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

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.

Download Full-text

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.

Download Full-text

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.

Download Full-text

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

Geological Society of America Bulletin ◽

10.1130/b36117.1 ◽

2021 ◽

Author(s):

Liana M. Agrios ◽

Kathy J. Licht ◽

Trevor Williams ◽

Sidney R. Hemming ◽

Lauren Welch ◽

...

Keyword(s):

Detrital Zircon ◽

Ice Sheet ◽

Weddell Sea ◽

Ice Streams ◽

Ice Flow ◽

Zircon Age ◽

Basal Ice ◽

Ice Stream ◽

Southern Side

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.

Download Full-text

Basal topographic controls on the stability of the West Antarctic ice sheet: lessons from Foundation Ice Stream

Annals of Glaciology ◽

10.1017/aog.2017.9 ◽

2017 ◽

Vol 58 (75pt2) ◽

pp. 193-198 ◽

Cited By ~ 1

Author(s):

Kathleen Huybers ◽

Gerard Roe ◽

Howard Conway

Keyword(s):

Sea Level ◽

Ice Sheet ◽

Weddell Sea ◽

Significant Advance ◽

Ice Streams ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Ice Stream ◽

Grounding Line

ABSTRACT Using observations of basal topography, ice thickness and modern accumulation rates, we use theory and a dynamic flowline model to examine the sensitivity of Antarctica's Foundation Ice Stream to changes in sea level, accumulation and buttressing at the grounding line. Our sensitivity studies demonstrate that the steep, upward-sloping basal topography inland from the grounding line serves to stabilize retreat of the ice stream, while the upward-sloping submarine topography downstream from the grounding line creates the potential for significant advance under conditions of modest sea-level lowering and/or increased accumulation rate. Extrapolating from Foundation Ice Stream, many nearby Weddell Sea sector ice streams are in a similar configuration, suggesting that the historical and projected responses of this sector's ice streams may contrast with those in the Amundsen or Ross Sea sectors. This work reaffirms that the greatest concerns for rapid West Antarctic Ice Sheet (WAIS) retreat are locations of reverse slopes, muted basal topography and limited lateral support.

Download Full-text

Sensitivity of the Weddell Sea sector ice streams to sub-shelf melting and surface accumulation

The Cryosphere ◽

10.5194/tc-8-2119-2014 ◽

2014 ◽

Vol 8 (6) ◽

pp. 2119-2134 ◽

Cited By ~ 28

Author(s):

A. P. Wright ◽

A. M. Le Brocq ◽

S. L. Cornford ◽

R. G. Bingham ◽

H. F. J. Corr ◽

...

Keyword(s):

Adaptive Mesh Refinement ◽

Reference Model ◽

Ice Sheet ◽

Deep Ocean ◽

Weddell Sea ◽

Ice Shelf ◽

Ice Streams ◽

Deep Ocean Water ◽

Grounding Line ◽

The Impact

Abstract. A recent ocean modelling study indicates that possible changes in circulation may bring warm deep-ocean water into direct contact with the grounding lines of the Filchner–Ronne ice streams, suggesting the potential for future ice losses from this sector equivalent to ~0.3 m of sea-level rise. Significant advancements have been made in our knowledge of both the basal topography and ice velocity in the Weddell Sea sector, and the ability to accurately model marine ice sheet dynamics, thus enabling an assessment to be made of the relative sensitivities of the diverse collection of ice streams feeding the Filchner–Ronne Ice Shelf. Here we use the BISICLES ice sheet model, which employs adaptive-mesh refinement to resolve grounding line dynamics, to carry out such an assessment. The impact of realistic perturbations to the surface and sub-shelf mass balance forcing fields from our 2000-year "reference" model run indicate that both the Institute and Möller ice streams are highly sensitive to changes in basal melting either near to their respective grounding lines, or in the region of the ice rises within the Filchner–Ronne Ice Shelf. These same perturbations have little impact, however, on the Rutford, Carlson or Foundation ice streams, while the Evans Ice Stream is found to enter a phase of unstable retreat only after melt at its grounding line has increased by 50% of likely present-day values.

Download Full-text

Ancient pre-glacial erosion surfaces preserved beneath the West Antarctic Ice Sheet

Earth Surface Dynamics Discussions ◽

10.5194/esurfd-2-681-2014 ◽

2014 ◽

Vol 2 (2) ◽

pp. 681-713

Author(s):

K. C. Rose ◽

N. Ross ◽

R. G. Bingham ◽

H. F. J. Corr ◽

F. Ferraccioli ◽

...

Keyword(s):

Ross Sea ◽

Ice Sheet ◽

Deep Ocean ◽

Ocean Basin ◽

Weddell Sea ◽

West Antarctica ◽

Ice Streams ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Wave Erosion

Abstract. We present ice-penetrating radar evidence for ~150 km wide planation surfaces beneath the upstream Institute and Möller Ice Streams, West Antarctica. Accounting for isostatic rebound under ice-free conditions, the surfaces would be around sea level. We, thus, interpreted the surfaces as ancient, marine erosion (wave-cut) platforms. The scale and geometry of the platforms are comparable to erosion surfaces identified in the Ross Sea embayment, on the opposite side of West Antarctica. Their formation is likely to have begun after the development of the deep ocean basin of the Weddell Sea (~160 Myr ago). In order to form wave-cut platforms, the sea must be relatively free of sea ice for a sustained period to allow wave erosion at wave base. As a consequence, the most recent period of sustained marine erosion is likely to be the Mid-Miocene Climatic Optimum (17–15 Ma), when warm atmospheric and oceanic temperatures would have prevented ice from blanketing the coast during periods of ice-sheet retreat. The erosion surfaces are preserved in this location due to the collective action of the Pirrit and Martin–Nash Hills on ice-sheet flow, which results in a region of slow flowing, cold-based ice downstream of this major topographic barrier. This investigation shows that smooth, flat subglacial topography does not always correspond with regions of either present or former fast ice flow, as has previously been assumed.

Download Full-text

Ice-flow patterns and dispersal of erratics at the southwestern margin of the last Scandinavian Ice Sheet: signature of palaeo-ice streams

Boreas ◽

10.1080/03009480310001074 ◽

2003 ◽

Vol 32 (1) ◽

pp. 130-148 ◽

Cited By ~ 1

Author(s):

KURT H. KJÆR ◽

MICHAEL HOUMARK-NIELSEN ◽

NIELS RICHARDT

Keyword(s):

Ice Sheet ◽

Flow Patterns ◽

Ice Streams ◽

Ice Flow ◽

Scandinavian Ice Sheet ◽

Southwestern Margin

Download Full-text

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.

Download Full-text