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Anders E. Carlson - One of the best experts on this subject based on the ideXlab platform.
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10Be dating Cordilleran-Laurentide Ice-Sheet separation during the last deglaciation
2020Co-Authors: Jorie Clark, Anders E. Carlson, Alberto V. Reyes, Glenn A. MilneAbstract:<p>During the last glacial maximum, the Cordilleran and Laurentide Ice Sheets met just to the east of the Canadian Rocky Mountains, forming an Ice-Sheet saddle. When this saddle disappeared has implications on deglacial global sea-level rise and abrupt climate change as well as human migration patterns to the Americas. We will present new 10-Be boulder ages from six sites on a ~1100 km transect along the Ice-Sheet suture zone, to date Cordilleran-Laurentide Ice-Sheet separation. Results will directly test whether or not Cordilleran-Laurentide separation contributed to abrupt sea-level rise during meltwater pulse 1a (14.6-14.3 ka) in response to abrupt B&#248;lling warming (14.6-14.0 ka).</p>
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Revised chronology of northwest Laurentide Ice-Sheet deglaciation from beryllium-10 exposure-dated erratics on the western Canadian Shield
2020Co-Authors: Alberto V. Reyes, Anders E. Carlson, J. R. ReiminkAbstract:<p>The timing of northwest Laurentide Ice-Sheet deglaciation is important for understanding how Ice-Sheet retreat, and associated meltwater discharge, may have been involved in abrupt climate change and rapid sea-level rise at the end of the last glaciation. However, the deglacial chronology across the western Canadian Shield is poorly understood, with only a handful of minimum-limiting <sup>14</sup>C dates and sparse cosmogenic nuclide exposure dates constraining the timing and pattern of northwest Laurentide Ice-Sheet retreat across >1000 km of Ice-Sheet retreat to the marine limit west of Hudson Bay. We present cosmogenic <sup>10</sup>Be surface exposure dating of glacial erratics at two sites, within a ~160,000 km<sup>2</sup> region with no reliable temporal constraints on Ice-margin retreat, to directly date the timing of northwest Laurentide Ice-Sheet deglaciation. Six erratics perched directly on bedrock at a site on the western edge of the Slave Craton have exposure ages between 12.8&#177;0.6 and 12.2&#177;0.6 thousand years ago (ka;&#160;&#177;1sigma). Five erratics on bedrock, sampled at a site 115 km up-Ice to the east, yielded exposure ages between 10.8&#177;0.5 and 11.6&#177;0.5 ka. When corrected for decreased atmospheric depth due to isostatic uplift since deglaciation, the error-weighted mean ages for the two sites indicate that the Laurentide Ice Sheet retreated through this region of the western Canadian Shield between 13.3&#177;0.2 and 11.8&#177;0.2 ka, or at least 1 kyr earlier than inferred from the canonical compilation of minimum-limiting <sup>14</sup>C dates for deglaciation and paleo-glaciological models. We tentatively infer a preliminary Ice-margin retreat rate of ~0.1 m kyr<sup>-1&#160;</sup>over this interval spanning much of the Younger Dryas which, compared to earlier estimates, implies a substantially lower volume of meltwater flux from the retreating northwest Laurentide Ice Sheet at this time. &#160;Additional exposure ages on glacial erratics across this data-poor region are needed for validation of existing deglacial Ice-Sheet models, which can in turn contribute to comprehensive testing of hypotheses related to northwest Laurentide Ice-Sheet retreat rate, abrupt deglacial sea-level rise, and potential forcing of associated climate change events.</p>
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Rapid Laurentide Ice-Sheet advance towards southern last glacial maximum limit during marine isotope stage 3
Quaternary Science Reviews, 2018Co-Authors: Anders E. Carlson, Lev Tarasov, Tamara PicoAbstract:Abstract Marine isotope stage (MIS) 3 (∼58–28 ka) is a period of intermediate global Ice volume between MIS 4 and the last glacial maximum of MIS 2. Here we report geologic evidence for southern Laurentide Ice-Sheet rapid growth to near its last glacial maximum extent after a period with limited Ice in the southernmost Hudson Bay lowland. A14C age on wood in lacustrine sediments interbedded with glacial tills in central-eastern Wisconsin dates a Laurentide Ice-Sheet advance southwards to an extent at least equivalent to at least its ∼17 ka deglacial limit by 39.1 ± 0.4 ka. This advance ended before 30.4 ± 0.9 ka based on another 14C date on wood in lacustrine sediment overlying the till layers. This advance is consistent with 14C ages from Michigan and Iowa, and Gulf of Mexico runoff records that support a concurrent southern Laurentide Ice-Sheet advance. We infer changes in North American Ice volume using Ice-Sheet model simulations from a large ensemble that are consistent with 14C-data and Gulf of Mexico-discharge constraints. The simulations show the Laurentide Ice Sheet growing from a volume equivalent to 25–30 m of global mean sea level (GMSL) before ∼40 ka to 40–45 m of GMSL at ∼40 ka, and reaching 65–70 m GMSL by ∼30 ka, consistent with glacial isostatic adjustment assessments of near-to intermediate-field sea-level data. We thus show from our terrestrial field data and Ice-Sheet model simulations that an individual Ice Sheet can grow rapidly, which has only been inferred previously for global Ice volume from GSML records.
