scholarly journals Late Cenozoic behaviour of two Transantarctic Mountain outlet glaciers

2021 ◽  
Author(s):  
◽  
Richard Jones
Keyword(s):  
Ross Sea ◽  
Ice Sheet ◽  
Late Cenozoic ◽  
Surface Exposure Dating ◽  
Exposure Dating ◽  
The Past ◽  
Ice Surface ◽  
Transantarctic Mountain ◽  
Grounding Line ◽  
Basal Sliding

<p>Earth’s climate is undergoing dramatic warming that is unprecedented in at least the last ~2000 years. Outlets of the Antarctic ice sheet are experiencing dynamic thinning, terminus retreat and mass loss, however, we are currently unable to accurately predict their future response. The drivers and mechanisms responsible for these observed changes can be better understood by studying the behaviour of outlet glaciers in the geological past. Here, I use cosmogenic nuclide surface-exposure dating and numerical glacier modelling to investigate the past configurations and dynamics of Transantarctic Mountain outlet glaciers, in the Ross Sea sector of Antarctica.  Numerical modelling was first applied to understand the present-day and past behaviour of Skelton Glacier. A suite of sensitivity experiments reveal that Skelton Glacier is most susceptible to atmospheric temperature through its affect on basal sliding near the groundingline. Under past climates, large changes occurred in the lower reaches of the glacier, with basal sliding and bedrock erosion predicted in the overdeepened basins during both the Pliocene and Quaternary. Skelton Glacier was likely much shorter and thinner during Pliocene interglacials, with warm-based sliding that extended along most of its length.  Informed by the glacier modelling, I applied surface-exposure dating to constrain past fluctuations in the geometry of Skelton Glacier. The lower reaches of the glacier were likely thicker at the Last Glacial Maximum (LGM), supporting the idea of buttressing by grounded ice in the Ross Sea during glacial periods. The glacier then thinned to near-modern surface elevations by ~5.8 ka before present (BP). Multiple isotope analysis (²⁶Al-¹⁰Be) and exposure-burial modelling indicates that Skelton Glacier has fluctuated between interglacial and glacial configurations probably at orbital frequencies since the Miocene. These data record a total of >10 Ma of exposure and 2.5 Ma of burial. An unexpected outcome is that the average cosmogenic production rate over this time appears to have been at least twice that of today.  The long-term dynamics of Transantarctic Mountain outlet glaciers are further explored at Mackay Glacier. Here, geomorphological evidence reveals that glaciers can both erode and preserve bedrock surfaces during the same glacial episode, with basal erosion controlled primarily by ice thickness. Mackay Glacier likely experienced a widespread erosive regime prior to the Quaternary and a polythermal glacier regime during the LGM.  Deglaciation following the LGM is constrained with (¹⁰Be) surface-exposure dating at Mackay Glacier. Samples collected at two nunataks, across four transects, reveal glacier thinning of >260 m between the LGM and ~200 years BP. Ice surface lowering was initially gradual, however an episode of rapid thinning is then recorded at ~6.8 ka BP, during a period of relative climatic and oceanic stability. This accelerated surface lowering occurred at a rate commensurate with modern observations of rapid ice sheet thinning, persisted for at least four centuries, and resulted in >180 m of ice loss. Numerical modelling indicates that ice surface drawdown resulted from ‘marine ice sheet instability’ as the grounding-line retreated through a deep glacial trough on the inner continental-shelf.  This research provides new geological constraints and quantitative predictions of the past behaviour of Transantarctic Mountain outlet glaciers. The basal conditions and discharge of these glaciers evolved through the Late Cenozoic in response to climate forcing at orbital timescales, but also to topographically-controlled feedbacks at centennial to millennial timescales. Importantly, under enhanced atmospheric warming, these results imply that such outlet glaciers could experience greater ice loss through increased basal sliding and unstable grounding-line retreat into overdeepened basins.</p>

scholarly journals Late Cenozoic behaviour of two Transantarctic Mountain outlet glaciers

