scholarly journals Coupled ice–till dynamics and the seeding of drumlins and bedrock forms

1999 ◽  
Vol 28 ◽  
pp. 221-230 ◽  
Author(s):  
Richard C. A. Hindmarsh
Keyword(s):  
Parameter Space ◽  
High Growth ◽  
Ice Thickness ◽  
Effective Pressure ◽  
Uniform Thickness ◽  
Physical Mechanisms ◽  
Applied Shear Stress ◽  
Ice Velocity ◽  
Internal Deformation ◽  
Kinematic Velocity

AbstractThe geomorphological effects of ice sliding over till, internal deformation of till and till sliding over bedrock are considered. Two questions are examined: (1) is the till-sheet flow unstable, i.e. is a layer of uniform thickness maintained or not, and (2) does the slip of till over bedrock cause amplification of relief of the bedrock? Such instabilities seem to be necessary to explain such features as drumlins and whaleback forms.It is found that the answer to (1) and (2) depends on the position of the system in a parameter space, defined by the till rheology, and applied shear stress, the effective pressure at the ice—till interface, the thickness of ice and till and the wavelength of the instability. Two configurations are considered: one where the wavelength of the perturbation is much less than the the ice-thickness, which is related to the classical Nye—Kamb solution for flow over bumps; and one where the wavelength is much greater than the ice thickness, where the mechanics are described by the shallow-ice approximation. In both cases, substantial areas of parameter space, where till-sheet and bedrock modes are unstable, are found. The conceptually related Smalley—Unwin bifurcation is re-examined.The physical mechanisms by which ice and till flows couple are examined. At very short wavelengths (~10 m), the ice is so rigid that it forces till waves to move at the ice velocity; while at long wavelengths (~1000 m), the flows become essentially uncoupled and till waves move at the kinematic velocity. At intermediate wavelengths (~100 m), high growth rates occur ; this is postulated to be the scale of drumlin seeding.

scholarly journals ‘Calving laws’, ‘sliding laws’ and the stability of tidewater glaciers

2007 ◽  
Vol 46 ◽  
pp. 123-130 ◽  
Author(s):  
Douglas I. Benn ◽  
Nicholas R.J. Hulton ◽  
Ruth H. Mottram
Keyword(s):  
Water Depth ◽  
Ice Thickness ◽  
Strain Rates ◽  
Effective Pressure ◽  
Ice Shelves ◽  
Tidewater Glaciers ◽  
Surface Gradient ◽  
Ice Velocity ◽  
Calving Rate ◽  
The Stability

AbstractA new calving criterion is introduced, which predicts calving where the depth of surface crevasses equals ice height above sea level. Crevasse depth is calculated from strain rates, and terminus position and calving rate are therefore functions of ice velocity, strain rate, ice thickness and water depth. We couple the calving criterion with three ‘sliding laws’, in which velocity is controlled by (1) basal drag, (2) lateral drag and (3) a combination of the two. In model 1, velocities and strain rates are dependent on effective pressure, and hence ice thickness relative to water depth. Imposed thinning can lead to acceleration and terminus retreat, and ice shelves cannot form. In model 2, ice velocity is independent of changes in ice thickness unless accompanied by changes in surface gradient. Velocities are strongly dependent on channel width, and calving margins tend to stabilize at flow-unit widenings. Model 3 exhibits the combined characteristics of the other two models, and suggests that calving glaciers are sensitive to imposed thickness changes if basal drag provides most resistance to flow, but stable if most resistance is from lateral drag. Ice shelves can form if reduction of basal drag occurs over a sufficiently long spatial scale. In combination, the new calving criterion and the basal–lateral drag sliding function (model 3) can be used to simulate much of the observed spectrum of behaviour of calving glaciers, and present new opportunities to model ice-sheet response to climate change.

