Modelling debris transport within glaciers by advection in a full-Stokes ice flow model

Abstract. Glaciers with extensive surface debris cover respond differently to climate forcing than those without supraglacial debris. In order to include debris-covered glaciers in projections of glaciogenic runoff and sea level rise and to understand the paleoclimate proxy recorded by such glaciers, it is necessary to understand the manner and timescales over which a supraglacial debris cover develops. Because debris is delivered to the glacier by processes that are heterogeneous in space and time, and these debris inclusions are altered during englacial transport through the glacier system, correctly determining where, when and how much debris is delivered to the glacier surface requires knowledge of englacial transport pathways and deformation. To achieve this, we present a model of englacial debris transport in which we couple an advection scheme to a full-Stokes ice flow model. The model performs well in numerical benchmark tests, and we present both 2-D and 3-D glacier test cases that, for a set of prescribed debris inputs, reproduce the englacial features, deformation thereof and patterns of surface emergence predicted by theory and observations of structural glaciology. In a future step, coupling this model to (i) a debris-aware surface mass balance scheme and (ii) a supraglacial debris transport scheme will enable the co-evolution of debris cover and glacier geometry to be modelled.

Download Full-text

Modelling debris transport within glaciers by advection in a full-Stokes ice flow model

10.5194/tc-2017-92 ◽

2017 ◽

Author(s):

Anna Wirbel ◽

Alexander Helmut Jarosch ◽

Lindsey Nicholson

Keyword(s):

Flow Model ◽

Glacier Surface ◽

Ice Flow ◽

Transport Pathways ◽

Surface Mass ◽

Glacier System ◽

Debris Cover ◽

Debris Transport ◽

Extensive Surface ◽

Paleoclimate Proxy

Abstract. Glaciers with extensive surface debris cover respond differently to climate forcing than those without supraglacial debris. In order to include debris-covered glaciers in projections of glaciogenic runoff and sea-level rise, and to understand the paleoclimate proxy recorded by such glaciers it is necessary to understand the manner and timescales over which a supraglacial debris cover develops. As debris is delivered to the glacier by processes that are heterogeneous in space and time, and these debris inclusions are altered during englacial transport through the glacier system, correctly determining where, when, and how much, debris is delivered to the glacier surface requires that the englacial transport pathways and deformation can be known. To achieve this, we present a model of englacial debris transport in which we couple an advection scheme to a full-Stokes ice flow model. The model performs well in numerical benchmark tests, and we present both 2D and 3D steady-state glacier test cases that, for a set of prescribed debris inputs, reproduce the englacial features, deformation thereof, and patterns of surface emergence predicted by theory and observations of structural glaciology. In a future step, coupling this model to a (i) debris-aware surface mass-balance scheme and (ii) supraglacial debris transport scheme will enable the co-evolution of debris-cover and glacier geometry to be modelled.

Download Full-text

Evaluating Simplified Numerical Models of Debris-Covered Glaciers

10.5194/egusphere-egu21-11578 ◽

2021 ◽

Author(s):

James C. Ferguson ◽

Tobias Bolch ◽

Andreas Vieli

Keyword(s):

Numerical Models ◽

Spatial Scales ◽

Global Scale ◽

Glacier Surface ◽

Ice Dynamics ◽

Surface Mass ◽

Wide Range ◽

Debris Cover ◽

Debris Transport ◽

Modelling Studies

The transient response of debris-covered glaciers to a changing climate is governed by nonlinear feedbacks between ice dynamics, debris transport, and glacier geometry and that act over a wide range of temporal and spatial scales. Current numerical models that are able to accurately represent the relevant physical processes are computationally expensive since they must track the debris transport not only at the glacier surface but also englacially. This makes such models difficult to use for simulations at the regional to global scale.In order to address this challenge, we developed a fully coupled numerical model that solves both englacial debris transport and ice flow and includes the effect of debris cover on surface ablation. We use this model to evaluate different simplified approaches to modelling debris-covered glaciers. These simplifications include parametrized 1-D debris transport models, parametrized models of surface mass balance that include debris cover effects, and zero-dimensional models. We compare the model performances using a number of tests with an idealized synthetic glacier geometry and a range of forcings, thereby allowing for an evaluation of the relative merits of each approach. A key goal of this work is to provide guidance and tools for modelling studies involving debris cover at the regional to global scale.

