Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum

Stokes, Chris R.

doi:10.18172/cig.3237

Cited by 40 publications

(43 citation statements)

References 240 publications

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“…Giant glacial grooves and other highly elongate landforms had been reported several decades earlier (Smith, 1948;Dean, 1953), but not explicitly linked to ice streaming, which is not surprising given that ice streams had yet to be fully recognised in modern ice sheets (see sections 'The discovery and definition of ice streams' and 'West Antarctic ice streams and "Glaciology's Grand Unsolved Denton and Hughes (1981) hypothesised location of ice streams in the northern hemisphere ice sheets (from Stokes and Clark, 2001). Although largely based on topographic inference and some notion of spatial self-organisation, many of these ice stream locations have since been confirmed in recent inventories derived from detailed mapping of ice stream beds, such as the Laurentide Ice Sheet (Margold et al, 2015a), which is shown in (b), and taken from Stokes (2017).…”

Section: Giant Glacial Grooves and Mega-scale Glacial Lineationsmentioning

confidence: 97%

“…(a) Denton and Hughes () hypothesised location of ice streams in the northern hemisphere ice sheets (from Stokes and Clark, ). Although largely based on topographic inference and some notion of spatial self‐organisation, many of these ice stream locations have since been confirmed in recent inventories derived from detailed mapping of ice stream beds, such as the Laurentide Ice Sheet (Margold et al ., ), which is shown in (b), and taken from Stokes (). [Colour figure can be viewed at wileyonlinelibrary.com]…”

Section: Identification and Characterisation Of The Beds Of Palaeo Icmentioning

confidence: 99%

“…However, these results were strongly dependent on the choice of parameters selected. The appeal of this mechanism is that it can simulate the regularity and spatial organisation of MSGLs (Spagnolo et al, 2014;2017). Moreover, this process has since been incorporated into a more sophisticated treatment that combines both fluvial sediment transport and the coupled flow of ice and sediment to produce a continuum of ribbed moraine, drumlins and MSGLs (Fowler and Chapwanya, 2014).…”

Section: Future Challenges and Opportunities: Moving From Form To Promentioning

confidence: 99%

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Geomorphology under ice streams: Moving from form to process

Stokes

2017

Earth Surf Processes Landf

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Ice streams are integral components of an ice sheet's mass balance and directly impact on sea level. Their flow is governed by processes at the ice-bed interface which create landforms that, in turn, modulate ice stream dynamics through their influence on bed topography and basal shear stresses. Thus, ice stream geomorphology is critical to understanding and modelling ice streams and ice sheet dynamics. This paper reviews developments in our understanding of ice stream geomorphology from a historical perspective, with a focus on the extent to which studies of modern and palaeo-ice streams have converged to take us from a position of near-complete ignorance to a detailed understanding of their bed morphology. During the 1970s and 1980s, our knowledge was limited and largely gleaned from geophysical investigations of modern ice stream beds in Antarctica. Very few palaeo-ice streams had been identified with any confidence. During the 1990s, however, glacial geomorphologists began to recognise their distinctive geomorphology, which included distinct patterns of highly elongated mega-scale glacial lineations, ice stream shear margin moraines, and major sedimentary depocentres. However, studying relict features could say little about the time-scales over which this geomorphology evolved and under what glaciological conditions. This began to be addressed in the early 2000s, through continued efforts to scrutinise modern ice stream beds at higher resolution, but our current understanding of how landforms relate to processes remains subject to large uncertainties, particularly in relation to the mechanisms and time-scales of sediment erosion, transport and deposition, and how these lead to the growth and decay of subglacial bedforms. This represents the next key challenge and will require even closer cooperation between glaciology, glacial geomorphology, sedimentology, and numerical modelling, together with more sophisticated methods to quantify and analyse the anticipated growth of geomorphological data from beneath active ice streams.