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Final Laurentide Ice-Sheet deglaciation and Holocene climate-sea level change
Quaternary Science Reviews, 2016Co-Authors: David J. Ullman, Anders E. Carlson, Peter U. Clark, Steven W. Hostetler, Joshua K. Cuzzone, Glenn A. Milne, Kelsey Winsor, Marc A. CaffeeAbstract:Abstract Despite elevated summer insolation forcing during the early Holocene, global Ice Sheets retained nearly half of their volume from the Last Glacial Maximum, as indicated by deglacial records of global mean sea level (GMSL). Partitioning the GMSL rise among potential sources requires accurate dating of Ice-Sheet extent to estimate Ice-Sheet volume. Here, we date the final retreat of the Laurentide Ice Sheet with 10 Be surface exposure ages for the Labrador Dome, the largest of the remnant Laurentide Ice domes during the Holocene. We show that the Labrador Dome deposited moraines during North Atlantic cold events at ∼10.3 ka, 9.3 ka and 8.2 ka, suggesting that these regional climate events helped stabilize the retreating Labrador Dome in the early Holocene. After Hudson Bay became seasonally Ice free at ∼8.2 ka, the majority of Laurentide Ice-Sheet melted abruptly within a few centuries. We demonstrate through high-resolution regional climate model simulations that the thermal properties of a seasonally Ice-free Hudson Bay would have increased Laurentide Ice-Sheet ablation and thus contributed to the subsequent rapid Labrador Dome retreat. Finally, our new 10 Be chronology indicates full Laurentide Ice-Sheet had completely deglaciated by 6.7 ± 0.4 ka, which re quires that Antarctic Ice Sheets contributed 3.6–6.5 m to GMSL rise since 6.3–7.1 ka.
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Laurentide Ice-Sheet instability during the last deglaciation
Nature Geoscience, 2015Co-Authors: David J. Ullman, Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Joseph M. LicciardiAbstract:The factors leading to the full retreat of Ice Sheets during deglaciation are debated. Numerical modelling suggests that the Laurentide Ice Sheet retreated only after a threshold for warming and radiative forcing was passed in the Holocene.
Joseph M. Licciardi - One of the best experts on this subject based on the ideXlab platform.
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Laurentide Ice-Sheet instability during the last deglaciation
Nature Geoscience, 2015Co-Authors: David J. Ullman, Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Joseph M. LicciardiAbstract:The factors leading to the full retreat of Ice Sheets during deglaciation are debated. Numerical modelling suggests that the Laurentide Ice Sheet retreated only after a threshold for warming and radiative forcing was passed in the Holocene.
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Surface‐melt driven Laurentide Ice Sheet retreat during the early Holocene
Geophysical Research Letters, 2009Co-Authors: Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Elizabeth A. Obbink, David J. Ullman, Joseph M. LicciardiAbstract:Received 21 September 2009; revised 3 November 2009; accepted 30 November 2009; published 30 December 2009. [1] To better understand mechanisms of Ice-Sheet decay, we investigate the surface mass balance of the Laurentide Ice Sheet (LIS) during the early Holocene, a period of known rapid LIS retreat. We use a surface energy-mass balance model (EMBM) driven with conditions derived from an equilibrium atmosphere-ocean general circulation model 9 kilo-years ago simulation. Our EMBM indicates a net LIS surface mass balance of 0.67 ± 0.13 m yr 1 , with losses primarily due to enhanced boreal summer insolation and warmer summers. This rate of loss compared to LIS volume reconstructions suggests that surface ablation accounted for 74 ± 22% of the LIS mass loss with the remaining loss likely driven by dynamics resulting in basal sliding and calving. Thus surface melting likely played a governing role in the retreat and disappearance of this Ice Sheet. Citation: Carlson, A. E., F. S. Anslow, E. A. Obbink, A. N. LeGrande, D. J. Ullman, and J. M. Licciardi (2009), Surface-melt driven Laurentide Ice Sheet retreat during the early Holocene, Geophys. Res. Lett., 36, L24502, doi:10.1029/ 2009GL040948.
