scholarly journals Debris characteristics and ice-shelf dynamics in the ablation region of the McMurdo Ice Shelf, Antarctica

2006 ◽  
Vol 52 (177) ◽  
pp. 223-234 ◽  
Author(s):  
Neil Glasser ◽  
Becky Goodsell ◽  
Luke Copland ◽  
Wendy Lawson
Keyword(s):  
Ross Sea ◽  
Ice Shelf ◽  
Low Velocity ◽  
Flow Forming ◽  
Ice Shelves ◽  
Surface Ablation ◽  
Debris Transport ◽  
Shelf Dynamics ◽  
Ground Penetrating ◽  
Thickness Measurements

AbstractThis paper presents observations and measurements of debris characteristics and ice-shelf dynamics in the ablation region of the McMurdo Ice Shelf in the Ross Sea sector of Antarctica. Ice-shelf surface processes and dynamics are inferred from a combination of sedimentological descriptions, ground-penetrating radar investigations and through ablation, velocity and ice-thickness measurements. Field data show that in the study area the ice shelf moves relatively slowly (1.5–18.3ma–1), has high ablation rates (43–441 mm during 2003/04 summer) and is thin (6–22 m). The majority of debris on the ice shelf was originally transported into the area by a large and dynamic ice-sheet/ice-shelf system at the Last Glacial Maximum. This debris is concentrated on the ice-shelf surface and is continually redistributed by surface ablation (creating an ice-cored landscape of large debris-rich mounds), ice-shelf flow (forming medial moraines) and meltwater streams (locally reworking material and redistributing it across the ice-shelf surface). A conceptual model for supraglacial debris transport by contemporary Antarctic ice shelves is presented, which emphasizes these links between debris supply, surface ablation and ice-shelf motion. Low-velocity ice shelves such as the McMurdo Ice Shelf can maintain and sequester a debris load for thousands of years, providing a mechanism by which ice shelves can accumulate sufficient debris to contribute to sediment deposition in the oceans.

scholarly journals Assessment of historical changes (1959-2012) and the causes of recent break-ups of the Petersen ice shelf, Nunavut, Canada

2015 ◽  
Vol 56 (69) ◽  
pp. 65-76 ◽  
Author(s):  
Adrienne White ◽  
Luke Copland ◽  
Derek Mueller ◽  
Wesley Van Wychen
Keyword(s):  
Loss Rate ◽  
Open Water ◽  
Shelf Area ◽  
Ice Shelf ◽  
Pack Ice ◽  
The Mean ◽  
Landfast Sea Ice ◽  
Ice Pressure ◽  
Ground Penetrating ◽  
Thickness Measurements

AbstractAerial photography and satellite imagery of the Petersen ice shelf, Nunavut, Canada, from 1959 to 2012 show that it was stable until June 2005, after which a series of major calving events in the summers of 2005, 2008, 2011 and 2012 resulted in the loss of ∼61% of the June 2005 ice-shelf area. This recent series of calving events was initiated by the loss of extensive regions of ˃50-year-old multi-year landfast sea ice from the front of the ice shelf in summer 2005. Each subsequent calving event has been preceded by open-water conditions and resulting loss of pack-ice pressure across the front of the ice shelf, and most occurred during record warm summers. Ground-penetrating radar (GPR) ice thickness measurements and RADARSAT-2 derived observations of surface motion indicate that tributary glaciers provided total ice input of 1.19-5.65 Mta–1 to the ice shelf from 2011 to 2012, far below the mean surface loss rate of 28.45 Mta–1. With recent losses due to calving and little evidence for current basal freeze-on, this suggests that the Petersen ice shelf will no longer exist by the 2040s, or sooner if further major calving events occur.

