ice streams
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2022 ◽  
Author(s):  
Meghana Ranganathan ◽  
Jack-William Barotta ◽  
Colin Meyer ◽  
Brent Minchew

Liquid water within glacier ice and at the glacier beds exerts a significant control on ice flow and glacier stability through a number of processes, including altering the rheology of the ice and lubricating the bed. Some of this water is generated as melt in regions of rapid deformation, including shear margins, due to heating by viscous dissipation. However, how much meltwater is generated and drained from shear margins remains unclear. Here, we apply a model that describes the evolution of ice temperature, melting, and water transport within deforming ice to estimate the flux of meltwater from shear margins in glaciers. We derive analytical expressions for ice temperature, effective pressure, and porosity in zones of temperate ice, and we apply this model to estimate the flux from three Antarctic glaciers: Bindschadler and MacAyeal Ice Streams, Pine Island Glacier, and Byrd Glacier. We show that the flux of meltwater from shear margins in these regions may be as significant as the meltwater produced by frictional heating at the bed, with average fluxes of ~1000-2000 m^3 yr^ -1. This contribution of shear heating to meltwater flux at the bed may thus affect both the rheology of the ice as well as sliding at the bed, both key controls on fast ice flow.


2021 ◽  
Author(s):  
Lu Li ◽  
Alan Aitken ◽  
Mark Lindsay ◽  
Bernd Kulessa

Abstract Antarctica preserves Earth’s largest ice sheet which, in response to climate warming, may lose ice mass and raise sea level by several metres. The ice-sheet bed exerts critical controls on dynamic mass loss through feedbacks between water and heat fluxes, topographic forcing and basal sliding. Here we show that through hydrogeological processes, sedimentary basins amplify critical feedbacks that are known to impact ice-sheet retreat dynamics. We create a high-resolution subglacial bedrock classification for Antarctica by applying a supervised machine learning method to geophysical data, revealing the distribution of sedimentary basins. Sedimentary basins are found in the upper reaches of Antarctica’s most rapidly changing ice streams, including Thwaites and Pine Island Glaciers. Hydro-mechanical numerical modelling reveals that where sedimentary basins exist, water discharge rate scales with the rate of ice unloading and the resulting hydrological instabilities are likely to amplify further retreat and unloading. These results indicate that the presence of a sedimentary bed in the catchment focuses instabilities that increase the vulnerability of the ice streams to rapid retreat and enhanced dynamic mass loss.


2021 ◽  
pp. 1-15
Author(s):  
Francesca A. M. Falcini ◽  
Maarten Krabbendam ◽  
Katherine A. Selby ◽  
David M. Rippin

Abstract Palaeo-glacial landforms can give insights into bed roughness that currently cannot be captured underneath contemporary-ice streams. A few studies have measured bed roughness of palaeo-ice streams but the bed roughness of specific landform assemblages has not been assessed. If glacial landform assemblages have a characteristic bed-roughness signature, this could potentially be used to constrain where certain landform assemblages exist underneath contemporary-ice sheets. To test this, bed roughness was calculated along 5 m × 5 m resolution transects (NEXTMap DTM, 5 m resolution), which were placed over glacial landform assemblages (e.g. drumlins) in the UK. We find that a combination of total roughness and anisotropy of roughness can be used to define characteristic roughness signatures of glacial landform assemblages. The results show that different window sizes are required to determine the characteristic roughness for a wide range of landform types and to produce bed-roughness signatures of these. Mega scale glacial lineations on average have the lowest bed-roughness values and are the most anisotropic landform assemblage.


Author(s):  
Liana M. Agrios ◽  
Kathy J. Licht ◽  
Trevor Williams ◽  
Sidney R. Hemming ◽  
Lauren Welch ◽  
...  

