Factors influencing the basal temperatures of a High Arctic polythermal glacier

AbstractA number of glaciers in the Canadian High Arctic are composed primarily of cold ice, but the ice at or near their beds reaches the pressure-melting point (PMP) in the ablation zone. Past modelling studies have suggested that the basal temperatures of some of these glaciers reach the PMP where they should not, indicating that they are not in thermal equilibrium with present-day surface air temperatures. To investigate the possible reasons for thermal disequilibria in such glaciers, a two-dimensional ice temperature model was used to simulate the inferred thermal characteristics of John Evans Glacier, Ellesmere Island. Results indicate that while surface refreezing and historical ice-thickness changes have had a warming effect upon basal ice temperatures, supraglacial meltwater reaching the glacier bed provides the single most critical heat source for explaining the apparent thermal disequilibrium between present-day inferred ice–bed temperatures and those modelled under present-day boundary conditions.

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Interannual Variability of Landfast Ice Thickness in the Canadian High Arctic, 1950-89

ARCTIC ◽

10.14430/arctic1402 ◽

1992 ◽

Vol 45 (3) ◽

Cited By ~ 52

Author(s):

Ross D. Brown ◽

Phil Cote

Keyword(s):

Interannual Variability ◽

High Arctic ◽

Ice Thickness ◽

Canadian High Arctic ◽

Landfast Ice

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Influence of the Arctic Circumpolar Vortex on the Mass Balance of Canadian High Arctic Glaciers

Journal of Climate ◽

10.1175/jcli4268.1 ◽

2007 ◽

Vol 20 (18) ◽

pp. 4586-4598 ◽

Cited By ~ 34

Author(s):

Alex S. Gardner ◽

Martin Sharp

Keyword(s):

Mass Balance ◽

Regime Shift ◽

High Arctic ◽

Western Hemisphere ◽

The Arctic ◽

Glacier Mass Balance ◽

Canadian High Arctic ◽

Circumpolar Vortex ◽

Eastern Hemisphere ◽

Air Temperatures

Abstract Variability in July mean surface air temperatures from 1963 to 2003 accounted for 62% of the variance in the regional annual glacier mass balance signal for the Canadian High Arctic. A regime shift to more negative regional glacier mass balance occurred between 1986 and 1987, and is linked to a coincident shift from lower to higher mean July air temperatures. Both the interannual changes and the regime shifts in regional glacier mass balance and July air temperatures are related to variations in the position and strength of the July circumpolar vortex. In years when the July vortex is “strong” and its center is located in the Western Hemisphere, positive mass balance anomalies prevail. In contrast, highly negative mass balance anomalies occur when the July circumpolar vortex is either weak or strong without elongation over the Canadian High Arctic, and its center is located in the Eastern Hemisphere. The occurrence of westerly positioned July vortices has decreased by 40% since 1987. The associated shift to a dominantly easterly positioned July vortex was associated with an increased frequency of tropospheric ridging over the Canadian High Arctic, higher surface air temperatures, and more negative regional glacier mass balance.

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Mapping thermal and hydrological conditions beneath a polythermal glacier with radio-echo sounding

Journal of Glaciology ◽

10.3189/172756501781832377 ◽

2001 ◽

Vol 47 (157) ◽

pp. 232-242 ◽

Cited By ~ 50

Author(s):

Luke Copland ◽

Martin Sharp

Keyword(s):

Thermal Structure ◽

Basal Layer ◽

Equipotential Surface ◽

High Arctic ◽

Hydrological Conditions ◽

Glacier Terminus ◽

Radio Echo Sounding ◽

Pressure Melting ◽

Polythermal Glacier ◽

Echo Sounding

AbstractSpatial patterns in residual bed reflection power (BRPr), derived from ground-based radio-echo sounding, were mapped and interpreted in terms of the thermal and hydrological conditions at the base of a high-Arctic polythermal glacier (John Evans Glacier, Ellesmere Island, Canada). BRPr is the residual from a statistical relationship between measured bed reflection power and ice thickness that describes the rate of dielectric loss with depth in the glacier. We identified three types of thermal structure: (a) Positive BRPr and an internal reflecting horizon occur over the glacier terminus. The reflecting horizon is interpreted as the boundary between warm and cold ice, and suggests the presence of a warm basal layer. (b) Positive BRPr occurs without an internal reflector in the upper part of the ablation zone. This suggests that ice is at the pressure-melting point only at the bed. (c) Negative BRPr without an internal reflector occurs in all other regions, suggesting cold ice at the bed. Where BRPr is positive, its pattern is similar to the pattern of subglacial water flow predicted from the form of the subglacial hydraulic equipotential surface. This suggests that hydrological conditions at the glacier bed are a major control on BRPr, probably because the dielectric contrast between ice and water is higher than that between ice and other subglacial materials.