Modeling ocean eddies and their effects on ice shelf basal melt rate in the Ross Sea

2020 ◽  
Author(s):  
Stefanie Mack ◽  
Mike Dinniman ◽  
John Klinck ◽  
Dennis McGillicuddy, Jr. ◽  
Laurie Padman
Keyword(s):  
Ross Sea ◽  
Mesoscale Eddies ◽  
Ocean Model ◽  
Grid Spacing ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ocean Eddies ◽  
Ross Ice Shelf ◽  
Winter Conditions ◽  
Light Surface

<div>Ice shelf basal melt rates around Antarctica are affected by the advection of warm Circumpolar Deep Water (CDW) onto the continental shelf and under the ice shelf. In ocean models, resolving mesoscale eddies is necessary to capture eddy fluxes of CDW and estimate basal melt rates of ice shelves. Where and when (not if) eddies are resolved in an ocean model depends on the baroclinic Rossby radius and thus on stratification and latitude. The Ross Sea presents some interesting scientific questions in two regards: first, it is weakly stratified in winter conditions, lowering the radius of deformation; and second, the Ross Ice Shelf melts mainly from dense shelf water at the grounding line and from light surface water at the ice shelf front, rather than CDW. An investigation using a ROMS (Regional Ocean Modelling System) model of the Ross Sea reveals that portions of the domain (48% in well-mixed winter conditions, and 33% in stratified summer conditions) do not resolve mesoscale eddies even at a horizontal grid spacing of 1.5 km. We find that smaller grid spacing (1.5 km versus 5 km) leads to increased eddy generation in the model, and eddies that cross the ice shelf front in both directions. However, there is no significant change in basal melt between low and high resolution simulations. While even higher resolution is needed to fully represent eddies in the Ross Sea, the processes that control basal melt of the Ross Ice Shelf may not be strongly affected by these eddies.</div>

scholarly journals Tectonic and oceanographic controls on Abbot Ice Shelf thickness and stability

2013 ◽  
Vol 7 (6) ◽  
pp. 5509-5540
Author(s):  
J. R. Cochran ◽  
S. S. Jacobs ◽  
K. J. Tinto ◽  
R. E. Bell
Keyword(s):  
Gravity Data ◽  
Ice Sheets ◽  
Airborne Gravity ◽  
Data Sets ◽  
Surface Mixed Layer ◽  
Rift Basins ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ice Water ◽  
Thickness Measurements

Abstract. Ice shelves play key roles in stabilizing Antarctica's ice sheets and returning freshwater to the Southern Ocean. Improved data sets of ice shelf draft and underlying bathymetry are important for assessing ocean–ice interactions and modeling ice response to climate change. The long, narrow Abbot Ice Shelf south of Thurston Island produces large volumes of meltwater but is in overall mass balance unlike other ice shelves in the region that are losing mass. Here we invert NASA Operation IceBridge (OIB) airborne gravity data over the Abbot region to obtain sub-ice bathymetry, and combine OIB elevation and ice thickness measurements to estimate ice draft. A series of asymmetric fault-bounded rift basins underlie the Abbot Ice shelf west of 94° W and also the Cosgrove Ice Shelf to the south. The ice sheet bed in areas surrounding the Abbot is near or above sea level, consistent with stable grounding lines. Sub-ice water column depths along OIB flight lines are sufficiently deep to allow warm deep and thermocline waters near the western Abbot ice front to circulate through much of the ice shelf cavity. Abbot Ice Shelf drafts averaging ∼200 m, about 30 m less than the Bedmap2 compilation, are coincident with the summer transition between the ocean surface mixed layer and upper thermocline. The ice feeding the Abbot crosses the relatively stable southern grounding lines and is rapidly thinned by the warmest inflow. While the system is presently in equilibrium, the overall draft is sensitive to the thickness of the cold Antarctic surface water overlying the thermocline.

