Lake Store Finnsjøen – a key for understanding Lateglacial/early Holocene vegetation and ice sheet dynamics in the central Scandes Mountains

Antarctic ice streams are associated with pressurized subglacial meltwater but the role this water plays in the dynamics of the streams is not known. To address this, we present a model of subglacial water flow below ice sheets, and particularly below ice streams. The base-level flow is fed by subglacial melting and is presumed to take the form of a rough-bedded film, in which the ice is supported by larger clasts, but there is a millimetric water film which submerges the smaller particles. A model for the film is given by two coupled partial differential equations, representing mass conservation of water and ice closure. We assume that there is no sediment transport and solve for water film depth and effective pressure. This is coupled to a vertically integrated, higher order model for ice-sheet dynamics. If there is a sufficiently small amount of meltwater produced (e.g. if ice flux is low), the distributed film and ice sheet are stable, whereas for larger amounts of melt the ice–water system can become unstable, and ice streams form spontaneously as a consequence. We show that this can be explained in terms of a multi-valued sliding law, which arises from a simplified, one-dimensional analysis of the coupled model.

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Greenland land-terminating glaciers velocity trends during the last two decades

10.5194/egusphere-egu21-2084 ◽

2021 ◽

Author(s):

Paul Halas ◽

Jeremie Mouginot ◽

Basile de Fleurian ◽

Petra Langebroek

Keyword(s):

Water Pressure ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Melting ◽

Limited Area ◽

Ice Dynamics ◽

Basal Sliding ◽

Surface Melt ◽

Ice Sheet Dynamics ◽

The Impact

<div> <p>Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise.&#160;Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding.&#160;The sliding component&#160;of glaciers has been observed to be strongly related to surface melting, as water&#160;can eventually&#160;reach the bed and impact&#160;the subglacial water pressure, affecting the basal sliding.&#160;&#160;</p> </div><div> <p>The link between ice velocities and surface melt on multi-annual time scale is still not totally understood&#160;even though it&#160;is of major importance with expected increasing surface melting.&#160;Several studies showed&#160;some&#160;correlation between an increase in surface melt and a slowdown in&#160;velocities, but&#160;there is no&#160;consensus&#160;on those trends.&#160;Moreover&#160;those&#160;investigations&#160;only&#160;presented results&#160;in a limited area over&#160;Southwest&#160;Greenland.&#160;&#160;</p> </div><div> <p>Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.&#160;&#160;</p> </div><div> <p>Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration.&#160;This trend however does not seem to be observed on the whole ice sheet and is probably&#160;specific&#160;to&#160;this region&#8217;s&#160;climate forcing.&#160;</p> </div><div> <p>Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.</p> </div>

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Implications for the lithospheric structure of Greenland by applying different heat flow models

10.5194/egusphere-egu21-10689 ◽

2021 ◽

Author(s):

Agnes Wansing ◽

Jörg Ebbing ◽

Mareen Lösing ◽

Sergei Lebedev ◽

Nicolas Celli ◽

...

Keyword(s):

Heat Flow ◽

Heat Dissipation ◽

Ice Sheet ◽

Magnetic Data ◽

Similarity Function ◽

Lithospheric Structure ◽

Temperature Structure ◽

Geothermal Heat ◽

Flow Models ◽

Ice Sheet Dynamics

<p>The lithospheric structure of Greenland is still poorly known due to its thick ice sheet, the sparseness of seismological stations, and the limitation of geological outcrops near coastal areas. As only a few geothermal measurements are available for Greenland, one must rely on geophysical models. Such models of Moho and LAB depths and sub-ice geothermal heat-flow vary largely.</p><p>Our approach is to model the lithospheric architecture by geophysical-petrological modelling with LitMod3D. The model is built to reproduce gravity observations, the observed elevation with isostasy assumptions and the velocities from a tomography model. Furthermore, we adjust the thermal parameters and the temperature structure of the model to agree with different geothermal heat flow models. We use three different heat flow models, one from machine learning, one from a spectral analysis of magnetic data and another one which is compiled from a similarity study with tomography data.</p><p>For the latter, a new shear wave tomography model of Greenland is used. Vs-depth profiles from Greenland are compared with velocity profiles from the US Array, where a statistical link between Vs profiles and surface heat flow has been established. A similarity function determines the most similar areas in the U.S. and assigns the mean heat-flow from these areas to the corresponding area in Greenland.</p><p>The geothermal heat flow models will be further used to discuss the influence on ice sheet dynamics by comparison to friction heat and viscous heat dissipation from surface meltwater.</p>

