The cavity under the Amery Ice Shelf, East Antarctica

AbstractOcean circulation under ice shelves and associated rates of melting and freezing are strongly influenced by the shape of the sub-ice-shelf cavity. We have refined an existing method and used additional in situ measurements to estimate the cavity shape under the Amery Ice Shelf, East Antarctica. A finite-element hydrodynamic ocean-tide model was used to simulate the major tidal constituents for a range of different sub-Amery Ice Shelf cavity water-column thicknesses. The data are adjusted in the largely unsurveyed southern region of the ice-shelf cavity by comparing the complex error between simulated tides and in situ tides, derived from GPS observations. We show a significant improvement in the simulated tides, with a combined complex error of 1.8 cm, in comparison with past studies which show a complex error of ∼5.3 cm. Our bathymetry incorporates ice-draft data at the grounding line and seismic surveys, which have provided a considerable amount of new data. This technique has particular application when the water column beneath ice shelves is inaccessible and in situ GPS data are available.

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Evaluation of basal melting parameterisations using in situ ocean and melting observations from the Amery Ice Shelf, East Antarctica

10.5194/os-2021-111 ◽

2021 ◽

Author(s):

Madelaine Gamble Rosevear ◽

Benjamin Keith Galton-Fenzi ◽

Craig Stevens

Keyword(s):

Freezing Point ◽

Acoustic Doppler Current Profiler ◽

Current Speed ◽

East Antarctica ◽

Ice Shelf ◽

Ice Shelves ◽

Amery Ice Shelf ◽

Current Profiler ◽

Basal Melting

Abstract. Ocean driven melting of Antarctic ice shelves is causing grounded ice to be lost from the Antarctic continent at an accelerating rate. However, the ocean processes governing ice shelf melting are not well understood, contributing to uncertainty in projections of Antarctica's contribution to sea level. Here, we analyse oceanographic data and in situ measurements of ice shelf melt collected from an instrumented mooring beneath the centre of the Amery Ice Shelf, East Antarctica. This is the first direct measurement of basal melting from the Amery Ice Shelf, and was made through the novel application of an upwards-facing Acoustic Doppler Current Profiler (ADCP). ADCP data were also used to map a region of the ice base, revealing a steep topographic feature or “scarp” in the ice with vertical and horizontal scales of ~20 m and ~40 m respectively. The annually-averaged ADCP-derived melt rate of 0.51 ± 0.18 m yr−1 is consistent with previous modelling results and glaciological estimates, and there is significant seasonal variation in melting with a maximum in May and a minimum in September. Melting is driven by temperatures ~0.2 °C above the local freezing point and background and tidal currents, which have typical speeds of ~3.0 cm s−1 and 10.0 cm s−1 respectively. We use the coincident measurements of ice shelf melt and oceanographic forcing to evaluate parameterisations of ice-ocean interactions, and find that parameterisations in which there is an explicit dependence of the melt rate on current speed beneath the ice tend to overestimate the local melt rate at AM06 by between 200 % and 400 %, depending on the choice of drag coefficient. A convective parameterisation in which melting is a function of the slope of the ice base is also evaluated and is shown to under-predict melting by 20 % at this site. Using available observations from other ice shelves, we show that a common current speed-dependent parameterisation overestimates melting at all but the coldest, most energetic cavity conditions.

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Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica

Nature Communications ◽

10.1038/s41467-021-23534-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Masahiro Minowa ◽

Shin Sugiyama ◽

Masato Ito ◽

Shiori Yamane ◽

Shigeru Aoki

Keyword(s):

Freezing Point ◽

East Antarctica ◽

Ice Shelf ◽

Rate Estimate ◽

Ice Shelves ◽

Plume Water ◽

Warm Deep Water ◽

Glacier Ice ◽

Basal Melting

AbstractBasal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302–12 m-thick ocean cavity beneath 234–412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65–0.95°C, leading to a mean basal melt rate estimate of 1.42 m a−1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

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Velocities of the Amery Ice Shelf's primary tributary glaciers, 2004–12

Antarctic Science ◽

10.1017/s0954102015000231 ◽

2015 ◽

Vol 27 (5) ◽

pp. 511-523 ◽

Cited By ~ 4

Author(s):

M.L. Pittard ◽

J.L. Roberts ◽

C.S. Watson ◽

B.K. Galton-Fenzi ◽

R.C. Warner ◽

...