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Mass and enthalpy budget evolution during the surge of a polythermal glacier: a test of theory

Journal of Glaciology ◽

10.1017/jog.2019.63 ◽

2019 ◽

Vol 65 (253) ◽

pp. 717-731 ◽

Cited By ~ 5

Author(s):

Douglas I. Benn ◽

Robert L. Jones ◽

Adrian Luckman ◽

Johannes J. Fürst ◽

Ian Hewitt ◽

...

Keyword(s):

Frictional Heating ◽

Drainage System ◽

Frictional Heat ◽

Balance Theory ◽

Ice Thickness ◽

Resolution Time ◽

Geothermal Heat ◽

Ice Surface ◽

Air Temperatures ◽

Polythermal Glacier

AbstractAnalysis of a recent surge of Morsnevbreen, Svalbard, is used to test predictions of the enthalpy balance theory of surging. High-resolution time series of velocities, ice thickness and crevasse distribution allow key elements of the enthalpy (internal energy) budget to be quantified for different stages of the surge cycle. During quiescence (1936–1990), velocities were very low, and geothermal heat slowly built-up enthalpy at the bed. Measurable mass transfer and frictional heating began in 1990–2010, then positive frictional heating-velocity feedbacks caused gradual acceleration from 2010 to 2015. Rapid acceleration occurred in summer 2016, when extensive crevassing and positive air temperatures allowed significant surface to bed drainage. The surge front reached the terminus in October 2016, coincident with a drop in velocities. Ice plumes in the fjord are interpreted as discharge of large volumes of supercooled water from the bed. Surge termination was prolonged, however, indicating persistence of an inefficient drainage system. The observations closely match predictions of the theory, particularly build-up of enthalpy from geothermal and frictional heat, and surface meltwater, and the concomitant changes in ice-surface elevation and velocity. Additional characteristics of the surge reflect spatial processes not represented in the model, but can be explained with respect to enthalpy gradients.

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Ice-shelf collapse, climate change, and habitat loss in the Canadian high Arctic

Polar Record ◽

10.1017/s0032247400026954 ◽

2001 ◽

Vol 37 (201) ◽

pp. 133-142 ◽

Cited By ~ 52

Author(s):

W. F. Vincent ◽

J.A.E. Gibson ◽

M.O. Jeffries

Keyword(s):

Warming Trend ◽

High Arctic ◽

Aerial Photographs ◽

Northern Coast ◽

Ice Shelf ◽

Canadian High Arctic ◽

Air Temperatures ◽

Biological Environment ◽

Ice Water ◽

Reduction In Area

AbstractEarly explorers in the Canadian high Arctic described a fringe of thick, landfast ice along the 500-km northern coast of Ellesmere Island. This article shows from analyses of historical records, aerial photographs, and satellite imagery (ERS-1, SPOT, RADARSAT-1) that this ancient ice feature (‘Ellesmere Ice Shelf’) underwent a 90% reduction in area during the course of the twentieth century. In addition, hydrographic profiles in Disraeli Fiord (83°N, 74°W) suggest that the ice-shelf remnant that presently dams the fiord (Ward Hunt Ice Shelf) decreased in thickness by 13 m (27%) from 1967 to 1999. Mean annual air temperatures at nearby Alert station showed a significant warming trend during the last two decades of this period, and a significant decline in the number of freezing degree days per annum. The ice-dammed fiord provides a stratified physical and biological environment (epishelf lake) of a type that is otherwise restricted to Antarctica. Extensive meltwater lakes occur on the surface of the ice shelf and support a unique microbial food web. The major contraction of these ice–water habitats foreshadows a much broader loss of marine cryo-ecosystems that will accompany future wanning in the high Arctic.

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Microbial Life beneath a High Arctic Glacier

Applied and Environmental Microbiology ◽

10.1128/aem.66.8.3214-3220.2000 ◽

2000 ◽

Vol 66 (8) ◽

pp. 3214-3220 ◽

Cited By ~ 260

Author(s):

Mark L. Skidmore ◽

Julia M. Foght ◽

Martin J. Sharp

Keyword(s):

