Detrital geochronology and lithologic signatures of Weddell Sea Embayment ice streams, Antarctica—Implications for subglacial geology and ice sheet history

Tills from moraines adjacent to major ice streams of the Weddell Sea Embayment contain distinct detrital zircon (n = 5304) and K-bearing mineral age populations (n = 323) that, when combined with pebble composition data, can be used to better understand Antarctica’s subglacial geology and ice sheet history. Till representing the Institute, Foundation, Academy, Recovery and Slessor Ice Streams each have distinct detrital zircon age populations. Detrital Ar-Ar ages are mostly younger than zircon ages, and distinctive populations include 270−300 Ma (Institute), 170−190 Ma (Foundation), and 1200−1400 Ma (Recovery), which are not easily explained by known outcrops. Pebble fractions of the Foundation and Academy tills are most diverse with up to >40% exotic erratics. The southern side of the Recovery Glacier has fossiliferous limestone erratics. Mixing models created using a nonlinear squares curve-fitting approach were developed to evaluate contributors of zircons to Foundation Ice Stream till. These model results and pebble lithology data both indicate that unexposed (subglacial) bedrock is mixed with exposed rocks to produce the observed till. Notably, the model required limited local Patuxent Formation input to the Foundation till’s zircon population. Our data suggest that sandstones underlie the Foundation Ice Stream and Recovery Glacier troughs, which has a bearing on basal ice flow conditions and results in geological controls on ice stream location. This geo- and thermo-chronological characterization of the ice streams will enable ice-rafted debris in Weddell Sea marine sediments to be traced back to its sources and interpreted in terms of ice stream dynamics.

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Drivers of abrupt Holocene shifts in West Antarctic ice stream direction determined from combined ice sheet modelling and geologic signatures

Antarctic Science ◽

10.1017/s0954102014000613 ◽

2014 ◽

Vol 26 (6) ◽

pp. 674-686 ◽

Cited By ~ 16

Author(s):

C.J. Fogwill ◽

C.S.M. Turney ◽

N.R. Golledge ◽

D.H. Rood ◽

K. Hippe ◽

...

Keyword(s):

Flow Direction ◽

Ice Sheet ◽

Weddell Sea ◽

Last Deglaciation ◽

Ice Streams ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Ice Stream ◽

Ice Sheet Modelling

AbstractDetermining the millennial-scale behaviour of marine-based sectors of the West Antarctic Ice Sheet (WAIS) is critical to improve predictions of the future contribution of Antarctica to sea level rise. Here high-resolution ice sheet modelling was combined with new terrestrial geological constraints (in situ14C and 10Be analysis) to reconstruct the evolution of two major ice streams entering the Weddell Sea over 20 000 years. The results demonstrate how marked differences in ice flux at the marine margin of the expanded Antarctic ice sheet led to a major reorganization of ice streams in the Weddell Sea during the last deglaciation, resulting in the eastward migration of the Institute Ice Stream, triggering a significant regional change in ice sheet mass balance during the early to mid Holocene. The findings highlight how spatial variability in ice flow can cause marked changes in the pattern, flux and flow direction of ice streams on millennial timescales in this marine ice sheet setting. Given that this sector of the WAIS is assumed to be sensitive to ocean-forced instability and may be influenced by predicted twenty-first century ocean warming, our ability to model and predict abrupt and extensive ice stream diversions is key to a realistic assessment of future ice sheet sensitivity.

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Of isbræ and ice streams

Annals of Glaciology ◽

10.3189/172756403781816347 ◽

2003 ◽

Vol 36 ◽

pp. 66-72 ◽

Cited By ~ 88

Author(s):

Martin Truffer ◽

Keith A. Echelmeyer

Keyword(s):