2021 ◽  
Author(s):  
◽  
Richard Jones
Keyword(s):  
Ross Sea ◽  
Ice Sheet ◽  
Late Cenozoic ◽  
Surface Exposure Dating ◽  
Exposure Dating ◽  
The Past ◽  
Ice Surface ◽  
Transantarctic Mountain ◽  
Grounding Line ◽  
Basal Sliding

<p>Earth’s climate is undergoing dramatic warming that is unprecedented in at least the last ~2000 years. Outlets of the Antarctic ice sheet are experiencing dynamic thinning, terminus retreat and mass loss, however, we are currently unable to accurately predict their future response. The drivers and mechanisms responsible for these observed changes can be better understood by studying the behaviour of outlet glaciers in the geological past. Here, I use cosmogenic nuclide surface-exposure dating and numerical glacier modelling to investigate the past configurations and dynamics of Transantarctic Mountain outlet glaciers, in the Ross Sea sector of Antarctica.  Numerical modelling was first applied to understand the present-day and past behaviour of Skelton Glacier. A suite of sensitivity experiments reveal that Skelton Glacier is most susceptible to atmospheric temperature through its affect on basal sliding near the groundingline. Under past climates, large changes occurred in the lower reaches of the glacier, with basal sliding and bedrock erosion predicted in the overdeepened basins during both the Pliocene and Quaternary. Skelton Glacier was likely much shorter and thinner during Pliocene interglacials, with warm-based sliding that extended along most of its length.  Informed by the glacier modelling, I applied surface-exposure dating to constrain past fluctuations in the geometry of Skelton Glacier. The lower reaches of the glacier were likely thicker at the Last Glacial Maximum (LGM), supporting the idea of buttressing by grounded ice in the Ross Sea during glacial periods. The glacier then thinned to near-modern surface elevations by ~5.8 ka before present (BP). Multiple isotope analysis (²⁶Al-¹⁰Be) and exposure-burial modelling indicates that Skelton Glacier has fluctuated between interglacial and glacial configurations probably at orbital frequencies since the Miocene. These data record a total of >10 Ma of exposure and 2.5 Ma of burial. An unexpected outcome is that the average cosmogenic production rate over this time appears to have been at least twice that of today.  The long-term dynamics of Transantarctic Mountain outlet glaciers are further explored at Mackay Glacier. Here, geomorphological evidence reveals that glaciers can both erode and preserve bedrock surfaces during the same glacial episode, with basal erosion controlled primarily by ice thickness. Mackay Glacier likely experienced a widespread erosive regime prior to the Quaternary and a polythermal glacier regime during the LGM.  Deglaciation following the LGM is constrained with (¹⁰Be) surface-exposure dating at Mackay Glacier. Samples collected at two nunataks, across four transects, reveal glacier thinning of >260 m between the LGM and ~200 years BP. Ice surface lowering was initially gradual, however an episode of rapid thinning is then recorded at ~6.8 ka BP, during a period of relative climatic and oceanic stability. This accelerated surface lowering occurred at a rate commensurate with modern observations of rapid ice sheet thinning, persisted for at least four centuries, and resulted in >180 m of ice loss. Numerical modelling indicates that ice surface drawdown resulted from ‘marine ice sheet instability’ as the grounding-line retreated through a deep glacial trough on the inner continental-shelf.  This research provides new geological constraints and quantitative predictions of the past behaviour of Transantarctic Mountain outlet glaciers. The basal conditions and discharge of these glaciers evolved through the Late Cenozoic in response to climate forcing at orbital timescales, but also to topographically-controlled feedbacks at centennial to millennial timescales. Importantly, under enhanced atmospheric warming, these results imply that such outlet glaciers could experience greater ice loss through increased basal sliding and unstable grounding-line retreat into overdeepened basins.</p>

scholarly journals Past and present dynamics of Skelton Glacier, Transantarctic Mountains

