Erosion by Continental Ice Sheets

Abstract Some of the problems with earlier theories for erosion and transport by ice sheets are discussed, and it is noted that those theories cannot simply account for the often-reported finding that most till is derived from bedrock only a few tens of kilometers up-glacier. Considerations of the mass balance of debris in transport lead to the conclusion that ice sheets are capable of transporting most debris only a short distance. The theory that the break-up of bedrock is mostly a preglacial process is developed. The advancing ice sheet collects the debris and then deposits it after a short travel. As the ice sheet first advances over the regolith, debris is frozen onto the base and is carried until basal melting due to geothermal and frictional heat causes lodgment till deposition. Most debris is deposited during the advance of the ice sheet and is carried only a short distance. A generally small amount of debris is carried at higher levels and is deposited during ice standstill and retreat as melt-out and ablation tills. The present theory makes many predictions, among them, that most till units are not traceable over long distances, that thick till sequences represent unstable glacier margins and not necessarily long periods of glacier occupation, and that lodgment tills are to be interpreted in terms of ice advances and ablation tills in terms of ice retreats. This paper is published in full in Journal of Geology, Vol. 86, No. 4, 1978, p. 516–24.

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Erosion by Continental Ice Sheets

Journal of Glaciology ◽

10.3189/s0022143000029981 ◽

1979 ◽

Vol 23 (89) ◽

pp. 401-402

Author(s):

I. M. Whillans

Keyword(s):

Mass Balance ◽

Short Distance ◽

Ice Sheets ◽

Ice Sheet ◽

Present Theory ◽

Frictional Heat ◽

Break Up ◽

Basal Melting ◽

Continental Ice Sheets

AbstractSome of the problems with earlier theories for erosion and transport by ice sheets are discussed, and it is noted that those theories cannot simply account for the often-reported finding that most till is derived from bedrock only a few tens of kilometers up-glacier. Considerations of the mass balance of debris in transport lead to the conclusion that ice sheets are capable of transporting most debris only a short distance.The theory that the break-up of bedrock is mostly a preglacial process is developed. The advancing ice sheet collects the debris and then deposits it after a short travel. As the ice sheet first advances over the regolith, debris is frozen onto the base and is carried until basal melting due to geothermal and frictional heat causes lodgment till deposition. Most debris is deposited during the advance of the ice sheet and is carried only a short distance. A generally small amount of debris is carried at higher levels and is deposited during ice standstill and retreat as melt-out and ablation tills.The present theory makes many predictions, among them, that most till units are not traceable over long distances, that thick till sequences represent unstable glacier margins and not necessarily long periods of glacier occupation, and that lodgment tills are to be interpreted in terms of ice advances and ablation tills in terms of ice retreats.This paper is published in full in Journal of Geology, Vol. 86, No. 4, 1978, p. 516–24.

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Time-scales and degrees of freedom operating in the evolution of continental ice-sheets

Transactions of the Royal Society of Edinburgh Earth Sciences ◽

10.1017/s0263593300020861 ◽

1990 ◽

Vol 81 (4) ◽

pp. 371-384 ◽

Cited By ~ 28

Author(s):

Richard C. A. Hindmarsh

Keyword(s):

Mass Balance ◽

Degrees Of Freedom ◽

Large Scale ◽

Numerical Models ◽

Perturbation Expansion ◽

Ice Sheets ◽

Ice Sheet ◽

Plane Flow ◽

Surface Mass ◽

Continental Ice Sheets

ABSTRACTComprehensible explanations of the operation of earth climate systems should consist of descriptions of the operation of a few degrees of freedoms. Qualitative interpretations of results from large-scale numerical models generally follow this principle, but do not render formal definitions of the precise nature of such degrees of freedom.At its simplest, ice-sheet kinematics requires knowledge of the evolving height and span. Rheology and surface mass-balance impose different requirements upon the co-evolution of these variables, meaning a two-degree of freedom model is over-prescribed. By means of a perturbation expansion about the analytic similarity solution for viscous spreading, eigenfunctions corresponding to degrees of freedom in the ice-sheet profile are obtained, and are used to decompose mass-balance distributions. Only a few eigenfunctions are needed to replicate numerical models, implying that ice-sheets in plane flow may operate with fewer than ten degrees of freedom.Unstable evolution of ice-sheets can occur, when the operation of a very large number of degrees of freedom can be manifested. Previous work is reviewed and new results for the unstable transformation of valley glaciers into ice-sheets are presented. Phasing of initiation may be an unpredictable phenomenon.