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surface melt driven Laurentide Ice Sheet retreat during the early holocene
Geophysical Research Letters, 2009Co-Authors: Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Elizabeth A. Obbink, D J Ullman, Joseph M. LicciardiAbstract:Received 21 September 2009; revised 3 November 2009; accepted 30 November 2009; published 30 December 2009. [1] To better understand mechanisms of Ice-Sheet decay, we investigate the surface mass balance of the Laurentide Ice Sheet (LIS) during the early Holocene, a period of known rapid LIS retreat. We use a surface energy-mass balance model (EMBM) driven with conditions derived from an equilibrium atmosphere-ocean general circulation model 9 kilo-years ago simulation. Our EMBM indicates a net LIS surface mass balance of 0.67 ± 0.13 m yr 1 , with losses primarily due to enhanced boreal summer insolation and warmer summers. This rate of loss compared to LIS volume reconstructions suggests that surface ablation accounted for 74 ± 22% of the LIS mass loss with the remaining loss likely driven by dynamics resulting in basal sliding and calving. Thus surface melting likely played a governing role in the retreat and disappearance of this Ice Sheet. Citation: Carlson, A. E., F. S. Anslow, E. A. Obbink, A. N. LeGrande, D. J. Ullman, and J. M. Licciardi (2009), Surface-melt driven Laurentide Ice Sheet retreat during the early Holocene, Geophys. Res. Lett., 36, L24502, doi:10.1029/ 2009GL040948.
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Rapid early Holocene deglaciation of the Laurentide Ice Sheet
Nature Geoscience, 2008Co-Authors: Anders E. Carlson, Allegra N. Legrande, Delia W Oppo, Rosemarie E Came, Gavin A. Schmidt, Faron S. Anslow, Joseph M. Licciardi, Elizabeth A. ObbinkAbstract:The demise of the Laurentide Ice Sheet during the early Holocene epoch is the most recent and best constrained disappearance of a large Ice Sheet in the Northern Hemisphere, and thus allows an assessment of rates of Ice-Sheet decay as well as attendant contributions to sea level rise. Here, we use terrestrial and marine records of the deglaciation to identify two periods of rapid melting during the final demise of the Laurentide Ice Sheet, when melting Ice contributed about 1.3 and 0.7cm of sea level rise per year, respectively. Our simulations with a fully coupled ocean‐atmosphere model suggest that increased ablation due to enhanced early Holocene boreal summer insolation was the predominant cause of Laurentide Ice-Sheet retreat. Although the surface radiative forcing in boreal summer during the early Holocene is twIce as large as the greenhouse-gas forcing expected by the year 2100, the associated increase in summer surface air temperatures is very similar. We conclude that our geologic evidence for a rapid retreat of the Laurentide Ice Sheet may therefore describe a prehistoric precedent for mass balance changes of the Greenland Ice Sheet over the coming century.
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Deglaciation of a Soft-Bedded Laurentide Ice Sheet
Quaternary Science Reviews, 1998Co-Authors: Joseph M. Licciardi, Peter U. Clark, John W. Jenson, Douglas R MacayealAbstract:We present a series of numerical reconstructions of the Laurentide Ice Sheet during the last deglaciation (18–7 14C ka) that evaluates the sensitivity of Ice-Sheet geometry to subglacial sediment deformation. These reconstructions assume that the Laurentide Ice Sheet flowed over extensive areas of water-saturated, deforming sediment (soft beds) corresponding to the St. Lawrence lowland, the Great Lakes region, the western prairies of the U.S. and Canada, and the Hudson Bay and Hudson Strait regions. Sediment rheology is based on a constitutive law that incorporates experimental results from late Wisconsin till deposited by the Laurentide Ice Sheet which suggest only mildly nonlinear viscoplastic behavior. By varying the effective viscosity of till, we produced four reconstructions for the Ice Sheet during the last glacial maximum 18 14C ka, and two reconstructions each of the Ice Sheet at 14, 13, 12, 11 and 10 14C ka. We also produced one reconstruction for 9, 8.4, 8, and 7 14C ka. Reconstructions that assume a low effective viscosity for all areas of deforming sediment show a multidomed Ice Sheet with a large bowl-shaped depression over Hudson Bay and thin Ice (
David J. Ullman - One of the best experts on this subject based on the ideXlab platform.
