by stress, temperature, grain size, and composition (water content and partial melt). The influence of these controlling parameters can be inferred from geophysical observations such as seismic and magnetotelluric (MT) measurements, which are useful for imaging the subsurface of the Earth but do not directly constrain viscosity. These observations can be used to improve constraints on viscosity using a three-step conversion process: (1) constrain temperature from MT, seismic, and other data; (2) constrain compositional structure from MT and seismic data (water content of nominally anhydrous minerals from MT, partial melt content from MT and seismics); and finally, (3) convert the calculated thermal and compositional structures into a constrained viscosity structure. In each conversion process, we can assess and quantify the involved uncertainties. Furthermore, we determine the dominant deformation regime in order to accurately interpret the sensitivity of viscosity to its controlling parameters. For instance, water content strongly affects viscosity for the dislocation-accommodated grain-boundary sliding (dis-GBS) and dislocation creep regimes, while diffusion creep and dis-GBS are highly sensitive to grain size. Stress and grain size are important parameters for determining where these critical transitions may occur. Although neither MT nor seismic velocity observations place strong constraints on grain size, information about seismic attenuation or tectonic history can potentially provide information about grain–size. Overall, we find that seismic and MT observations together can significantly improve estimates of mantle viscosity, and in particular can place useful constraints on the amplitude of regional variations in mantle viscosity. Such constraints will be particularly useful for studies to estimate the impact of such variations on GIA processes.</p>

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