A record of slush and water extent on Antarctic ice shelves from 2013 to present day

2021 ◽  
Author(s):  
Rebecca Dell ◽  
Alison Banwell ◽  
Neil Arnold ◽  
Ian Willis ◽  
Anna Ruth W. Halberstadt ◽  
...  
Keyword(s):  
Clustering Algorithm ◽  
Google Earth ◽  
Expert Elicitation ◽  
Water Bodies ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Air Temperatures ◽  
Run Off ◽  
Shelf Dynamics

<p>Supraglacial melt is observed across the majority of Antarctic ice shelves and is expected to increase in line with rising air temperatures. Surface meltwater may run off the ice shelf edge and into the ocean, or be stored within firn pore spaces (slush) and supraglacial water bodies (ponds, lakes or streams). When stored either as slush or supraglacial water bodies, the water can indirectly impact ice shelf dynamics, and potentially facilitate ice shelf collapse. Numerous studies have quantified ice shelf meltwater in supraglacial water bodies, however, despite its importance, no studies exist that quantify the extent of slush on a pan-Antarctic scale.</p><p>Here, we develop a supervised classifier in Google Earth Engine capable of identifying both slush and ponded water on a pan-Antarctic scale using Landsat 8 imagery. We train and test our classifier on six ice shelves: (1) Nivlisen, (2) Roi Baudouin, (3) Amery, (4) Shackleton, (5) Nansen, (6) George VI. A k-means clustering algorithm is applied to selected Landsat 8 training scenes, and the output clusters are manually interpreted to form training classes (i.e. slush, water, and other surface types (e.g. blue ice, dirty ice)). These training classes are then used to train a Random Forest Classifier, and the accuracy of the outputs are assessed using expert elicitation. Overall, the classifier accuracy for water and slush is 78 % and 70 % respectively. The validated classifier is then applied to numerous ice shelves across Antarctica, in order to produce estimates of slush and water extent from 2013 to the present day.</p>

Two Rare Pustulose/spinose Morphotypes of Benthic Foraminifera from Eastern Ross Sea, Antarctica

2019 ◽  
Vol 49 (4) ◽  
pp. 405-422 ◽  
Author(s):  
Wojciech. Majewski ◽  
Jarosław Stolarski ◽  
Philip J. Bart
Keyword(s):  
Benthic Foraminifera ◽  
Ross Sea ◽  
Molecular Data ◽  
Food Resources ◽  
Ice Shelf ◽  
Deep Basin ◽  
Ice Shelves ◽  
Bottom Currents ◽  
Grounding Line ◽  
Limited Food

Abstract Habitats proximal to grounded ice and below ice shelves are rarely studied for microfossils. A recently described, well-resolved deglaciation record from the Whales Deep Basin of the eastern Ross Sea provided an opportunity to study sub-fossil foraminifera in such settings. Among other foraminiferal taxa, two forms with pustulose/spinose ornamentation were especially important as they were restricted to habitats associated with proximity to the calving front or presence of an ice-shelf. Based on gradation from strongly pustulose/spinose to typical morphologies and existing molecular data, these rarely reported forms are considered to be morphotypes of Globocassidulina biora (Crespin, 1960) and Trifarina earlandi (Parr, 1950). They seemed to flourish in polynya areas near grounding-line and in sub-ice-shelf environments with bottom currents. Their unusual morphologies may be a response to limited food resources. These foraminifera deserve special attention because they appear to be restricted to extreme Antarctic environments and hence are potentially very important for paleoenvironmental reconstructions.

scholarly journals The internal structure of the Brunt Ice Shelf from ice-penetrating radar analysis and implications for ice shelf fracture

2018 ◽  
Vol 12 (10) ◽  
pp. 3361-3372 ◽  
Author(s):  
Edward C. King ◽  
Jan De Rydt ◽  
G. Hilmar Gudmundsson
Keyword(s):  
Stress Field ◽  
Physical Properties ◽  
Internal Structure ◽  
Ground Penetrating Radar ◽  
Flow Speed ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Rift Propagation ◽  
Grounding Line ◽  
Ground Penetrating

