scholarly journals Nonequilibrium air clathrate hydrates in Antarctic ice: a paleopiezomdter for polar ice caps

1993 ◽  
Vol 90 (23) ◽  
pp. 11416-11418 ◽  
Author(s):  
H Craig ◽  
H Shoji ◽  
C C Langway
Keyword(s):  
Phase Boundary ◽  
Numerical Models ◽  
Equilibrium Phase ◽  
Vertical Displacement ◽  
Polar Ice ◽  
Ice Flow ◽  
Air Bubble ◽  
Ice Caps ◽  
General Parameter ◽  
Approximate Composition

"Craigite," the mixed-air clathrate hydrate found in polar ice caps below the depth of air-bubble stability, is a clathrate mixed crystal of approximate composition (N2O2).6H2O. Recent observations on the Byrd Station Antarctic core show that the air hydrate is present at a depth of 727 m, well above the predicted depth for the onset of hydrate stability. We propose that the air hydrate occurs some 100 m above the equilibrium phase boundary at Byrd Station because of "piezometry"--i.e., that the anomalous depth of hydrate occurrence is a relic of a previous greater equilibrium depth along the flow trajectory, followed by vertical advection of ice through the local phase-boundary depth. Flowline trajectories in the ice based on numerical models show that the required vertical displacement does indeed occur just upstream of Byrd Station. Air-hydrate piezometry can thus be used as a general parameter to study the details of ice flow in polar ice caps and the metastable persistence of the clathrate phase in regions of upwelling blue ice.

scholarly journals Enhancement factors for grounded ice and ice shelves inferred from an anisotropic ice-flow model

2010 ◽  
Vol 56 (199) ◽  
pp. 805-812 ◽  
Author(s):  
Ying Ma ◽  
Olivier Gagliardini ◽  
Catherine Ritz ◽  
Fabien Gillet-Chaulet ◽  
Gaël Durand ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Actual State ◽  
Polar Ice ◽  
Ice Flow ◽  
Ice Shelves ◽  
State Of Stress ◽  
Asymptotic Models ◽  
Enhancement Factors ◽  
Definition Of ◽  
Stress And Strain Rate

AbstractPolar ice is known to be one of the most anisotropic natural materials. For a given fabric the polycrystal viscous response is strongly dependent on the actual state of stress and strain rate. Within an ice sheet, grounded-ice parts and ice shelves have completely different stress regimes, so one should expect completely different impacts of ice anisotropy on the flow. The aim of this work is to quantify, through the concept of enhancement factors, the influence of ice anisotropy on the flow of grounded ice and ice shelves. For this purpose, a full-Stokes anisotropic marine ice-sheet flowline model is used to compare isotropic and anisotropic diagnostic velocity fields on a fixed geometry. From these full-Stokes results, we propose a definition of enhancement factors for grounded ice and ice shelves, coherent with the asymptotic models used for these regions. We then estimate realistic values for the enhancement factors induced by ice anisotropy for grounded ice and ice shelves.

scholarly journals Stokes’s Theorem, Data, and the Polar Ice Caps

2018 ◽  
Vol 125 (9) ◽  
pp. 830-834
Author(s):  
Yuliy Baryshnikov ◽  
Robert Ghrist
Keyword(s):  
Polar Ice ◽  
Ice Caps

On the relation between ice thickness changes and glacier speed-up, with application to Pine Island Glacier in West Antarctica 

2021 ◽  
Author(s):  
Jan De Rydt ◽  
Ronja Reese ◽  
Fernando Paolo ◽  
G Hilmar Gudmundsson
Keyword(s):  
Numerical Solutions ◽  
Numerical Models ◽  
Flow Speed ◽  
Ice Thickness ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Flow ◽  
Spatially Distributed ◽  
Speed Up ◽  
Induced Changes

