CALCULATING THE SLIDING VELOCITY OF THE RAINY LOBE OF THE LAURENTIDE ICE SHEET USING MASS BALANCE CALCULATIONS AND LARGEST CLAST SIZE IN LODGEMENT TILLS

Simulating the Early Holocene demise of the Laurentide Ice Sheet with BISICLES (public trunk revision 3298)

Geoscientific Model Development ◽

10.5194/gmd-13-4555-2020 ◽

2020 ◽

Vol 13 (9) ◽

pp. 4555-4577

Author(s):

Ilkka S. O. Matero ◽

Lauren J. Gregoire ◽

Ruza F. Ivanovic

Keyword(s):

Mass Balance ◽

General Circulation ◽

Ice Sheet ◽

Circulation Model ◽

Early Holocene ◽

Laurentide Ice Sheet ◽

Hudson Bay ◽

Surface Mass Balance ◽

Surface Mass ◽

The North

Abstract. Simulating the demise of the Laurentide Ice Sheet covering Hudson Bay in the Early Holocene (10–7 ka) is important for understanding the role of accelerated changes in ice sheet topography and melt in the 8.2 ka event, a century long cooling of the Northern Hemisphere by several degrees. Freshwater released from the ice sheet through a surface mass balance instability (known as the saddle collapse) has been suggested as a major forcing for the 8.2 ka event, but the temporal evolution of this pulse has not been constrained. Dynamical ice loss and marine interactions could have significantly accelerated the ice sheet demise, but simulating such processes requires computationally expensive models that are difficult to configure and are often impractical for simulating past ice sheets. Here, we developed an ice sheet model setup for studying the Laurentide Ice Sheet's Hudson Bay saddle collapse and the associated meltwater pulse in unprecedented detail using the BISICLES ice sheet model, an efficient marine ice sheet model of the latest generation which is capable of refinement to kilometre-scale resolutions and higher-order ice flow physics. The setup draws on previous efforts to model the deglaciation of the North American Ice Sheet for initialising the ice sheet temperature, recent ice sheet reconstructions for developing the topography of the region and ice sheet, and output from a general circulation model for a representation of the climatic forcing. The modelled deglaciation is in agreement with the reconstructed extent of the ice sheet, and the associated meltwater pulse has realistic timing. Furthermore, the peak magnitude of the modelled meltwater equivalent (0.07–0.13 Sv) is compatible with geological estimates of freshwater discharge through the Hudson Strait. The results demonstrate that while improved representations of the glacial dynamics and marine interactions are key for correctly simulating the pattern of Early Holocene ice sheet retreat, surface mass balance introduces by far the most uncertainty. The new model configuration presented here provides future opportunities to quantify the range of plausible amplitudes and durations of a Hudson Bay ice saddle collapse meltwater pulse and its role in forcing the 8.2 ka event.

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Mass Balance and Sliding Velocity of the Puget Lobe of the Cordilleran Ice Sheet During the Last Glaciation

Quaternary Research ◽

10.1016/0033-5894(86)90001-3 ◽

1986 ◽

Vol 25 (3) ◽

pp. 269-280 ◽

Cited By ~ 22

Author(s):

Derek B. Booth

Keyword(s):

Mass Balance ◽

Pacific Northwest ◽

Flow Direction ◽

Ice Sheet ◽

Equilibrium Line ◽

Sliding Velocity ◽

Equilibrium Line Altitude ◽

Temperature And Precipitation ◽

The Pacific ◽

Cordilleran Ice Sheet

An estimate of the sliding velocity and basal meltwater discharge of the Puget lobe of the Cordilleran ice sheet can be calculated from its reconstructed extent, altitude, and mass balance. Lobe dimensions and surface altitudes are inferred from ice limits and flow-direction indicators. Net annual mass balance and total ablation are calculated from relations empirically derived from modern maritime glaciers. An equilibrium-line altitude between 1200 and 1250 m is calculated for the maximum glacial advance (ca. 15,000 yr B.P.) during the Vashon Stade of the Fraser Glaciation. This estimate is in accord with geologic data and is insensitive to plausible variability in the parameters used in the reconstruction. Resultant sliding velocities are as much as 650 m/a at the equilibrium line, decreasing both up- and downglacier. Such velocities for an ice sheet of this size are consistent with nonsurging behavior. Average meltwater discharge increases monotonically downglacier to 3000 m3/sec at the terminus and is of a comparable magnitude to ice discharge over much of the glacier's ablation area. Paleoclimatic inferences derived from this reconstruction are consistent with previous, independently derived studies of late Pleistocene temperature and precipitation in the Pacific Northwest.

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Optimising a regional Antarctic Ice Sheet model to investigate basal conditions and initialise transient experiments

10.5194/egusphere-egu21-13125 ◽

2021 ◽

Author(s):

Rupert Gladstone ◽

Yufang Zhang ◽

Thomas Zwinger ◽

Fabien Gillet-Chaulet ◽

Michael Wolovick ◽

...