scholarly journals Geometry and Dynamics of a Surge-type Glacier

1977 ◽  
Vol 18 (79) ◽  
pp. 181-194 ◽  
Author(s):  
R. Bindschadler ◽  
W. D. Harrison ◽  
C. F. Raymond ◽  
R. Crosson
Keyword(s):  
Steady State ◽  
Stress Distribution ◽  
Internal Stress ◽  
Ice Thickness ◽  
Surface Slope ◽  
Local Surface ◽  
Order Of Magnitude ◽  
Internal Deformation ◽  
Longitudinal Profiles ◽  
Similar Depth

AbstractMeasurement of geometry, motion, and mass balance from Variegated Glacier, Alaska portray conditions in this surge-type glacier close to the mid-point of its 20 year surge cycle. Comparison of longitudinal profiles of ice depth, surface slope, and surface speed indicate that the motion occurs largely by internal deformation assuming the ice deforms according to the experimental law of Glen. Surface speed is not noticeably affected by local surface slope on the scale of the ice thickness or smaller, but correlates well with slope determined on a longitudinal averaging scale about one order of magnitude larger than the ice depth. The rate of motion on Variegated Glacier agrees well with rates on non-surge type temperate glaciers which have similar depth and slope. Although the (low regime at the time of the measurements is apparently typical of temperate glaciers, a large discrepancy between the balance flux needed for steady state and the actual flux is indicative of a rapidly changing surface elevation profile and internal stress distribution.

scholarly journals Optimization of a Sea Ice Model Using Basinwide Observations of Arctic Sea Ice Thickness, Extent, and Velocity

2006 ◽  
Vol 19 (7) ◽  
pp. 1089-1108 ◽  
Author(s):  
Paul A. Miller ◽  
Seymour W. Laxon ◽  
Daniel L. Feltham ◽  
Douglas J. Cresswell
Keyword(s):  
Sea Ice ◽  
Parameter Space ◽  
National Laboratory ◽  
Arctic Sea Ice ◽  
Strength Parameter ◽  
Ice Thickness ◽  
Dimensional Parameter ◽  
Sea Ice Thickness ◽  
Basin Scale ◽  
Ice Model

Abstract A stand-alone sea ice model is tuned and validated using satellite-derived, basinwide observations of sea ice thickness, extent, and velocity from the years 1993 to 2001. This is the first time that basin-scale measurements of sea ice thickness have been used for this purpose. The model is based on the CICE sea ice model code developed at the Los Alamos National Laboratory, with some minor modifications, and forcing consists of 40-yr ECMWF Re-Analysis (ERA-40) and Polar Exchange at the Sea Surface (POLES) data. Three parameters are varied in the tuning process: Ca, the air–ice drag coefficient; P*, the ice strength parameter; and α, the broadband albedo of cold bare ice, with the aim being to determine the subset of this three-dimensional parameter space that gives the best simultaneous agreement with observations with this forcing set. It is found that observations of sea ice extent and velocity alone are not sufficient to unambiguously tune the model, and that sea ice thickness measurements are necessary to locate a unique subset of parameter space in which simultaneous agreement is achieved with all three observational datasets.

scholarly journals Quiescent-phase evolution of a surge-type glacier: Black Rapids Glacier, Alaska, U.S.A.

1996 ◽  
Vol 42 (140) ◽  
pp. 110-122 ◽  
Author(s):  
T.A. Heinrichs ◽  
L.R. Mayo ◽  
K.A. Echelmeyer ◽  
W.D. Harrison
Keyword(s):  
Phase Evolution ◽  
Ice Thickness ◽  
Alaska Range ◽  
Thickness Change ◽  
Quiescent Phase ◽  
Cyclical Fluctuations ◽  
Ice Velocity ◽  
The Mean ◽  
Black Rapids Glacier ◽  
Speed Fluctuations