2016 ◽  
Vol 28 (5) ◽  
pp. 371-386 ◽  
Author(s):  
R.S. Jones ◽  
N.R. Golledge ◽  
A.N. Mackintosh ◽  
K.P. Norton
Keyword(s):  
Ice Sheets ◽  
Atmospheric Temperature ◽  
Ice Thickness ◽  
Surface Slope ◽  
Flow Sensitivity ◽  
The Past ◽  
Transantarctic Mountain ◽  
Grounding Line ◽  
Basal Sliding ◽  
Transantarctic Mountains

AbstractAny future changes in the volume of Antarctica’s ice sheets will depend on the dynamic response of outlet glaciers to shifts in environmental conditions. In the Transantarctic Mountains, this response is probably heavily dependent on the geometry of the system, but few studies have quantified the sensitivity of these glaciers to environmental forcings. Here we investigated the controls, along-flow sensitivity and time-dependent dynamics of Skelton Glacier. Three key outcomes were: i) present-day flow is governed primarily by surface slope, which responds to reduced valley width and large bed undulations, ii) Skelton Glacier is more susceptible to changes in atmospheric temperature than precipitation through its effect on basal sliding near the grounding line, and iii) under conditions representative of Pliocene and Quaternary climates large changes in ice thickness and velocity would have occurred in the lower reaches of the glacier. Based on these new quantitative predictions of the past and present dynamics of Skelton Glacier, we suggest that similar Transantarctic Mountain outlet glaciers could experience greater ice loss in their confined, lower reaches through increased basal sliding and ocean melt under warmer-than-present conditions. These effects are greatest where overdeepenings exist near the grounding line.

scholarly journals Last Glacial Maximum-Holocene Glacial and Depositional History From Sediment Cores at Coulman High Beneath the Ross Ice Shelf, Antarctica

2021 ◽  
Author(s):  
◽  
Sanne M Maas
Keyword(s):  
Last Glacial Maximum ◽  
Ross Sea ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Open Water ◽  
Glacial Maximum ◽  
Ice Shelf ◽  
Last Glacial ◽  
Ross Ice Shelf ◽  
Grounding Line

<p>Sediment Cores collected from the shallow sub-sea floor beneath the Ross Ice Shelf at Coulman High have been analysed using sedimentological techniques to constrain the retreat history of the Last Glacial Maximum (LGM) ice sheet in the Ross Embayment, and to determine when the modern-day calving line location of the Ross Ice Shelf was established. A characteristic vertical succession of facies was identified in these cores, that can be linked to ice sheet and ice shelf extent in the Ross Embayment. The base of this succession consists of unconsolidated, clast rich muddy diamicts, and is interpreted to be deposited subglacially or in a grounding line proximal environment on account of a distinct provenance in the clast content which can only be attributed to subglacial transport from the Byrd Glacier 400 km to the south of the drill site. This is overlain by a mud with abundant clasts, similar in character to a granulated facies that has been documented previously in the Ross Sea, and is interpreted as being a characteristic grounding line lift-o facies in a sub-ice shelf setting. These glacial proximal facies pass upward into a mud, which comprises three distinctive units. i) Muds with sub-mm scale laminae resulting from traction currents occurring near the grounding line in a sub-ice shelf environment overlain by, ii) muds with sub-mm scale laminae and elevated biogenic content (diatoms and foraminifera) and sand/gravel clasts, interpreted as being deposited in open water conditions, passing up into a iii) bioturbated mud, interpreted as being deposited in sub-ice shelf environment, proximal to the calving line. The uppermost facies consists of a 20 cm thick diatom ooze with abundant clasts and pervasive bioturbation, indicative of a condensed section deposited during periodically open marine conditions. During post-LGM retreat of the ice sheet margin in western Ross Sea, and prior to the first open marine conditions at Coulman High, it is hypothesized that the grounding and calving line were in relative close proximity to each other. As the calving line became "pinned" in the Ross Island region, the grounding line likely continued its retreat toward its present day location. New corrected radiocarbon ages on the foraminifera shells in the interval of laminated muds with clasts, provide some of the first inorganic ages from the Ross Sea, and strengthen inferences from previous studies, that the first open marine conditions in the vicinity of Ross Island were 7,600 14C yr BP. While retreat of the calving line south of its present day position is implied during this period of mid-Holocene warmth prior to its re-advance, at present it is not possible to constrain the magnitude of retreat or attribute this to climate change rather than normal calving dynamics.</p>

