scholarly journals Fabric and texture at Siple Dome, Antarctica

2005 ◽  
Vol 51 (173) ◽  
pp. 281-290 ◽  
Author(s):  
C.L. Diprinzio ◽  
L.A. Wilen ◽  
R.B. Alley ◽  
J.J. Fitzpatrick ◽  
M.K. Spencer ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Age ◽  
West Antarctica ◽  
Ice Flow ◽  
Thin Sections ◽  
Fine Grained ◽  
Additional Information ◽  
Siple Dome ◽  
History Of ◽  
Last Ice Age

AbstractPreferred c-axis orientations are present in the firn at Siple Dome, West Antarctica, and recrystallization begins as shallow as 200 m depth in ice below –20°C, based on digital analysis of c-axis fabrics, grain-sizes and other characteristics of 52 vertical thin sections prepared in the field from the kilometer-long Siple Dome ice core. The shallowest section analyzed, from 22 m, shows clustering of c axes toward the vertical. By 200 m depth, girdle fabric and other features of recrystallized ice are evident in layers (or regions), separated by layers (regions) of typically finer-grained ice lacking evidence of recrystallization. Ice from about 700–780m depth, which was deposited during the last ice age, is especially fine-grained, with strongly vertical c axes, but deeper ice shows much larger crystals and strong evidence of recrystallization. Azimuthal asymmetry of some c-axis fabrics, trends in grain-size, and other indicators reveal additional information on processes and history of ice flow at Siple Dome.

Evidence for a large surface ablation zone in central East Antarctica during the last Ice Age

2003 ◽  
Vol 59 (1) ◽  
pp. 114-121 ◽  
Author(s):  
Martin J. Siegert ◽  
Richard C. A. Hindmarsh ◽  
Gordon S. Hamilton
Keyword(s):  
Ice Core ◽  
Remote Sensing Data ◽  
Ice Age ◽  
Internal Layers ◽  
Ice Flow ◽  
Glacial Ice ◽  
Ice Surface ◽  
Ice Flows ◽  
Last Ice Age ◽  
The Hill

AbstractInternal isochronous ice sheet layers, recorded by airborne ice-penetrating radar, were measured along an ice flowline across a large (>1 km high) subglacial hill in the foreground of the Transantarctic Mountains. The layers, dated through an existing stratigraphic link with the Vostok ice core, converge with the ice surface as ice flows over the hill without noticeable change to their separation with each other or the ice base. A two-dimensional ice flow model that calculates isochrons and particle flowpaths and accounts for ice flow over the hill under steady-state conditions requires net ablation (via sublimation) over the stoss face for the predicted isochrons to match the measured internal layers. Satellite remote sensing data show no sign of exposed ancient ice at this site, however. Given the lack of exposed glacial ice, surface balance conditions must have changed recently from the net ablation that is predicted at this site for the last 85,000 years to accumulation.

scholarly journals Mapping c-axis fabrics to study physical processes in ice

1995 ◽  
Vol 41 (137) ◽  
pp. 197-203 ◽  
Author(s):  
R. B. Alley ◽  
A.J. Gow ◽  
D.A. Meese
Keyword(s):  
Grain Size ◽  
Spatial Distribution ◽  
Ice Core ◽  
West Antarctica ◽  
Physical Processes ◽  
Thin Sections ◽  
Additional Information ◽  
Average Grain Size ◽  
Scatter Plots

AbstractMapping the spatial distribution of c-axis orientations in ice thin sections is not much more difficult than preparing c-axis scatter plots but can reveal additional information about processes responsible for the observed fabric and texture of the ice. Distributions of angles between c axes of neighboring grains from the Byrd Station (West Antarctica) ice core suggest that polygonization causes average grain-size to stabilize below 400 m depth.

scholarly journals Mapping c-axis fabrics to study physical processes in ice

1995 ◽  
Vol 41 (137) ◽  
pp. 197-203 ◽  
Author(s):  
R. B. Alley ◽  
A.J. Gow ◽  
D.A. Meese
Keyword(s):  
Grain Size ◽  
Spatial Distribution ◽  
Ice Core ◽  
West Antarctica ◽  
Physical Processes ◽  
Thin Sections ◽  
Additional Information ◽  
Average Grain Size ◽  
Scatter Plots

AbstractMapping the spatial distribution ofc-axis orientations in ice thin sections is not much more difficult than preparingc-axis scatter plots but can reveal additional information about processes responsible for the observed fabric and texture of the ice. Distributions of angles betweencaxes of neighboring grains from the Byrd Station (West Antarctica) ice core suggest that polygonization causes average grain-size to stabilize below 400 m depth.

scholarly journals 10,000 years of melt history of the 2015 Renland ice core, EastGreenland

2019 ◽  
Author(s):  
Tetsuro Taranczewski ◽  
Johannes Freitag ◽  
Olaf Eisen ◽  
Bo Vinther ◽  
Sonja Wahl ◽  
...  
Keyword(s):  
Ice Core ◽  
Greenland Ice Sheet ◽  
Ice Age ◽  
Strong Increase ◽  
Past Century ◽  
Additional Information ◽  
The Past ◽  
Ice Cap ◽  
History Of ◽  
Paleoclimate Records