<p>Pine Island Glacier in West Antarctica is among the fastest changing glaciers worldwide. Much of its fast-flowing central trunk is thinning and accelerating, a process thought to have been triggered by ocean-induced changes in ice-shelf buttressing. The measured acceleration in response to perturbations in ice thickness is a non-trivial manifestation of several poorly-understood physical processes, including the transmission of stresses between the ice and underlying bed. To enable robust projections of future ice flow, it is imperative that numerical models include an accurate representation of these processes. Here we combine the latest data with analytical and numerical solutions of SSA ice flow to show that the recent increase in flow speed of Pine Island Glacier is only compatible with observed patterns of thinning if a spatially distributed, predominantly plastic bed underlies large parts of the central glacier and its upstream tributaries.</p>

scholarly journals Resonant Forcing of the Climate System in Subharmonic Modes

2020 ◽  
Vol 8 (1) ◽  
pp. 60 ◽  
Author(s):  
Jean-Louis Pinault
Keyword(s):  
Climate Variability ◽  
Atmospheric Carbon Dioxide ◽  
Rossby Waves ◽  
Thermohaline Circulation ◽  
Climate System ◽  
Ice Age ◽  
Polar Ice ◽  
Ice Caps ◽  
Resonant Forcing

During recent decades observation of climate archives has raised several questions. Concerning the mid-Pleistocene transition problem, conflicting sets of hypotheses highlight either the role of ice sheets or atmospheric carbon dioxide in causing the increase in duration and severity of ice age cycles. The role of the solar irradiance modulations in climate variability is frequently referenced but the underlying physical justifications remain most mysterious. Here, we extend the key mechanisms involving the oceanic Rossby waves in climate variability, to very long-period, multi-frequency Rossby waves winding around the subtropical gyres. Our study demonstrates that the climate system responds resonantly to solar and orbital forcing in eleven subharmonic modes. We advocate new hypotheses on the evolution of the past climate, implicating the deviation between forcing periods and natural periods according to the subharmonic modes, and the polar ice caps while challenging the role of the thermohaline circulation.

Temperatures in Polar Ice Caps

Nature ◽  
1959 ◽  
Vol 184 (4692) ◽  
pp. 1056-1057 ◽  
Author(s):  
UWE RADOK
Keyword(s):  
Polar Ice ◽  
Ice Caps

Landscapes of cold-centred Late Wisconsinan ice caps, Arctic Canada

1993 ◽  
Vol 17 (2) ◽  
pp. 223-247 ◽  
Author(s):  
Arthur S. Dyke
Keyword(s):  
Canadian Arctic ◽  
Thermal Conditions ◽  
Flow Patterns ◽  
Flow Conditions ◽  
Ice Flow ◽  
Zone Width ◽  
Ice Caps ◽  
Ice Cap ◽  
Late Wisconsinan ◽  
Subglacial Meltwater

Uplands of the Canadian Arctic Islands supported Late Wisconsinan ice caps that developed two landscape zones reflecting basal thermal conditions regulated by long-sustained ice flow patterns. Central cold-based zones protected older glacial and preglacial landscapes while peripheral warm-based zones scoured and otherwise altered their beds. Some geomorphic effects are independent of ice cap scale, others vary with scale. For ice caps of 30 km radius or more, scour-zone width remains proportionally constant to flowline length under similar flow conditions. But intensity of scouring, ice moulding of drift and rock eminences, size and abundance of subglacial meltwater features, and development of end moraines increase with ice cap size. Ice caps became entirely cold based early in retreat as the boundary between warm and cold ice shifted outward, probably because ice thinned and flow slackened. The frozen margins deflected meltwater, thus maximizing formation of lateral meltwater channels throughout retreat. The landform record of cold-based glaciers in this region is easily interpreted. Hence, regional ice sheet models invoking or based on the premise that cold-based ice leaves no geomorphic record seem untenable.

scholarly journals Warm-based basal sediment entrainment and far-field Pleistocene origin evidenced in central Transantarctic blue ice through stable isotopes and internal structures

2018 ◽  
Vol 64 (244) ◽  
pp. 185-196 ◽  
Author(s):  
JOSEPH A. GRALY ◽  
KATHY J. LICHT ◽  
CHRISTINE M. KASSAB ◽  
BROXTON W. BIRD ◽  
MICHAEL R. KAPLAN
Keyword(s):  
Stable Isotopes ◽  
Ice Core ◽  
Far Field ◽  
Ice Flow ◽  
Air Bubble ◽  
Internal Structures ◽  
Flow Speeds ◽  
Sediment Entrainment ◽  
Stable Isotopes Of Water ◽  
Basal Melting

