Ice Sheet Geometry Research Articles

Formation and disintegration of the Antarctic ice sheet

A model of the Antarctic ice sheet has been used to simulate the ice sheet in warmer climates, in order to investigate what kind of ice-sheet geometries one can reasonably expect under what kind of climatic conditions and to discover which physical mechanisms may be involved to explain them. The results of these experiments reveal the considerable stability of; in particular, the East Antarctic ice sheet. It would require a temperature rise of between 17 and 20 K above present levels to remove this ice sheet from the subglacial basins in the interior of the continent and of 25 K to melt down the Antarctic ice sheet completely. For a temperature rise below 5 K, the model actually predicts a larger Antarctic ice sheet than today as a result of increased snowfall, whereas the west Antarctic ice sheet was round not to survive temperatures more than 8–10 K above present values. Furthermore, basal temperature conditions in these experiments point to the problems involved in raising the base of the ice sheet to the pressure-melting point over the large areas necessary to consider the possibility of sliding instability. These results bear on a lively debate regarding the late Cenozoic glacial history of Antarctica. Particularly, based on these findings, it is difficult to reconcile a highly variable East Antarctic ice sheet until the Pliocene with modest warming recorded in, for instance, the deep-sea records for the late Neogene.

Glaciological Modelling of the Late Cenozoic East Antarctic Ice Sheet: Stability or Dynamism?

On the basis of geological arguments, two widely different hypotheses have been proposed for the late-Tertiary glacial history of East Antarctica. Theseinvoke ice-sheet reconstructions ranging from severe glaciation completely burying the Transantarctic Mountains to a situation, in which an unstable EastAntarctic Ice Sheet repeatedly collapses to produce ice-free conditions over interior basins. Experiments were performed with a 3-D model of the Antarctic IceSheet to determine the ice sheet geometries to be expected under various kinds of climatic conditions and the physical mechanisms that may be involved. Theresults supported the concept of a stable East Antarctic Ice Sheet with respect to a climatic warming, and pointed to the glaciological difficulties involved toexplain an ice-free corridor over the Pensacola and Wilkes subglacial basins. The latter event is a crucial element in the 'waxing and waning ice sheethypothesis' and would require a temperature rise of between 17 and 20K above present levels. For a temperature rise of less than 5K, the model actuallypredicts a larger Antarctic Ice Sheet than today as a result of increased snowfall, whereas the West Antarctic Ice Sheet was found not to survive temperatures8-10K above present values. Furthermore, basal temperature conditions in these experiments point to the difficulties involved in raising the ice-sheet base tothe pressure melting point over the large areas necessary to consider the possibility of sliding instability. A further sensitivity study in terms of topographicaland climatic boundary conditions showed that even with a flat bedrock and mass-balance parameters stretched to their limits, the ice sheet would still need atemperature rise of the order of +15K to melt down entirely. Based on these findings, it appears difficult to reconcile a highly variable East Antarctic Ice Sheetwith the modest warmings recorded in, for instance, the deep sea records for the late Neogene.

Late Wisconsin iceberg-calving rates and ice-sheet mass balance reconstructed from paleo-sea levels, Mount Desert Island, Maine

Research Article| February 01, 1991 Late Wisconsin iceberg-calving rates and ice-sheet mass balance reconstructed from paleo-sea levels, Mount Desert Island, Maine Thomas V. Lowell Thomas V. Lowell 1Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221-0013 Search for other works by this author on: GSW Google Scholar Author and Article Information Thomas V. Lowell 1Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221-0013 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1991) 19 (2): 155–158. https://doi.org/10.1130/0091-7613(1991)019<0155:LWICRA>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Thomas V. Lowell; Late Wisconsin iceberg-calving rates and ice-sheet mass balance reconstructed from paleo-sea levels, Mount Desert Island, Maine. Geology 1991;; 19 (2): 155–158. doi: https://doi.org/10.1130/0091-7613(1991)019<0155:LWICRA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Ice sheets terminating in water may provide geologic evidence to reconstruct iceberg-calving rates and hence provide insight to ice-sheet mass balance at certain locations. Recent work reported an empirical relation for 12 modern tidewater glaciers in Alaska in which iceberg-calving rate is directly related to the average water depth. The former Laurentide ice sheet split into tidewater glaciers in the troughs of Mount Desert Island, Maine, and deposited moraine banks as sea level transgressed onto the island. Paleoshorelines were at least 65 m and probably as high as 90 m above present-day sea level. With 75 m shoreline elevation, the average water-depth values correspond to iceberg calving rates of 650 to 2100 m/yr. The total ice-volume flux minus the iceberg-calving flux is equal to the rate of change in terminus position times the terminus area. Because the terminus is stationary when moraines are deposited, the calving flux is equal to the discharge flux at that time. Calculated discharge fluxes for Mount Desert Island range from 0.65 to 2.9 x 105 m3/yr; the average is 1.7 x 105 m3/yr across a unit width of the terminus. Consideration of the ice-sheet geometry and estimated precipitation and temperature conditions indicates that most of this flux must come from ice-sheet thinning rather than mass accumulation. The geometry of this analysis dictates that all of these estimates are minimum values. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Laurentide ice sheet through the last glacial cycle: the topology of drift lineations as a key to the dynamic behaviour of former ice sheets