AbstractBlack Rapids Glacier, a surge-type glacier in the Alaska Range, most recently surged in 1936–37 and is currently in its quiescent phase. Mass balance, ice velocity and thickness change have been measured at three to ten sites from 1972 to 1994. The annual speed has undergone cyclical fluctuations of as much as 45% about the mean speed. Ice thickness and surface slope did not change enough to cause the speed fluctuations through changes in ice deformation, which indicates that they are being drinven by changes in basal motion. The behavior of Black Rapids Glacier during this quiescent phase is significantly different from that of Variegated Glacier, another well-studied surge-type glacier in Alaska. The present medial-moraine configuration of Black Rapids Glacier indicates that a surge could occur at any time. However, ice velocity data indicate that the next surge may not be imminent. We belive that there is little chance that the next surge will cross and dam the Delta River.

Climatic characteristics of drift ice in the northern Barents Sea

2019 ◽  
Vol 11 (3) ◽  
pp. 800-811
Author(s):  
Chenglin Duan ◽  
Sheng Dong ◽  
Zhifeng Wang ◽  
Zhenkun Liao
Keyword(s):  
Barents Sea ◽  
Ice Thickness ◽  
Climate Forecast ◽  
Forecast System ◽  
Climate Forecast System ◽  
Climate Forecast System Reanalysis ◽  
Ice Velocity ◽  
Environmental Prediction ◽  
Climatic Characteristics

Abstract In this paper, a preliminary climatic description of the long-term offshore drift ice characteristics in the northern Barents Sea has been investigated from 1987 to 2016 based on the satellite ice motion datasets from National Snow and Ice Data Center (NSIDC) and reanalysis ice thickness datasets from National Centers for Environmental Prediction (NCEP)-Climate Forecast System Reanalysis (CFSR) and Climate Forecast System Version 2 (CFSv2). Both the ice velocity and thickness conditions have been studied at the three fixed locations from west to east. Annual and monthly drift ice roses indicate that the directions from WSW to SE are primarily prevailing, particularly in winter months. Besides, the annual ice speed extremums exceeding 40 cm s–1 mostly occur in the southerly directions from November to April. For the ice thickness, results reveal that it is prominently distributed in a thicker interval between 70 and 120 cm, and a thinner interval between 20 and 70 cm. The annual thickness maxima approximately range from 90 to 170 cm, primarily occurring from May to June, and demonstrate a light decreasing trend.

scholarly journals Geometry and ice dynamics of the Darwin–Hatherton glacial system, Transantarctic Mountains

2017 ◽  
Vol 63 (242) ◽  
pp. 959-972
Author(s):  
METTE K. GILLESPIE ◽  
WENDY LAWSON ◽  
WOLFGANG RACK ◽  
BRIAN ANDERSON ◽  
DONALD D. BLANKENSHIP ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ross Ice Shelf ◽  
Basal Ice ◽  
Grounding Line ◽  
Ice Flows ◽  
Ice Velocity ◽  
The Mean

ABSTRACTThe Darwin–Hatherton Glacial system (DHGS) connects the East Antarctic Ice Sheet (EAIS) with the Ross Ice Shelf and is a key area for understanding past variations in ice thickness of surrounding ice masses. Here we present the first detailed measurements of ice thickness and grounding zone characteristics of the DHGS as well as new measurements of ice velocity. The results illustrate the changes that occur in glacier geometry and ice flux as ice flows from the polar plateau and into the Ross Ice Shelf. The ice discharge and the mean basal ice shelf melt for the first 8.5 km downstream of the grounding line amount to 0.24 ± 0.05 km3 a−1 and 0.3 ± 0.1 m a−1, respectively. As the ice begins to float, ice thickness decreases rapidly and basal terraces develop. Constructed maps of glacier geometry suggest that ice drainage from the EAIS into the Darwin Glacier occurs primarily through a deep subglacial canyon. By contrast, ice thins to <200 m at the head of the much slower flowing Hatherton Glacier. The glaciological field study establishes an improved basis for the interpretation of glacial drift sheets at the link between the EAIS and the Ross Ice Sheet.