Tills from moraines adjacent to major ice streams of the Weddell Sea Embayment contain distinct detrital zircon (n = 5304) and K-bearing mineral age populations (n = 323) that, when combined with pebble composition data, can be used to better understand Antarctica’s subglacial geology and ice sheet history. Till representing the Institute, Foundation, Academy, Recovery and Slessor Ice Streams each have distinct detrital zircon age populations. Detrital Ar-Ar ages are mostly younger than zircon ages, and distinctive populations include 270−300 Ma (Institute), 170−190 Ma (Foundation), and 1200−1400 Ma (Recovery), which are not easily explained by known outcrops. Pebble fractions of the Foundation and Academy tills are most diverse with up to >40% exotic erratics. The southern side of the Recovery Glacier has fossiliferous limestone erratics. Mixing models created using a nonlinear squares curve-fitting approach were developed to evaluate contributors of zircons to Foundation Ice Stream till. These model results and pebble lithology data both indicate that unexposed (subglacial) bedrock is mixed with exposed rocks to produce the observed till. Notably, the model required limited local Patuxent Formation input to the Foundation till’s zircon population. Our data suggest that sandstones underlie the Foundation Ice Stream and Recovery Glacier troughs, which has a bearing on basal ice flow conditions and results in geological controls on ice stream location. This geo- and thermo-chronological characterization of the ice streams will enable ice-rafted debris in Weddell Sea marine sediments to be traced back to its sources and interpreted in terms of ice stream dynamics.


2021 ◽  
pp. 1-12
Author(s):  
Hsien-Wang Ou

Abstract In Part 1, we have considered the dynamics of topographically confined glaciers, which may undergo surge cycles when the bed becomes temperate. In this Part 2, we consider the ice discharge over a flatbed, which would self-organize into alternating stream/ridge pairs of wet/frozen beds. The meltwater drainage, no longer curbed by the bed trough, would counter the conductive cooling to render a minimum bed strength at some intermediate width, toward which the stream would evolve over centennial timescale. At this stationary state, the stream width is roughly twice the geometric mean of the stream height and length, which is commensurate with its observed width. Over a flatbed, streams invariably interact, and we deduce that the neighboring ones would exhibit compensating cycles of maximum velocity and stagnation over the centennial timescale. This deduction is consistent with observed time variation of Ross ice streams B and C (ISB/C), which is thus a manifestation of the natural cycle. Moreover, the model uncovers an overlooked mechanism of the ISC stagnation: as ISB widens following its reactivation, it narrows ISC to augment the loss of the meltwater, leading to its stagnation. This stagnation is preceded by ice thickening hence opposite to the thinning-induced surge termination.


2021 ◽  
Vol 13 (10) ◽  
pp. 4635-4651
Author(s):  
Izabela Szuman ◽  
Jakub Z. Kalita ◽  
Marek W. Ewertowski ◽  
Chris D. Clark ◽  
Stephen J. Livingstone ◽  
...  

Abstract. Here we present a comprehensive dataset of glacial geomorphological features covering an area of 65 000 km2 in central west Poland, located along the southern sector of the last Scandinavian Ice Sheet, within the limits of the Baltic Ice Stream Complex. The GIS dataset is based on mapping from a 0.4 m high-resolution digital elevation model derived from airborne light detection and ranging data. Ten landform types have been mapped: mega-scale glacial lineations, drumlins, marginal features (moraine chains, abrupt margins, edges of ice-contact fans), ribbed moraines, tunnel valleys, eskers, geometrical ridge networks, and hill–hole pairs. The map comprises 5461 individual landforms or landform parts, which are available as vector layers in GeoPackage format at https://doi.org/10.5281/zenodo.4570570 (Szuman et al., 2021a). These features constitute a valuable data source for reconstructing and modelling the last Scandinavian Ice Sheet extent and dynamics from the Middle Weichselian Scandinavian Ice Sheet advance, 50–30 ka, through the Last Glacial Maximum, 25–21 ka, and Young Baltic advances, 18–15 ka. The presented data are particularly useful for modellers, geomorphologists, and glaciologists.


Geomorphology ◽  
2021 ◽  
pp. 108009
Author(s):  
Ívar Örn Benediktsson ◽  
Nína Aradóttir ◽  
Ólafur Ingólfsson ◽  
Skafti Brynjólfsson

2021 ◽  
Author(s):  
Liana Marie Agrios ◽  
Kathy J. Licht ◽  
et al.

Description of rock samples chosen for U-Pb analysis, along with U-Pb and Ar-Ar data tables.


2021 ◽  
Author(s):  
Liana Marie Agrios ◽  
Kathy J. Licht ◽  
et al.

Description of rock samples chosen for U-Pb analysis, along with U-Pb and Ar-Ar data tables.


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