Ice Sheet ◽

Shear Zones ◽

West Antarctica ◽

Ice Streams ◽

Ice Flow ◽

Bed Topography ◽

Ice Stream ◽

Fast Ice ◽

Fast Flow ◽

End Members

AbstractFast-flowing ice streams and outlet glaciers provide the major avenues for ice flow from past and present ice sheets. These ice streams move faster than the surrounding ice sheet by a factor of 100 or more. Several mechanisms for fast ice-stream flow have been identified, leading to a spectrum of different ice-stream types. In this paper we discuss the two end members of this spectrum, which we term the “ice-stream” type (represented by the Siple Coast ice streams in West Antarctica) and the “isbræ” type (represented by Jakobshavn Isbræ in Greenland). The typical ice stream is wide, relatively shallow (∼1000 m), has a low surface slope and driving stress (∼10 kPa), and ice-stream location is not strongly controlled by bed topography. Fast flow is possible because the ice stream has a slippery bed, possibly underlain by weak, actively deforming sediments. The marginal shear zones are narrow and support most of the driving stress, and the ice deforms almost exclusively by transverse shear. The margins seem to be inherently unstable; they migrate, and there are plausible mechanisms for such ice streams to shut down. The isbræ type of ice stream is characterized by very high driving stresses, often exceeding 200 kPa. They flow through deep bedrock channels that are significantly deeper than the surrounding ice, and have steep surface slopes. Ice deformation includes vertical as well as lateral shear, and basal motion need not contribute significantly to the overall motion. The marginal shear zone stend to be wide relative to the isbræ width, and the location of isbræ and its margins is strongly controlled by bedrock topography. They are stable features, and can only shut down if the high ice flux cannot be supplied from the adjacent ice sheet. Isbræs occur in Greenland and East Antarctica, and possibly parts of Pine Island and Thwaites Glaciers, West Antarctica. In this paper, we compare and contrast the two types of ice streams, addressing questions such as ice deformation, basal motion, subglacial hydrology, seasonality of ice flow, and stability of the ice streams.

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Thermomechanical modelling of the Scandinavian ice sheet: implications for ice-stream formation

Annals of Glaciology ◽

10.3189/172756499781821733 ◽

1999 ◽

Vol 28 ◽

pp. 83-89 ◽

Cited By ~ 28

Author(s):

A. J. Payne ◽

D.J. Baldwin

Keyword(s):

Three Dimensional ◽

Ice Sheet ◽

Ice Streams ◽

Ice Flow ◽

Low Viscosity ◽

Ice Stream ◽

Scandinavian Ice Sheet ◽

The Baltic ◽

Stream Formation ◽

Initial Results

AbstractThis work attempts to explain the fan-like landform assemblages observed in satellite images of the area covered by the former Scandinavian ice sheet (SIS). These assemblages have been interpreted as evidence of large ice streams within the SIS. If this interpretation is correct, then it calls into doubt current theories on the formation of ice streams. These theories regard soft sediment and topographic troughs as being the key determinants of ice-stream location. Neither can be used to explain the existence of ice streams on the flat, hard-rock area of the Baltic Shield. Initial results from a three-dimensional, thermomechanical ice-sheet model indicate that interactions between ice flow, form and temperature can create patterns similar to those mentioned above. The model uses a realistic, 20 km resolution gridded topography and a simple parameterization of accumulation and ablation. It produces patterns of maximum ice-sheet extent, which are similar to those reconstructed from the area’s glacial geomorphology. Flow in the maximum, equilibrium ice sheet is dominated by wedges of warm, low-viscosity, fast-flowing ice. These are separated by areas of cold, slow-flowing ice. This patterning appears to develop spontaneously as the modelled ice sheet grows.

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The U-Pb detrital zircon signature of West Antarctic ice stream tills in the Ross embayment, with implications for Last Glacial Maximum ice flow reconstructions

Antarctic Science ◽

10.1017/s0954102014000315 ◽

2014 ◽

Vol 26 (6) ◽

pp. 687-697 ◽

Cited By ~ 17

Author(s):

Kathy J. Licht ◽

Andrea J. Hennessy ◽

Bethany M. Welke

Keyword(s):

Last Glacial Maximum ◽

Detrital Zircon ◽

Ross Sea ◽

Ice Sheet ◽

Glacial Maximum ◽

Ice Streams ◽

The West ◽

Zircon Age ◽

Last Glacial ◽

West Antarctic

AbstractGlacial till samples collected from beneath the Bindschadler and Kamb ice streams have a distinct U-Pb detrital zircon signature that allows them to be identified in Ross Sea tills. These two sites contain a population of Cretaceous grains 100–110 Ma that have not been found in East Antarctic tills. Additionally, Bindschadler and Kamb ice streams have an abundance of Ordovician grains (450–475 Ma) and a cluster of ages 330–370 Ma, which are much less common in the remainder of the sample set. These tracers of a West Antarctic provenance are also found east of 180° longitude in eastern Ross Sea tills deposited during the last glacial maximum (LGM). Whillans Ice Stream (WIS), considered part of the West Antarctic Ice Sheet but partially originating in East Antarctica, lacks these distinctive signatures. Its U-Pb zircon age population is dominated by grains 500–550 Ma indicating derivation from Granite Harbour Intrusive rocks common along the Transantarctic Mountains, making it indistinguishable from East Antarctic tills. The U-Pb zircon age distribution found in WIS till is most similar to tills from the west-central Ross Sea. These data provide new specific targets for ice sheet models and can be applied to pre-LGM deposits in the Ross Sea.

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Deglaciation and future stability of the Coats Land ice margin, Antarctica

The Cryosphere ◽

10.5194/tc-12-2383-2018 ◽

2018 ◽

Vol 12 (7) ◽

pp. 2383-2399 ◽

Cited By ~ 6

Author(s):

Dominic A. Hodgson ◽

Kelly Hogan ◽

James M. Smith ◽

James A. Smith ◽

Claus-Dieter Hillenbrand ◽

...

