scholarly journals Observations of a rift in the Ronne Ice Shelf, Antarctica

1994 ◽  
Vol 40 (134) ◽  
pp. 187-189
Author(s):  
E.C. King
Keyword(s):  
Weddell Sea ◽  
Surface Elevation ◽  
Water Interface ◽  
Ice Shelf ◽  
Seismic Profiling ◽  
Ice Water

AbstractDuring seismic profiling on the northwest Ronne Ice Shelf Antarctica, a rift in the ice shelf was encountered. The rift trends southeast to northwest and is located approximately 30 km inland from the present-day ice front The rift is 340 m wide and the surface elevation of the ice shelf drops by 14.65 m over the axis of the rift. The rift has an asymmetrical base with a near-vertical ice-water interface on its northeast flank and a more gently dipping ice-water interface forming its southeastern flank. The ice shelf thins from a thickness of 350 m away from the rift to a thickness of 225 m at the rift axis. The rift is the probable location of a future major calving event on this section of the Ronne Ice Shelf, an event which would release an iceberg of up to 30 km by 180 km into the Weddell Sea.

scholarly journals Observations of a rift in the Ronne Ice Shelf, Antarctica

1994 ◽  
Vol 40 (134) ◽  
pp. 187-189 ◽  
Author(s):  
E.C. King
Keyword(s):  
Weddell Sea ◽  
Surface Elevation ◽  
Water Interface ◽  
Ice Shelf ◽  
Seismic Profiling ◽  
Ice Water

Abstract During seismic profiling on the northwest Ronne Ice Shelf Antarctica, a rift in the ice shelf was encountered. The rift trends southeast to northwest and is located approximately 30 km inland from the present-day ice front The rift is 340 m wide and the surface elevation of the ice shelf drops by 14.65 m over the axis of the rift. The rift has an asymmetrical base with a near-vertical ice-water interface on its northeast flank and a more gently dipping ice-water interface forming its southeastern flank. The ice shelf thins from a thickness of 350 m away from the rift to a thickness of 225 m at the rift axis. The rift is the probable location of a future major calving event on this section of the Ronne Ice Shelf, an event which would release an iceberg of up to 30 km by 180 km into the Weddell Sea.

scholarly journals Platelet ice and the land-fast sea ice of McMurdo Sound, Antarctica

2001 ◽  
Vol 33 ◽  
pp. 21-27 ◽  
Author(s):  
Inga J. Smith ◽  
Patricia J. Langhorne ◽  
Timothy G. Haskell ◽  
H. Joe Trodahl ◽  
Russell Frew ◽  
...  
Keyword(s):  
Sea Ice ◽  
Isotopic Analysis ◽  
Field Work ◽  
Weddell Sea ◽  
Water Interface ◽  
Ice Shelf ◽  
Columnar Growth ◽  
Mcmurdo Sound ◽  
Ice Water ◽  
Platelet Ice

AbstractDendritic crystals of platelet ice appear beneath the columnar land-fast sea ice of McMurdo Sound, Antarctica. These leaf-like crystals are frozen into place by the advancing columnar growth. The platelets most probably begin to appear during July although in some parts of the Sound they may not appear at all. In addition, the amount and extent of platelet ice within the Sound varies from year to year. Previous authors have suggested that the formation of platelet ice is linked to the presence of the nearby ice shelf. It is a matter of debate whether these platelets form at depth and then float upwards or whether they grow in slightly supercooled water at the ice/water interface. The phenomenon is similar to that observed in the Weddell Sea region, but previous authors have suggested the two regions may experience different processes. This paper presents the results of field-work conducted in McMurdo Sound in 1999. Ice-structure analysis, isotopic analysis and salinity and temperature measurements near the ice/water interface are presented. Freezing points are calculated, and the possible existence of supercooling is discussed in relation to existing conjectures about the origin of platelets.

scholarly journals The Dynamics of the Ross Ice Shelf Revealed by Radio Echo-Sounding

1979 ◽  
Vol 24 (90) ◽  
pp. 295-307 ◽  
Author(s):  
C. S. Neal
Keyword(s):  
Dielectric Loss ◽  
Water Interface ◽  
Ice Shelf ◽  
Flow Lines ◽  
Regional Variations ◽  
Distinctive Features ◽  
Ross Ice Shelf ◽  
Radio Echo Sounding ◽  
Ice Water ◽  
Echo Sounding

AbstractRadio-echo data have yielded information on the dynamics of the Ross Ice Shelf. Distinctive features present on the radio-echo records have been used to delineate several flow lines on the ice shelf. Measurement of the power returned from the ice-water interface has revealed regional variations in the r.f. dielectric loss of Ross Ice Shelf ice. These variations are used to indicate zones of bottom melting and freezing.