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Final Laurentide Ice-Sheet deglaciation and Holocene climate-sea level change
Quaternary Science Reviews, 2016Co-Authors: David J. Ullman, Anders E. Carlson, Peter U. Clark, Steven W. Hostetler, Joshua K. Cuzzone, Glenn A. Milne, Kelsey Winsor, Marc A. CaffeeAbstract:Abstract Despite elevated summer insolation forcing during the early Holocene, global Ice Sheets retained nearly half of their volume from the Last Glacial Maximum, as indicated by deglacial records of global mean sea level (GMSL). Partitioning the GMSL rise among potential sources requires accurate dating of Ice-Sheet extent to estimate Ice-Sheet volume. Here, we date the final retreat of the Laurentide Ice Sheet with 10 Be surface exposure ages for the Labrador Dome, the largest of the remnant Laurentide Ice domes during the Holocene. We show that the Labrador Dome deposited moraines during North Atlantic cold events at ∼10.3 ka, 9.3 ka and 8.2 ka, suggesting that these regional climate events helped stabilize the retreating Labrador Dome in the early Holocene. After Hudson Bay became seasonally Ice free at ∼8.2 ka, the majority of Laurentide Ice-Sheet melted abruptly within a few centuries. We demonstrate through high-resolution regional climate model simulations that the thermal properties of a seasonally Ice-free Hudson Bay would have increased Laurentide Ice-Sheet ablation and thus contributed to the subsequent rapid Labrador Dome retreat. Finally, our new 10 Be chronology indicates full Laurentide Ice-Sheet had completely deglaciated by 6.7 ± 0.4 ka, which re quires that Antarctic Ice Sheets contributed 3.6–6.5 m to GMSL rise since 6.3–7.1 ka.
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Laurentide Ice-Sheet instability during the last deglaciation
Nature Geoscience, 2015Co-Authors: David J. Ullman, Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Joseph M. LicciardiAbstract:The factors leading to the full retreat of Ice Sheets during deglaciation are debated. Numerical modelling suggests that the Laurentide Ice Sheet retreated only after a threshold for warming and radiative forcing was passed in the Holocene.
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southern Laurentide Ice Sheet retreat synchronous with rising boreal summer insolation
Geology, 2015Co-Authors: Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, David J. Ullman, Marc W. Caffee, Angus K Moore, Kent M SyversonAbstract:Establishing the precise timing for the onset of Ice-Sheet retreat at the end of the Last Glacial Maximum (LGM) is critical for delineating mechanisms that drive deglaciations. Uncertainties in the timing of Ice-margin retreat and global Ice-volume change allow a variety of plausible deglaciation triggers. Using boulder 10 Be surface exposure ages, we date initial southern Laurentide Ice-Sheet (LIS) retreat from LGM moraines in Wisconsin (USA) to 23.0 ± 0.6 ka, coincident with retreat elsewhere along the southern LIS and synchronous with the initial rise in boreal summer insolation 24–23 ka. We show with climate-surface mass balance simulations that this small increase in boreal summer insolation alone is potentially sufficient to drive enhanced southern LIS surface ablation. We also date increased southern LIS retreat after ca. 20.5 ka likely driven by an acceleration in rising isolation. This near-instantaneous southern LIS response to boreal summer insolation before any rise in atmospheric CO 2 supports the Milankovic hypothesis of orbital forcing of deglaciations.