Keyword(s):

Surface Velocity ◽

Ice Shelf ◽

Ice Flow ◽

Ice Shelves ◽

Ice Surface ◽

Amery Ice Shelf ◽

Landsat 7 ◽

One Year ◽

Shelf Region

AbstractMonitoring the rate of ice flow into ice shelves is vital to understanding how, where and when mass changes occur in Antarctica. Previous observations of ice surface velocity indicate that the Amery Ice Shelf and tributary glaciers have been relatively stable over the period 1968 to 1999. This study measured the displacement of features on the ice surface over a sequence of Landsat 7 images separated by approximately one year and spanning 2004 to 2012 using the surface feature tracking software IMCORR. The focus is on the region surrounding the southern grounding zone of the Amery Ice Shelf and its primary tributary glaciers: the Fisher, Lambert and Mellor glaciers. No significant changes in surface velocity were observed over this period. Accordingly, the velocity fields from each image pair between 2004 and 2012 were used to synthesize an average velocity dataset of the Amery Ice Shelf region and to compare it to previously published velocity datasets and in situ global positioning system velocity observations. No significant change in ice surface velocities was found between 2004 and 2012 in the Amery Ice Shelf region, which suggests that it continues to remain stable.

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Investigating the climate variability in the Totten area using NEMO-LIM regional model.

10.5194/egusphere-egu2020-8075 ◽

2020 ◽

Author(s):

Guillian Van Achter ◽

Charles Pelletier ◽

Thierry Fichefet

Keyword(s):

Sea Ice ◽

Ocean Circulation ◽

Ice Sheet ◽

Regional Model ◽

East Antarctica ◽

Shelf Area ◽

Ice Shelf ◽

Ice Shelves ◽

Landfast Ice ◽

The Impact

The Totten ice shelf drains over 570 000 km&#178; of East Antarctica. Most of the ice sheet that drains through the Totten ice-shelf is from Aurora Subglacial Basin and is marine based making the region potentially vulnerable to rapid ice sheet colapse. Understanding how the changes in ocean circulation and properties are causing increased basal melt of Antarctic ice shelves is crucial for predicting future sea level rise. In the context of the The PARAMOUR project (decadal predictability and variability of polar climate: the role of atmosphere-ocean-cryosphere multiscale interaction), we use a high resolution NEMO-LIM 3.6 regional model to investigate the variability and the predictability of the coupled climate system over the Totten area in East Antarctica. In this poster, we will present our on-going work about the impact of landfast ice over the variability of the system. Landfast ice is sea ice that is fastened to the coastline, to the sea floor along shoals or to grouded icebergs. Current sea ice models are unable to represent very crudely the formation, maintenance and decay of coastal landfast ice. We applyed several parameterization for modeling landfast ice over the Totten ice shelf area.

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Ocean mixing and heat transport processes observed under the Ross Ice Shelf control its basal melting

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1910760117 ◽

2020 ◽

Vol 117 (29) ◽

pp. 16799-16804 ◽

Cited By ~ 1

Author(s):

Craig Stevens ◽

Christina Hulbe ◽

Mike Brewer ◽

Craig Stewart ◽

Natalie Robinson ◽

...

