scholarly journals Strain-induced phase changes within cold basal ice from Taylor Glacier, Antarctica, indicated by textural and gas analyses

2005 ◽  
Vol 51 (175) ◽  
pp. 611-619 ◽  
Author(s):  
Denis Samyn ◽  
Sean J. Fitzsimons ◽  
Reginald D. Lorrain
Keyword(s):  
Thermal Conditions ◽  
Significant Loss ◽  
Phase Changes ◽  
Ductile Deformation ◽  
Geochemical Evolution ◽  
Gas Composition ◽  
Outlet Glacier ◽  
Basal Ice ◽  
Gas Measurements ◽  
Taylor Glacier

AbstractThis paper reports detailed textural and gas measurements conducted in cold basal ice (–17°C from the margin of Taylor Glacier, an outlet glacier of the East Antarctic ice sheet. The analyzed samples were retrieved from a basal ice sequence excavated at the end of a subglacial tunnel dug near the glacier snout. The basal sequence exhibits two contrasting ice facies, defined as the englacial and stratified facies. On the one hand, analysis of ice crystal textures from the basal ice sequence provides evidence for localized ductile deformation, especially within the stratified facies where significant dynamic recrystallization was detected. On the other hand, high-resolution gas analyses reveal that strong changes in gas composition occurred at the structural interfaces of the stratified facies. These gas composition changes are typical of melting–refreezing processes but are not associated with any significant loss of gas volume. Given the specific subglacial thermal conditions at the margin of Taylor Glacier, we interpret this phenomenon as resulting from microscopic phase changes involving selective gas redistribution through the pre-melt phase. It is argued that such processes may play an important role in the post-genetic geochemical evolution of cold debris-laden ice and may be enhanced through intense strain conditions.

scholarly journals Influence of debris-rich basal ice on flow of a polar glacier

2014 ◽  
Vol 60 (223) ◽  
pp. 989-1006 ◽  
Author(s):  
Erin C. Pettit ◽  
Erin N. Whorton ◽  
Edwin D. Waddington ◽  
Ronald S. Sletten
Keyword(s):  
Low Temperatures ◽  
Ablation Rate ◽  
Surface Velocity ◽  
Inverse Theory ◽  
Limited Data ◽  
Outlet Glacier ◽  
Basal Ice ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Taylor Glacier

AbstractAt Taylor Glacier, a cold-based outlet glacier of the East Antarctic ice sheet, observed surface speeds in the terminus region are 20 times greater than those predicted using Glen’s flow law for cold (–17°C), thin (100 m) ice. Rheological properties of the clean meteoric glacier ice and the underlying deformable debris-rich basal ice can be inferred from surface-velocity and ablation-rate profiles using inverse theory. Here, with limited data, we use a two-layer flowband model to examine two end-member assumptions about the basal-ice properties: (1) uniform softness with spatially variable thickness and (2) uniform thickness with spatially variable softness. We find that the basal ice contributes 85–98% to the observed surface velocity in the terminus region. We also find that the basal-ice layer must be 10–15 m thick and 20–40 times softer than clean Holocene-age glacier ice in order to match the observations. Because significant deformation occurs in the basal ice, our inverse problem is not sensitive to variations in the softness of the meteoric ice. Our results suggest that despite low temperatures, highly deformable basal ice may dominate flow of cold-based glaciers and rheologically distinct layers should be incorporated in models of polar-glacier flow.

scholarly journals Discharge of debris from ice at the margin of the Greenland ice sheet

2002 ◽  
Vol 48 (161) ◽  
pp. 192-198 ◽  
Author(s):  
Peter G. Knight ◽  
Richard I. Waller ◽  
Carrie J. Patterson ◽  
Alison P. Jones ◽  
Zoe P. Robinson
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Rate ◽  
Outlet Glacier ◽  
Tidewater Glaciers ◽  
Sediment Production ◽  
Basal Ice ◽  
Order Of Magnitude ◽  
Sediment Transfer ◽  
A Minor

