scholarly journals Satellite altimetry detection of ice-shelf-influenced fast ice

2021 ◽  
Vol 15 (8) ◽  
pp. 4099-4115
Author(s):  
Gemma M. Brett ◽  
Daniel Price ◽  
Wolfgang Rack ◽  
Patricia J. Langhorne
Keyword(s):  
Sea Ice ◽  
Drill Hole ◽  
Ice Thickness ◽  
Shelf Water ◽  
Radar Altimeter ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Fast Ice ◽  
Ice Shelf Water ◽  
The Mean

Abstract. The outflow of supercooled Ice Shelf Water from the conjoined Ross and McMurdo ice shelf cavity augments fast ice thickness and forms a thick sub-ice platelet layer in McMurdo Sound. Here, we investigate whether the CryoSat-2 satellite radar altimeter can consistently detect the higher freeboard caused by the thicker fast ice combined with the buoyant forcing of a sub-ice platelet layer beneath. Freeboards obtained from CryoSat-2 were compared with 4 years of drill-hole-measured sea ice freeboard, snow depth, and sea ice and sub-ice platelet layer thicknesses in McMurdo Sound in November 2011, 2013, 2017 and 2018. The spatial distribution of higher CryoSat-2 freeboard concurred with the distributions of thicker ice-shelf-influenced fast ice and the sub-ice platelet layer. The mean CryoSat-2 freeboard was 0.07–0.09 m higher over the main path of supercooled Ice Shelf Water outflow, in the centre of the sound, relative to the west and east. In this central region, the mean CryoSat-2-derived ice thickness was 35 % larger than the mean drill-hole-measured fast ice thickness. We attribute this overestimate in satellite-altimeter-obtained ice thickness to the additional buoyant forcing of the sub-ice platelet layer which had a mean thickness of 3.90 m in the centre. We demonstrate the capability of CryoSat-2 to detect higher Ice Shelf Water-influenced fast ice freeboard in McMurdo Sound. Further development of this method could provide a tool to identify regions of ice-shelf-influenced fast ice elsewhere on the Antarctic coastline with adequate information on the snow layer.

scholarly journals Satellite altimetry detection of ice shelf-influenced fast ice

2020 ◽  
Author(s):  
Gemma M. Brett ◽  
Daniel Price ◽  
Wolfgang Rack ◽  
Patricia J. Langhorne
Keyword(s):  
Sea Ice ◽  
Drill Hole ◽  
Ice Thickness ◽  
Shelf Water ◽  
Radar Altimeter ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Fast Ice ◽  
Ice Shelf Water ◽  
The Mean

Abstract. The outflow of supercooled Ice Shelf Water from the conjoined Ross and McMurdo ice shelf cavity augments fast ice thickness and forms a thick sub-ice platelet layer in McMurdo Sound. Here, we investigate whether the CryoSat-2 satellite radar altimeter can detect the higher freeboard caused by the thicker fast ice and the buoyant forcing of the sub-ice platelet layer beneath. Freeboards obtained from CryoSat-2 were compared with four years of drill hole measured sea ice freeboard, snow depth, and sea ice and sub-ice platelet layer thicknesses in McMurdo Sound in November of 2011, 2013, 2017 and 2018. The spatial distribution of higher CryoSat-2 freeboard concurred with the distributions of thicker ice shelf-influenced fast ice and the sub-ice platelet layer. The mean CryoSat-2 freeboard was 0.07–0.09 m higher over the main path of supercooled Ice Shelf Water outflow, in the centre of the sound, relative to the west and east. In this central region, the mean CryoSat-2 derived ice thickness was 35 % larger than the mean drill hole measured fast ice thickness. We attribute this overestimate in satellite altimeter obtained ice thickness to the additional buoyant forcing of the sub-ice platelet layer. We demonstrate the capability of CryoSat-2 to detect higher Ice Shelf Water influenced fast ice freeboard in McMurdo Sound and the wider application of this method as a potential tool to identify regions of ice shelf-influenced fast ice elsewhere on the Antarctic coastline.

