A comparison of different ways of dealing with isostasy: examples from modelling the Antarctic ice sheet during the last glacial cycle

The bedrock isostatic response exerts a strong control on ice-sheet dynamics and is therefore always taken into account in ice-sheet models. This paper reviews the various methods normally used in the ice-sheet modelling community to deal with the bedrock response and compares these with a more sophisticated full-Earth model. Each of these bedrock treatments, five in total, is coupled with a three-dimensional thermomechanical ice-sheet model under the same forcing conditions to simulate the Antarctic ice sheet during the last glacial cycle. The outputs of the simulations are compared on the basis of the time-dependent behaviour for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over Antarctica. This comparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns. It furthermore demonstrates the deficiencies inherent to the diffusion equation in modelling the complex deformation within the mantle. Nevertheless, when characteristic parameters are varied within their range of uncertainty, differences within one single method are often of the same order as those between the various methods. This overview finally attempts to point out the main advantages and drawbacks of each of these methods and to determine which one is most appropriate depending on the specific modelling requirements.

Download Full-text

Modeling the Antarctic ice sheet

Annals of Glaciology ◽

10.1017/s0260305500014130 ◽

1997 ◽

Vol 25 ◽

pp. 259-268 ◽

Cited By ~ 4

Author(s):

Mikhail Verbitsky ◽

Barry Saltzman

Keyword(s):

Three Dimensional ◽

Ice Sheet ◽

Glacial Cycle ◽

Antarctic Ice Sheet ◽

Thermodynamic Equation ◽

Last Glacial ◽

Ice Stream ◽

Basal Melting ◽

The Antarctic ◽

The Last Glacial

A three-dimensional (3-D), high-resolution, non-linearly viscous, non-isothermal ice-sheet model is employed to calculate the “present-day” equilibrium regime of the Antarctic ice sheet and its evolution during the last glacial cycle. The model is augmented by an approximate formula for ice-sheet basal temperature, based on a scaling of the thermodynamic equation for the ice flow. Steady-state solutions for both the shape and extent of the areas of basal melting (or freezing) are shown to be in good agreement with those obtained from the solution of the full 3-D thermodynamic equation. The solution for the basal temperature field of the West Antaretie Siple Coast produces areas at the pressure-melting point separated by strips of frozen-to-bed ice, the structure of which is reminiscent of Ice Streams A–E. This configuration appears to be robust, preserving its features in spite of climatic changes during the last glacial cycle. Ice Stream C seems to be more vulnerable to stagnation, switching to a passive mode at least once during the penultimate interglacial. We conjecture that the peculiarities of local topography determine the unique behavior of Ice Stream C: reduced basal stress and, consequently, relatively weak warming due to internal friction and basal sliding is not able to counteract the advective cooling during the periods of increased snowfall rate.

Download Full-text

Modeling the Antarctic ice sheet

Annals of Glaciology ◽

10.3189/s0260305500014130 ◽

1997 ◽

Vol 25 ◽

pp. 259-268 ◽

Cited By ~ 4

Author(s):

Mikhail Verbitsky ◽

Barry Saltzman

Keyword(s):

Three Dimensional ◽

Ice Sheet ◽

Glacial Cycle ◽

Antarctic Ice Sheet ◽

Thermodynamic Equation ◽

Last Glacial ◽

West Antarctic ◽

Ice Stream ◽

The Antarctic ◽

The Last Glacial

A three-dimensional (3-D), high-resolution, non-linearly viscous, non-isothermal ice-sheet model is employed to calculate the “present-day” equilibrium regime of the Antarctic ice sheet and its evolution during the last glacial cycle. The model is augmented by an approximate formula for ice-sheet basal temperature, based on a scaling of the thermodynamic equation for the ice flow. Steady-state solutions for both the shape and extent of the areas of basal melting (or freezing) are shown to be in good agreement with those obtained from the solution of the full 3-D thermodynamic equation. The solution for the basal temperature field of the West Antarctic Siple Coast produces areas at the pressure-melting point separated by strips of frozen-to-bed ice, the structure of which is reminiscent of Ice Streams A–E. This configuration appears to be robust, preserving its features in spite of climatic changes during the last glacial cycle. Ice Stream C seems to be more vulnerable to stagnation, switching to a passive mode at least once during the penultimate interglacial. We conjecture that the peculiarities of local topography determine the unique behavior of Ice Stream C: reduced basal stress and, consequently, relatively weak warming due to internal friction and basal sliding is not able to counteract the advective cooling during the periods of increased snowfall rate.