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

scholarly journals Numerical modelling of a fast-flowing outlet glacier: experiments with different basal conditions

1996 ◽  
Vol 23 ◽  
pp. 237-246 ◽  
Author(s):  
Frank Pattyn
Keyword(s):  
Deformation Process ◽  
Drainage Basin ◽  
Ice Sheet ◽  
Outlet Glacier ◽  
Transient Behaviour ◽  
Cyclic Behaviour ◽  
System A ◽  
Basal Ice ◽  
Equal Importance ◽  
Fully Coupled

Recent observations in Shirase Drainage Basin. Enderby Land, Antarctica, show that the ice sheet is thinning at the considerable rate of 0.5–1.0 m a −1. Surface velocities in the stream area reach more than 2000 ma−1, making Shirase Glacier one of the fastest-flowing glaciers in East Antarctica. A numerical investigation of the present stress field in Shirase Glacier shows the existence of a large transition zone 200 km in length where both shearing and stretching are of equal importance, followed by a stream zone of approximately 50 km, where stretching is the major deformation process.In order to improve insight into the present transient behaviour of the ice-sheet system, a two-dimensional time-dependent flowline model has been developed, taking into account the ice-stream mechanics. Both bedrock adjustment and ice temperature are taken into account and the temperature field is fully coupled to the ice-sheet velocity field.Experiments were carried out with different basal motion conditions in order to understand their influence on the dynamic behaviour of the ice sheet and the stream area in particular. Results revealed that when basal motion becomes the dominant deformation process, (partial) disintegration of the ice sheet is counteracted by colder basal-ice temperatures due to higher advection rates. This gives rise to a cyclic behaviour in ice-sheets response and large changes in local imbalance values.

scholarly journals Thermal conditions at the bed of the Laurentide ice sheet in Maine during deglaciation: implications for esker formation

2007 ◽  
Vol 53 (183) ◽  
pp. 646-658 ◽  
Author(s):  
Roger LeB. Hooke ◽  
James Fastook
Keyword(s):  
Ice Sheet ◽  
Drainage System ◽  
Thermal Conditions ◽  
Temperature Gradients ◽  
Laurentide Ice Sheet ◽  
Glacier Surface ◽  
Basal Ice ◽  
Viscous Heat ◽  
Additional Water ◽  
The University

The University of Maine Ice Sheet Model was used to study basal conditions during retreat of the Laurentide ice sheet in Maine. Within 150 km of the margin, basal melt rates average ∼5 mm a−1 during retreat. They decline over the next 100 km, so areas of frozen bed develop in northern Maine during retreat. By integrating the melt rate over the drainage area typically subtended by an esker, we obtained a discharge at the margin of ~1.2 m3 s-1. While such a discharge could have moved the material in the Katahdin esker, it was likely too low to build the esker in the time available. Additional water from the glacier surface was required. Temperature gradients in the basal ice increase rapidly with distance from the margin. By conducting upward into the ice all of the additional viscous heat produced by any perturbation that increases the depth of flow in a flat conduit in a distributed drainage system, these gradients inhibit the formation of sharply arched conduits in which an esker can form. This may explain why eskers commonly seem to form near the margin and are typically segmented, with later segments overlapping onto earlier ones.

Thermal and Optical Analysis of a Stacked Photobioreactor Design

2013 ◽  
Author(s):  
Aadhar Jain ◽  
Erica E. Jung ◽  
Michael Kalontarov ◽  
David Erickson
Keyword(s):  
Thermal Characteristics ◽  
Thermal Conditions ◽  
Close Packing ◽  
Significant Loss ◽  
Design Parameters ◽  
Optical Analysis ◽  
Optimal Range ◽  
Slab Waveguides ◽  
Localized Delivery ◽  
Photobioreactor Design