scholarly journals Estimates of the refreezing rate in an ice-shelf borehole

2013 ◽  
Vol 59 (217) ◽  
pp. 938-948 ◽  
Author(s):  
Kenneth G. Hughes ◽  
Pat J. Langhorne ◽  
Michael J.M. Williams
Keyword(s):  
Sea Water ◽  
Salt Water ◽  
Heat Fluxes ◽  
Water Interface ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Flux Model ◽  
Thick Region ◽  
Ice Water ◽  
Heat Flux Model

AbstractThe refreezing rate of a borehole drilled through a 252 m thick region of the Ross Ice Shelf, Antarctica, is determined using oceanographic measurements over two periods of a day. We first use a method based on the conservation of salt in the supercooled salt water of the borehole. This is compared to a model using a numerical solution of the heat equation to find the temperature distribution in the host ice, allowing ice growth to be calculated from the balance of heat fluxes at the ice/water interface. This second method broadly confirms the refreezing rates deduced from salinity measurements, giving confidence in the generalization of this simple heat-flux model to predict refreezing rates of other boreholes. Predictions from both are subject to uncertainty due to the poorly defined value of the solid fraction of ice that freezes in a supercooled volume of sea water. This is taken to be 0.5 ± 0.1 throughout this study. The predicted rates are also strongly dependent on the initial and boundary conditions chosen, but results show the initial diameter of 600 mm decreases at a rate of ∼3–5 mm h−1 in an ice shelf with a minimum temperature of −22°C.

scholarly journals Special Aspects of the Central Part of Filchner-Ronne Ice Shelf, Antarctica

1988 ◽  
Vol 11 ◽  
pp. 173-179 ◽  
Author(s):  
F. Thyssen
Keyword(s):  
Sea Water ◽  
Lower Layer ◽  
Hot Water ◽  
Surface Elevation ◽  
Ice Thickness ◽  
Water Interface ◽  
Ice Shelf ◽  
Margin Area ◽  
High Absorption ◽  
Made In

Aero-measurements during the 1983–84 and 1985–86 field seasons showed that the ice in the central part of Filchner-Ronne Ice Shelf is more than 250 m thicker than has been assumed previously. In the margin area a double layering of the ice was found, with disappearing bottom reflections farther inland. High absorption of approximately 0.3 dB/m in the lower layer and a decreasing reflectivity at the ice / sea-water interface, probably caused by bottom freezing, have been estimated. Aero-measurements were used to map the surface elevation of the ice, with an accuracy of approximately 3 m. From the plot of ice thickness against surface elevation it was possible to obtain a calibration curve for isostatic conditions. Large deviations from this plot with an ice thickness which is apparently too small (they seem to be isostatic anomalies) were found in the central part of the ice shelf. The true ice thickness could easily be calculated and mapped from these anomalies and the electromagnetically measured thickness. From the map based on flights made in 1983–84 the site for a bore hole was chosen in the central part of the ice shelf with an estimated ice thickness of about 450 m, instead of the less than 200 m deduced by an electromagnetic reflection (EMR) method. Hot-water drilling by the ground party of our group (H. Engelhardt and J. Determann) revealed an ice thickness of 465 m at this site.

scholarly journals The Dynamics of the Ross Ice Shelf Revealed by Radio Echo-Sounding

1979 ◽  
Vol 24 (90) ◽  
pp. 295-307 ◽  
Author(s):  
C. S. Neal
Keyword(s):  
Dielectric Loss ◽  
Water Interface ◽  
Ice Shelf ◽  
Flow Lines ◽  
Regional Variations ◽  
Distinctive Features ◽  
Ross Ice Shelf ◽  
Radio Echo Sounding ◽  
Ice Water ◽  
Echo Sounding

AbstractRadio-echo data have yielded information on the dynamics of the Ross Ice Shelf. Distinctive features present on the radio-echo records have been used to delineate several flow lines on the ice shelf. Measurement of the power returned from the ice-water interface has revealed regional variations in the r.f. dielectric loss of Ross Ice Shelf ice. These variations are used to indicate zones of bottom melting and freezing.

scholarly journals Special Aspects of the Central Part of Filchner-Ronne Ice Shelf, Antarctica

1988 ◽  
Vol 11 ◽  
pp. 173-179 ◽  
Author(s):  
F. Thyssen
Keyword(s):  
Sea Water ◽  
Lower Layer ◽  
Hot Water ◽  
Surface Elevation ◽  
Ice Thickness ◽  
Water Interface ◽  
Ice Shelf ◽  
Margin Area ◽  
High Absorption ◽  
Made In