ABSTRACTStudy of satellite images from most of the area of the Canadian mainland once covered by the Laurentide ice sheet reveals a complex pattern of superimposed drift lineations. They are believed to have formed subglacially and parallel to ice flow. Aerial photographs reveal patterns of superimposition which permit the sequence of lineation patterns to be identified. The sequential lineation patterns are interpreted as evidence of shifting patterns of flow in an evolving ice sheet. Flow stages are recognised which reflect roughly synchronous integrated patterns of ice sheet flow. Comparison with stratigraphic sections in the Hudson Bay Lowlands suggests that all the principal stages may have formed during the last, Wisconsinan, glacial cycle. Analogy between Flow stage lineation patterns and the form and flow patterns of modern ice sheets permits reconstruction of patterns of ice divides and centres of mass which moved by 1000–2000 km during the glacial period. There is evidence that during the early Wisconsinan, ice sheet formation in Keewatin may have been independent of that in Labrador–Quebec, and that these two ice masses joined to form a major early Wisconsinan ice sheet. Subsequently the western dome decayed whilst the eastern dome remained relatively stable. A western dome then re-formed, and fused with the eastern dome to form the late Wisconsinan ice sheet before final decay.Because of strong coupling between three-dimensional ice sheet geometry and atmospheric circulation, it is suggested that the major changes of geometry must have been associated with large scale atmospheric circulation changes.Lineation patterns suggest very little erosional/depositional activity in ice divide regions, and can be used to reconstruct large scale patterns of erosion/deposition.The sequence of flow stages through time provides an integrative framework allowing sparse stratigraphic data to be used most efficiently in reconstructing ice sheet history in time and space.

A Numerical Study of Plane Ice-Sheet Flow

AbstractThe plane steady flow of a grounded ice sheet is numerically analysed using the approximate model of Morland or Hutter. In this, the ice behaves as a non-linear viscous fluid with a strongly temperature-dependent rate factor, and ice sheets are assumed to be long and shallow. The climate is assumed to be prescribed via the accumulation/ablation distribution and the surface temperature, both of which are functions of position and unknown height. The rigid base exerts external forcings via the normal heat flow, the geothermal heat, and a given basal sliding condition connecting the tangential velocity, tangential traction, and normal traction. The functional relations are those of Morland (1984) or motivated by his work. We use equations in his notation.The governing equations and boundary conditions in dimensionless form are briefly stated and dimensionless variables are related to their physical counterparts. The thermo-mechanical parabolic boundary-value problem, found to depend on physical scales, constitutive properties, and external forcing functions, has been numerically solved. For reasons of stability, the numerical integration must proceed from the ice divide towards the margin, which requires a special analysis of the ice divide. We present this analysis and then describe the versatility and limitations of the constructed computer code.Results of extensive computations are shown. In particular, we prove that the Morland–Hutter model for ice sheets is only applicable when sliding is sufficiently large (satisfying inequality (30)). In the range of the validity of this inequality, it is then demonstrated that of all physical scaling parameters only a single π-product influences the geometry and the flow within the ice sheet. We analyse the role played by advection, diffusion, and dissipation in the temperature distribution, and discuss the significance of the rheological non-linearities. Variations of the external forcings, such as accumulation/ablation conditions, free surface temperature, and geothermal heat, demonstrate the sensitivity of the ice-sheet geometry to accumulation conditions and the robustness of the flow to variations in the thermal state. We end with a summary of results and a critical review of the model.

