Regional stagnation of the western Keewatin ice sheet and the significance of meltwater corridors and eskers, northern Canada

The glacial landsystem of western Keewatin region, northern Canada, consists of three significant events. First, was regional emplacement of subglacial sediments, mainly till (a pre-existing landscape). Second, was regional-scale erosion (land surface modification) leading to development of an integrated, anabranched network of meltwater drainage routes producing meltwater corridors. Third, was deposition of an extensive array of eskers, and related forms, within meltwater corridors. Integration of field observations, mapping and remotely-sensed data allow us to link scoured bedrock and till surfaces, truncated drumlins, scour pits, glaciofluvial terraces, boulder lags, and the extensive network of erosional corridors, as part of regional meltwater erosion events. The network of long (~100-200 km), relatively wide (~1-3 km) meltwater corridors record confined subglacial erosion that scoured sediment (and bedrock) prior to glaciofluvial sedimentation (predominately eskers). Despite considerable sediment erosion along corridors, moraines and other ice-marginal deposits are rare on the western Keewatin landscape. The absence of these features is inconsistent with deglacial models relying on step-wise active retreat of the ice-margin. Instead, we propose that deglaciation of the western Keewatin Sector of the Laurentide Ice Sheet (LIS) was controlled by regional thinning and stagnation. These findings raise fundamental questions about deglacial patterns and processes and thus suggest that further evaluation and revision of existing models of deglacial chronology for this sector of the LIS is needed..

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LGM Summer Climate on the Southern Margin of the Laurentide Ice Sheet: Wet or Dry?*

Journal of Climate ◽

10.1175/jcli3480.1 ◽

2005 ◽

Vol 18 (16) ◽

pp. 3317-3338 ◽

Cited By ~ 47

Author(s):

David H. Bromwich ◽

E. Richard Toracinta ◽

Robert J. Oglesby ◽

James L. Fastook ◽

Terence J. Hughes

Keyword(s):

Boundary Conditions ◽

Great Plains ◽

Land Surface ◽

Thermal Gradient ◽

Mesoscale Model ◽

Ice Sheet ◽

Laurentide Ice Sheet ◽

Low Level ◽

Summer Climate ◽

Southern Margin

Abstract Regional climate simulations are conducted using the Polar fifth-generation Pennsylvania State University (PSU)–NCAR Mesoscale Model (MM5) with a 60-km horizontal resolution domain over North America to explore the summer climate of the Last Glacial Maximum (LGM: 21 000 calendar years ago), when much of the continent was covered by the Laurentide Ice Sheet (LIS). Output from a tailored NCAR Community Climate Model version 3 (CCM3) simulation of the LGM climate is used to provide the initial and lateral boundary conditions for Polar MM5. LGM boundary conditions include continental ice sheets, appropriate orbital forcing, reduced CO2 concentration, paleovegetation, modified sea surface temperatures, and lowered sea level. The simulated LGM summer climate is characterized by a pronounced low-level thermal gradient along the southern margin of the LIS resulting from the juxtaposition of the cold ice sheet and adjacent warm ice-free land surface. This sharp thermal gradient anchors the midtropospheric jet stream and facilitates the development of synoptic cyclones that track over the ice sheet, some of which produce copious liquid precipitation along and south of the LIS terminus. Precipitation on the southern margin is orographically enhanced as moist southerly low-level flow (resembling a contemporary Great Plains low-level jet configuration) in advance of the cyclone is drawn up the ice sheet slope. Composites of wet and dry periods on the LIS southern margin illustrate two distinctly different atmospheric flow regimes. Given the episodic nature of the summer rain events, it may be possible to reconcile the model depiction of wet conditions on the LIS southern margin during the LGM summer with the widely accepted interpretation of aridity across the Great Plains based on geological proxy evidence.

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Regional-scale meltwater erosion and deposition patterns, northern Quebec, Canada

Annals of Glaciology ◽

10.3189/1996aog22-1-85-92 ◽

1996 ◽

Vol 22 ◽

pp. 85-92 ◽

Cited By ~ 2

Author(s):

T. A. Brennand ◽

J. Shaw ◽

D. R. Sharpe

Keyword(s):

Regional Scale ◽

Ice Sheet ◽

Laurentide Ice Sheet ◽

Outburst Flood ◽

Erosion And Deposition ◽

Sedimentary Characteristics ◽

Large Sector ◽

Glaciofluvial Deposits ◽

Flow Convergence ◽

Local Patterns

Glaciofluvial ridges, several hundred kilometres long, are commonly referred to as interlobate moraines because they appear to have formed at the convergence of two distinct ice lobes. Flow convergence is indicated by patterns of striations, streamlined forms and eskers. The so-called interlobate moraines are also thought to have formed asynchronously as the ice margin retreated. By contrast, we argue that the Harricana moraine of northern Quebec, Canada, formed following flow convergence in a regional-scale subglacial outburst flood. Flowlines constructed from streamlined bedforms mapped on the glacial map of Canada, reinterpretation of these streamlined forms as products of meltwater erosion, and field records of erosional marks (S-forms) in bedrock and glaciofluvial deposits to the lee of bedrock highs support this model. The effects of this flow convergence on the ice-sheet topography and drainage controlled the location of the broad conduit in which the Harricana moraine was deposited. Continued flow in this conduit and melting of the conduit walls explain the local patterns of striae, the supply of debris to the conduit, and the morphological and sedimentary characteristics of the moraine itself. From these characteristics, we conclude that the moraine was formed synchronously. This conclusion, if correct, is instructive regarding the deglacial hydrological organization of a large sector of the Laurentide ice sheet.