Keyword(s):

Mass Balance ◽

Large Scale ◽

Water Pressure ◽

Ice Sheet ◽

Dominant Mode ◽

Temperature Structure ◽

Sliding Velocity ◽

Basal Resistance ◽

Glacier System ◽

Modelling Studies

Computer models for ice sheet dynamics are the primary tools for making future predictions of ice sheet behaviour, marine ice sheet instability, and ice sheet contributions to sea level change. &#160;Such modelling studies face a number of challenges, and we consider here two examples. &#160;The dominant mode of flow for ice streams is sliding at the bed, and the physical processes that control sliding are hard to observe. Ice sheet models often prescribe basal resistance as a function of sliding velocity. &#160;But laboratory experiments and real-world observations indicate that basal resistance is also dependent on the water pressure in the sub-glacial hydrologic system, a property that is hard to constrain. &#160;Initialising an ice sheet model for future projections is usually implemented either by a multi-millennial spin up or else by optimisation simulations, both of which have significant drawbacks. &#160;In particular, long spin-up simulations cannot easily ensure a close match to present-day ice geometry, and optimisations cannot easily ensure an overall ice sheet mass balance that matches the present-day mass balance.Using a 3D Stokes-flow ice dynamic model, we carry out optimisations for two Antarctic catchments: The Pine Island Glacier (PIG) in West Antarctica and the Lambert-Amery Glacier System (LAGS) in East Antarctica. &#160;We optimise both the basal resistance and flow enhancement in order to minimise discrepancy between modelled and observed (from satellite) horizontal velocities at the ice upper surface. &#160;We use these optimised model configurations to estimate the transient mass trend and also look at the 3D velocity field, its sensitivity to choice of boundary conditions in the normal direction at upper and lower surfaces, and its implications for the 3D temperature structure. &#160;These simulations provide an estimate of the present-day thermo-mechanical state of the PIG and LAGS.We demonstrate that constraining only horizontal velocity in the optimisations can lead to unrealistic normal velocities at the upper surface. &#160;We show that this can, in turn, strongly impact on the catchment&#8217;s total mass budget (through locally unconstrained thinning/thickening rates) and lead to a large-scale bias in temperatures simulated using the optimised model with the steady state assumption, due to unphysical advection of heat through the ice upper surface.We employ the optimised model to estimate basal melt, due mainly to friction heat, and drive a subglacial hydrology model beneath the PIG, providing a model-based estimate of the distribution of basal water pressure. &#160;We use this, along with simulated sliding velocity and basal resistance, to evaluate some commonly used sliding relations.

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Modeling the surface mass-balance response of the Laurentide Ice Sheet to Bølling warming and its contribution to Meltwater Pulse 1A

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2011.07.008 ◽

2012 ◽

Vol 315-316 ◽

pp. 24-29 ◽

Cited By ~ 9

Author(s):

Anders E. Carlson ◽

David J. Ullman ◽

Faron S. Anslow ◽

Feng He ◽

Peter U. Clark ◽

...

Keyword(s):

Mass Balance ◽

Ice Sheet ◽

Laurentide Ice Sheet ◽

Surface Mass Balance ◽

Surface Mass

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Simulating the Early Holocene demise of the Laurentide Ice Sheet with BISICLES (public trunk revision 3298)

10.5194/gmd-2019-304 ◽

2019 ◽

Author(s):

Ilkka S. O. Matero ◽

Lauren J. Gregoire ◽

Ruza F. Ivanovic

Keyword(s):

Mass Balance ◽

General Circulation ◽

Ice Sheet ◽

Circulation Model ◽

Early Holocene ◽

Laurentide Ice Sheet ◽

Hudson Bay ◽

Surface Mass Balance ◽

Surface Mass ◽

The North

Abstract. Simulating the demise of the Laurentide Ice Sheet covering the Hudson Bay in the early Holocene (10-7 ka) is important for understanding the role of accelerated changes in ice sheet topography and melt in the 8.2 ka event, a century long cooling of the Northern Hemisphere by several degrees. Freshwater released from the ice sheet through a surface mass balance instability (known as the saddle collapse) has been suggested as a major forcing for the 8.2 ka event, but the temporal evolution of this pulse has not been constrained. Dynamical ice loss and marine interactions could have significantly accelerated the ice sheet demise, but simulating such processes requires computationally expensive models that are difficult to configure and are often impractical for simulating past ice sheets. Here, we developed an ice sheet model setup for studying the Laurentide Ice Sheet’s Hudson Bay saddle collapse and the associated meltwater pulse in unprecedented detail using the BISICLES ice sheet model, an efficient marine ice sheet model of the latest generation, capable of refinement to kilometre-scale resolution and higher-order ice flow physics. The setup draws on previous efforts to model the deglaciation of the North American Ice Sheet for initialising the ice sheet temperature, recent ice sheet reconstructions for developing the topography of the region and ice sheet, and output from a general circulation model for a representation of the climatic forcing. The modelled deglaciation is in agreement with the reconstructed extent of the ice sheet and the associated meltwater pulse has realistic timing. Furthermore,the peak magnitude of the modelled meltwater equivalent (0.07–0.13 Sv) is compatible with geological estimates of freshwater discharge through the Hudson Strait. The results demonstrate that while improved representation of the glacial dynamics and marine interactions are key for correctly simulating the pattern of early Holocene ice sheet retreat, surface mass balance introduces by far the most uncertainty. The new model configuration presented here provides future opportunities to quantify the range of plausible amplitudes and durations of a Hudson Bay ice saddle collapse meltwater pulse and its role in forcing the 8.2 ka event.

Download Full-text