scholarly journals The Variation in the Ice Sheet of Mizuho Plateau, East Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 219
Author(s):  
Shinji Mae
Keyword(s):  
Accumulation Rate ◽  
Ice Sheet ◽  
Ice Cores ◽  
Simple Calculation ◽  
Ice Surface ◽  
Basal Ice ◽  
Basal Sliding ◽  
Radio Echo Sounding ◽  
Antarctic Research ◽  
Basal Shear

The Japanese Antarctic Research Expedition (JARE) has conducted glaciological studies on Mizuho Plateau since 1981. We have already reported that the ice sheet flowing from Mizuho Plateau into Shirase Glacier is thinning at a rate of about 70 cm/year and that the profile of the distribution of basal shear stress is similar to that of surging glaciers. A 5 year glaciological programme on Mizuho Plateau and in east Queen Maud Land is now being carried out and we have obtained the following new results: (1) The ice sheet in the down-stream region (where ice elevation is lower than about 2400 m) is thinning, based on measurements of horizontal and vertical flow velocity, strain-rate, the slope of the ice surface, the accumulation rate and densification of snow. (2) δ18O analysis of deep ice cores obtained at Mizuho Station (2240 m a.s.l.) and point G2 (1730 m a.s.l.) shows that δ18O increased about 200 years ago at Mizuho Station and about 400 years ago at point G2. If we can assume that the increase in δ18O is caused by the thinning of the ice sheet, then this result means that this thinning propagates to up-stream areas. (3) Radio-echo-sounding measurements on Mizuho Plateau show that the ice base in the down-stream region is wet. This supports the result described in (1), since the basal sliding due to a wet base causes ice-sheet thinning, as proposed in our previous studies. In summary, a possible explanation of ice-sheet variation on Mizuho Plateau is as follows: the thinning of the ice sheet, caused by the basal sliding due to basal ice melting, started at Shirase Glacier and has been propagating up-stream to reach its present position. A simple calculation, using flow velocities, shows that the thinning started at Shirase Glacier about 1500–2000 years ago.

scholarly journals Modelling of a marine glacier and ice-sheet-ice-shelf transition zone based on asymptotic analysis

1996 ◽  
Vol 23 ◽  
pp. 59-67 ◽  
Author(s):  
Vladimir A. Chugunov ◽  
Alexander V. Wilchinsky
Keyword(s):  
Boundary Conditions ◽  
Transition Zone ◽  
Spatial Scales ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Stream Length ◽  
Glacier Surface ◽  
Ice Surface ◽  
Grounding Line ◽  
The Difference

All parts of a two-dimensional, isothermal, stationary marine glacier (grounded ice sheet, ice shelf and transition zone) with constant viscosity are analysed by perturbation methods. In so doing, all zones of different flow patterns can be considered separately. Correlations between spatial scales for all parts can be expressed in terms of the typical ice-surface slope distant from the ocean, which reflects exterior conditions of the glacier’s existence. In considering the ice-sheet–ice-shelf transition zone, a small parameter characterizing the difference between ice and water densities is used. Such an analysis allows us to find boundary conditions at the grounding line for the grounded ice mass. Glacier-surface profiles are determined by numerical methods. The grounding-line position found by using the boundary conditions derived in this paper differs from that obtained by using Thomas and Bentley’s (1978) boundary conditions by about 10% of the grounded ice-stream length.