scholarly journals Airborne mapping of the sub-ice platelet layer under fast ice in McMurdo Sound, Antarctica

2021 ◽  
Vol 15 (1) ◽  
pp. 247-264
Author(s):  
Christian Haas ◽  
Patricia J. Langhorne ◽  
Wolfgang Rack ◽  
Greg H. Leonard ◽  
Gemma M. Brett ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Sea Ice ◽  
Drill Hole ◽  
Small Scale ◽  
Shelf Water ◽  
Forward Modelling ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Thickness Variability ◽  
Ice Shelf Water

Abstract. Basal melting of ice shelves can result in the outflow of supercooled ice shelf water, which can lead to the formation of a sub-ice platelet layer (SIPL) below adjacent sea ice. McMurdo Sound, located in the southern Ross Sea, Antarctica, is well known for the occurrence of a SIPL linked to ice shelf water outflow from under the McMurdo Ice Shelf. Airborne, single-frequency, frequency-domain electromagnetic induction (AEM) surveys were performed in November of 2009, 2011, 2013, 2016, and 2017 to map the thickness and spatial distribution of the landfast sea ice and underlying porous SIPL. We developed a simple method to retrieve the thickness of the consolidated ice and SIPL from the EM in-phase and quadrature components, supported by EM forward modelling and calibrated and validated by drill-hole measurements. Linear regression of EM in-phase measurements of apparent SIPL thickness and drill-hole measurements of “true” SIPL thickness yields a scaling factor of 0.3 to 0.4 and rms error of 0.47 m. EM forward modelling suggests that this corresponds to SIPL conductivities between 900 and 1800 mS m−1, with associated SIPL solid fractions between 0.09 and 0.47. The AEM surveys showed the spatial distribution and thickness of the SIPL well, with SIPL thicknesses of up to 8 m near the ice shelf front. They indicate interannual SIPL thickness variability of up to 2 m. In addition, they reveal high-resolution spatial information about the small-scale SIPL thickness variability and indicate the presence of persistent peaks in SIPL thickness that may be linked to the geometry of the outflow from under the ice shelf.

scholarly journals Airborne mapping of the sub-ice platelet layer under fast ice in McMurdo Sound, Antarctica

2020 ◽  
Author(s):  
Christian Haas ◽  
Patricia J. Langhorne ◽  
Wolfgang Rack ◽  
Greg H. Leonard ◽  
Gemma M. Brett ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Sea Ice ◽  
Forward Modeling ◽  
Drill Hole ◽  
Small Scale ◽  
Shelf Water ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Thickness Variability ◽  
Ice Shelf Water

Abstract. Basal melting of ice shelves can result in the outflow of supercooled ice shelf water, which can lead to the formation of a sub-ice platelet layer (SIPL) below adjacent sea ice. McMurdo Sound, located in the southern Ross Sea, Antarctica, is well known for the occurrence of a SIPL linked to ice shelf water outflow from under the McMurdo Ice Shelf. Airborne, single frequency, frequency-domain electromagnetic induction (AEM) surveys were performed in November of 2009, 2011, 2013, 2016, and 2017 to map the thickness and spatial distribution of the landfast sea ice and underlying, porous SIPL. We developed a simple method to retrieve the thickness of the consolidated ice and SIPL from the EM inphase and quadrature components, supported by EM forward modeling, and calibrated and validated by drill-hole measurements. Linear regression of EM inphase measurements of apparent SIPL thickness and drill-hole measurements of true SIPL thickness yields a scaling factor of 0.3 to 0.4, and rms error of 0.47 m. EM forward modeling suggests that this corresponds to SIPL conductivities between 900 and 1800 mS/m, with associated SIPL solid fractions between 0.09 and 0.47. The AEM surveys showed the spatial distribution and thickness of the SIPL well, with SIPL thicknesses of up to 8 m near the ice shelf front. They indicate interannual SIPL thickness variability of up to 2 m. In addition, they reveal high-resolution spatial information about the small-scale SIPL thickness variability, and indicate the presence of persistent peaks in SIPL thickness that may be linked to the geometry of the outflow from under the ice shelf.

