Last Glacial Maximum ice sheet dynamics in Arctic Canada inferred from young erratics perched on ancient tors

Briner, Jason P.; Miller, Gifford H.; Davis, P. Thompson; Bierman, Paul R.; Caffee, M.

doi:10.1016/s0277-3791(03)00003-9

Cited by 135 publications

(94 citation statements)

References 38 publications

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“…If the former is correct, this would mean that the trimline used to delineate the glacier extent in the accumulation area, and from which ice surface elevation contour lines are usually drawn (e.g., Benz-Meier, 2003;Kelly et al, 2004;Bini et al, 25 2009; Wirsig et al, 2016), does not represent the ice surface but an englacial cold-temperate ice transition layer that indicates the limit of glacial erosion (Florineth, 1998). In several, more polar paleo ice sheets (British Isle, Scandinavia, Canada), several studies have pointed out the existence of uneroded bedrock surfaces beneath ice sheets that have survived multiple glaciations under frozen, cold-based basal conditions (e.g., Fabel et al, 2002;Briner et al, 2003;Ballantyne and Stone, 2015). The same situation is also believed to exist in some places under Antarctica (Creyts et al, 2014).…”

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confidence: 99%

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

Cohen¹,

Gillet-Chaulet²,

Haeberli³

et al. 2017

Preprint

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Abstract. At the Last Glacial Maximum (LGM), the Rhine glacier in the Swiss Alps covered an area of about 16,000 km 2 .As part of an integrative study about the safety of repositories for radioactive waste under ice age conditions in Switzerland, we modeled the Rhine glacier using a fully-coupled, three-dimensional, transient, thermo-mechanical Stokes flow model down to a horizontal resolution of about 500 m. The accumulation and ablation gradients that roughly reproduced the geomorphic reconstructions of glacial extent and ice thickness suggested extremely cold (T July ∼ 0 • C at the glacier terminus) and dry (∼ 10 5 to 20% of today's precipitation) climatic conditions. Forcing the numerical simulations with warmer and wetter conditions that better matched LGM climate proxy records yielded a glacier on average 500 to 700 m thicker than geomorphic reconstructions.Mass balance gradients also controlled ice velocities, fluxes, and sliding speeds. These gradients, however, had only a small effect on basal conditions. All simulations indicated that basal ice reached the pressure melting point over much of the Rhine and Linth piedmont lobes, and also in the glacial valleys that fed these lobes. Only the outer margin of the lobes, bedrock highs ). In the lobes, despite low surface slopes and low basal shear stresses, sliding dictated main fluxes of ice which closely followed bedrock topography: ice was channeled in between bedrock highs along troughs, some of which coincided with glacially eroded overdeepenings. These sliding conditions may have favored glacial erosion by abrasion and quarrying. 20Our results confirmed general earlier findings but provided more insights into the detailed flow and basal conditions of the Rhine glacier at the LGM. Our model results suggested that the trimline could have been buried by a significant thickness of cold ice. These findings have significant implications for interpreting trimlines in the Alps and for our understanding of ice-climate interactions.

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confidence: 99%

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

Cohen¹,

Gillet-Chaulet²,

Haeberli³

et al. 2017

Preprint

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“…Arctic Canada Briner et al, 2003), and Scandinavia (Stroeven et al,44 2002). Cold-based ice also existed in mid-latitude regions, especially at high elevations (Bierman 45 et al, 2015) and along thin ice sheet margins (Colgan et al, 2002).…”

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confidence: 99%

“…Cold-based ice also existed in mid-latitude regions, especially at high elevations (Bierman 45 et al, 2015) and along thin ice sheet margins (Colgan et al, 2002). Since cosmic rays attenuate 46 as they pass through Earth materials at a rate controlled by density, burial by ~10 m of ice causes 47 production of nuclides by spallation to become negligible (Lal, 1988 1999; Briner et al, 2003;Briner et al, 2006;Corbett et al, 2013;Håkansson et al, 2008;Kaplan 56 et al, 2001;Marquette et al, 2004;Stroeven et al, 2002;Sugden et al, 2005).…”