Abstract. The rate and direction of rift propagation through ice shelves depend on both the stress field and the heterogeneity (or otherwise) of the physical properties of the ice. The Brunt Ice Shelf in Antarctica has recently developed new rifts, which are being actively monitored as they lengthen and interact with the internal structure of the ice shelf. Here we present the results of a ground-penetrating radar survey of the Brunt Ice Shelf aimed at understanding variations in the internal structure. We find that there are flow bands composed mostly of thick (ca. 250 m) meteoric ice interspersed with thinner (ca. 150 m) sections of ice shelf that have a large proportion of sea ice and seawater-saturated firn. Therefore the ice shelf is, in essence, a series of ice tongues cemented together with ice mélange. The changes in structure are related both to the thickness and flow speed of ice at the grounding line and to subsequent processes of firn accumulation and brine infiltration as the ice shelf flows towards the calving front. It is shown that rifts propagating through the Brunt Ice Shelf preferentially skirt the edges of blocks of meteoric ice and slow their rate of propagation when forced by the stress field to break through them, in contrast to the situation on other ice shelves where rift propagation speeds up in meteoric ice.

scholarly journals Widespread collapse of the Ross Ice Shelf during the late Holocene

2016 ◽  
Vol 113 (9) ◽  
pp. 2354-2359 ◽  
Author(s):  
Yusuke Yokoyama ◽  
John B. Anderson ◽  
Masako Yamane ◽  
Lauren M. Simkins ◽  
Yosuke Miyairi ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Late Holocene ◽  
Ross Sea ◽  
Sediment Cores ◽  
Ocean Modeling ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Grounding Line ◽  
Western Ross Sea

The stability of modern ice shelves is threatened by atmospheric and oceanic warming. The geologic record of formerly glaciated continental shelves provides a window into the past of how ice shelves responded to a warming climate. Fields of deep (−560 m), linear iceberg furrows on the outer, western Ross Sea continental shelf record an early post-Last Glacial Maximum episode of ice-shelf collapse that was followed by continuous retreat of the grounding line for ∼200 km. Runaway grounding line conditions culminated once the ice became pinned on shallow banks in the western Ross Sea. This early episode of ice-shelf collapse is not observed in the eastern Ross Sea, where more episodic grounding line retreat took place. More widespread (∼280,000 km2) retreat of the ancestral Ross Ice Shelf occurred during the late Holocene. This event is recorded in sediment cores by a shift from terrigenous glacimarine mud to diatomaceous open-marine sediment as well as an increase in radiogenic beryllium (10Be) concentrations. The timing of ice-shelf breakup is constrained by compound specific radiocarbon ages, the first application of this technique systematically applied to Antarctic marine sediments. Breakup initiated around 5 ka, with the ice shelf reaching its current configuration ∼1.5 ka. In the eastern Ross Sea, the ice shelf retreated up to 100 km in about a thousand years. Three-dimensional thermodynamic ice-shelf/ocean modeling results and comparison with ice-core records indicate that ice-shelf breakup resulted from combined atmospheric warming and warm ocean currents impinging onto the continental shelf.

scholarly journals Ice Shelves: A Review

1979 ◽  
Vol 24 (90) ◽  
pp. 273-286 ◽  
Author(s):  
Robert H. Thomas
Keyword(s):  
Indirect Evidence ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Flat Slabs ◽  
Amery Ice Shelf ◽  
Ice Flows ◽  
Shelf Dynamics ◽  
The Antarctic ◽  
Considerable Detail

AbstractIce shelves form where ice flows off the Antarctic ice sheet onto the sea to produce rather flat slabs of floating ice which, for the theoretician, are the simplest of all large ice masses. Boundary conditions are well defined, conditions change very slowly over distances that are large compared with ice thickness, and horizontal velocities are independent of depth. Unconfined ice shelves can be used as giant creep machines to investigate the ice flow law at low stresses. Further inland, where movement is hampered by obstructions such as grounded ice rises and by shear between the ice shelf and its sides, the ice shelf transmits a backpressure which tends to restrict drainage from the ice sheets that feed it. Wastage from ice shelves is principally by calving and by bottom melting. There has been no direct measurement of bottom-melting rates, but indirect evidence suggests that, near the seaward edges of ice shelves, bottom-melting rates may exceed one metre per year, with significant melting within about 100 km of the ice front. Further inland there may be bottom freezing, and analysis of cores taken from the Amery Ice Shelf indicate that bottom-freezing rates average 0.5 m a–1over a distance of 200 km. Such high freezing-rates are probably exceptional, and, beneath the Ross Ice Shelf, freezing appears to be insignificant even at a distance of 400 km from the ice front.Because of their accessibility ice shelves have been studied in considerable detail, but many problems remain. In particular we need to improve our understanding of basal flux, ice-shelf dynamics near the grounding line, the calving of icebergs, and the state of equilibrium of ice rises. In addition there is a clear need for basic data from the Filchner-Ronne ice shelf.