Download Full-text

Debris-induced stagnation and ensuing morphological evolution of a central Himalayan glacier

10.5194/egusphere-egu21-7143 ◽

2021 ◽

Author(s):

Purushottam Kumar Garg ◽

Aparna Shukla ◽

Santosh Kumar Rai ◽

Jairam Singh Yadav

Keyword(s):

Remote Sensing ◽

Morphological Evolution ◽

Remote Sensing Data ◽

Google Earth ◽

Lateral Moraine ◽

Central Himalaya ◽

Ablation Zone ◽

Glacier Surface ◽

Glacier System ◽

Debris Cover

This study presents field evidences (October 2018) and remote sensing measurements (2000-2020) to show stagnant conditions of lower ablation zone (LAZ) of the &#8216;companion glacier&#8217;, central Himalaya, India and its implication on the morphological evolution. The Companion glacier is named so as it accompanied the Chorabari glacier (widely studied benchmark glacier in the central Himalaya) in the distant past. Supraglacial debris thickness, supraglacial ponds anf other morphological features (e.g. lateral moraine height, supraglacial mounds) were measured/observed in the field. Glacier area, length, debris extent, surface elevation change and surface ice velocity were estimated using satellite remote sensing data from Landsat-TM/ETM+/OLI, Sentinel-MSI, Terra-ASTER and SRTM, Cartosat-1 and Google Earth images. Results show that the glacier has very small accumulation area and it is mainly fed by avalanches. The headwall of glacier is very steep which causes frequent avalanches leading to voluminous debris addition to the glacier system. Consequently, about 80% area of the glacier is debris-covered. The debris is very thick in the LAZ exceeding several meters in the LAZ and comprised of big boulders making debris thickness measurements practically impossible particularly in the snout region. However, debris thickness decreases with increasing distance from the snout and is in the order of 20-40 cm at about 2.5 km upglacier. The huge debris cover has protected the glacier ice from rapid melting. That&#8217;s why surface lowering of the glacier is less as compared to nearby Chorabari glacier. Moreover, due to (a) less mass supply from upper reaches and (b) huge debris cover, the glacier movement is very slow. The movement is too low that is allowed vegetation (some big grasses with wooded stems) to grow and survive on the glacier surface. The slow moving LAZ also causing bulging on the upper ablation zone (UAZ). Consequently, several mounds have developed on the UAZ. Thin debris slides down from mounds exposing the ice underneath for melting. Owing to these processes, spot melting is now a dominant mechanism of glacier wastage in the companion glacier. Thus, it can be summarized that careful field observations along with remote sensing estimates can be very important for understanding the glacier evolution.

Download Full-text

Volcanic synchronization of Dome Fuji and Dome C Antarctic deep ice cores over the past 216 kyr

Climate of the Past ◽

10.5194/cp-11-1395-2015 ◽

2015 ◽

Vol 11 (10) ◽

pp. 1395-1416 ◽

Cited By ~ 13

Author(s):

S. Fujita ◽

F. Parrenin ◽

M. Severi ◽

H. Motoyama ◽

E. W. Wolff

Keyword(s):