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confidence: 99%

Constraining multi-stage exposure-burial scenarios for boulders preserved beneath cold-based glacial ice in Thule, northwest Greenland

Corbett

Bierman

Rood

2016

Earth and Planetary Science Letters

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Boulders and landscapes preserved beneath cold-based, nonerosive glacial ice violate assumptions associated with simple cosmogenic exposure dating. In such a setting, simple single isotope exposure ages over estimate the latest period of surface exposure; hence, alternate approaches are required to constrain the multi-stage exposure/burial histories of such samples. Here, we report 28 paired analyses of 10Be and 26Al in boulder samples from Thule, northwest Greenland. We use numerical models of exposure and burial as well as Monte Carlo simulations to constrain glacial chronology and infer process in this Arctic region dominated by cold-based ice. We investigate three specific cases that can arise with paired nuclide data: (1) exposure ages that are coeval with deglaciation and 26Al/10Be ratios consistent with constant exposure; (2) exposure ages that pre-date deglaciation and 26Al/10Be ratios consistent with burial following initial exposure; and (3) exposure ages that predate deglaciation and 26Al/10Be ratios consistent with constant exposure. Most glacially-transported boulders in Thule have complex histories; some were exposed for tens of thousands of years and buried for at least hundreds of thousands of years, while others underwent only limited burial. These boulders were recycled through different generations of till over multiple glacial/interglacial cycles, likely experiencing partial or complete shielding during interglacial periods due to rotation or shallow burial by sediments. Our work demonstrates that the landscape in Thule, like many high-latitude landscapes, was shaped over long time durations and multiple glacial and interglacial periods throughout the Quaternary. January 28, 2016To the Editor:After performing a second set of revisions from two reviewers, we are resubmitting our manuscript, Constraining Multi-Stage Exposure-Burial Scenarios for Boulders Preserved Beneath Cold-Based Glacial Ice in Thule, Northwest Greenland, for publication in Earth and Planetary Science Letters.We appreciated the additional comments from the two Reviewers who revisited the manuscript and are glad to hear that our first round of revisions was effective. During this second round, we focused on making the minor wording changes suggested and providing additional information about quantification of Al in samples. Attached, you will find a list of the reviewers' suggestions and details about how we incorporated those suggestions.We are optimistic that these minor revisions have finished polishing the manuscript to ready it for publication. Thank you in advance for considering our revised draft. Thank you for the re-submission of this paper and for dealing so thoroughly with the comments of the previous reviewers. As I suggested I would in my decision letter last time, I sent the revision to two of the previous reviewers. Both or these are very happy with the revision and have only minor comments.Please could you attend to the final points listed below on your revised manuscript, and then I will be able to ...

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“…1). We target boulders as much as possible, given that they are less likely to contain inheritance from prior periods of exposure (Hallet and Putkonen, 1994;Putkonen and Swanson, 2003;Putkonen and O'Neal, 2006;Balco, 2011;Heyman et al, 2011); bedrock is only sampled when boulders are not available because nuclides created during prior periods of exposure can be preserved in bedrock beneath cold-based ice (e.g., Bierman et al, 1999Bierman et al, , 2015Colgan et al, 2002;Briner et al, 2003;Goehring et al, 2008). Our goal is production of a 3D-model of deglaciation of the mountains of the northern New England area to assess ice volume changes over time.…”

Section: Research Strategy Samplingmentioning

confidence: 99%

Guidebook for Field Trips in Western Maine and Northern New Hampshire

Johnson¹,

Eusden²

2017

New England Intercollegiate Geological Conference 2017

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Last Glacial Maximum ice sheet dynamics in Arctic Canada inferred from young erratics perched on ancient tors

Cited by 135 publications

References 38 publications

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum

Constraining multi-stage exposure-burial scenarios for boulders preserved beneath cold-based glacial ice in Thule, northwest Greenland

Guidebook for Field Trips in Western Maine and Northern New Hampshire

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