Continued northward expansion of the Ross Ice Shelf, Antarctica

1998 ◽  
Vol 27 ◽  
pp. 93-98 ◽  
Author(s):  
Harry J. R. Keys ◽  
Stanley S. Jacobs ◽  
Lawson W. Brigham
Keyword(s):  
Ross Sea ◽  
Shelf Area ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Front Advance ◽  
Northward Expansion ◽  
High Elevations ◽  
The Antarctic ◽  
Local Variability

The last major calving event along the Ross Ice Shelf (RIS, Antarctica) front occurred a decade ago, following a substantial increase in the rate of ice-front advance in the few years preceding the event. This “B-9” event, on the eastern part of the front between Edward VII Peninsula and Roosevelt Island, removed ≈ 5100 km2of ice, about 100 years of advance in that sector, but reduced the ice-shelf area by only 1%. Since 1987 the entire ice front has continued to advance, more than regaining the area lost during the B-9 event. The western front is now well north of any position recorded during the last 150 years, and it lias not experienced major calving forat least 90 years. Ice-front heights generally decrease from east to west, but local variability is high. Elevations are relatively low from 171° to 177° W, the location of “warm” Modified Circumpolar Deep Water circulation beneath the outer ice shelf. Modern heights considerably exceed historical heights between 179° Wand 178° E and are lower west of 174° E, probably due to recent dynamic changes such as rifting and the western advance. The general advance of the RIS front and the period of several decades to more than a century that elapses between major calving events is consistent with a relatively stable ice front. This contrasts with several smaller ice shelves along the Antarctic Peninsula and McMurdo Ice Shelf in the Ross Sea which have retreated substantially during the past few decades.

scholarly journals Changes in climate, ocean and ice-sheet conditions in the Ross embayment, Antarctica, at 6 ka

1998 ◽  
Vol 27 ◽  
pp. 305-310 ◽  
Author(s):  
Eric J. Steig ◽  
Charles P. Hart ◽  
James W. C. White ◽  
Wendy L. Cunningham ◽  
Mathew D. Davis ◽  
...  
Keyword(s):  
Sea Ice ◽  
Late Holocene ◽  
Environmental Changes ◽  
Ross Sea ◽  
Ice Core ◽  
Sediment Cores ◽  
Methanesulfonic Acid ◽  
Ice Shelf ◽  
Radiocarbon Dates ◽  
Ice Shelves

Evidence from the Ross embayment, Antarctica, suggests an abrupt cooling and a concomitant increase in sea-ice cover at about 6000 BP (6 ka). Stable-isotope (δD) concentrations in the Taylor Dome ice core, at the western edge of the Ross embayment, decline rapidly after 6 ka, and continue to decline through the late Holocene. Methanesulfonic acid concentrations at Taylor Dome show opposite trends to δD Sediment cores from the western Ross Sea show a percentage minimum for the sea-ice diatom Fragilariopsis curta between 9 and 6 ka, whenTaylor Dome δD values are highest, followed by an increase through the late Holocene. Radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the Ross embayment ceased at about 6 ka, coincident with the environmental changes inferred from the sediment and ice-core records. The similarity in timing suggests an important role for climate in controlling the evolution of ice-shelf margins following the end of the last glaciation.

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