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Surface‐melt driven Laurentide Ice Sheet retreat during the early Holocene
Geophysical Research Letters, 2009Co-Authors: Anders E. Carlson, Allegra N. Legrande, Faron S. Anslow, Elizabeth A. Obbink, David J. Ullman, Joseph M. LicciardiAbstract:Received 21 September 2009; revised 3 November 2009; accepted 30 November 2009; published 30 December 2009. [1] To better understand mechanisms of Ice-Sheet decay, we investigate the surface mass balance of the Laurentide Ice Sheet (LIS) during the early Holocene, a period of known rapid LIS retreat. We use a surface energy-mass balance model (EMBM) driven with conditions derived from an equilibrium atmosphere-ocean general circulation model 9 kilo-years ago simulation. Our EMBM indicates a net LIS surface mass balance of 0.67 ± 0.13 m yr 1 , with losses primarily due to enhanced boreal summer insolation and warmer summers. This rate of loss compared to LIS volume reconstructions suggests that surface ablation accounted for 74 ± 22% of the LIS mass loss with the remaining loss likely driven by dynamics resulting in basal sliding and calving. Thus surface melting likely played a governing role in the retreat and disappearance of this Ice Sheet. Citation: Carlson, A. E., F. S. Anslow, E. A. Obbink, A. N. LeGrande, D. J. Ullman, and J. M. Licciardi (2009), Surface-melt driven Laurentide Ice Sheet retreat during the early Holocene, Geophys. Res. Lett., 36, L24502, doi:10.1029/ 2009GL040948.
Peter U. Clark - One of the best experts on this subject based on the ideXlab platform.
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Final Laurentide Ice-Sheet deglaciation and Holocene climate-sea level change
Quaternary Science Reviews, 2016Co-Authors: David J. Ullman, Anders E. Carlson, Peter U. Clark, Steven W. Hostetler, Joshua K. Cuzzone, Glenn A. Milne, Kelsey Winsor, Marc A. CaffeeAbstract:Abstract Despite elevated summer insolation forcing during the early Holocene, global Ice Sheets retained nearly half of their volume from the Last Glacial Maximum, as indicated by deglacial records of global mean sea level (GMSL). Partitioning the GMSL rise among potential sources requires accurate dating of Ice-Sheet extent to estimate Ice-Sheet volume. Here, we date the final retreat of the Laurentide Ice Sheet with 10 Be surface exposure ages for the Labrador Dome, the largest of the remnant Laurentide Ice domes during the Holocene. We show that the Labrador Dome deposited moraines during North Atlantic cold events at ∼10.3 ka, 9.3 ka and 8.2 ka, suggesting that these regional climate events helped stabilize the retreating Labrador Dome in the early Holocene. After Hudson Bay became seasonally Ice free at ∼8.2 ka, the majority of Laurentide Ice-Sheet melted abruptly within a few centuries. We demonstrate through high-resolution regional climate model simulations that the thermal properties of a seasonally Ice-free Hudson Bay would have increased Laurentide Ice-Sheet ablation and thus contributed to the subsequent rapid Labrador Dome retreat. Finally, our new 10 Be chronology indicates full Laurentide Ice-Sheet had completely deglaciated by 6.7 ± 0.4 ka, which re quires that Antarctic Ice Sheets contributed 3.6–6.5 m to GMSL rise since 6.3–7.1 ka.
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Rapid Holocene Deglaciation of the Labrador Sector of the Laurentide Ice Sheet
Journal of Climate, 2007Co-Authors: Anders E. Carlson, Peter U. Clark, Grant M. Raisbeck, Edward J. BrookAbstract:Abstract Retreat of the Laurentide Ice Sheet (LIS) following the Last Glacial Maximum 21 000 yr BP affected regional to global climate and accounted for the largest proportion of sea level rise. Although the late Pleistocene LIS retreat chronology is relatively well constrained, its Holocene chronology remains poorly dated, limiting our understanding of its role in Holocene climate change and sea level rise. Here new 10Be cosmogenic exposure ages on glacially deposited boulders are used to date the final disappearance of the Labrador sector of the LIS (LS-LIS). These data suggest that following the deglaciation of the southeastern Hudson Bay coastline at 8.0 ± 0.2 cal ka BP, the southwestern margin of the LS-LIS rapidly retreated ∼600 km in 140 yr and most likely in ∼600 yr at a rate of ∼900 m yr−1, with final deglaciation by 6.8 ± 0.2 10Be ka. The disappearance of the LS-LIS ∼6.8 10Be ka and attendant reduction in freshwater runoff may have induced the formation of Labrador Deep Seawater, while the loss ...