Keyword(s):

Water Column ◽

Ocean Circulation ◽

Central Region ◽

Significant Proportion ◽

Transport Processes ◽

Hot Water ◽

Valuable Insight ◽

Ice Shelf ◽

Ice Shelves ◽

Ross Ice Shelf

The stability of large Antarctic ice shelves has important implications for global sea level, sea ice area, and ocean circulation. A significant proportion of ice mass loss from these ice shelves is through ocean-driven melting which is controlled by largely unobserved oceanic thermodynamic and circulatory processes in the cavity beneath the ice shelf. Here we use direct measurements to provide evidence of the changing water column structure in the cavity beneath the Ross Ice Shelf, the planet’s largest ice shelf by area. The cavity water column data exhibit both basal and benthic boundary layers, along with evidence of tidally modulated and diffusively convecting internal mixing processes. A region of thermohaline interleaving in the upper–middle water column indicates elevated diffusion and the potential to modify the cavity circulation. The measurements were recorded using the Aotearoa New Zealand Ross Ice Shelf Program hot water drill borehole melted in the central region of the shelf in December 2017 (HWD2), only the second borehole through the central region of the ice shelf, following J9 in 1977. These data, and comparison with the 1977 data, provide valuable insight into ice shelf cavity circulation and aid understanding of the evolution of the presently stable Ross Ice Shelf.

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SEASONAL COMPARISON OF VELOCITY OF THE EASTERN TRIBUTARY GLACIERS, AMERY ICE SHELF, ANTARCTICA, USING SAR OFFSET TRACKING

ISPRS Annals of Photogrammetry Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-annals-iv-2-w5-595-2019 ◽

2019 ◽

Vol IV-2/W5 ◽

pp. 595-600

Author(s):

S. D. Jawak ◽

S. Kumar ◽

A. J. Luis ◽

P. H. Pandit ◽

S. F. Wankhede ◽

...

Keyword(s):

Primary Objective ◽

Velocity Estimation ◽

East Antarctica ◽

Surface Velocity ◽

Ice Shelf ◽

Ice Shelves ◽

Tracking Method ◽

Amery Ice Shelf ◽

Glacier Velocity ◽

Offset Tracking

Abstract. Antarctica and Greenland are two major Earth’s continental ice shelves which play an important role in influencing Earth’s energy balance through their high albedo. The ice sheets comprise of grounded ice or the continental glaciers and their associated ice shelves. Surface velocity is an important parameter that needs to be monitored to understand the glacier dynamics. Marine terminating glaciers have higher velocity than land terminating glaciers. Therefore, ice shelves are generally observed to have higher velocity as compared to continental glaciers. The focus of this study is Amery ice shelf (AIS) which is the third largest ice shelf located in east Antarctica terminating into the Prydz Bay on the eastern Antarctica. The surface ice-flow velocity of AIS is very high compared to its surrounding glaciers which flows at a rate of 1400&thinsp;m&thinsp;a&minus;1 and drains about 8% of the Antarctic ice sheet. AIS is fed by different glaciers and ice streams at the head, as well as from the western and eastern side of the ice shelf before it terminates into the ocean. The primary objective of this study was to compute velocity of the eastern tributary glaciers of AIS using SAR from Sentinel-1 data. The secondary objective was to compare the winter and summer velocities of the glaciers for 2017&ndash;2018. The offset tracking method has been applied to the ground range detected (GRD) product obtained from Sentinel-1 satellite. This method is suitable for regions with higher glacier velocity where interferometry is generally affected by the loss of coherence. The offset tracking method works by tracking the features on the basis of another feature and calculates the offset between the two features in the images. Two tributary glaciers near the Clemence massif and another glacier near the Pickering Nunatak feed into this ice shelf from the eastern glacial basin region that drains ice from the American Highland, east Antarctica. The glaciers near the Clemence massif showed low annual velocity which ranged from 100&thinsp;m&thinsp;a&minus;1 at the head to &sim;300&thinsp;m&thinsp;a&minus;1 near the end of the glacier, where it merges with AIS. The glaciers flowing near the Pickering Nunatak exhibited moderate velocity ranging from 150&thinsp;m&thinsp;a&minus;1 at its head and reaching up to 450&thinsp;m&thinsp;a&minus;1 near the tongue. The summer velocity (March 2018) was observed to be higher than the velocity in winter (July 2017) and the difference between the summer and the winter velocities was found to be between 50&thinsp;m&thinsp;a&minus;1 and 130&thinsp;m&thinsp;a&minus;1. The results for the velocity were obtained at 120&thinsp;m resolution and were compared with the previous MEaSUREs (Making Earth System Data Records for Use in Research Environments) yearly velocity at 450&thinsp;m and 1&thinsp;km resolution provided by National Snow and Ice Data Center portal. The results were evaluated using statistical measure- bias and the accuracy was derived using the root mean square error. The bias did not exceed 20&thinsp;m&thinsp;a&minus;1 for the three glaciers and the accuracy was observed to be more than 85% for most of the regions. The accuracy of the results suggests that the offset tracking technique is useful for future velocity estimation in the regions of high glacier velocity.