Age Differences ◽

Flow Model ◽

Ice Cores ◽

Ice Flow ◽

Surface Mass ◽

The Past ◽

The One ◽

Mis 5E ◽

Age Constraints ◽

Mis 5

Abstract. Two deep ice cores, Dome Fuji (DF) and EPICA Dome C (EDC), drilled at remote dome summits in Antarctica, were volcanically synchronized to improve our understanding of their chronologies. Within the past 216 kyr, 1401 volcanic tie points have been identified. DFO2006 is the chronology for the DF core that strictly follows O2 / N2 age constraints with interpolation using an ice flow model. AICC2012 is the chronology for five cores, including the EDC core, and is characterized by glaciological approaches combining ice flow modelling with various age markers. A precise comparison between the two chronologies was performed. The age differences between them are within 2 kyr, except at Marine Isotope Stage (MIS) 5. DFO2006 gives ages older than AICC2012, with peak values of 4.5 and 3.1 kyr at MIS 5d and MIS 5b, respectively. Accordingly, the ratios of duration (AICC2012 / DFO2006) range between 1.4 at MIS 5e and 0.7 at MIS 5a. When making a comparison with accurately dated speleothem records, the age of DFO2006 agrees well at MIS 5d, while the age of AICC2012 agrees well at MIS 5b, supporting their accuracy at these stages. In addition, we found that glaciological approaches tend to give chronologies with younger ages and with longer durations than age markers suggest at MIS 5d–6. Therefore, we hypothesize that the causes of the DFO2006–AICC2012 age differences at MIS 5 are (i) overestimation in surface mass balance at around MIS 5d–6 in the glaciological approach and (ii) an error in one of the O2 / N2 age constraints by ~ 3 kyr at MIS 5b. Overall, we improved our knowledge of the timing and duration of climatic stages at MIS 5. This new understanding will be incorporated into the production of the next common age scale. Additionally, we found that the deuterium signals of ice, δDice, at DF tends to lead the one at EDC, with the DF lead being more pronounced during cold periods. The lead of DF is by +710 years (maximum) at MIS 5d, −230 years (minimum) at MIS 7a and +60 to +126 years on average.

Download Full-text

A system of conservative regridding for ice/atmosphere coupling in a GCM

Geoscientific Model Development Discussions ◽

10.5194/gmdd-6-6493-2013 ◽

2013 ◽

Vol 6 (4) ◽

pp. 6493-6568 ◽

Cited By ~ 4

Author(s):

R. Fischer ◽

S. Nowicki ◽

M. Kelley ◽

G. A. Schmidt

Keyword(s):

Finite Element ◽

General Circulation ◽

Flow Model ◽

Source Code ◽

Circulation Model ◽

Surface Mass Balance ◽

Ice Flow ◽

Surface Mass ◽

Flow Models ◽

Ice Model

Abstract. The method of elevation classes has proven to be a useful way for a low-resolution general circulation model (GCM) to produce high-resolution downscaled surface mass balance fields, for use in one-way studies coupling GCMs and ice flow models. Past uses of elevation classes have been a cause of non-conservation of mass and energy, caused by inconsistency in regridding schemes chosen to regrid to the atmosphere vs. downscaling to the ice model. This causes problems for two-way coupling. A strategy that resolves this conservation issue has been designed and is presented here. The approach identifies three grids between which data must be regridded, and five transformations between those grids required by a typical coupled GCM–ice flow model. This paper shows how each of those transformations may be achieved in a consistent, conservative manner. These transformations are implemented in GLINT2, a library used to couple GCMs with ice models. Source code and documentation are available for download. Confounding real-world issues are discussed, including the use of projections for ice modeling, how to handle dynamically changing ice geometry, and modifications required for finite element ice models.

Download Full-text

Assessing Controls on Ice Dynamics at Crane Glacier, Antarctic Peninsula Using a Numerical Ice Flow Model

10.18122/td.1846.boisestate ◽

2021 ◽

Author(s):

Rainey Aberle

Keyword(s):

Antarctic Peninsula ◽

Flow Model ◽

Ice Shelf ◽

Ice Dynamics ◽

Ice Flow ◽

Surface Mass ◽

Climate Conditions ◽

Ice Shelves ◽

Tidewater Glacier ◽

Mass Discharge

The widespread retreat of glaciers and the collapse of ice shelves along the Antarctic Peninsula has been attributed to atmospheric and oceanic warming, which promotes mass loss. However, several glaciers on the eastern peninsula that were buttressed by the Larsen A and B ice shelves prior to collapse in 1995 and 2002, respectively, have been advancing in recent years. This asymmetric pattern of rapid retreat and long-term re-advance is similar to the tidewater glacier cycle, which can occur largely independent of climate forcing. Here, I use a width- and depth-integrated numerical ice flow model to investigate glacier response to ice shelf collapse and the influence of changing climate conditions at Crane Glacier, formerly a tributary of the Larsen B ice shelf, over the last ~10 years. Sensitivity tests to explore the influence of perturbations in surface mass balance and submarine melt (up to 10 m a-1) and fresh water impounded in crevasses (up to 10 m) on glacier dynamics reveal that by 2100, the modeled mass discharge ranges from 0.53-98 Gt a-1, with the most substantial changes due to surface melt-induced thinning. My findings suggest that the growth of a floating ice tongue can hinder enhanced flow, allowing the grounding zone to remain steady for many decades, analogous to the advancing stage of the tidewater glacier cycle. Additionally, former tributary glaciers can take several decades to geometrically adjust to ice shelf collapse at their terminal boundary while elevated glacier discharge persists.