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Deglaciation of a Soft-Bedded Laurentide Ice Sheet
Quaternary Science Reviews, 1998Co-Authors: Joseph M. Licciardi, Peter U. Clark, John W. Jenson, Douglas R MacayealAbstract:We present a series of numerical reconstructions of the Laurentide Ice Sheet during the last deglaciation (18–7 14C ka) that evaluates the sensitivity of Ice-Sheet geometry to subglacial sediment deformation. These reconstructions assume that the Laurentide Ice Sheet flowed over extensive areas of water-saturated, deforming sediment (soft beds) corresponding to the St. Lawrence lowland, the Great Lakes region, the western prairies of the U.S. and Canada, and the Hudson Bay and Hudson Strait regions. Sediment rheology is based on a constitutive law that incorporates experimental results from late Wisconsin till deposited by the Laurentide Ice Sheet which suggest only mildly nonlinear viscoplastic behavior. By varying the effective viscosity of till, we produced four reconstructions for the Ice Sheet during the last glacial maximum 18 14C ka, and two reconstructions each of the Ice Sheet at 14, 13, 12, 11 and 10 14C ka. We also produced one reconstruction for 9, 8.4, 8, and 7 14C ka. Reconstructions that assume a low effective viscosity for all areas of deforming sediment show a multidomed Ice Sheet with a large bowl-shaped depression over Hudson Bay and thin Ice (
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deglaciation of a soft bedded Laurentide Ice Sheet
Quaternary Science Reviews, 1998Co-Authors: Joseph M. Licciardi, Peter U. Clark, John W. Jenson, Douglas R MacayealAbstract:We present a series of numerical reconstructions of the Laurentide Ice Sheet during the last deglaciation (18–7 14C ka) that evaluates the sensitivity of Ice-Sheet geometry to subglacial sediment deformation. These reconstructions assume that the Laurentide Ice Sheet flowed over extensive areas of water-saturated, deforming sediment (soft beds) corresponding to the St. Lawrence lowland, the Great Lakes region, the western prairies of the U.S. and Canada, and the Hudson Bay and Hudson Strait regions. Sediment rheology is based on a constitutive law that incorporates experimental results from late Wisconsin till deposited by the Laurentide Ice Sheet which suggest only mildly nonlinear viscoplastic behavior. By varying the effective viscosity of till, we produced four reconstructions for the Ice Sheet during the last glacial maximum 18 14C ka, and two reconstructions each of the Ice Sheet at 14, 13, 12, 11 and 10 14C ka. We also produced one reconstruction for 9, 8.4, 8, and 7 14C ka. Reconstructions that assume a low effective viscosity for all areas of deforming sediment show a multidomed Ice Sheet with a large bowl-shaped depression over Hudson Bay and thin Ice (<1000 m above modern sea-level) over the western and southern margins. Those reconstructions that assume a higher effective viscosity of till in the Hudson Bay region than for the western and southern margins also show a multidomed Ice Sheet but with considerably thicker Ice over Hudson Bay and a more northerly position of the central Ice divide. These two different geometries may represent Ice-Sheet orographic changes associated with a Heinrich event. Further increases in effective viscosity of till, approaching the effective viscosity of Ice, would result in a high, monolithic Ice dome centered over Hudson Bay, reinforcing the notion that a multidomed Ice Sheet reflects the distribution of substrate geology. Modeled Ice-surface geometry at the last glacial maximum shows many of the same general features as previous reconstructions that incorporate deformable beds. Our reconstructions with higher effective till viscosities in Hudson Bay also agree with the Ice-4G reconstructions (Peltier, 1994), which are based on inversion of relative sea-level data, for the early part of the last deglaciation (18–13 14C ka), but then depart significantly from Ice-4G beginning at about 12 14C ka due to differing assumptions of the history of deglaciation. Modeled Ice volume for the last glacial maximum suggests a glacioeustatic change of 50–55 m by a soft-bedded Laurentide Ice Sheet; this would increase as the effective viscosity of till increases. Subsequent Ice-volume changes through the last deglaciation generally parallel the trend of eustatic rise recorded at Barbados, New Guinea, and Tahiti, but suggest that the Laurentide Ice Sheet was not the source of meltwater pulse 1A.
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Numerical reconstruction of a soft-bedded Laurentide Ice Sheet during the last glacial maximum
Geology, 1996Co-Authors: Peter U. Clark, Douglas R Macayeal, Joseph M. Licciardi, John W. JensonAbstract:We used a numerical Ice-Sheet model to reconstruct the North American Laurentide Ice Sheet during the last glacial maximum. Our model simulates Ice-Sheet conditions that can be specified experimentally as either a rigid substrate (hard bed) or a wet, deformable till (soft bed); basal sliding is excluded. We use geologic records of former basal Ice-Sheet processes to prescribe the distribution of hard and soft beds. Our reconstruction of the Laurentide Ice Sheet is significantly lower in Ice-surface height and contains less Ice volume than the CLIMAP (maximum) reconstruction. In contrast, our reconstruction agrees well with the Ice-4G reconstruction, both in height and volume. Because the Ice-4G reconstruction is based on the inversion of relative sea-level data, whereas our reconstruction is based on glacial geology and Ice mechanics, this agreement suggests that soft beds provide a glaciological mechanism to explain the shape and volume of the Laurentide Ice Sheet that is most consistent with observations of relative sea-level change and other geodynamic considerations.