Keyword(s):

Structural Integrity ◽

Ice Sheet ◽

Weddell Sea ◽

Ice Streams ◽

Ice Shelves ◽

Last Glacial ◽

Ice Stream ◽

Loss Of Contact ◽

Seismic Reflection Profiles ◽

Glacial Advance

Abstract. The East Antarctic Ice Sheet discharges into the Weddell Sea via the Coats Land ice margin. We have used geophysical data to determine the changing ice-sheet configuration in this region through its last glacial advance and Holocene retreat and to identify constraints on its future stability. Methods included high-resolution multibeam bathymetry, sub-bottom profiles, seismic-reflection profiles, sediment core analysis and satellite altimetry. These provide evidence that Coats Land glaciers and ice streams merged with the palaeo-Filchner Ice Stream during the last glacial advance. Retreat of this ice stream from 12 848 to 8351 cal. yr BP resulted in its progressive southwards decoupling from Coats Land outlet glaciers. Moraines and grounding-zone wedges document the subsequent retreat and thinning of these glaciers, their loss of contact with the bed and the formation of ice shelves, which re-advanced to pinning points on topographic highs at the distal end of the troughs. Once fully detached from the bed, these ice shelves were predisposed to rapid retreat back to coastal grounding lines. This was due to reverse-bed slopes, the consequent absence of further pinning points in the troughs and potentially to the loss of structural integrity resulting from weaknesses inherited at the grounding line. These processes explain why there are no large ice shelves in the eastern Weddell Sea between 75.5 and 77∘ S.

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Deglaciation and future stability of the Coats Land ice margin, Antarctica

10.5194/tc-2018-9 ◽

2018 ◽

Cited By ~ 1

Author(s):

Dominic A. Hodgson ◽

Kelly Hogan ◽

James Smith ◽

James A. Smith ◽

Claus-Dieter Hillenbrand ◽

...

Keyword(s):

Seismic Reflection ◽

Structural Integrity ◽

Ice Sheet ◽

Weddell Sea ◽

Ice Streams ◽

Ice Shelves ◽

Ice Stream ◽

Grounding Line ◽

Loss Of Contact ◽

Seismic Reflection Profiles

Abstract. The East Antarctic Ice Sheet discharges into the Weddell Sea via the Coats Land ice margin. We have used geophysical data to determine the changing ice sheet configuration in this region through its last advance and retreat, and identify constraints on its future stability. Methods included high-resolution multibeam-bathymetry, sub-bottom profiles, seismic-reflection profiles, sediment core analysis and satellite altimetry. These provide evidence that Coats Land glaciers and ice streams merged with the palaeo-Filchner Ice Stream during the last ice advance. Retreat of this ice stream from 12.8 to 8.4 cal kyr BP resulted in its progressive southwards decoupling from Coats Land glaciers. Moraines and grounding-zone wedges document the subsequent retreat and thinning of these glaciers, loss of contact with the bed, and the formation of ice shelves, which re-advanced to pinning points on topographic highs at the distal end of their troughs. Once detached from the bed, the ice shelves were predisposed to rapid retreat back to coastal grounding lines due to reverse-bed slopes, the absence of further pinning points, and potentially to the loss of structural integrity propagating from the grounding line. These processes explain why there are no large ice shelves from 75.5-77° S.

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Distribution of basal melting and freezing beneath tributaries of Ice Stream C: implication for the Holocene decay of the West Antarctic ice sheet

Annals of Glaciology ◽

10.3189/172756403781816112 ◽

2003 ◽

Vol 36 ◽

pp. 273-282 ◽

Cited By ~ 26

Author(s):

Stefan W. Vogel ◽

Slawek Tulaczyk ◽

Ian R. Joughin

Keyword(s):