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A case for cold-based continental ice sheets — a transient thermal model

Journal of Glaciology ◽

10.3189/s0022143000030513 ◽

1996 ◽

Vol 42 (140) ◽

pp. 37-42 ◽

Cited By ~ 1

Author(s):

Jan T. Heine ◽

David F. Mctigue

Keyword(s):

Heat Flux ◽

Ice Sheets ◽

Ice Sheet ◽

Initial Surface ◽

Glacial Cycle ◽

Geothermal Heat ◽

History Of ◽

Basal Melting ◽

Continental Ice Sheets ◽

Transient Thermal

AbstractA finite-difference numerical model is used to simulate the temperature profile at the center of an ice sheet throughout the course of a glaciation. The ice sheet is gradually built to a thickness of 3000 m over about 10 000 years, starting on permafrost. A geothermal heat flux is applied at large depth. For an initial surface temperature of –12.5°C, our model shows that basal melting occurs 72000 years after the onset of the glaciation. The important parameters determining the basal temperatures are the initial temperature of the ice and substrate, the rate of downward advection of cold ice and, to a lesser extent, the thickness of the ice sheet. The growth history of the ice sheet does not significantly influence the time at which basal melting occurs. Our results show the possibility that the central parts of the continental ice sheets were cold-based for a significant part of their existence. Heating due to the geothermal heat flux cannot account for basal melting during most or all of a glacial cycle. These results may help to explain the existence of preserved land forms under the ice sheets.

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A case for cold-based continental ice sheets — a transient thermal model

Journal of Glaciology ◽

10.1017/s0022143000030513 ◽

1996 ◽

Vol 42 (140) ◽

pp. 37-42 ◽

Cited By ~ 8

Author(s):

Jan T. Heine ◽

David F. Mctigue

Keyword(s):

Heat Flux ◽

Ice Sheets ◽

Ice Sheet ◽

Initial Surface ◽

Glacial Cycle ◽

Geothermal Heat ◽

History Of ◽

Basal Melting ◽

Continental Ice Sheets ◽

Transient Thermal

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Subglacial Discharge of the Greenland Ice Sheet from Basal Melt

10.5194/egusphere-egu21-7304 ◽

2021 ◽

Author(s):

Nanna Bjørnholt Karlsson ◽

Anne M Solgaard ◽

Kenneth D Mankoff ◽

Fabien Gillet-Chaulet ◽

Joseph A. MacGregor ◽

...

Keyword(s):

Mass Balance ◽

Total Mass ◽

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Frictional Heat ◽

Geothermal Heat ◽

Surface Mass ◽

Ice Volume ◽

Friction Term

The total mass balance of ice sheets is determined using estimates of ice volume change from satellite altimetry, measurements of gravity changes, or by differencing solid ice discharge and surface mass balance. The basal melt is only implicitly included in the first two and entirely neglected by the last method. Here, we show that the basal mass loss of the Greenland Ice Sheet is a non-negligible component of the total mass budget. We estimate that the basal melt is 21.4 +4.4/-4.0 Gt per year corresponding to 8% of the ice sheet&#8217;s total mass balance. The basal melt is composed of three separate terms; melt caused by frictional heat, geothermal heat and heat from surface meltwater, respectively, and the basal friction term is responsible for half of the basal melt.Importantly, the geothermal and friction heat are active year round. This implies that a quantifiable volume of freshwater is discharged into the Greenlandic fjords during the winter where the ice-fjord interactions often are assumed dormant. Here, we present basal melt volumes from different outlet glaciers that discharge into Greenlandic fjords. We compare the basal melt to the freshwater volumes generated by surface meltwater, and identify locations where basal melt volumes are comparable to surface meltwater during the winter.

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Continental Ice Sheets and the Planetary Radiation Budget

Quaternary Research ◽

10.1016/0033-5894(80)90016-2 ◽

1980 ◽

Vol 14 (3) ◽

pp. 349-359 ◽

Cited By ~ 18

Author(s):

J. Oerlemans

Keyword(s):