scholarly journals Uncertainties in mass balance estimation of the Antarctic Ice Sheet using the input and output method

2021 ◽  
Author(s):  
Yijing Lin ◽  
Yan Liu ◽  
Zhitong Yu ◽  
Xiao Cheng ◽  
Qiang Shen ◽  
...  
Keyword(s):  
Mass Balance ◽  
Scale Effect ◽  
Ice Sheet ◽  
Ice Thickness ◽  
Clear Understanding ◽  
Antarctic Ice Sheet ◽  
Grounding Line ◽  
Ice Velocity ◽  
The Antarctic ◽  
The Impact

Abstract. The input-output method (IOM) is one of the most popular methods of estimating the ice sheet mass balance (MB), with a significant advantage in presenting the dynamics response of ice to climate change. Assessing the uncertainties of the MB estimation using the IOM is crucial to gaining a clear understanding of the Antarctic ice-sheet mass budget. Here, we introduce a framework for assessing the uncertainties in the MB estimation due to the methodological differences in the IOM, the impact of the parameterization and scale effect on the modeled surface mass balance (SMB, input), and the impact of the uncertainties of ice thickness, ice velocity, and grounding line data on ice discharge (D, output). For the assessment of the D’s uncertainty, we present D at a fine scale. Compared with the goal of determining the Antarctic MB within an uncertainty of 15 Gt yr−1, we found that the different strategies employed in the methods cause considerable uncertainties in the annual MB estimation. The uncertainty of the RACMO2.3 SMB caused by its parameterization can reach 20.4 Gt yr−1, while that due to the scale effect is up to 216.7 Gt yr−1. The observation precisions of the MEaSUREs InSAR-based velocity (1–17 m yr−1), the airborne radio-echo sounder thickness (±100 m), and the MEaSUREs InSAR-based grounding line (±100 m) contribute uncertainties of 17.1 Gt yr−1, 10.5 ± 2.7 Gt yr−1 and 8.0~27.8 Gt yr−1 to the D, respectively. However, the D’s uncertainty due to the remarkable ice thickness data gap, which is represented by the thickness difference between the BEDMAP2 and the BedMachine reaches 101.7 Gt yr−1, which indicates its dominant cause of the future D’s uncertainty. In addition, the interannual variability of D caused by the annual changes in the ice velocity and ice thickness are considerable compared with the target uncertainty of 15 Gt yr−1, which cannot be ignored in annual MB estimations.

scholarly journals Ice-stream surface texture, sticky spots, waves and breathers: the coupled flow of ice, till and water

1998 ◽  
Vol 44 (148) ◽  
pp. 589-614 ◽  
Author(s):  
Richard C. A. Hindmarsh
Keyword(s):  
Water Flow ◽  
Parameter Space ◽  
Rate Constants ◽  
Water Pressure ◽  
Water System ◽  
Effective Pressure ◽  
Coupled Flow ◽  
Ice Surface ◽  
Ice Stream ◽  
Meso Scale

AbstractThis paper addresses the coupling of flows of ice, till and water, and the issue of whether such coupling provides mechanisms for meso-scale (kilometres to tens of kilometres) variability in ice-sheet flow and texture. The question of whether effective pressures at the ice-bed interface are statically or hydraulically controlled is examined in this paper. The answer is scale dependent, and has a significant effect on the relationship between ice surface and basal topography.The consequences of these considerations on till flow, coupled ice–till flow and coupled ice, till and water flow are examined. An analysis of till-flow kinematics and shock formation is carried out. The linear stability of coupled long-wavelength ice-till flow is analysed, and regions in parameter space where this flow is unstable, with rather small rate constants are found. Upstream-moving ice surface waves are predicted. The linear stablity of coupled ice–till–water flow is examined, where water flow is modelled using a basal flow system with effective-pressure-dependent properties. Again, regions in parameter space where the system is linearly unstable are found, this time with relatively rapid rate constants. The water pressure exhibits “breather” modes.These analyses assume that there is a substantial basal traction. A problem with models of ice streams wholly restrained at the side is identified: they seem to predict erosion rates which are unfeasibly large.There appears to be sufficient variability in the ice–till– water system to potentially explain texture in ice-stream surfaces, variations in ice-stream thickness of tens of metres not directly relatable to topography, and waves moving upstream or downstream. Most importantly, the ice-stream–bed system is shown to exhibit meso-scale variability simply by coupling ice flow according to the shallow-ice approximation, till flow according to the hydrostatic thin-till approximation and water flow according to an effective-pressure-dependent hydraulics.