In this work, we present thermal and optical analysis of a stacked photobioreactor design for growth of fuel producing photosynthetic cyanobacteria to achieve significantly higher volume and energy efficiency as compared to traditional photobioreactor designs. Our photobioreactor design incorporates racks of propagating slab waveguides [1], stacked over each other with spacing of a few hundred microns, in order to optimize light, fluid and gas delivery — the three essential ingredients for cyanobacterial growth — to the cyanobacteria growing in between the racks. The use of propagating slab waveguides provides a mechanism for efficient localized delivery of light to the cyanobacteria. However, it is important to analyze the light distribution of such waveguide systems in the photobioreactors to ensure they always remain within the optimal range for the bacteria. Further, the close packing of cyanobacteria in a closed system raises concerns regarding heat entrapment within the reactor, due to the heat produced as waste by the cyanobacteria. Higher temperatures can lead to a significant loss in efficiency in fuel producing and growth centers of the bacteria. Therefore it is important to design the reactor with appropriate thermal conditions for constraining the temperatures within optimal range for the bacteria. Here we attempt to simulate the thermal characteristics of such a system and estimate the temperature map of the system, and use these to dictate the design parameters and characteristics of the photobioreactor.

scholarly journals An englacial hydrologic system of brine within a cold glacier: Blood Falls, McMurdo Dry Valleys, Antarctica

2017 ◽  
Vol 63 (239) ◽  
pp. 387-400 ◽  
Author(s):  
JESSICA A. BADGELEY ◽  
ERIN C. PETTIT ◽  
CHRISTINA G. CARR ◽  
SLAWEK TULACZYK ◽  
JILL A. MIKUCKI ◽  
...  
Keyword(s):  
Latent Heat ◽  
Flow Direction ◽  
Salt Content ◽  
Mcmurdo Dry Valleys ◽  
Dry Valleys ◽  
Outlet Glacier ◽  
Air Temperatures ◽  
Radio Echo Sounding ◽  
Hydrologic System ◽  
Taylor Glacier

ABSTRACTTaylor Glacier hosts an active englacial hydrologic system that feeds Blood Falls, a supraglacial outflow of iron-rich subglacial brine at the terminus, despite mean annual air temperatures of −17°C and limited surface melt. Taylor Glacier is an outlet glacier of the East Antarctic ice sheet that terminates in Lake Bonney, McMurdo Dry Valleys. To image and map the brine feeding Blood Falls, we used radio echo sounding to delineate a subhorizontal zone of englacial brine upstream from Blood Falls and elongated in the ice flow direction. We estimate volumetric brine content in excess of 13% within 2 m of the central axis of this zone, and likely much higher at its center. Brine content decreases, but remains detectable, up to 45 m away along some transects. Hence, we infer a network of subparallel basal crevasses allowing injection of pressurized subglacial brine into the ice. Subglacial brine is routed towards Blood Falls by hydraulic potential gradients associated with deeply incised supraglacial valleys. The brine remains liquid within the subglacial and englacial environments through latent heat of freezing coupled with elevated salt content. Our findings suggest that cold glaciers could support freshwater hydrologic systems through localized warming by latent heat alone.

scholarly journals Buried ice in Kennar Valley: a late Pleistocene remnant of Taylor Glacier

2017 ◽  
Vol 29 (3) ◽  
pp. 239-251 ◽  
Author(s):  
Kate M. Swanger
Keyword(s):  
Late Pleistocene ◽  
Ice Cores ◽  
Dry Valleys ◽  
Patterned Ground ◽  
Outlet Glacier ◽  
Air Bubble ◽  
Isotopic Analyses ◽  
Stable Isotopic ◽  
Glacier Ice ◽  
Taylor Glacier