Ice Sheet ◽

Ice Streams ◽

The West ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

The Holocene ◽

West Antarctic ◽

Basal Ice ◽

Ice Stream ◽

Basal Melting

AbstractIce-stream tributaries connect the relatively slow-moving interior of the West Antarctic ice sheet (WAIS) with the fast-flowing Siple Coast ice streams. Basal water underneath these ice streams reduces basal resistance and enables the fast motion of the ice. Basal melting being the only source for this water, it is important to include the distribution of basal melting and freezing into numerical models assessing the stability of the WAIS. However, it is very difficult to constrain its distribution from existing field observations. Past borehole observations confirmed the presence of a wet bed at Byrd Station in the WAIS interior and at different locations within Siple Coast ice streams. However, the recent discovery of a 12–25m thick sediment-laden bubble-free basal ice layer at the UpC boreholes indicates that basal freezing is either currently occurring or had occurred upstream during the last glacial–interglacialcycle.We use a flowline model of ice thermodynamics to assess and quantify the spatial and temporal distribution of basal melting and freezing beneath Ice Stream C tributaries, taking into account the geothermal flux, shear heating and heat conduction away from the bed. Under the assumption that the ice was moving over a weak bed (τb =1–10 kPa) our model is able to reproduce a layer of frozen-on ice similar in thickness to the UpC “sticky spot” basal ice layer. Increased basal melting in the early Holocene possibly could have initiated the Holocene decay of the WAIS, whereas increased freezing rates over the past few thousand years could have decreased the amount of basal water in the system, resulting in a strengthening of the bed. This is consistent with current force-budget calculations for ice-stream tributaries and with observed stoppages and slow-downs of ice streams.

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Abraded rock landforms (whalebacks) developed under ice streams in mountain areas

Annals of Glaciology ◽

10.3189/1996aog22-1-9-16 ◽

1996 ◽

Vol 22 ◽

pp. 9-16 ◽

Cited By ~ 12

Author(s):

Ian S. Evans

Keyword(s):

Flow Direction ◽

Ice Sheet ◽

Ice Streams ◽

Mountain Areas ◽

Ice Flow ◽

Coast Mountains ◽

Mountain Ranges ◽

Low Viscosity ◽

Basal Ice ◽

Cordilleran Ice Sheet

Like many mountain ranges, the Coast Mountains of British Columbia, Canada, have undergone both local and ice-sheet glaciation. Effects of ice sheets are concentrated along major valleys and on adjacent spurs and passes which carried strong flows of diffluent ice. The major valleys are broad glacial troughs with frequent rock basins. Their slopes are broken into rounded, steep-sided bosses whalebacks abraded on all sides: they are of the order of 100 m to 1 km long, and 10 m high. In the southern Coast Mountains, the distribution of these whalebacks is consistent with a proposed pattern of former ice streams 1.0–2.1 km thick, within the Cordilleran ice sheet. They are best developed where geological structures parallel the valley and thus the former ice-flow direction, but they are found on a range of lithologies and some are transverse to structure. The whalebacks provide an impression of glacial streamlining, and occasionally grade into rock drumlins. Roches moutonnées are rare in the major troughs.It is hypothesised that these whalebacks and rock drumlins develop under ice streams of Greenland or East Antarctic type, sliding rapidly over bedrock and exploiting rock weaknesses to produce streamlined features. Lee slopes are abraded when thick ice suppresses bed separation, even with rapid flow; basal ice of low viscosity would aid this suppression. Water pressures under the ice streams may have remained high, so that lee-side plucking was rare; such plucking is most likely where pressure fluctuates dramatically, and especially when lee cavities under active ice reach atmospheric pressure.

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Abraded rock landforms (whalebacks) developed under ice streams in mountain areas

Annals of Glaciology ◽

10.1017/s0260305500015159 ◽

1996 ◽

Vol 22 ◽

pp. 9-16 ◽

Cited By ~ 36

Author(s):

Ian S. Evans

Keyword(s):

Flow Direction ◽

Ice Sheet ◽

Ice Streams ◽

Mountain Areas ◽

Ice Flow ◽

Coast Mountains ◽

Mountain Ranges ◽

Low Viscosity ◽

Basal Ice ◽

Cordilleran Ice Sheet

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The role of subglacial hydrology in ice streams with elevated geothermal heat flux

Journal of Glaciology ◽

10.1017/jog.2020.8 ◽

2020 ◽

Vol 66 (256) ◽

pp. 303-312

Author(s):

Silje Smith-Johnsen ◽

Basile de Fleurian ◽

Kerim H. Nisancioglu

Keyword(s):

Heat Flux ◽

Ice Sheet ◽

Complex Surface ◽

Surface Velocity ◽

Ice Streams ◽

Geothermal Heat ◽

Ice Flow ◽

Ice Stream ◽

The Impact

AbstractThe spatial distribution of geothermal heat flux (GHF) under ice sheets is largely unknown. Nonetheless, it is an important boundary condition in ice-sheet models, and suggested to control part of the complex surface velocity patterns observed in some regions. Here we investigate the effect of including subglacial hydrology when modelling ice streams with elevated GHF. We use an idealised ice stream geometry and a thermomechanical ice flow model coupled to subglacial hydrology in the Ice Sheet System Model (ISSM). Our results show that the dynamic response of the ice stream to elevated GHF is greatly enhanced when including the interactive subglacial hydrology. On the other hand, the impact of GHF on ice temperature is reduced when subglacial hydrology is included. In conclusion, the sensitivity of ice stream dynamics to GHF is likely to be underestimated in studies neglecting subglacial hydrology.

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