Download Full-text

A NEW METHOD TO SIMULATE THE ANTARCTIC ICE SHEET OVER THE LAST GLACIAL CYCLE USING A COUPLED 3D GIA – ICE DYNAMIC MODEL

10.1130/abs/2020am-359854 ◽

2020 ◽

Author(s):

C.J. van Calcar ◽

◽

B. de Boer ◽

B. Blank ◽

W. van der Wal

Keyword(s):

Dynamic Model ◽

Ice Sheet ◽

New Method ◽

Glacial Cycle ◽

Antarctic Ice Sheet ◽

Last Glacial ◽

The Antarctic ◽

The Last Glacial

Download Full-text

The effect of the GIA feedback loop on the evolution of the Antarctic Ice sheet over the last glacial cycle using a coupled 3D GIA – Ice Dynamic model

10.5194/egusphere-egu21-15773 ◽

2021 ◽

Author(s):

Caroline van Calcar ◽

Bas de Boer ◽

Bas Blank ◽

Roderik van de Wal ◽

Wouter van der Wal

Keyword(s):

Feedback Loop ◽

Ice Sheet ◽

Line Position ◽

Glacial Cycle ◽

Antarctic Ice Sheet ◽

Last Glacial ◽

Grounding Line ◽

The Antarctic ◽

Lateral Variations ◽

The Last Glacial

<p>The Earth&#8217;s surface and interior deform due to a changing load of the Antarctic Ice Sheet (AIS) during the last glacial cycle, called Glacial Isostatic Adjustment (GIA). This deformation changes the surface height of the ice sheet and indirectly the groundling line position. These changes in surface height and grounding line position influence the evolution of the AIS and consequently, again the load on the Earth&#8217;s surface. As a result, GIA operates as a negative feedback loop and could stabilize the evolution of the AIS. This feedback maybe particularly relevant for relatively low viscosities of the mantle in West Antarctica which lead to a relatively fast response time of the bedrock due to changes in the West Antarctic Ice Sheet loading. Most studies capture this process by ignoring lateral variations in the viscosity of the mantle and the stabilizing GIA feedback loop. Here we present a new method to couple an ice sheet model to a GIA model at a variable timestep in the order of a thousand years. Several experiments have been done using different radial and lateral varying rheologies for simulations of the last glacial cycle. It is shown that the effect of including lateral variations and accounting for the stabilizing GIA feedback is up to 80 kilometers for the grounding line position and 400 meters for the ice thickness. The largest differences are observed close to the grounding line of the Ronne ice shelf and at several locations in East Antarctica. The total ice volume of the AIS increases by 0.5 percent over 5000 years when including the 3D GIA feedback loops in the coupled model. These results quantify the local importance of including GIA feedback effects in ice dynamic models when simulating the Antarctic Ice Sheet evolution over the full glacial cycle. &#160;</p>

Download Full-text

Introduction

Antarctic Science ◽

10.1017/s0954102098000315 ◽

1998 ◽

Vol 10 (3) ◽

pp. 225-226

Author(s):

Ian D. Goodwin ◽

Carol J. Pudsey

Keyword(s):

Regional Differences ◽

Late Quaternary ◽

Ice Sheet ◽

List Type ◽

Glacial Cycle ◽

The Holocene ◽

Last Glacial ◽

Glacial Stage ◽

The Antarctic ◽

The Last Glacial

This issue contains a group of papers selected from those presented at the 1st workshop of the SCAR-GLOCHANT and IGBP-PAGES cosponsored programme on the Late Quaternary Sedimentary Record of the Antarctic Ice Margin Evolution (ANTIME), held in Hobart, 6-1 1 July 1997. ANTIME is focused on the circurn Antarctic reconstruction of palaeoclimate, palaeoenvironment, and ice sheet palaeogeography throughout the last glacial cycle. There were 65 participants from Australia, USA, UK, Italy, Spain, Japan, Sweden, Germany and Russia at the workshop. The participants included representatives of PAGES, IMAGES, and INQUA. The workshop included three scientific sessions on: Extent, timing and regional differences during Glacial Stage 2 (10–30 kyr BP) in Antarctica, from the terrestrial and marine records;Climatic, environmental and glacial events during the Holocene;Late Quaternary geochronological problems in Antarctica.