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SHaKTI: Subglacial Hydrology and Kinetic Transient Interactions v1.0

10.5194/gmd-2018-58 ◽

2018 ◽

Author(s):

Aleah Sommers ◽

Harihar Rajaram ◽

Mathieu Morlighem

Keyword(s):

Water Pressure ◽

Ice Sheet ◽

Governing Equations ◽

Model Formulation ◽

Seasonal Behavior ◽

Wide Transition ◽

Transient Interactions ◽

Ice Sheet Dynamics ◽

Hydrology Modeling ◽

Single Set

Abstract. Subglacial hydrology has a significant influence on ice sheet dynamics, yet remains poorly understood. Complex feedbacks play out between the liquid water and the ice, with constantly changing drainage geometry and flow mechanics. A clear tradition has been established in the subglacial hydrology modeling literature of distinguishing between channelized (efficient) and distributed (inefficient) drainage systems or components. Imposing a distinction that changes the governing physics under different flow regimes, however, may not allow for the full array of drainage characteristics to arise. Here, we present a new subglacial hydrology model: SHaKTI (Subglacial Hydrology and Kinetic Transient Interactions). In this model formulation, a single set of governing equations is applied over the entire domain, with a spatially and temporally varying transmissivity that allows for representation of the wide transition between turbulent and laminar flow, and the geometry of each element is allowed to evolve accordingly to form sheet and channel configurations. The model is implemented as a solution in the Ice Sheet System Model (ISSM). We include steady and transient examples to demonstrate features and capabilities of the model, and we are able to reproduce seasonal behavior of the subglacial water pressure that is consistent with observed seasonal velocity behavior in many Greenland outlet glaciers, supporting the notion that subglacial hydrology may be a key influencer in shaping these patterns.

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The Holocene thermal maximum in the Nordic Seas: the impact of Greenland Ice Sheet melt and other forcings in a coupled atmosphere–sea-ice–ocean model

Climate of the Past ◽

10.5194/cp-9-1629-2013 ◽

2013 ◽

Vol 9 (4) ◽

pp. 1629-1643 ◽

Cited By ~ 23

Author(s):

M. Blaschek ◽

H. Renssen

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

Early Holocene ◽

Surface Cooling ◽

Holocene Climate ◽

Nordic Seas ◽

The Holocene ◽

Holocene Thermal Maximum ◽

Thermal Maximum ◽

The Impact

Abstract. The relatively warm early Holocene climate in the Nordic Seas, known as the Holocene thermal maximum (HTM), is often associated with an orbitally forced summer insolation maximum at 10 ka BP. The spatial and temporal response recorded in proxy data in the North Atlantic and the Nordic Seas reveals a complex interaction of mechanisms active in the HTM. Previous studies have investigated the impact of the Laurentide Ice Sheet (LIS), as a remnant from the previous glacial period, altering climate conditions with a continuous supply of melt water to the Labrador Sea and adjacent seas and with a downwind cooling effect from the remnant LIS. In our present work we extend this approach by investigating the impact of the Greenland Ice Sheet (GIS) on the early Holocene climate and the HTM. Reconstructions suggest melt rates of 13 mSv for 9 ka BP, which result in our model in an ocean surface cooling of up to 2 K near Greenland. Reconstructed summer SST gradients agree best with our simulation including GIS melt, confirming that the impact of the early Holocene GIS is crucial for understanding the HTM characteristics in the Nordic Seas area. This implies that modern and near-future GIS melt can be expected to play an active role in the climate system in the centuries to come.