Download Full-text

Early 21st-century glacier surface mass balance across High Mountain Asia derived from remote sensing

10.5194/egusphere-egu2020-9330 ◽

2020 ◽

Author(s):

Evan Miles ◽

Michael McCarthy ◽

Amaury Dehecq ◽

Marin Kneib ◽

Stefan Fugger ◽

...

Keyword(s):

Remote Sensing ◽

Mass Balance ◽

Surface Velocity ◽

High Mountain ◽

Surface Mass Balance ◽

Equilibrium Line Altitude ◽

Glacier Surface ◽

Surface Mass ◽

Early 21St Century ◽

Debris Cover

Glaciers in High Mountain Asia have experienced intense scientific scrutiny in the past decade due to their hydrological and societal importance. The explosion of freely-available satellite observations has greatly advanced our understanding of their thinning, motion, and overall mass losses, and it has become clear that they exhibit both local and regional variations due to debris cover, surging and climatic regime. However, our understanding of glacier accumulation and ablation rates is limited to a few individual sites, and altitudinal surface mass balance is essentially unknown across the vast region.Here we combine recent assessments of ice thickness and surface velocity to correct observed glacier thinning rates for mass redistribution in a flowband framework to derive the first estimates of altitudinal glacier surface mass balance across the region. We first evaluate our results at the glacier scale with all available glaciological field measurements (27 glaciers), then analyze 4665 glaciers (we exclude surging and other anomalous glaciers) comprising 43% of area and 36% of mass for glaciers larger than 2 km2 in the region. The surface mass balance results allow us to determine the equilibrium line altitude for each glacier for the period 2000-2016.&#160; We then aggregate our altitudinal and hypsometric surface mass balance results to produce idealised profiles for distinct subregions, enabling us to consider the subregional heterogeneity of mass balance and the importance of debris-covered ice for the region&#8217;s overall ablation.We find clear patterns of ELA variability across the region. &#160;9% of glaciers accumulate mass over less than 10% of their area on average for the study period. These doomed&#160; glaciers are concentrated in Nyainqentanglha, which also has the most negative mass balance of the subregions, whereas accumulation area ratios of 0.7-0.9 are common for glaciers in the neutral-balance Karakoram and Kunlun Shan. We find that surface debris extent is negatively correlated with ELA, explaining up to 1000 m of variability across the region and reflecting the importance of avalanching as a mass input for debris-covered glaciers at lower elevations. However, in contrast with studies of thinning rates alone, we find a clear melt reduction for low-elevation debris-covered glacier areas, consistent across regions, largely resolving the &#8216;debris cover anomaly&#8217;.&#160;&#160;Our results provide a comprehensive baseline for the health of the High Asian ice reservoirs in the early 21st Century. The estimates of altitudinal surface mass balance and ELAs will additionally enable novel strategies for the calibration of glacier and hydrological models. Finally, our results emphasize the potential of combined remote-sensing observations to understand the environmental factors and physical processes responsible for High Asia&#8217;s heterogeneous patterns of recent glacier evolution.

Download Full-text

Ice flow modelling to constrain the surface mass balance and ice discharge of San Rafael Glacier, Northern Patagonia Icefield

Journal of Glaciology ◽

10.1017/jog.2018.46 ◽

2018 ◽

Vol 64 (246) ◽

pp. 568-582 ◽

Cited By ~ 3

Author(s):

GABRIELA COLLAO-BARRIOS ◽

FABIEN GILLET-CHAULET ◽

VINCENT FAVIER ◽

GINO CASASSA ◽

ETIENNE BERTHIER ◽

...