Download Full-text

Excess ice loads in the Indian Ocean sector of East Antarctica during the last glacial period

Geology ◽

10.1130/g48830.1 ◽

2021 ◽

Author(s):

Takeshige Ishiwa ◽

Jun’ichi Okuno ◽

Yusuke Suganuma

Keyword(s):

Sea Level ◽

Last Glacial Maximum ◽

Ice Sheet ◽

Glacial Maximum ◽

Antarctic Ice Sheet ◽

Last Glacial ◽

Indian Ocean Sector ◽

Ocean Sector ◽

The Antarctic ◽

The Last Glacial

An accurate reconstruction of the Antarctic Ice Sheet is essential in order to develop an understanding of ice-sheet responses to global climate changes. However, the erosive nature of ice-sheet expansion and the difficulty of accessing much of Antarctica make it challenging to obtain field-based evidence of ice-sheet and sea-level changes before the Last Glacial Maximum. Limited sedimentary records from Lützow-Holm and Prydz Bays in East Antarctica demonstrate that the sea level during Marine Isotope Stage 3 was close to the present level despite the global sea-level drop lower than –40 m. We demonstrate glacial isostatic adjustment modeling with refined Antarctic Ice Sheet loading histories. Our experiments reveal that the Indian Ocean sector of the Antarctic Ice Sheet would have been required to experience excess ice loads before the Last Glacial Maximum in order to explain the observed sea-level highstands during Marine Isotope Stage 3. As such, we suggest that the Antarctic Ice Sheet partly reached its maximum thickness before the global Last Glacial Maximum.

Download Full-text

Streaming flow in an ice sheet through a glacial cycle

Annals of Glaciology ◽

10.3189/172756403781816293 ◽

2003 ◽

Vol 36 ◽

pp. 117-128 ◽

Cited By ~ 19

Author(s):

Geoffrey S. Boulton ◽

Magnus Hagdorn ◽

Nicholas R.J. Hulton

Keyword(s):

Three Dimensional ◽

Ice Sheet ◽

Glacial Cycle ◽

Ice Streams ◽

Geological Evidence ◽

Last Glacial ◽

Bed Topography ◽

Basal Melting ◽

Realistic Topography ◽

The Last Glacial

AbstractGeological evidence indicates that the flow of the last European ice sheet was dominated by numerous large ice streams. Although some were ephemeral, most were sustained along well-defined axes at least during the period of retreat after the Last Glacial Maximum. A thermomechanically coupled three-dimensional numerical ice-sheet model has been used to simulate the ice sheet through the whole of the last glacial cycle, but with a spatial resolution that is high enough to capture streaming behaviour. An experiment with a smoothed bed is used to explore the self-organizing behaviour of streams when they are not forced by bed topography. On such a bed, streams typically have a width of 1–10 km, much narrower than the inferred European ice streams. An experiment using a realistic topography suggests that widths of ice streams are strongly influenced by topography, and tend to be of order 100 km. Moreover, even where the topography is muted, it stabilizes the locations of ice streams which, once formed, tend to be sustained along pre-existing axes. The model creates patterns of streaming that are similar to inferred patterns, suggesting strong topographic forcing. In a simulation using a realistic bed in which the ice was very cold and basal melting rarely occurred, streams were again very narrow. Widespread streaming under low driving stresses tends to reduce ice-sheet thicknesses compared with weak streaming or models that do not produce streaming. Consequently, ice thicknesses are smaller and tend to be consistent with the results of sea-level inversions based on geophysical Earth models.

Download Full-text

The Antarctic Ice Sheet During the Last Glacial-Interglacial Cycle: A Three-Dimensional Experiment

Annals of Glaciology ◽

10.1017/s0260305500008387 ◽

1990 ◽

Vol 14 ◽

pp. 115-119 ◽

Cited By ~ 62

Author(s):

Philippe Huybrechts

Keyword(s):

Sea Level ◽

Three Dimensional ◽

Ice Sheet ◽

Weddell Sea ◽

The West ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

Last Glacial ◽

West Antarctic ◽

The Last Glacial

A complete three-dimensional thermo-mechanical ice-shect model for the entire Antarctic ice sheet, including an ice shelf, grounding line-dynamics and isostatic bed adjustment, is employed to simulate the response of the ice sheet during the last glacial-interglacial cycle with respect to changing environmental conditions. To do this, the Vostok temperature signal is used to force changes in surface temperature and accumulation rate and sea level prescribed by a piecewise linear sawtooth function. Model calculations started at 160 ka B.P. In line with glacial geological evidence, the most pronounced fluctuations are found in the West Antarctic ice sheet and appear to be essentially controlled by changes in eustatic sea level. Grounding occurs more readily in the Weddell Sea than in the Ross Sea and, due to the long time scales involved, the ice sheet does not reach its full glacial extent until 16 ka B.p. The concomitant disintegration of the West Antarctic ice sheet is triggered by a rise in sea level and takes around 6000 years to complete. The ice sheet then halts close to the present state and no collapse takes place. This Holocene deglaciation appears to have added 6–8 million km3 of ice to the world oceans, corresponding with an Antarctic contribution to world-wide sea level of 12–15 m.

Download Full-text