A Numerical Study of Plane Ice-Sheet Flow

AbstractThe plane steady flow of a grounded ice sheet is numerically analysed using the approximate model of Morland or Hutter. In this, the ice behaves as a non-linear viscous fluid with a strongly temperature-dependent rate factor, and ice sheets are assumed to be long and shallow. The climate is assumed to be prescribed via the accumulation/ablation distribution and the surface temperature, both of which are functions of position and unknown height. The rigid base exerts external forcings via the normal heat flow, the geothermal heat, and a given basal sliding condition connecting the tangential velocity, tangential traction, and normal traction. The functional relations are those of Morland (1984) or motivated by his work. We use equations in his notation.The governing equations and boundary conditions in dimensionless form are briefly stated and dimensionless variables are related to their physical counterparts. The thermo-mechanical parabolic boundary-value problem, found to depend on physical scales, constitutive properties, and external forcing functions, has been numerically solved. For reasons of stability, the numerical integration must proceed from the ice divide towards the margin, which requires a special analysis of the ice divide. We present this analysis and then describe the versatility and limitations of the constructed computer code.Results of extensive computations are shown. In particular, we prove that the Morland–Hutter model for ice sheets is only applicable when sliding is sufficiently large (satisfying inequality (30)). In the range of the validity of this inequality, it is then demonstrated that of all physical scaling parameters only a single π-product influences the geometry and the flow within the ice sheet. We analyse the role played by advection, diffusion, and dissipation in the temperature distribution, and discuss the significance of the rheological non-linearities. Variations of the external forcings, such as accumulation/ablation conditions, free surface temperature, and geothermal heat, demonstrate the sensitivity of the ice-sheet geometry to accumulation conditions and the robustness of the flow to variations in the thermal state. We end with a summary of results and a critical review of the model.

Deformation in the Vicinity of Ice Divides

AbstractNumerical calculations by finite elements show that the variation of horizontal velocity with depth in the vicinity of a symmetric, isothermal, non-slipping ice ridge deforming on a flat bed is approximately consistent with prediction from laminar flow theory except in a zone within about four ice thicknesses of the divide. Within this near-divide zone horizontal shear strain-rate is less concentrated near the bottom and downward velocity is less rapid in comparison to the flanks. The profiles over depth of horizontal and vertical velocity approach being linear and parabolic respectively. Calculations for various surface elevation profiles show these velocity profile shapes are insensitive to the ice-sheet geometry.

Deformation in the Vicinity of Ice Divides

AbstractNumerical calculations by finite elements show that the variation of horizontal velocity with depth in the vicinity of a symmetric, isothermal, non-slipping ice ridge deforming on a flat bed is approximately consistent with prediction from laminar flow theory except in a zone within about four ice thicknesses of the divide. Within this near-divide zone horizontal shear strain-rate is less concentrated near the bottom and downward velocity is less rapid in comparison to the flanks. The profiles over depth of horizontal and vertical velocity approach being linear and parabolic respectively. Calculations for various surface elevation profiles show these velocity profile shapes are insensitive to the ice-sheet geometry.

A time‐dependent ice sheet model: Preliminary results

A numerical model of ice sheet flow is developed, and preliminary results are described. This model includes vertical resolution of temperature, stress, and strain rate which represents a considerable improvement over previous vertically averaged ice sheet models. The model follows the flow of ice along a flow line within an ice sheet drainage basin. Longitudinal stresses and basal sliding are included. Basal sliding is dependent on the base shear stress and a specified distribution of basal water pressure. The numerical methods used to solve the coupled set of stress and velocity equations for the static and time‐evolutionary cases are discussed. A steady state profile simulating an ice stream is calculated for a particular set of input parameters, and changes in the profile are examined for different choices of parameters. Preliminary studies of response behavior are completed using a simplified ice sheet geometry with a fixed terminus or grounding line. The results of these studies illustrate ice sheet thinning in response to a lowered sea level or to a reduction in the extent of ice rises (or pinning points) within ice shelves.