Progress report on the Antarctic ice sheet

Polar Record ◽  
1960 ◽  
Vol 10 (64) ◽  
pp. 3-10 ◽  
Author(s):  
G. de Q. Robin
Keyword(s):  
Sea Level ◽  
Ross Sea ◽  
Ice Sheet ◽  
Great Depth ◽  
Progress Report ◽  
The Other ◽  
The Past ◽  
History Of ◽  
Antarctic Continent ◽  
The Antarctic

The art, science and sport of conducting scientific traverses across the Antarctic continent has advanced so rapidly during the past decade that we are making considerable progress towards understanding the main characteristics of that continent and its ice mantle. Many reports of recent work are provisional, so some changes of detail in the following account may eventually prove necessary. Nevertheless, some major features are now well established, such as the great depth of the subglacial floor to the east of the Ross Sea, and the observations that show considerable sections of the rock of East Antarctica† to be above sea level. On the other hand, the past glaciological history of the continent and the state of the present mass balance of the ice sheet still need much more investigation before we can be satisfied with the answers. The continued activity in Antarctica should result in our knowledge of the continent advancing much further during the coming decade.

scholarly journals Last Glacial Maximum-Holocene Glacial and Depositional History From Sediment Cores at Coulman High Beneath the Ross Ice Shelf, Antarctica

2021 ◽  
Author(s):  
◽  
Sanne M Maas
Keyword(s):  
Last Glacial Maximum ◽  
Ross Sea ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Open Water ◽  
Glacial Maximum ◽  
Ice Shelf ◽  
Last Glacial ◽  
Ross Ice Shelf ◽  
Grounding Line

<p>Sediment Cores collected from the shallow sub-sea floor beneath the Ross Ice Shelf at Coulman High have been analysed using sedimentological techniques to constrain the retreat history of the Last Glacial Maximum (LGM) ice sheet in the Ross Embayment, and to determine when the modern-day calving line location of the Ross Ice Shelf was established. A characteristic vertical succession of facies was identified in these cores, that can be linked to ice sheet and ice shelf extent in the Ross Embayment. The base of this succession consists of unconsolidated, clast rich muddy diamicts, and is interpreted to be deposited subglacially or in a grounding line proximal environment on account of a distinct provenance in the clast content which can only be attributed to subglacial transport from the Byrd Glacier 400 km to the south of the drill site. This is overlain by a mud with abundant clasts, similar in character to a granulated facies that has been documented previously in the Ross Sea, and is interpreted as being a characteristic grounding line lift-o facies in a sub-ice shelf setting. These glacial proximal facies pass upward into a mud, which comprises three distinctive units. i) Muds with sub-mm scale laminae resulting from traction currents occurring near the grounding line in a sub-ice shelf environment overlain by, ii) muds with sub-mm scale laminae and elevated biogenic content (diatoms and foraminifera) and sand/gravel clasts, interpreted as being deposited in open water conditions, passing up into a iii) bioturbated mud, interpreted as being deposited in sub-ice shelf environment, proximal to the calving line. The uppermost facies consists of a 20 cm thick diatom ooze with abundant clasts and pervasive bioturbation, indicative of a condensed section deposited during periodically open marine conditions. During post-LGM retreat of the ice sheet margin in western Ross Sea, and prior to the first open marine conditions at Coulman High, it is hypothesized that the grounding and calving line were in relative close proximity to each other. As the calving line became "pinned" in the Ross Island region, the grounding line likely continued its retreat toward its present day location. New corrected radiocarbon ages on the foraminifera shells in the interval of laminated muds with clasts, provide some of the first inorganic ages from the Ross Sea, and strengthen inferences from previous studies, that the first open marine conditions in the vicinity of Ross Island were 7,600 14C yr BP. While retreat of the calving line south of its present day position is implied during this period of mid-Holocene warmth prior to its re-advance, at present it is not possible to constrain the magnitude of retreat or attribute this to climate change rather than normal calving dynamics.</p>

scholarly journals Mid-Holocene thinning of David Glacier, Antarctica: Chronology and Controls