Abstract. An ice core drilled in 2015 on the Renland ice cap at the eastern margin of Greenland has been inspected with regard to its melt content. The thickness of a melt layer reflects the temperature level at the time of melt generation. Hence the melt layers are an indicator of past regional summer temperatures in East Greenland, a region where paleoclimate records are sparse. Melt layers have been identified almost along the whole core, resulting in a melt record reaching back 10,000 years. By gathering additional information about melt rates as well as high-resolution densities in two shallow cores, we developed an approach to correct the annual melt content for the ice volume that gets lost by the thinning process. The result is a melt record with decadal- to centennial- scale resolution for the last two millennia, and the most accurate Holocene climate record for Eastern Greenland so far. The observed changes of annual melt rates show a warm early Holocene, with melt rates higher than in the recent past century, and minimum melting during the Little Ice Age. Current melt rates show a strong increase for the early 20th century as well as for the time since the end of the past century, with the recent 2012 extreme melting of the Greenland Ice Sheet being the strongest melt event in the past 500 years.

scholarly journals The crossover stress, anisotropy and the ice flow law at Siple Dome, West Antarctica

2011 ◽  
Vol 57 (201) ◽  
pp. 39-52 ◽  
Author(s):  
Erin C. Pettit ◽  
Edwin D. Waddington ◽  
William D. Harrison ◽  
Throstur Thorsteinsson ◽  
Daniel Elsberg ◽  
...  
Keyword(s):  
Threshold Value ◽  
Ice Age ◽  
Nonlinear Flow ◽  
West Antarctica ◽  
Linear Deformation ◽  
Ice Flow ◽  
Siple Dome ◽  
Flow Mechanisms ◽  
Flow Law

AbstractWe used observations and modeling of Siple Dome, West Antarctica, a ridge ice divide, to infer the importance of linear deformation mechanisms in ice-sheet flow. We determined the crossover stress (a threshold value of the effective deviatoric stress below which linear flow mechanisms dominate over nonlinear flow mechanisms) by combining measurements of ice properties with in situ deformation rate measurements and a finite-element ice flow model that accounts for the effects of viscous anisotropy induced by preferred crystal-orientation fabric. We found that a crossover stress of 0.18 bar produces the best match between predicted and observed deformation rates. For Siple Dome, this means that including a linear term in the flow law is necessary, but generally the flow is still dominated by the nonlinear (Glen; n = 3) term. The pattern of flow near the divide at Siple Dome is also strongly affected by crystal fabric. Measurements of sonic velocity, which is a proxy for vertically oriented crystal fabric, suggest that a bed-parallel shear band exists several hundred meters above the bed within the Ice Age ice.

Tephrochronology of the Siple Dome ice core, West Antarctica: correlations and sources

2011 ◽  
Vol 30 (13-14) ◽  
pp. 1602-1614 ◽  
Author(s):  
Nelia W. Dunbar ◽  
Andrei V. Kurbatov
Keyword(s):  
Ice Core ◽  
West Antarctica ◽  
Siple Dome

scholarly journals Paleontology of the Bears Ears National Monument: history of exploration and designation of the monument

2018 ◽  
Author(s):  
Jessica Uglesich ◽  
Robert J Gay ◽  
M. Allison Stegner ◽  
Adam K Huttenlocker ◽  
Randall B Irmis
Keyword(s):  
Fossil Record ◽  
Landscape Scale ◽  
Ice Age ◽  
Bureau Of Land Management ◽  
National Monument ◽  
Resource Protection ◽  
History Of ◽  
Last Ice Age ◽  
Dry Climates ◽  
Cretaceous Period

Bears Ears National Monument (BENM) is a new, landscape-scale national monument jointly administered by the Bureau of Land Management and the Forest Service in southeastern Utah as part of the National Conservation Lands system. As initially designated, BENM encompasses 1.3 million acres of land with exceptionally fossiliferous rock units. These units comprise a semi-continuous depositional record from the Pennsylvanian Period through the middle of the Cretaceous Period. Additional Quaternary and Holocene deposits are known from unconsolidated river gravels and cave deposits. The fossil record from BENM provides unique insights into several important paleontological periods of time, including the Pennsylvanian-Permian transition from fully aquatic to more fully terrestrial tetrapods; the rise of the dinosaurs following the Triassic-Jurassic extinction; and the response of ecosystems in dry climates to sudden temperature increases at the end of the last ice age and across the Holocene. While the paleontological resources of BENM are extensive, they have historically been under-studied. Here we summarize prior paleontological work in BENM and review the data used to support paleontological resource protection in the 2016 BENM proclamation.

scholarly journals Migration of the Siple Dome ice divide, West Antarctica

1998 ◽  
Vol 44 (148) ◽  
pp. 643-652 ◽  
Author(s):  
N. A. Nereson ◽  
C. F. Raymond ◽  
E. D. Waddington ◽  
R. W. Jacobel
Keyword(s):  
Migration Rate ◽  
Internal Layer ◽  
Internal Layers ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Flow Models ◽  
The Past ◽  
Siple Dome ◽  
Local Accumulation