Douglas R Macayeal - One of the best experts on this subject based on the ideXlab platform.
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Deglaciation of a Soft-Bedded Laurentide Ice Sheet
Quaternary Science Reviews, 1998Co-Authors: Joseph M. Licciardi, Peter U. Clark, John W. Jenson, Douglas R MacayealAbstract:We present a series of numerical reconstructions of the Laurentide Ice Sheet during the last deglaciation (18–7 14C ka) that evaluates the sensitivity of Ice-Sheet geometry to subglacial sediment deformation. These reconstructions assume that the Laurentide Ice Sheet flowed over extensive areas of water-saturated, deforming sediment (soft beds) corresponding to the St. Lawrence lowland, the Great Lakes region, the western prairies of the U.S. and Canada, and the Hudson Bay and Hudson Strait regions. Sediment rheology is based on a constitutive law that incorporates experimental results from late Wisconsin till deposited by the Laurentide Ice Sheet which suggest only mildly nonlinear viscoplastic behavior. By varying the effective viscosity of till, we produced four reconstructions for the Ice Sheet during the last glacial maximum 18 14C ka, and two reconstructions each of the Ice Sheet at 14, 13, 12, 11 and 10 14C ka. We also produced one reconstruction for 9, 8.4, 8, and 7 14C ka. Reconstructions that assume a low effective viscosity for all areas of deforming sediment show a multidomed Ice Sheet with a large bowl-shaped depression over Hudson Bay and thin Ice (
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deglaciation of a soft bedded Laurentide Ice Sheet
Quaternary Science Reviews, 1998Co-Authors: Joseph M. Licciardi, Peter U. Clark, John W. Jenson, Douglas R MacayealAbstract:We present a series of numerical reconstructions of the Laurentide Ice Sheet during the last deglaciation (18–7 14C ka) that evaluates the sensitivity of Ice-Sheet geometry to subglacial sediment deformation. These reconstructions assume that the Laurentide Ice Sheet flowed over extensive areas of water-saturated, deforming sediment (soft beds) corresponding to the St. Lawrence lowland, the Great Lakes region, the western prairies of the U.S. and Canada, and the Hudson Bay and Hudson Strait regions. Sediment rheology is based on a constitutive law that incorporates experimental results from late Wisconsin till deposited by the Laurentide Ice Sheet which suggest only mildly nonlinear viscoplastic behavior. By varying the effective viscosity of till, we produced four reconstructions for the Ice Sheet during the last glacial maximum 18 14C ka, and two reconstructions each of the Ice Sheet at 14, 13, 12, 11 and 10 14C ka. We also produced one reconstruction for 9, 8.4, 8, and 7 14C ka. Reconstructions that assume a low effective viscosity for all areas of deforming sediment show a multidomed Ice Sheet with a large bowl-shaped depression over Hudson Bay and thin Ice (<1000 m above modern sea-level) over the western and southern margins. Those reconstructions that assume a higher effective viscosity of till in the Hudson Bay region than for the western and southern margins also show a multidomed Ice Sheet but with considerably thicker Ice over Hudson Bay and a more northerly position of the central Ice divide. These two different geometries may represent Ice-Sheet orographic changes associated with a Heinrich event. Further increases in effective viscosity of till, approaching the effective viscosity of Ice, would result in a high, monolithic Ice dome centered over Hudson Bay, reinforcing the notion that a multidomed Ice Sheet reflects the distribution of substrate geology. Modeled Ice-surface geometry at the last glacial maximum shows many of the same general features as previous reconstructions that incorporate deformable beds. Our reconstructions with higher effective till viscosities in Hudson Bay also agree with the Ice-4G reconstructions (Peltier, 1994), which are based on inversion of relative sea-level data, for the early part of the last deglaciation (18–13 14C ka), but then depart significantly from Ice-4G beginning at about 12 14C ka due to differing assumptions of the history of deglaciation. Modeled Ice volume for the last glacial maximum suggests a glacioeustatic change of 50–55 m by a soft-bedded Laurentide Ice Sheet; this would increase as the effective viscosity of till increases. Subsequent Ice-volume changes through the last deglaciation generally parallel the trend of eustatic rise recorded at Barbados, New Guinea, and Tahiti, but suggest that the Laurentide Ice Sheet was not the source of meltwater pulse 1A.