2020 ◽  
Author(s):  
Jamey Stutz ◽  
Andrew Mackintosh ◽  
Kevin Norton ◽  
Ross Whitmore ◽  
Carlo Baroni ◽  
...  
Keyword(s):  
Numerical Modelling ◽  
Flow Line ◽  
Ice Sheet ◽  
Outlet Glacier ◽  
Exposure Dating ◽  
Ice Surface ◽  
Geological Past ◽  
Climate Interactions ◽  
Glacier Flow ◽  
Exposure Ages

Abstract. Quantitative satellite observations provide a comprehensive assessment of ice sheet mass loss over the last four decades, but limited insights into long-term drivers of ice sheet change. Geological records can extend the observational record and aid our understanding of ice sheet–climate interactions. Here we present the first millennial-scale reconstruction of David Glacier, the largest East Antarctic outlet glacier in Victoria Land. We use surface exposure dating of glacial erratics deposited on nunataks to reconstruct changes in ice surface elevation through time. We then use numerical modelling experiments to determine the drivers of glacial thinning. Thinning profiles derived from 45 10Be and 3He surface exposure ages show that David Glacier experienced rapid thinning up to 2 m/yr during the mid-Holocene (~ 6,500 years ago). Thinning stabilised at 6 kyr, suggesting initial formation of the Drygalski Ice Tongue at this time. Our work, along with terrestrial cosmogenic nuclide records from adjacent glaciers, shows simultaneous glacier thinning in this sector of the Transantarctic Mountains occurred ~ 3 kyr after the retreat of marine-based grounded ice in the western Ross Embayment. The timing and rapidity of the reconstructed thinning at David Glacier is similar to reconstructions in the Amundsen and Weddell embayments. In order to identify the potential causes of these rapid changes along the David Glacier, we use a glacier flow line model designed for calving glaciers and compare modelled results against our geological data. We show that glacier thinning and marine-based grounding line retreat is initiated by interactions between enhanced sub-ice shelf melting and reduced lateral buttressing, leading to Marine Ice Sheet Instability. Such rapid glacier thinning events are not captured in continental or sector-scale numerical modelling reconstructions for this period. Together, our chronology and modelling suggest a ~ 2,000-year period of dynamic thinning in the recent geological past.

scholarly journals Modelling dynamic ice-sheet boundaries and grounding line migration using the level set method

2020 ◽  
Vol 66 (259) ◽  
pp. 766-776
Author(s):  
M. Alamgir Hossain ◽  
Sam Pimentel ◽  
John M. Stockie
Keyword(s):  
Level Set Method ◽  
Level Set ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Numerical Approach ◽  
Ice Surface ◽  
Grounding Line ◽  
High Degree ◽  
Ice Water ◽  
Benchmark Solutions

AbstractComputing predictions of future sea level that include well-defined uncertainty bounds requires models that are capable of robustly simulating the evolution of ice sheets and glaciers. Ice flow behaviour is known to be sensitive to the location and geometry of dynamic ice boundaries such as the grounding line (GRL), terminus position and ice surface elevation, so that any such model should track these interfaces with a high degree of accuracy. To address this challenge, we implement a numerical approach that uses the level-set method (LSM) that accurately models the evolution of the ice–air and ice–water interface as well as capturing topological changes in ice-sheet geometry. This approach is evaluated by comparing simulations of grounded and marine-terminating ice sheets to various analytical and numerical benchmark solutions. A particular advantage of the LSM is its ability to explicitly track the moving margin and GRL while using a fixed grid finite-difference scheme. Our results demonstrate that the LSM is an accurate and robust approach for tracking the ice surface interface and terminus for advancing and retreating ice sheets, including the transient marine ice-sheet interface and GRL positions.

Sign in / Sign up

Export Citation Format

Share Document