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Marine ice sheet experiments with the Community Ice Sheet Model

The Cryosphere ◽

10.5194/tc-15-3229-2021 ◽

2021 ◽

Vol 15 (7) ◽

pp. 3229-3253

Author(s):

Gunter R. Leguy ◽

William H. Lipscomb ◽

Xylar S. Asay-Davis

Keyword(s):

Ice Sheet ◽

Ice Flow ◽

Friction Law ◽

Friction Laws ◽

Basal Friction ◽

Grounding Line ◽

Hydrological System ◽

Flow Approximation ◽

Intercomparison Project ◽

Ice Sheet Dynamics

Abstract. Ice sheet models differ in their numerical treatment of dynamical processes. Simulations of marine-based ice are sensitive to the choice of Stokes flow approximation and basal friction law and to the treatment of stresses and melt rates near the grounding line. We study the effects of these numerical choices on marine ice sheet dynamics in the Community Ice Sheet Model (CISM). In the framework of the Marine Ice Sheet Model Intercomparison Project 3d (MISMIP3d), we show that a depth-integrated, higher-order solver gives results similar to a 3D (Blatter–Pattyn) solver. We confirm that using a grounding line parameterization to approximate stresses in the grounding zone leads to accurate representation of ice sheet flow with a resolution of ∼2 km, as opposed to ∼0.5 km without the parameterization. In the MISMIP+ experimental framework, we compare different treatments of sub-shelf melting near the grounding line. In contrast to recent studies arguing that melting should not be applied in partly grounded cells, it is usually beneficial in CISM simulations to apply some melting in these cells. This suggests that the optimal treatment of melting near the grounding line can depend on ice sheet geometry, forcing, or model numerics. In both experimental frameworks, ice flow is sensitive to the choice of basal friction law. To study this sensitivity, we evaluate friction laws that vary the connectivity between the basal hydrological system and the ocean near the grounding line. CISM yields accurate results in steady-state and perturbation experiments at a resolution of ∼2 km (arguably 4 km) when the connectivity is low or moderate and ∼1 km (arguably 2 km) when the connectivity is strong.

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The Cordilleran Ice Sheet: One Hundred and Fifty Years of Exploration and Discovery

Géographie physique et Quaternaire ◽

10.7202/032874ar ◽

2007 ◽

Vol 45 (3) ◽

pp. 269-280 ◽

Cited By ~ 13

Author(s):

Lionel E. Jackson, ◽

John J. Clague

Keyword(s):

World War Ii ◽

Research Effort ◽

Ice Sheet ◽

Early Period ◽

Transitional Period ◽

Marine Geology ◽

Ice Sheet Dynamics ◽

Cordilleran Ice Sheet ◽

Regional Fluctuations ◽

Glacial Landforms

ABSTRACT Present concepts about the Cordilleran Ice Sheet are the product of observations and ideas of several generations of earth scientists. The limits of glaciation in the Cordillera were established in the last half of the nineteenth century by explorers and naturalists, notably G. M. Dawson, R. G. McConnell, and T. C. Chamberlin. By the turn of the century, the gross configuration of the Cordilleran Ice Sheet had been determined, but the causes of glaciation and ice-sheet dynamics remained poorly understood. This early period of exploration and discovery was followed by a transitional period, from about 1900 to 1950, during which a variety of glacial landforms and deposits were explained (e.g., Channeled Scablands of Washington; "white silts" of southern British Columbia), and conceptual models of the growth and decay of the ice sheet were proposed. Shortly after World War II, there was a dramatic increase in research into all aspects of glaciation in the Canadian Cordillera which has continued unabated to the present. Part of the research effort during this period has been directed at resolving the Cordilleran Ice Sheet in both time and space. Local and regional fluctuations of the ice sheet have been reconstructed through stratigraphie and sedimentological studies, supported by radiocarbon and other dating techniques. Compilations of late Pleistocene ice-flow directions have shown that the Cordilleran Ice Sheet was a mass of coalescent glaciers flowing in a complex fashion from many montane source areas. During the postwar period, research has also begun or advanced significantly in several other disciplines, notably glaciology, process sedimen-tology, geomorphology, paleoecology, and marine geology. Attempts are now being made to quantitatively model the Cordilleran Ice Sheet using computers and the geological database assembled by past generations of earth scientists.

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