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The effects of ocean warming on melting and ocean circulation under the Amery Ice Shelf, East Antarctica

Annals of Glaciology ◽

10.3189/1998aog27-1-75-80 ◽

1998 ◽

Vol 27 ◽

pp. 75-80 ◽

Cited By ~ 25

Author(s):

M.J.M. Williams ◽

R. C. Warner ◽

W. F. Budd

Keyword(s):

Mass Balance ◽

Ocean Circulation ◽

Three Dimensional ◽

Ocean Model ◽

Ocean Warming ◽

East Antarctica ◽

Ice Shelf ◽

Temperature Changes ◽

Amery Ice Shelf ◽

Basal Melting

Using a three-dimensional ocean model specially adapted to the ocean cavity under the Amery Ice Shelf, we investigated the present ocean circulation and pattern of ice-shelf basal melting and freezing, the differences which would result from temperature changes in the seas adjacent to the Amery Ice Shelf, and the ramifications of these changes for the mass balance of the ice shelf. Under present conditions we estimate the net loss from the Amery Ice Shelf from excess basal melting over freezing at approximately 7.8 Gt a−1. This comprises a gross loss of 11.4 Gt a−1 at a mean rate of 0.42 m a−1, which is partially offset by freezing-on of 3.6 Gt a−1, at a mean rate of 0.19 m a−1. When the adjacent seas were assumed to warm by 1°C, we found the net melt increased to 31.6 Gt a−1, comprising 34.6 Gt a−1 of gross melt and 3.0 Gt a−1 of freezing.

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Rapid formation of an ice doline on Amery Ice Shelf, East Antarctica

10.5194/egusphere-egu21-14157 ◽

2021 ◽

Author(s):

Roland Warner ◽

Helen Fricker ◽

Susheel Adusumilli ◽

Philipp Arndt ◽

Jonathan Kingslake ◽

...

Keyword(s):

High Resolution ◽

Abrupt Change ◽

East Antarctica ◽

Lake Basin ◽

Ice Shelf ◽

Ice Shelves ◽

Amery Ice Shelf ◽

Rapid Formation ◽

Stereo Photogrammetry ◽

Extensive Surface

Surface meltwater accumulating on Antarctica&#8217;s floating ice shelves can drive fractures through to the ocean and potentially cause their collapse, leading to enhanced ice discharge from the continent. Surface melting in Antarctica is predicted to increase significantly during coming decades, but the implications for ice shelf stability are unknown. We are still learning how meltwater forms, flows and alters the surface, and that rapid water-driven changes are not limited to summer. The southern Amery Ice Shelf in East Antarctica already has an extensive surface meltwater system and provides us with an opportunity to study melt processes in detail. We present high-resolution satellite data (imagery, ICESat-2 altimetry and elevation models from WorldView stereo-photogrammetry) revealing an abrupt change extending across ~60 km2 of the ice shelf surface in June 2019 (midwinter). We interpret this as drainage of an englacial lake through to the ocean below in less than three days. This left an uneven depression in the ice shelf surface, 11 km2 in area and as much as 80 m deep, with a bed of fractured ice: an &#8220;ice doline&#8221;. The englacial lake had lain beneath the perennially ice-covered portion of a 20 km2 meltwater lake. The reduced mass loading on the floating ice shelf after the drainage event resulted in flexure, with uplift of up to 36 m around the former lake. Applying an elastic flexural model to the uplift profiles suggests the loss of 0.75&#160;km3 of water to the ocean. In summer 2020, we observed meltwater accumulating in a new lake basin created by the flexure. ICESat-2 observations profiled a new narrow meltwater channel (20&#160;m wide and 3&#160;m deep), rapidly incised inside the doline as meltwater spilled over from the new lake and started refilling the depression. This study demonstrates how high-resolution geodetic measurements from ICESat-2 and WorldView can explore critical fine-scale ice shelf processes. The insights gained will greatly improve our ability to model these processes, ultimately improving the accuracy of our projections.