Mass Balance ◽

Climate Model ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Age ◽

Surface Elevation ◽

Radiation Budget ◽

Radiation Balance ◽

Ice Mass Balance ◽

Continental Ice Sheets

AbstractThe interaction between continential ice sheets and the planetary radiation budget is potentially important in climate-sensitivity studies. A simple ice-sheet model incorporated in an energybalance climate model provides a tool for studying this interaction in a quantitative way. Experiments in which the ice-sheet model is coupled step by step to the climate model show that ice sheets hardly affect the zonal mean radiation balance because the albedo feedback due to sea ice and snow cover is dominating. The model requires a 5% drop in the solar constant to create ice sheets of ice-age size.If the feedback between surface elevation and ice-mass balance is included (in a very crude way), the ice-sheet size (L, measured southward from 70°N) becomes much more sensitive to in insolation. For a range of normalized solar constants, roughly from 0.98 to 1.02, two stable solutions exist: L ⋍ 0 and L ⋍ 2000 km. This result demonstrates that the response of ice sheets to insolation variations is far from linear. It also stresses the need for explicit modeling of the ice-mass balance of ice sheets, particularly its dependence on surface elevation.

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Basal Melt of the Greenland Ice Sheet: The Invisible Mass Budget Term

10.5194/egusphere-egu2020-6943 ◽

2020 ◽

Author(s):

Nanna Bjørnholt Karlsson ◽

Anne Munck Solgaard ◽

Kenneth D. Mankoff ◽

Jason E. Box ◽

Michele Citterio ◽

...

Keyword(s):

Mass Balance ◽

Total Mass ◽

Heat Dissipation ◽

Frictional Heating ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Frictional Heat ◽

Geothermal Heat ◽

Surface Mass ◽

Basal Melting

The Greenland ice sheet has been one of largest sources of sea-level rise since the early 2000s. The total mass balance of the ice sheet is typically determined using one of the following methods: estimates of ice volume change from satellite altimetry, measurements of changes in gravity, and by considering the difference between solid ice discharge and surface mass balance (often referred to as the input&#8211;output method). In spite of an overall agreement between the different methods, uncertainties remain regarding the relative contribution from individual processes, and to date the basal melt has never been explicitly included in total mass balance estimates. Here, we present the first estimate of the contribution from basal melting to the total mass balance. We partition the basal melt into three terms; melt caused by frictional heat, geothermal heat and viscous heat dissipation, respectively. Combined, the three terms contribute approximately 25 Gt per year of basal melt to the total mass loss equivalent to 5% of the average solid ice discharge (average value of 1986-2018 discharge). This is equivalent to the ice discharge from the entire northeastern sector. We find that basal melting also accounts for between 5% and 30% of observed thinning in most major glacier outlets. Over our observation period (winter 2017/18), close to 2/3 of the basal melt is due to frictional heating from fast moving ice. This term is expected to increase in the future, as ice streams are likely to expand and speed up in response to rising temperatures.

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Melting and freezing under Antarctic ice shelves from a combination of ice-sheet modelling and observations

Journal of Glaciology ◽

10.1017/jog.2017.42 ◽

2017 ◽

Vol 63 (240) ◽

pp. 731-744 ◽

Cited By ~ 3

Author(s):

JORGE BERNALES ◽

IRINA ROGOZHINA ◽

MAIK THOMAS

Keyword(s):

Mass Balance ◽

Ice Sheet ◽

Model Parameters ◽

Ice Shelf ◽

Ice Shelves ◽

Continental Scale ◽

Model Set ◽

Set Up ◽

Basal Melting ◽

The Antarctic

ABSTRACTIce-shelf basal melting is the largest contributor to the negative mass balance of the Antarctic ice sheet. However, current implementations of ice/ocean interactions in ice-sheet models disagree with the distribution of sub-shelf melt and freezing rates revealed by recent observational studies. Here we present a novel combination of a continental-scale ice flow model and a calibration technique to derive the spatial distribution of basal melting and freezing rates for the whole Antarctic ice-shelf system. The modelled ice-sheet equilibrium state is evaluated against topographic and velocity observations. Our high-resolution (10-km spacing) simulation predicts an equilibrium ice-shelf basal mass balance of −1648.7 Gt a−1 that increases to −1917.0 Gt a−1 when the observed ice-shelf thinning rates are taken into account. Our estimates reproduce the complexity of the basal mass balance of Antarctic ice shelves, providing a reference for parameterisations of sub-shelf ocean/ice interactions in continental ice-sheet models. We perform a sensitivity analysis to assess the effects of variations in the model set-up, showing that the retrieved estimates of basal melting and freezing rates are largely insensitive to changes in the internal model parameters, but respond strongly to a reduction of model resolution and the uncertainty in the input datasets.