AbstractBuried glacier ice is common in the McMurdo Dry Valleys and under ideal climatic and geomorphological conditions may be preserved for multimillion-year timescales. This study focuses on the analysis of ~300 m2 of buried glacier ice in lower Kennar Valley, Quartermain Range. The mapped ice is clean,<10 m thick and covered by a~25 cm sandy drift. The mouth of Kennar Valley is occupied by a lobe of Taylor Glacier, an outlet glacier from Taylor Dome. Based on ice–sediment characteristics, air bubble concentrations and stable isotopic analyses from three ice cores, the lower Kennar Valley ice is glacial in origin. These data coupled with a previously reported exposure age chronology indicate that the buried ice was deposited by a late Pleistocene advance of Taylor Glacier, probably during an interglacial interval. The surface of the buried glacier ice exhibits a patterned ground morphology characterized by small, dome-shaped polygons with deep troughs. This shape possibly reflects the final stages of ice loss, as stagnant, isolated ice pinnacles sublimate in place. This study highlights how polygon morphology can be used to infer the thickness of clean buried ice and its geomorphological stability throughout Antarctica, as well as other in cold, arid landscapes.

scholarly journals Draft Genome Sequence of Paenisporosarcina sp. Strain TG-20, a Psychrophilic Bacterium Isolated from the Basal Ice of Taylor Glacier

2012 ◽  
Vol 194 (23) ◽  
pp. 6636-6636
Author(s):  
Jun Hyuck Lee ◽  
Hye Yeon Koh ◽  
Sung Gu Lee ◽  
Shawn Doyle ◽  
Brent C. Christner ◽  
...  
Keyword(s):  
Genome Sequence ◽  
Draft Genome ◽  
Draft Genome Sequence ◽  
Psychrophilic Bacterium ◽  
Protein Coding ◽  
Content Type ◽  
Basal Ice ◽  
Subsurface Environments ◽  
Taylor Glacier ◽  
Rna Genes

ABSTRACTWe report the draft genome sequence ofPaenisporosarcinasp. strain TG-20, which is 4.12 Mb in size and consists of 4,071 protein-coding genes and 76 RNA genes. The genome sequence ofPaenisporosarcinasp. TG-20 may provide useful information about molecular adaptations that enhance survival in icy subsurface environments.

Early Palaeozoic intracratonic shears and post-tectonic cooling in the Rauer Group, Prydz Bay, East Antarctica constrained by40Ar/39Ar thermochronology

2007 ◽  
Vol 19 (3) ◽  
pp. 339-353 ◽  
Author(s):  
Christopher J.L. Wilson ◽  
Cameron Quinn ◽  
Laixi Tong ◽  
David Phillips
Keyword(s):  
Structural Evolution ◽  
Thermal Conditions ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Prydz Bay ◽  
Cooling Rates ◽  
Deformation Event ◽  
Thermal Histories ◽  
Early Palaeozoic ◽  
Field Variability

AbstractThe Rauer Group, in Prydz Bay, contains reworked Archaean-Proterozoic crust in high-strain zones that formed during a pervasive high-temperature ductile deformation event related to intracratonic mechanisms. The effects of this event extend southwards from Prydz Bay into the southern Prince Charles Mountains. The associated structural evolution involved development of ductile and brittle structures that formed during an approximately north–south directed transpressional deformation event that is confined to high-grade (>800°C) shear zones in the Rauer Group. Minerals from the Rauer Group, yield40Ar/39Ar cooling ages ranging from 560 to 460 Ma. Thermal histories derived from hornblende, biotite and feldspar suggest that the onset of rapid cooling began sometime prior to 510 Ma with cooling rates ofc. 42 to 33°C myr-1fromc. 510 Ma toc. 500 Ma. Whereas,40Ar/39Ar data obtained from plagioclase and K–feldspar suggest a slower cooling fromc. 500 Ma toc. 460 Ma with cooling rates from 5 to 2°C myr-1. These results demonstrate that the early Palaeozoic cooling history and comparable palaeostress regimes are regionally extensive, which has important implications for the tectonothermal and stress-field variability across Gondwana. The elevated thermal conditions would induce lithospheric weakening and promote the early Palaeozoic intraplate orogeny observed in eastern Antarctica with the development of a large intracratonic shear system.

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