AbstractThe non-linearity of the ice-flow law or a local accumulation low over an ice divide can cause isochrones (internal layers) to be shallower under the divide relative to the flanks, forming a “divide bump” in the internal layer pattern. This divide signature is analyzed using ice-flow models and inverse techniques to detect and quantify motion of the Siple Dome ice divide, West Antarctica. The principal feature indicating that migration has occurred is a distinct tilt of the axis of the peaks of the warped internal layers beneath the divide. The calculated migration rate is 0.05-0.50 m a−1 toward Ice Stream D and depends slightly on whether the divide bump is caused by the non-linearity of ice flow or by a local accumulation low. Our calculations also suggest a strong south-north accumulation gradient of 5-10 x 10−6 a−1 in a narrow zone north of the divide. A consequence of divide migration is that pre-Holocene ice is thickest about 0.5 km south of the present divide position. Divide motion indicates that non-steady processes, possibly associated with activity of the bounding ice streams, are affecting the geometry of Siple Dome. The migration rate is sufficiently slow that the divide bump is maintained in the internal layer pattern at all observable depths. This suggests that major asynchronous changes in the elevation or position of the bounding ice streams are unlikely over at least the past 103-104 years.

scholarly journals The elevation history of ice streams and the spatial accumulation pattern along the Siple Coast of West Antarctica inferred from ground-based radar data from three inter-ice-stream ridges

2001 ◽  
Vol 47 (157) ◽  
pp. 303-313 ◽  
Author(s):  
N. A. Nereson ◽  
C. F. Raymond
Keyword(s):  
Spatial Pattern ◽  
Internal Layer ◽  
Windward Side ◽  
West Antarctica ◽  
Ice Streams ◽  
Amundsen Sea ◽  
The Past ◽  
Ice Stream ◽  
Siple Dome ◽  
History Of

AbstractMeasurements of the surface and internal layer geometry from ice-penetrating radar and global positioning system surveys on three inter-ice-stream ridges in West Antarctica (Siple Dome, ridge DE and ridge BC) are examined with ice-flow models to infer (1) the history of the divide position at each site and (2) the spatial pattern of accumulation across the ridges. We find that the divide position is most steady at Siple Dome, somewhat steady at ridge DE and highly variable at ridge BC. Data from Siple Dome and ridge DE show evidence for steady northward motion of the ice divide for the past few thousand years. The layers beneath ridge BC suggest a 5 km northward shift of the divide position within the past several hundred years. Assuming the divide shifts are all due to changing elevation of the bounding ice streams, we infer the relative elevation history for segments of Ice Streams B–E. The northward displacement of the divide for all ridges implies a progressive relative thinning of the ice streams from E to B, with most dramatic recent thinning (100 m in <103 years) of Ice Stream B relative to Ice Stream C. Analysis of the internal layer pattern across the ridges indicates a south–north accumulation gradient with higher accumulation rates on the northern flanks of the ridges in all three cases. The inferred accumulation distribution is nearly uniform on the northern flanks, decreases sharply within a few ice thicknesses across the divides, and then decreases gradually farther to the south. The north/south decrease is strongest for ridge DE and weakest for ridge BC. This spatial pattern and the reduction in gradient strength with distance from the Amundsen Sea is consistent with the hypothesis that storms from the Amundsen Sea carry moisture first south then west over West Antarctica and deposit more snow on the windward side of ridges due to orographic lifting. This pattern has been stable for at least the past several thousand years.

scholarly journals Characterization and formation of melt layers in polar snow: observations and experiments from West Antarctica

2005 ◽  
Vol 51 (173) ◽  
pp. 307-312 ◽  
Author(s):  
Sarah B. Das ◽  
Richard B. Alley
Keyword(s):  
Field Experiments ◽  
Preferential Flow ◽  
Ice Core ◽  
Ice Cores ◽  
West Antarctica ◽  
Near Surface ◽  
Fine Grained ◽  
Ice Core Record ◽  
Temperature Records ◽  
Polar Snow

AbstractSurface melting rarely occurs across most of the Antarctic ice sheet, away from the warmer coastal regions. Nonetheless, isolated melt features are preserved in the firn and ice in response to infrequent and short-lived melting events. An understanding of the formation and occurrence of these melt layers will help us to interpret records of past melt occurrences from polar ice cores such as the Siple Dome ice-core record from West Antarctica. A search in the near-surface firn in West Antarctica found that melt features are extremely rare, and consist of horizontal, laterally continuous, one to a few millimeter thick, ice layers with few air bubbles. The melt layers found date from the 1992/93 and 1991/92 summers. Field experiments to investigate changes in stratigraphy taking place during melt events reproduced melt features as seen in the natural stratigraphy. Melting conditions of varying intensity were created by passively heating the near-surface air for varying lengths of time inside a clear plastic hotbox. Melt layers formed due entirely to preferential flow and subsequent refreezing of meltwater from the surface into near-surface, fine-grained, crust layers. Continuous melt layers were formed experimentally when positive-degree-day values exceeded 1ºC-day, a value corresponding well with air-temperature records from automatic weather station sites where melt layers formed in the recent past.

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