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The response of large ice sheets to climatic change

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1992.0143 ◽

1992 ◽

Vol 338 (1285) ◽

pp. 235-242 ◽

Cited By ~ 23

Keyword(s):

Mass Balance ◽

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

Sea Level Change ◽

Mixing Ratio ◽

Ice Dynamics ◽

Environmental Models ◽

Level Change ◽

The Antarctic

The prediction of short-term (100 year) changes in the mass balance of ice sheets and longer-term (1000 years) variations in their ice volumes is important for a range of climatic and environmental models. The Antarctic ice sheet contains between 24 M km 3 and 29 M km 3 of ice, equivalent to a eustatic sea level change of between 60m and 72m. The annual surface accumulation is estimated to be of the order of 2200 Gtonnes, equivalent to a sea level change of 6 mm a -1 . Analysis of the present-day accumulation regime of Antarctica indicates that about 25% ( ca. 500 Gt a -1 ) of snowfall occurs in the Antarctic Peninsula region with an area of only 6.8% of the continent. To date most models have focused upon solving predictive algorithms for the climate-sensitivity of the ice sheet, and assume: (i) surface mass balance is equivalent to accumulation (i.e. no melting, evaporation or deflation); (ii) percentage change in accumulation is proportional to change in saturation mixing ratio above the surface inversion layer; and (iii) there is a linear relation between mean annual surface air tem perature and saturation mixing ratio. For the A ntarctic Peninsula with mountainous terrain containing ice caps, outlet glaciers, valley glaciers and ice shelves, where there can be significant ablation at low levels and distinct climatic regimes, models of the climate response must be more complex. In addition, owing to the high accumulation and flow rates, even short- to medium -term predictions must take account of ice dynamics. Relationships are derived for the mass balance sensitivity and, using a model developed by Hindmarsh, the transient effects of ice dynamics are estimated. It is suggested that for a 2°C rise in mean annual surface tem perature over 40 years, ablation in the A ntarctic Peninsula region would contribute at least 1.0 mm to sea level rise, offsetting the fall of 0.5 mm contributed by increased accum ulation.

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Exploring the complex uncertainties in coupled climate-ice simulations of the Last Glacial Maximum

10.5194/egusphere-egu21-6693 ◽

2021 ◽

Author(s):

Lauren Gregoire ◽

Niall Gandy ◽

Lachlan Astfalck ◽

Robin Smith ◽

Ruza Ivanovic ◽

...

Keyword(s):

Mass Balance ◽

Last Glacial Maximum ◽

Ice Sheets ◽

Ice Sheet ◽

Glacial Maximum ◽

Sea Surface ◽

Surface Mass ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

Simulating the co-evolution of climate and ice-sheets during the Quaternary is key to understanding some of the major abrupt changes in climate, ice and sea level. Indeed, events such as the Meltwater pulse 1a rapid sea level rise and Heinrich, Dansgaard&#8211;Oeschger and the 8.2 kyr climatic events all involve the interplay between ice sheets, the atmosphere and the ocean. Unfortunately, it is challenging to simulate the coupled Climate-Ice sheet system because small biases, errors or uncertainties in parts of the models are strongly amplified by the powerful interactions between the atmosphere and ice (e.g. ice-albedo and height-mass balance feedbacks). This leads to inaccurate or even unrealistic simulations of ice sheet extent and surface climate. To overcome this issue we need some methods to effectively explore the uncertainty in the complex Climate-Ice sheet system and reduce model biases. Here we present our approach to produce ensemble of coupled Climate-Ice sheet simulations of the Last Glacial maximum that explore the uncertainties in climate and ice sheet processes.We use the FAMOUS-ICE earth system model, which comprises a coarse-resolution and fast general circulation model coupled to the Glimmer-CISM ice sheet model. We prescribe sea surface temperature and sea ice concentrations in order to control and reduce biases in polar climate, which strongly affect the surface mass balance and simulated extent of the northern hemisphere ice sheets. We develop and apply a method to reconstruct and sample a range of realistic sea surface temperature and sea-ice concentration spatio-temporal field. These are created by merging information from PMIP3/4 climate simulations and proxy-data for sea surface temperatures at the Last Glacial Maximum with Bayes linear analysis. We then use these to generate ensembles of FAMOUS-ice simulations of the Last Glacial maximum following the PMIP4 protocol, with the Greenland and North American ice sheets interactively simulated. In addition to exploring a range of sea surface conditions, we also vary key parameters that control the surface mass balance and flow of ice sheets. We thus produce ensembles of simulations that will later be used to emulate ice sheet surface mass balance. &#160;

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