Extension of an Ice Shelf Water plume model beneath sea ice with application in McMurdo Sound, Antarctica

2014 ◽  
Vol 119 (12) ◽  
pp. 8662-8687 ◽  
Author(s):  
K. G. Hughes ◽  
P. J. Langhorne ◽  
G. H. Leonard ◽  
C. L. Stevens
Keyword(s):  
Sea Ice ◽  
Shelf Water ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Plume Model ◽  
Ice Shelf Water

scholarly journals The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice

2014 ◽  
Vol 8 (1) ◽  
pp. 999-1022 ◽  
Author(s):  
D. Price ◽  
W. Rack ◽  
P. J. Langhorne ◽  
C. Haas ◽  
G. Leonard ◽  
...  
Keyword(s):  
Sea Ice ◽  
Solid Fraction ◽  
Surface Elevation ◽  
Ice Thickness ◽  
Shelf Water ◽  
Ice Shelf ◽  
Sea Ice Thickness ◽  
Ice Shelves ◽  
Antarctic Sea Ice ◽  
Ice Shelf Water

Abstract. This is an investigation to quantify the influence of the sub-ice platelet layer on satellite measurements of total freeboard and their conversion to thickness of Antarctic sea ice. The sub-ice platelet layer forms as a result of the seaward advection of supercooled ice shelf water from beneath ice shelves. This ice shelf water provides an oceanic heat sink promoting the formation of platelet crystals which accumulate at the sea ice–ocean interface. The build-up of this porous layer increases sea ice freeboard, and if not accounted for, leads to overestimates of sea ice thickness from surface elevation measurements. In order to quantify this buoyant effect, the solid fraction of the sub-ice platelet layer must be estimated. An extensive in situ data set measured in 2011 in McMurdo Sound in the south-western Ross Sea is used to achieve this. We use drill-hole measurements and the hydrostatic equilibrium assumption to estimate a mean value for the solid fraction of this sub-ice platelet layer of 0.16. This is highly dependent upon the uncertainty in sea ice density. We test this value with independent Global Navigation Satellite System (GNSS) surface elevation data to estimate sea ice thickness. We find that sea ice thickness can be overestimated by up to 19%, with a mean deviation of 12% as a result of the influence of the sub-ice platelet layer. It is concluded that in close proximity to ice shelves this influence should be considered universally when undertaking sea ice thickness investigations using remote sensing surface elevation measurements.

scholarly journals The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice

2014 ◽  
Vol 8 (3) ◽  
pp. 1031-1039 ◽  
Author(s):  
D. Price ◽  
W. Rack ◽  
P. J. Langhorne ◽  
C. Haas ◽  
G. Leonard ◽  
...  
Keyword(s):  
Sea Ice ◽  
Solid Fraction ◽  
Surface Elevation ◽  
Ice Thickness ◽  
Shelf Water ◽  
Ice Shelf ◽  
Data Set ◽  
Sea Ice Thickness ◽  
Antarctic Sea Ice ◽  
Ice Shelf Water