Aero-measurements during the 1983–84 and 1985–86 field seasons showed that the ice in the central part of Filchner-Ronne Ice Shelf is more than 250 m thicker than has been assumed previously. In the margin area a double layering of the ice was found, with disappearing bottom reflections farther inland. High absorption of approximately 0.3 dB/m in the lower layer and a decreasing reflectivity at the ice / sea-water interface, probably caused by bottom freezing, have been estimated. Aero-measurements were used to map the surface elevation of the ice, with an accuracy of approximately 3 m. From the plot of ice thickness against surface elevation it was possible to obtain a calibration curve for isostatic conditions. Large deviations from this plot with an ice thickness which is apparently too small (they seem to be isostatic anomalies) were found in the central part of the ice shelf. The true ice thickness could easily be calculated and mapped from these anomalies and the electromagnetically measured thickness.From the map based on flights made in 1983–84 the site for a bore hole was chosen in the central part of the ice shelf with an estimated ice thickness of about 450 m, instead of the less than 200 m deduced by an electromagnetic reflection (EMR) method. Hot-water drilling by the ground party of our group (H. Engelhardt and J. Determann) revealed an ice thickness of 465 m at this site.

scholarly journals Sea-ice habitat minimizes grazing impact and predation risk for larval Antarctic krill

Polar Biology ◽  
2021 ◽  
Author(s):  
Carmen L. David ◽  
Fokje L. Schaafsma ◽  
Jan A. van Franeker ◽  
Evgeny A. Pakhomov ◽  
Brian P. V. Hunt ◽  
...  
Keyword(s):  
Sea Ice ◽  
Predation Risk ◽  
Water Column ◽  
Antarctic Krill ◽  
Standing Stock ◽  
Euphausia Superba ◽  
Grazing Impact ◽  
Water Interface ◽  
Winter Habitat ◽  
Ice Water

AbstractSurvival of larval Antarctic krill (Euphausia superba) during winter is largely dependent upon the presence of sea ice as it provides an important source of food and shelter. We hypothesized that sea ice provides additional benefits because it hosts fewer competitors and provides reduced predation risk for krill larvae than the water column. To test our hypothesis, zooplankton were sampled in the Weddell-Scotia Confluence Zone at the ice-water interface (0–2 m) and in the water column (0–500 m) during August–October 2013. Grazing by mesozooplankton, expressed as a percentage of the phytoplankton standing stock, was higher in the water column (1.97 ± 1.84%) than at the ice-water interface (0.08 ± 0.09%), due to a high abundance of pelagic copepods. Predation risk by carnivorous macrozooplankton, expressed as a percentage of the mesozooplankton standing stock, was significantly lower at the ice-water interface (0.83 ± 0.57%; main predators amphipods, siphonophores and ctenophores) than in the water column (4.72 ± 5.85%; main predators chaetognaths and medusae). These results emphasize the important role of sea ice as a suitable winter habitat for larval krill with fewer competitors and lower predation risk. These benefits should be taken into account when considering the response of Antarctic krill to projected declines in sea ice. Whether reduced sea-ice algal production may be compensated for by increased water column production remains unclear, but the shelter provided by sea ice would be significantly reduced or disappear, thus increasing the predation risk on krill larvae.

scholarly journals Tank study of physico-chemical controls on gas content and composition during growth of young sea ice

2002 ◽  
Vol 48 (161) ◽  
pp. 177-191 ◽  
Author(s):  
Jean-Louis Tison ◽  
Christian Haas ◽  
Marcia M. Gowing ◽  
Suzanne Sleewaegen ◽  
Alain Bernard
Keyword(s):  
Sea Ice ◽  
Sea Water ◽  
Bubble Nucleation ◽  
Water Dynamics ◽  
Gas Content ◽  
First Year ◽  
Water Interface ◽  
Atmospheric Gases ◽  
Physico Chemical ◽  
Ice Water

AbstractDuring an ice-tank experiment, samples were taken to study the processes of acquisition and alteration of the gas properties in young first-year sea ice during a complete growth–warming–cooling cycle. The goal was to obtain reference levels for total gas content and concentrations of atmospheric gases (O2, N2, CO2) in the absence of significant biological activity. The range of total gas-content values obtained (3.5–18 mL STP kg−1) was similar to previous measurements or estimates. However, major differences occurred between current and quiet basins, showing the role of the water dynamics at the ice–water interface in controlling bubble nucleation processes. Extremely high CO2concentrations were observed in all the experiments (up to 57% in volume parts). It is argued that these could have resulted from two unexpected biases in the experimental settings. Concentrations in bubbles nucleated at the interface are controlled by diffusion both from the ice–water interface towards the well-mixed reservoir and between the interface water and the bubble itself. This double kinetic effect results in a transition of the gas composition in the bubbles from values close to solubility in sea water toward values close to atmospheric, as the ice cover builds up.

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