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Platelet ice attachment to instrument strings beneath the Amery Ice Shelf, East Antarctica

Journal of Glaciology ◽

10.3189/2014jog13j082 ◽

2014 ◽

Vol 60 (220) ◽

pp. 383-393 ◽

Cited By ~ 5

Author(s):

M. Craven ◽

R.C. Warner ◽

B.K. Galton-Fenzi ◽

L. Herraiz-Borreguero ◽

S.W. Vogel ◽

...

Keyword(s):

Indirect Evidence ◽

East Antarctica ◽

Dense Layer ◽

Ice Accretion ◽

Ice Shelf ◽

Frazil Ice ◽

Amery Ice Shelf ◽

Pressure Changes ◽

Platelet Ice

AbstractOceanographic instruments suspended beneath the Amery Ice Shelf, East Antarctica, have recorded sporadic pressure decreases of 10–20 dbar over a few days at three sites where basal marine ice growth is expected. We attribute these events to flotation due to platelet ice accretion on the instrument moorings. Some events were transient, rapidly returning to pre-event pressures, probably through dislodgement of loosely attached crystals. Driven by these pressure changes, temperatures recorded by the shallowest instruments (within 20 m of the shelf base) tracked in situ freezing temperatures during the events. These observations provide indirect evidence for the presence of frazil ice in the sub-ice-shelf mixed layer and for active marine ice accretion. At one site we infer that a dense layer of platelet ice ˜1.5 m thick was accreted to the ice shelf over a 50 day period. Following some permanent abrupt pressure decreases (which we interpret as due to the lodgement of the uppermost instrument at the ice-shelf base), altered background trends in pressure suggest compaction rates of 3–4 m a–1 for the accreted basal platelet layer. Attachment of platelet ice and resulting displacement of moorings has ramifications for project design and instrument deployment, and implications for interpretation of oceanographic data from sub-ice-shelf environments.

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Surface meltwater drainage and ponding on Amery Ice Shelf, East Antarctica, 1973–2019

Journal of Glaciology ◽

10.1017/jog.2021.46 ◽

2021 ◽

pp. 1-14

Author(s):

Julian J. Spergel ◽

Jonathan Kingslake ◽

Timothy Creyts ◽

Melchior van Wessem ◽

Helen A. Fricker

Keyword(s):

Climate Model ◽

Regional Climate ◽

Drainage System ◽

East Antarctica ◽

Lake Area ◽

Ice Shelf ◽

Ice Shelves ◽

Lake Volume ◽

Amery Ice Shelf ◽

Elevation Model

Abstract Surface melting on Amery Ice Shelf (AIS), East Antarctica, produces an extensive supraglacial drainage system consisting of hundreds of lakes connected by surface channels. This drainage system forms most summers on the southern portion of AIS, transporting meltwater large distances northward, toward the ice front and terminating in lakes. Here we use satellite imagery, Landsat (1, 4 and 8), MODIS multispectral and Sentinel-1 synthetic aperture radar to examine the seasonal and interannual evolution of the drainage system over nearly five decades (1972–2019). We estimate seasonal meltwater input to one lake by integrating output from the regional climate model [Regional Atmospheric Climate Model (RACMO 2.3p2)] over its catchment defined using the Reference Elevation Model of Antarctica. We find only weak positive relationships between modeled seasonal meltwater input and lake area and between meltwater input and lake volume. Consecutive years of extensive melting lead to year-on-year expansion of the drainage system, potentially through a link between melt production, refreezing in firn and the maximum extent of the lakes at the downstream termini of drainage. These mechanisms are important when evaluating the potential of drainage systems to grow in response to increased melting, delivering meltwater to areas of ice shelves vulnerable to hydrofracture.

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