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LIVVkit 2.1: automated and extensible ice sheet model validation

Geoscientific Model Development ◽

10.5194/gmd-12-1067-2019 ◽

2019 ◽

Vol 12 (3) ◽

pp. 1067-1086 ◽

Cited By ~ 2

Author(s):

Katherine J. Evans ◽

Joseph H. Kennedy ◽

Dan Lu ◽

Mary M. Forrester ◽

Stephen Price ◽

...

Keyword(s):

Land Surface ◽

High Performance ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Earth System ◽

Remotely Sensed Data ◽

Surface Mass ◽

Community Earth System Model ◽

Southwest Region ◽

Temperature Radiation

Abstract. A collection of scientific analyses, metrics, and visualizations for robust validation of ice sheet models is presented using the Land Ice Verification and Validation toolkit (LIVVkit), version 2.1, and the LIVVkit Extensions repository (LEX), version 0.1. This software collection targets stand-alone ice sheet or coupled Earth system models, and handles datasets and analyses that require high-performance computing and storage. LIVVkit aims to enable efficient and fully reproducible workflows for postprocessing, analysis, and visualization of observational and model-derived datasets in a shareable format, whereby all data, methodologies, and output are distributed to users for evaluation. Extending from the initial LIVVkit software framework, we demonstrate Greenland ice sheet simulation validation metrics using the coupled Community Earth System Model (CESM) as well as an idealized stand-alone high-resolution Community Ice Sheet Model, version 2 (CISM2), coupled to the Albany/FELIX velocity solver (CISM-Albany or CISM-A). As one example of the capability, LIVVkit analyzes the degree to which models capture the surface mass balance (SMB) and identifies potential sources of bias, using recently available in situ and remotely sensed data as comparison. Related fields within atmosphere and land surface models, e.g., surface temperature, radiation, and cloud cover, are also diagnosed. Applied to the CESM1.0, LIVVkit identifies a positive SMB bias that is focused largely around Greenland's southwest region that is due to insufficient ablation.

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Postglacial Temperature Anomalies and Glacial Isostasy

Quaternary Research ◽

10.1016/0033-5894(83)90036-4 ◽

1983 ◽

Vol 19 (3) ◽

pp. 293-301

Author(s):

K. J. Tinkler

Keyword(s):

Land Surface ◽

Ice Sheet ◽

Lapse Rate ◽

Laurentide Ice Sheet ◽

Mean Annual Temperature ◽

Glacial Ice ◽

Temperature Changes ◽

A Site ◽

Variance Estimates ◽

Change In Mean

AbstractThe isostatic depression of an ice-free land surface, originally caused by glacial ice, ought to be converted into a change in mean annual temperature according to the usual value for the environmental lapse rate, 6.5°C/1000 m. Calculations are undertaken to show the temperature changes, relative to present values at a site, that can be expected from this effect during the retreat of a major continental ice sheet. It is concluded that when restrained rebound is taken into account temperatures relative to the present could vary from 0°C at the start of deglaciation to about +2.32°C at the final disappearance of the Laurentide Ice Sheet. The decay of the warmer-than-present temperatures towards their current values is controlled, in this model, by isostatic recovery of the land surface. Variance estimates are built into the model and suggest that the anomaly might be as small as 0.75°C or as large as 4.0°C depending on the choice of values for crucial components such as maximum ice thickness, the proportion of isostatic deformation, and the amount of restrained rebound achieved by the time a site become ice free.

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Regional-scale meltwater erosion and deposition patterns, northern Quebec, Canada

Annals of Glaciology ◽

10.1017/s0260305500015251 ◽

1996 ◽

Vol 22 ◽

pp. 85-92 ◽

Cited By ~ 13

Author(s):

T. A. Brennand ◽

J. Shaw ◽

D. R. Sharpe

Keyword(s):

Regional Scale ◽

Ice Sheet ◽

Laurentide Ice Sheet ◽

Outburst Flood ◽

Erosion And Deposition ◽

Sedimentary Characteristics ◽

Large Sector ◽

Glaciofluvial Deposits ◽

Flow Convergence ◽

Local Patterns

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LIVVkit 2.1: Automated and extensible ice sheet model validation

10.5194/gmd-2018-70 ◽

2018 ◽

Author(s):

Katherine J. Evans ◽

Joseph H. Kennedy ◽

Dan Lu ◽

Mary M. Forrester ◽

Stephen Price ◽

...

Keyword(s):

Land Surface ◽

High Performance ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Earth System ◽

Remotely Sensed Data ◽

Surface Mass ◽

Community Earth System Model ◽

Southwest Region ◽

Temperature Radiation

Abstract. A collection of scientific analyses, metrics, and visualizations for robust validation of ice sheet models is presented using the LIVVkit package, version 2.1. This software collection targets stand-alone ice sheet or coupled Earth system models, and handles datasets and operations that require high-performance computing and storage. LIVVkit aims to enable efficient and fully reproducible workflows for post-processing, analysis, and visualization of observational and model-derived datasets in a shareable format, whereby all data, methodologies, and output are distributed to users for evaluation. We demonstrate LIVVkit validation for a Greenland ice sheet simulation using the coupled Community Earth System Model, CESM, as well as an idealized stand-alone high-resolution ice sheet model, CISM-Albany. As one example of the capability, LIVVkit analyzes the degree to which models capture the surface mass balance (SMB) and identifies potential sources of bias, using recently available in-situ and remotely sensed data as comparison. Related fields within atmosphere and land surface models, e.g. surface temperature, radiation, and cloud cover, are also diagnosed. Applied to the CESM1.0, LIVVkit identifies a positive SMB bias that is focused largely around Greenland's southwest region that is due to insufficient ablation.

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