Abstract. This is an investigation to quantify the influence of the sub-ice platelet layer on satellite measurements of total freeboard and their conversion to thickness of Antarctic sea ice. The sub-ice platelet layer forms as a result of the seaward advection of supercooled ice shelf water from beneath ice shelves. This ice shelf water provides an oceanic heat sink promoting the formation of platelet crystals which accumulate at the sea ice–ocean interface. The build-up of this porous layer increases sea ice freeboard, and if not accounted for, leads to overestimates of sea ice thickness from surface elevation measurements. In order to quantify this buoyant effect, the solid fraction of the sub-ice platelet layer must be estimated. An extensive in situ data set measured in 2011 in McMurdo Sound in the southwestern Ross Sea is used to achieve this. We use drill-hole measurements and the hydrostatic equilibrium assumption to estimate a mean value for the solid fraction of this sub-ice platelet layer of 0.16. This is highly dependent upon the uncertainty in sea ice density. We test this value with independent Global Navigation Satellite System (GNSS) surface elevation data to estimate sea ice thickness. We find that sea ice thickness can be overestimated by up to 19%, with a mean deviation of 12% as a result of the influence of the sub-ice platelet layer. It is concluded that within 100 km of an ice shelf this influence might need to be considered when undertaking sea ice thickness investigations using remote sensing surface elevation measurements.

scholarly journals Responses of sub-ice platelet layer thickening rate and frazil-ice concentration to variations in ice-shelf water supercooling in McMurdo Sound, Antarctica

2019 ◽  
Vol 13 (1) ◽  
pp. 265-280 ◽  
Author(s):  
Chen Cheng ◽  
Adrian Jenkins ◽  
Paul R. Holland ◽  
Zhaomin Wang ◽  
Chengyan Liu ◽  
...  
Keyword(s):  
Sea Ice ◽  
Crystallographic Structure ◽  
Shelf Water ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Frazil Ice ◽  
Ice Concentration ◽  
Vertical Distributions ◽  
Linear Effects ◽  
Ice Shelf Water

Abstract. Persistent outflow of supercooled ice-shelf water (ISW) from beneath McMurdo Ice Shelf creates a rapidly growing sub-ice platelet layer (SIPL) with a unique crystallographic structure under the sea ice in McMurdo Sound, Antarctica. A vertically modified frazil-ice-laden ISW plume model that encapsulates the combined non-linear effects of the vertical distributions of supercooling and frazil concentration on frazil-ice growth is applied to McMurdo Sound and is shown to reproduce the observed ISW supercooling and SIPL distributions. Using this model, the dependence of the SIPL thickening rate and depth-averaged frazil-ice concentration on ISW supercooling in McMurdo Sound is investigated and found to be predominantly controlled by the vertical distribution of frazil concentration. The complex dependence on frazil concentration highlights the need to improve frazil-ice observations within the sea-ice–ocean boundary layer in McMurdo Sound.

scholarly journals Winter growth and tidal variability of the sub-ice platelet layer observed with electromagnetic induction soundings

2021 ◽  
Author(s):  
Gemma M. Brett ◽  
Gregory H. Leonard ◽  
Wolfgang Rack ◽  
Christian Haas ◽  
Patricia J. Langhorne ◽  
...  
Keyword(s):  
Layer Thickness ◽  
Electromagnetic Induction ◽  
Late Spring ◽  
Shelf Water ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Fast Ice ◽  
Ice Shelf Water ◽  
Second Year ◽  
Wind Events

Abstract. Here, we present the first electromagnetic induction time-series measurements of ice shelf-influenced fast ice and sub-ice platelet layer thickness over winter and in late spring in McMurdo Sound. Significant increases in sub-ice platelet layer thickness (~0.5–1 m) co-occurred with strong southerly wind events and satellite-observed polynya activity suggesting wind-driven surface circulation of supercooled Ice Shelf Water outflow from the McMurdo-Ross ice shelf cavity. Temporal variability observed in sub-ice platelet layer thickness on diurnal timescales correlated with tidally-induced current patterns previously observed in McMurdo Sound. The thickness of the sub-ice platelet layer increased on spring and neap ebb tides corresponding with northward currents circulating out from the ice shelf cavity. The late spring spatial distributions of first-year and second-year fast ice and sub-ice platelet layer thickness in McMurdo Sound were assessed with drill hole and electromagnetic induction surveys and were comparable to a previous four-year dataset. We resolved second-year fast ice thicknesses of 4 m with a substantial sub-ice platelet layer beneath of up to 11 m using electromagnetic induction techniques suggesting that the longer temporal persistence of the two-year-old fast ice allowed a substantially thicker sub-ice platelet layer to form. The variability observed in the sub-ice platelet layer indicates that a combination of the tides, wind-driven polynya activity and the presence of multi-year ice influences the circulation of Ice Shelf Water in the upper surface ocean and consequently sub-ice platelet layer formation over a range of timescales.