ABSTRACTStable isotopes of water (δ18O and δ2H) were measured in the debris-laden ice underlying an Antarctic blue ice moraine, and in adjoining Law Glacier in the central Transantarctic Mountains. Air bubble content and morphology were assessed in shallow ice core samples. Stable isotope measurements plot either on the meteoric waterline or are enriched from it. The data cluster in two groups: the ice underlying the moraine has a δ2H:δ18O slope of 5.35 ± 0.92; ice from adjoining portions of Law Glacier has a slope of 6.69 ± 1.39. This enrichment pattern suggests the moraine's underlying blue ice entrained sediment through refreezing processes acting in an open system. Glaciological conditions favorable to warm-based sediment entrainment occur 30–50 km upstream. Basal melting and refreezing are further evidenced by abundant vapor figures formed from internal melting of the ice crystals. Both the moraine ice and Law Glacier are sufficiently depleted of heavy isotopes that their ice cannot be sourced locally, but instead must be derived from far-field interior regions of the higher polar plateau. Modeled ice flow speeds suggest the ice must be at least 80 ka old, with Law Glacier's ice possibly dating to OIS 5 and moraine ice older still.

scholarly journals Grain Growth and Mechanical Behaviour of Polar Ice

1985 ◽  
Vol 6 ◽  
pp. 79-82 ◽  
Author(s):  
P. Duval
Keyword(s):  
Crystal Growth ◽  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Migration ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Polar Ice ◽  
Dislocation Glide ◽  
Ice Caps ◽  
Polar Snow

Crystal size in polar ice caps increases with depth from the snow surface down to several hundred meters. Data on crystal growth in isothermal polar snow and ice show the same linear relationship between the size of crystals and their age. This paper reviews the mechanical behavior of polar ice which exhibits grain growth. Grain boundary migration associated with grain growth appears to be an efficient accomodation process for grain boundary sliding and dislocation glide. For grain growth to occur, strain energy must always be lower than the free energy of boundaries. The sintering of ice particles in polar firn is energized by the pressure due to the overburden of snow. Dislocation creep must be taken into account to explain the densification rate in the intermediate and final stage Constants of power law creep should depend on the crystal growth rate.

scholarly journals Global change, Antarctic meteorite traps and the East Antarctic ice sheet

1993 ◽  
Vol 39 (132) ◽  
pp. 397-408 ◽  
Author(s):  
G. Delisle
Keyword(s):  
Numerical Models ◽  
Accumulation Rate ◽  
Theoretical Work ◽  
Snow Accumulation ◽  
Ice Thickness ◽  
Ice Caps ◽  
Ice Cap ◽  
Field Evidence ◽  
Victoria Land ◽  
Late Tertiary

AbstractNumerical models to assess the principal response of large ice caps to climatic changes are used as a guide to the interpretation of field evidence of changes in the glaciological regime in the coastal areas of Victoria Land and north Victoria Land, Antarctica. Based on the theoretical work, the following scenario is proposed: areas within about 300 km from the coast of Victoria Land experienced (i) significantly shallower ice slopes and a lesser degree of glaciation during most of the late Tertiary, (ii) steep slopes and thicker ice than today during glacial stages, and (iii) moderate thinning of the ice in intervening interglacial stages.The model predicts, for central regions of Antarctica, a slightly thinner ice cap (lower snow-accumulation rate) during glacial stages, but an estimated 200 m thicker ice cap in warmer Tertiary climates than today. The calculated “Tertiary ice caps” indicate a probable tendency of periodic surges due to basal melting at the outer fringes.Only modest changes of the ice thickness in reasonably good agreement with the model predictions for the current interglacial stage have been observed on four blue-ice fields, all located within 250 km of the coastline. Investigated ice fields include two meteorite traps — the Allan Hills Icefield and the Frontier Mountain meteorite fields. Antarctic meteorite traps are sustained by very specific glaciological conditions — in particular, only moderate changes in ice thickness over time. The sub-ice topography of these fields was determined by radar measurements and reveals a former, very different glaciological regime, which is interpreted as being associated with glacial processes, operative during the late Tertiary.Field evidence for a hypsithermal event during the Holocene is presented.

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