scholarly journals A Numerical Investigation of The Large Scale Dynamics of Sea Ice

1979 ◽  
Vol 24 (90) ◽  
pp. 500-501
Author(s):  
W. D. Hibler
Keyword(s):  
Large Scale ◽  
Constitutive Law ◽  
The Arctic ◽  
Ice Thickness ◽  
Rigid Plastic ◽  
Continuity Equations ◽  
Near Shore ◽  
Ice Velocity ◽  
Arctic Ice ◽  
Thickness Variations

Abstract Several numerical simulations of the Arctic ice cover over a seasonal cycle are carried out. Two different types of constitutive laws are examined: rigid plastic and linear viscous. In both cases, the strength of the ice interaction is taken as a function of ice thickness and compactness. The thickness and compactness, in turn, evolve according to continuity equations which include thermodynamic source and sink terms. The simulations with the rigid-plastic law reproduce reasonable geographical ice-thickness variations, ice outflow, and ice-velocity characteristics. The viscous simulations (especially the Newtonian viscous case) produce less satisfactory geographical ice thickness variations, and near-shore velocity characteristics. In addition the Newtonian-viscous simulation produces highly unrealistic ice-edge effects in summer. The results are discussed in terms of the relative magnitudes of the shear and compressive strengths, and in terms of the non-linear versus linear dependence on deformation in the ice rheology. The portion of this study employing a plastic constitutive law is published in full in Journal of Physical Oceanography, Vol. 9, No. 4, 1979, p. 815–46.

scholarly journals On the assimilation of ice velocity and concentration data into large-scale sea ice models

Ocean Science ◽  
2007 ◽  
Vol 3 (2) ◽  
pp. 321-335 ◽  
Author(s):  
V. Dulière ◽  
T. Fichefet
Keyword(s):  
Data Assimilation ◽  
Sea Ice ◽  
Ocean Model ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Optimal Interpolation ◽  
Ice Thickness ◽  
Concentration Data ◽  
Ice Concentration ◽  
Ice Velocity

Abstract. Data assimilation into sea ice models designed for climate studies has started about 15 years ago. In most of the studies conducted so far, it is assumed that the improvement brought by the assimilation is straightforward. However, some studies suggest this might not be true. In order to elucidate this question and to find an appropriate way to further assimilate sea ice concentration and velocity observations into a global sea ice-ocean model, we analyze here results from a number of twin experiments (i.e. experiments in which the assimilated data are model outputs) carried out with a simplified model of the Arctic sea ice pack. Our objective is to determine to what degree the assimilation of ice velocity and/or concentration data improves the global performance of the model and, more specifically, reduces the error in the computed ice thickness. A simple optimal interpolation scheme is used, and outputs from a control run and from perturbed experiments without and with data assimilation are thoroughly compared. Our results indicate that, under certain conditions depending on the assimilation weights and the type of model error, the assimilation of ice velocity data enhances the model performance. The assimilation of ice concentration data can also help in improving the model behavior, but it has to be handled with care because of the strong connection between ice concentration and ice thickness. This study is first step towards real data assimilation into NEMO-LIM, a global sea ice-ocean model.

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