scholarly journals Variability Of Thermohaline Circulation Under An Ice Shelf

1990 ◽  
Vol 14 ◽  
pp. 338
Author(s):  
H.H. Hellmer
Keyword(s):  
Sea Ice ◽  
Boundary Conditions ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Melting Zone ◽  
Weddell Sea ◽  
Shelf Water ◽  
Ice Shelf ◽  
Grounding Line ◽  
Ice Shelf Water

The production of Antarctic Bottom Water is mainly influenced by Ice Shelf Water, which is formed through the modification of shelf water masses under huge ice shelves. To simulate this modification a two-dimensional thermohaline circulation model has been developed for a section perpendicular to the ice-shelf edge. Hydrographic data from the Filchner Depression enter into the model as boundary conditions. In the outflow region they also serve as a verification of model results. The standard solution reveals two circulation cells. The dominant one transports shelf water near the bottom toward the grounding line, where it begins to ascend along the inclined ice shelf. The contact with the ice shelf causes melting with a maximum rate of 1.5 m a−1 at the grounding line. Freezing and therefore the accumulation of “sea ice” at the bottom of the ice shelf occurs at the end of the melting zone at a rate on the order of 0.1 ma−1. Both rates are comparable with values estimated or predicted by models concerning ice-shelf dynamics. As one example of model sensitivity to changing boundary conditions, a higher sea-ice production in the southern Weddell Sea, as might be expected for a general climatic cooling event, is assumed. The resultant decrease/ increase in temperature/salinity of the inflow (Western Shelf Water) reduces the circulation under the ice shelf and therefore the outflow of Ice Shelf Water by 40%. The maximum melting and freezing rate decreases by 0.1 ma−1 and 0.01 m a−1, respectively. and the freezing zone shifts toward the grounding line by 100 km. In general the intensity of the circulation cells, the characteristics of Ice Shelf Water, the distribution of melting and freezing zones and the melting and freezing rates differ from the standard results with changing boundary conditions. These are the temperature and salinity of the inflow, the surface temperature at the top, and the extension and morphology of the ice shelf.

scholarly journals Response of sub-ice platelet layer thickening rate to variations in Ice Shelf Water supercooling in McMurdo Sound, Antarctica

2018 ◽  
Author(s):  
Chen Cheng ◽  
Adrian Jenkins ◽  
Paul R. Holland ◽  
Zhaomin Wang ◽  
Chengyan Liu ◽  
...  
Keyword(s):  
Nonlinear Effects ◽  
Crystallographic Structure ◽  
Shelf Water ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Frazil Ice ◽  
Ice Concentration ◽  
Vertical Distributions ◽  
Ice Shelf Water ◽  
The Vertical Distribution

Abstract. Persistent outflow of supercooled Ice Shelf Water (ISW) from beneath McMurdo Ice Shelf creates a sub-ice platelet layer (SIPL) having a unique crystallographic structure under the sea ice in McMurdo Sound (MMS), Antarctica. A new frazil-ice-laden ISW plume model that encapsulates the combined nonlinear effects of the vertical distributions of supercooling and frazil ice concentration (FIC) on frazil ice growth is applied to MMS, and is shown to reproduce the observed ISW supercooling and SIPL distributions. Using this model, the dependence of SIPL thickening rate on ISW supercooling in MMS is investigated. Results are found to be sensitive to the choice of frazil ice suspension index, which determines the vertical distribution of FIC. For each suspension index, SIPL thickening rate can be expressed as an exponential function of ISW supercooling. The complex dependence on FIC highlights the need to improve frazil ice observations within the ice-ocean boundary layer.

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