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Numerical reconstruction of a soft-bedded Laurentide Ice Sheet during the last glacial maximum
Geology, 1996Co-Authors: Peter U. Clark, Douglas R Macayeal, Joseph M. Licciardi, John W. JensonAbstract:We used a numerical Ice-Sheet model to reconstruct the North American Laurentide Ice Sheet during the last glacial maximum. Our model simulates Ice-Sheet conditions that can be specified experimentally as either a rigid substrate (hard bed) or a wet, deformable till (soft bed); basal sliding is excluded. We use geologic records of former basal Ice-Sheet processes to prescribe the distribution of hard and soft beds. Our reconstruction of the Laurentide Ice Sheet is significantly lower in Ice-surface height and contains less Ice volume than the CLIMAP (maximum) reconstruction. In contrast, our reconstruction agrees well with the Ice-4G reconstruction, both in height and volume. Because the Ice-4G reconstruction is based on the inversion of relative sea-level data, whereas our reconstruction is based on glacial geology and Ice mechanics, this agreement suggests that soft beds provide a glaciological mechanism to explain the shape and volume of the Laurentide Ice Sheet that is most consistent with observations of relative sea-level change and other geodynamic considerations.
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Ice rafted debris associated with binge purge oscillations of the Laurentide Ice Sheet
Paleoceanography, 1994Co-Authors: Richard B Alley, Douglas R MacayealAbstract:The North Atlantic sediment record suggests quasi-periodic (7000- to 12,000-year period) Ice-rafted debris (IRD) depositions during at least the last glacial period. The cause of these Heinrich events, as they are commonly known, is not fully understood; however, they may point to surges of the Ice stream that drained the Hudson Bay/Hudson Strait region of the Laurentide Ice Sheet. We investigate a simple conceptual model of Ice stream instability (the binge/purge model) to suggest ways in which the Ice stream could have entrained sufficient debris to account for the estimated mass of IRD associated with a typical Heinrich IRD layer in the North Atlantic (1.0 ± 0.3 × 1015 kg). We find that freezing of debris-laden Ice at the bed of the Ice stream during the brief (≈ 750 years) surge phase of the Ice stream's hypothesized binge/purge cycle can incorporate up to 5.1 × 1015 kg. This amount is sufficient to meet the constraints of the North Atlantic sediment record but by no means verifies the binge/purge model as the cause of Heinrich events.
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binge purge oscillations of the Laurentide Ice Sheet as a cause of the north atlantic s heinrich events
Paleoceanography, 1993Co-Authors: Douglas R MacayealAbstract:Ice-rafted debris in sediment cores from the North Atlantic suggests that the Laurentide Ice Sheet (LIS) periodically disgorged Icebergs in brief but violent episodes which occurred approximately every 7,000 years. Here, I propose that Heinrich events (i.e., what these episodes are called) were caused by free oscillations in the flow of the Laurentide Ice Sheet which arose because the floor of Hudson Bay and Hudson Strait is covered with soft, unconsolidated sediment that forms a slippery lubricant when thawed. The proposed Heinrich event cycle has two phases. The growth phase occurs when the sediment is frozen and the LIS is stranded (immobile) on a rigid bed. The volume of the LIS slowly grows during this phase at a rate dictated by snow accumulation. The purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway (i.e., an Ice stream such as those which occur in West Antarctica today) developes through Hudson Strait. The volume of the LIS rapidly equilibrates to the reduced basal friction during this phase by dumping Icebergs into the Labrador Sea. The periodicity T=π/κ(−kθsl2G∼)2≈7000 years of the proposed Heinrich event cycle is a function of the thermal conductivity and diffusivity of Ice, k and κ, respectively, the atmospheric sea level temperature θsl (in degrees Celsius), and the excess geothermal heat flux defined by G∼=G−kΓ where Γ is the atmospheric lapse rate, and G is the geothermal heat flux. Agreement between the predicted T and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism I propose. An alternative mechanism in which Heinrich events are forced by periodic variations in external climate is implausible, because periodic atmospheric temperature perturbations are strongly attenuated with depth in an Ice Sheet.