High Arctic ◽

Terrestrial Environment ◽

Ice Cap ◽

Subglacial Environment ◽

Basal Ice ◽

Nitrate Reducers ◽

In Situ Conditions ◽

Polythermal Glacier ◽

Arctic Glacier

ABSTRACT The debris-rich basal ice layers of a high Arctic glacier were shown to contain metabolically diverse microbes that could be cultured oligotrophically at low temperatures (0.3 to 4°C). These organisms included aerobic chemoheterotrophs and anaerobic nitrate reducers, sulfate reducers, and methanogens. Colonies purified from subglacial samples at 4°C appeared to be predominantly psychrophilic. Aerobic chemoheterotrophs were metabolically active in unfrozen basal sediments when they were cultured at 0.3°C in the dark (to simulate nearly in situ conditions), producing 14CO2from radiolabeled sodium acetate with minimal organic amendment (≥38 μM C). In contrast, no activity was observed when samples were cultured at subfreezing temperatures (≤−1.8°C) for 66 days. Electron microscopy of thawed basal ice samples revealed various cell morphologies, including dividing cells. This suggests that the subglacial environment beneath a polythermal glacier provides a viable habitat for life and that microbes may be widespread where the basal ice is temperate and water is present at the base of the glacier and where organic carbon from glacially overridden soils is present. Our observations raise the possibility that in situ microbial production of CO2 and CH4beneath ice masses (e.g., the Northern Hemisphere ice sheets) is an important factor in carbon cycling during glacial periods. Moreover, this terrestrial environment may provide a model for viable habitats for life on Mars, since similar conditions may exist or may have existed in the basal sediments beneath the Martian north polar ice cap.

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Distinct Bacterial Communities Exist beneath a High Arctic Polythermal Glacier

Applied and Environmental Microbiology ◽

10.1128/aem.00595-06 ◽

2006 ◽

Vol 72 (9) ◽

pp. 5838-5845 ◽

Cited By ~ 54

Author(s):

Maya Bhatia ◽

Martin Sharp ◽

Julia Foght

Keyword(s):

Bacterial Communities ◽

Drainage System ◽

High Arctic ◽

16S Rrna Genes ◽

Rrna Genes ◽

Polymorphism Analysis ◽

Basal Ice ◽

Seasonal Flow ◽

Glacial Environments ◽

Polythermal Glacier

ABSTRACT Bacterial communities reside in basal ice, sediment, and meltwater in the supra-, sub-, and proglacial environments of John Evans Glacier, Nunavut, Canada. We examined whether the subglacial bacterial community shares common members with the pro- and supraglacial communities, and by inference, whether it could be derived from communities in either of these environments (e.g., by ice overriding proglacial sediments or by in-wash of surface meltwaters). Terminal restriction fragment length polymorphism analysis of bacterial 16S rRNA genes amplified from these environments revealed that the subglacial water, basal ice, and sediment communities were distinct from those detected in supraglacial meltwater and proglacial sediments, with 60 of 142 unique terminal restriction fragments (T-RFs) detected exclusively in subglacial samples and only 8 T-RFs detected in all three environments. Supraglacial waters shared some T-RFs with subglacial water and ice, likely reflecting the seasonal flow of surface meltwater into the subglacial drainage system, whereas supraglacial and proglacial communities shared the fewest T-RFs. Thus, the subglacial community at John Evans Glacier appears to be predominantly autochthonous rather than allochthonous, and it may be adapted to subglacial conditions. Chemical analysis of water and melted ice also revealed differences between the supraglacial and proglacial environments, particularly regarding electrical conductivity and nitrate, sulfate, and dissolved organic carbon concentrations. Whereas the potential exists for common bacterial types to be broadly distributed throughout the glacial system, we have observed distinct bacterial communities in physically and chemically different glacial environments.

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Ice discharge error estimates using different cross-sectional area approaches: a case study for the Canadian High Arctic, 2016/17

Journal of Glaciology ◽

10.1017/jog.2018.48 ◽

2018 ◽

Vol 64 (246) ◽

pp. 595-608 ◽

Cited By ~ 4

Author(s):

PABLO SÁNCHEZ-GÁMEZ ◽

FRANCISCO J. NAVARRO

Keyword(s):

Cross Sections ◽

High Arctic ◽

Thickness Measurement ◽

Cross Sectional Area ◽

Medium Size ◽

Ice Thickness ◽

Sectional Area ◽

Canadian High Arctic ◽

Cross Sectional ◽

Ice Cap

ABSTRACTWe analyse the various error sources in the estimation of ice discharge through flux gates, distinguishing the cases with ice-thickness data available for glacier cross-sections or only along the centreline. For the latter, we analyse the performance of three U-shaped cross-sectional approaches. We apply this methodology to glaciers of the Canadian High Arctic. The velocity field is the main error source for small and medium-size glaciers (discharge <100 Mt a−1) with low velocities (<100 m a−1), while for large glaciers (discharge >100 Mt a−1) with high velocities (>100 m a−1) the error in cross-sectional area dominates. Thinning/thickening between ice-thickness and velocity measurements should be considered, as it implies systematic errors up to 8% in our study. The U-shaped parabolic approach, which allows for an adjusted estimation when the ice-thickness measurement point is displaced from the glacier centreline, performs best, with small bias and admissible standard error. We observe an increase of ice discharge from the main glaciers (Trinity and Wykeham) of the Prince of Wales Icefield from 2015 to 2016, by 5 and 20%, respectively, followed by a decrease in 2017, by 10 and 15%, respectively. Belcher Glacier, of the Devon Ice Cap, maintains similar discharges during 2015–17.

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