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Section: Giant Glacial Grooves and Mega-scale Glacial Lineationsmentioning

confidence: 97%

Section: Identification and Characterisation Of The Beds Of Palaeo Icmentioning

confidence: 99%

Section: Future Challenges and Opportunities: Moving From Form To Promentioning

confidence: 99%

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Geomorphology under ice streams: Moving from form to process

Stokes

2017

Earth Surf Processes Landf

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“…; Stroeven et al . ; Stokes ). In this context, knowledge of the temporal evolution of the Icelandic ice sheet (IIS) is of particular importance to understand the climatic interconnections between the Greenland and Eurasian ice sheets and the potential spatio‐temporal variability across the northern North Atlantic.…”

mentioning

confidence: 99%

“…; Palacios et al . ; Stokes ); however, it is still rarely applied to improve deglaciated surface studies in Iceland (Principato et al . ; Brynjólfsson et al .…”

mentioning

confidence: 99%

The rapid deglaciation of the Skagafjörður fjord, northern Iceland

Andrés

Palacios

Sæmundsson

et al. 2018

Boreas

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The Skagafjörður fjord in northern Iceland is located between the Tröllaskagi Peninsula in the east and the Skagi Peninsula in the west. The tributary valleys of the fjord originate in the highland area about 15 km north of the Hofsjökull icecap. The results of this work improve the knowledge of the deglaciation pattern in Skagafjörður and explore the adequacy of the 36Cl cosmic ray exposure dating method in an Icelandic environment, where this method has rarely been applied to deglaciated surfaces. The 36Cl dating method was applied to 13 rock samples taken on a transect from the coastal areas towards the highlands. All samples were obtained from rock outcrops with glacier‐polished surfaces from the Last Glaciation and from one of the few well‐preserved erratic boulders. The cosmogenic results, combined with previous radiocarbon results, indicate that the ice margin was situated in the outermost sector of Skagafjörður at approximately 17–15 ka BP. Subsequently, it retreated and occupied the central part of the fjord between 15 and 12 ka BP and then the innermost sector of the fjord about 11 ka BP. The samples collected between this position and the highlands show an average age of approximately 11 ka, indicating rapid deglaciation after the early Preboreal. These results agree with earlier studies of the deglaciation history of northern Iceland, reinforce previous deglaciation models in the area and enable a better understanding of glacial evolution in the North Atlantic from the Late Pleistocene to Holocene transition.

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Long-wavelength gravity field constraint on the lower mantle viscosity in North America

Reusen

Root

Szwillus

et al. 2020

Preprint

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The long-wavelength negative gravity anomaly over Hudson Bay coincides with the area depressed by the Laurentide Ice Sheet during the Last Glacial Maximum, suggesting that it is, at least partly, caused by glacial isostatic adjustment (GIA). Additional contributions to the static gravity field stem from surface dynamic topography, core-mantle boundary (CMB) topography, and density anomalies in the subsurface. Previous estimates of the contribution of GIA to the gravity anomaly range from 25% to more than 80%. However, these estimates did not include uncertainties in all components that contribute to the gravity field. In this study, we develop a forward model for the gravity anomaly based on density models and dynamic models, investigating uncertainty in all components. We derive lithospheric densities from equilibrium constraints but extend the concept of lithospheric isostasy to a force balance that includes the dynamic models. The largest uncertainty in the predicted gravity anomaly is due to the lower mantle viscosity, uncertainties in the ice history, the crustal model, the lithosphere-asthenosphere boundary, and the conversion from seismic velocities to density have a smaller effect. A preference for lower mantle viscosities >10 22 Pa s is found, in which case at least 60% of the observed long-wavelength gravity anomaly can be attributed to GIA. This lower bound on the lower mantle viscosity has implications for inferences based on models for mantle convection and GIA.Plain Language Summary About 26,000 years ago, vast parts of North America and Northern Europe were covered by ice sheets. These glaciations depressed the ground, which is rebounding ever since the ice sheets started melting. The rate of this rebound depends on the structure of the earth below it. In this paper, we obtain more insight into the structure of the earth. To do so, we use the gravitational field since we can observe small deviations in this field very precisely. Over Hudson Bay, we observe such a deviation. The observed gravity anomaly over Hudson Bay closely resembles the area previously covered by ice. One possible explanation for this anomaly is therefore the incomplete rebound of the land. To test this, we include the effects of previous glaciations and mantle flow in a model of the crust and the lithosphere. We vary the viscosities of the upper and lower mantle, which are important parameters when modeling glacial rebound and mantle flow. The best match is found for a stiff lower mantle, implying that at least 200 m of land uplift remains and that a minimum of 60% of this anomaly can be attributed to the depression caused by past glaciations.

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Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum

Cited by 40 publications

References 240 publications

Geomorphology under ice streams: Moving from form to process

Geomorphology under ice streams: Moving from form to process

The rapid deglaciation of the Skagafjörður fjord, northern Iceland

Long-wavelength gravity field constraint on the lower mantle viscosity in North America

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