Keyword(s):

Mass Balance ◽

Flow Model ◽

Surface Velocity ◽

Shear Stresses ◽

Surface Mass Balance ◽

Ice Dynamics ◽

Ice Flow ◽

Surface Mass ◽

Northern Patagonia ◽

San Rafael

ABSTRACTWe simulate the ice dynamics of the San Rafael Glacier (SRG) in the Northern Patagonia Icefield (46.7°S, 73.5°W), using glacier geometry obtained by airborne gravity measurements. The full-Stokes ice flow model (Elmer/Ice) is initialized using an inverse method to infer the basal friction coefficient from a satellite-derived surface velocity mosaic. The high surface velocities (7.6 km a−1) near the glacier front are explained by low basal shear stresses (<25 kPa). The modelling results suggest that 98% of the surface velocities are due to basal sliding in the fast-flowing glacier tongue (>1 km a−1). We force the model using different surface mass-balance scenarios taken or adapted from previous studies and geodetic elevation changes between 2000 and 2012. Our results suggest that previous estimates of average surface mass balance over the entire glacier (Ḃ) were likely too high, mainly due to an overestimation in the accumulation area. We propose that most of SRG imbalance is due to the large ice discharge (−0.83 ± 0.08 Gt a−1) and a slightly positiveḂ(0.08 ± 0.06 Gt a−1). The committed mass-loss estimate over the next century is −0.34 ± 0.03 Gt a−1. This study demonstrates that surface mass-balance estimates and glacier wastage projections can be improved using a physically based ice flow model.

Download Full-text

Transient glacier response with a higher-order numerical ice-flow model

Journal of Glaciology ◽

10.3189/172756502781831278 ◽

2002 ◽

Vol 48 (162) ◽

pp. 467-477 ◽

Cited By ~ 83

Author(s):

Frank Pattyn

Keyword(s):

Flow Model ◽

Higher Order ◽

Ice Flow ◽

Surface Mass ◽

Front Position ◽

Significant Difference ◽

Dynamic Experiments ◽

Stress Profiles ◽

Horizontal Grid ◽

Higher Order Models

AbstractIn this paper, a higher-order numerical flowline model is presented which is numerically stable and fast and can cope with very small horizontal grid sizes (<10 m). The model is compared with the results from Blatter and others (1998) on Haut Glacier d’Arolla, Switzerland, and with the European Ice-Sheet Modelling Initiative benchmarks (Huybrechts and others, 1996). Results demonstrate that the significant difference between calculated basal-drag and driving-stress profiles in a fixed geometry disappears when the glacier profile is allowed to react to the surface mass-balance conditions and reaches a steady state. Dynamic experiments show that the mass transfer in higher-order models occurs at a different speed in the accumulation and ablation areas and that the front position is more sensitive to migration compared to the shallow-ice approximation.

Download Full-text

Inverse solution of surface mass balance of Midtre Lovénbreen, Svalbard

Journal of Glaciology ◽

10.1017/jog.2017.26 ◽

2017 ◽

Vol 63 (240) ◽

pp. 593-602 ◽

Cited By ~ 2

Author(s):

ILONA VÄLISUO ◽

THOMAS ZWINGER ◽

JACK KOHLER

Keyword(s):

Mass Balance ◽

Field Measurements ◽

Surface Mass Balance ◽

Glacier Surface ◽

Ice Flow ◽

Surface Mass ◽

Time Period ◽

Digital Elevation ◽

Extended Time Period ◽

Compute Velocity

ABSTRACTWe investigate the temporal evolution and spatial distribution of mass balance on the glacier Midtre Lovénbreen, Svalbard. Running a diagnostic high-resolution full-stress ice flow model with geometries obtained from five digital elevation models (DEMs) in the period 1962–2005, we compute velocity fields and linearly interpolated volume change of the glacier. We evaluate the kinematic free surface equation using these model outputs to solve the surface mass balance (SMB). Monitoring data on Midtre Lovénbreen allows model results to be compared with point measurements from the glacier over several decades. This method allows us to estimate the mass balance over the entire glacier surface, beyond the spatially limited field measurements, and to derive past SMB over an extended time period.

Download Full-text