Mechanical analysis of pinning points in the Ross Ice Shelf, Antarctica

Still, Holly; Campbell, A. J.; Hulbe, Christina L.

doi:10.1017/aog.2018.31

Cited by 29 publications

(49 citation statements)

References 57 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…2c). Sticky spots are localised areas of higher resistance to basal sliding associated with undulations in the subglacial topography, or variations in till properties and basal water pressure (Alley, 1993;Stokes et al, 2007). Model initialisation results in a greater density of sticky spots on MacIS than on BIS, a result that is consistent with other inversions of observed velocities (Joughin et al, 2004;Sergienko et al, 2008), observations of icestream surface morphology and textures (Stephenson and Bindschadler, 1990;Bindschadler and Scambos, 1991), and seismic surveys (Anandakrishnan and Alley, 1994;Luthra et al, 2016).…”

Section: Basal Drag τ Bsupporting

confidence: 64%

“…For example, the speedup and grounding-line retreat of Pine Island Glacier following the loss of a pinning point has been documented by Bindschadler (2002), Rignot (2002), Jenkins et al (2010) and Arndt et al (2018). The individual force balance contributions of various Antarctic pinning points have been computed from observational data by Thomas (1973), Thomas (1979), Thomas and MacAyeal (1982), MacAyeal et al (1987), and Still et al (2019), but such calculations cannot address nonlocal effects. Flow buttressing numbers (Borstad et al, 2013;Fürst et al, 2016) provide a summary view of the non-local effects but do not quantify the pinning point contribution to individual resistive stresses.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Mechanics and dynamics of pinning points on the Shirase Coast, West Antarctica

Still

Hulbe

2021

The Cryosphere

Self Cite

View full text Add to dashboard Cite

Abstract. Ice rises and rumples, sites of localised ice-shelf grounding, modify ice-shelf flow by generating lateral and basal shear stresses, upstream compression, and downstream tension. Studies of pinning points typically quantify this role indirectly, through related metrics such as a buttressing number. Here, we quantify the dynamic effects of pinning points directly, by comparing model-simulated stress states in the Ross Ice Shelf (RIS) with and without a specific set of pinning points located downstream of the MacAyeal and Bindschadler ice streams (MacIS and BIS, respectively). Because ice properties are only known indirectly, the experiment is repeated with different realisations of the ice softness. While longitudinal stretching, and thus ice velocity, is smaller with the pinning points, flow resistance generated by other grounded features is also smaller. Conversely, flow resistance generated by other grounded features increases when the pinning points are absent, providing a non-local control on the net effect of the pinning points on ice-shelf flow. We find that an ice stream located directly upstream of the pinning points, MacIS, is less responsive to their removal than the obliquely oriented BIS. This response is due to zones of locally higher basal drag acting on MacIS, which may itself be a consequence of the coupled ice-shelf and ice-stream response to the pinning points. We also find that inversion of present-day flow and thickness for basal friction and ice softness, without feature-specific, a posteriori adjustment, leads to the incorrect representation of ice rumple morphology and an incorrect boundary condition at the ice base. Viewed from the perspective of change detection, we find that, following pinning point removal, the ice shelf undergoes an adjustment to a new steady state that involves an initial increase in ice speeds across the eastern ice shelf, followed by decaying flow speeds, as mass flux reduces thickness gradients in some areas and increases thickness gradients in others. Increases in ice-stream flow speeds persist with no further adjustment, even without sustained grounding-line retreat. Where pinning point effects are important, model tuning that respects their morphology is necessary to represent the system as a whole and inform interpretations of observed change.

show abstract

Section: Basal Drag τ Bsupporting

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Mechanics and dynamics of pinning points on the Shirase Coast, West Antarctica

Still

Hulbe

2021

The Cryosphere

Self Cite

View full text Add to dashboard Cite

show abstract

“…Ice rises are isolated flow centers with the only source of ice being local snow accumulation, whereas an ice rumple is primarily supplied by flow from an upstream ice shelf into a grounded region (Matsuoka et al, ). Ice rises control the large‐scale flow of ice shelves (Berger et al, ; Borstad et al, ; Fürst et al, ; Wearing et al, ) and act as pinning points, generating buttressing and controlling the flow of grounded ice upstream (Favier et al, ; Fürst et al, ; Goldberg et al, ; Gudmundsson, ; Still et al, ). The imprint of an ice rise on ice dynamics can be seen in the surface features produced as the ice deforms past the ice rise (Fahnestock et al, ), with crevassing produced in areas of high deformation.…”

Section: Introductionmentioning

confidence: 99%

Holocene Formation of Henry Ice Rise, West Antarctica, Inferred From Ice‐Penetrating Radar

Wearing

Kingslake

2019

JGR Earth Surface

View full text Add to dashboard Cite

Ice rises are regions of grounded ice embedded within floating ice shelves. The deformation of ice past them increases the back stress generated by the ice shelf, slowing the flow of the ice sheet. We present ground‐based ice‐penetrating radar data from Henry Ice Rise in the Ronne Ice Shelf, West Antarctica, that indicates regrounding during the Holocene. Relic crevasses and melt synclines are observed upstream of the present‐day grounding line. We conclude that these features formed during a previous flow configuration, from which the grounding line has since advanced to its current position. In agreement with previous work, our observations can be explained if initial grounding of the ice shelf occurred on a bathymetric high, forming an ice rumple that migrated upstream and temporarily ungrounded over the topographic high. The grounding line then advanced, preserving relic basal crevasses in the newly grounded ice. Using a simple ice‐flow model, we simulate the burial of these crevasses. While accounting for uncertainty in accumulation, firn density, radar‐derived depth, ice‐thickening history, initial crevasse height, and glacial isostatic adjustment, we estimate a burial time of 6 ± 2 kyr before present for the oldest relic crevasses, indicating that the ice rise formed at approximately this time. This potentially increased the buttressing generated by the Ronne Ice Shelf, causing thickening and advance of the ice sheet. By dating the formation and providing details of ice‐rise formation, these new results can provide useful constraints on both large‐scale ice‐sheet models and models of ice‐rumple and ice‐rise formation.

show abstract

“…Although Crary Ice Rise is significantly seaward of SLW, it is situated on a pronounced bathymetric high. Therefore, it is plausible that by grounding first, it provided backstress (Still et al, 2019), allowing ice thickening and slow-down to aid the process of grounding line re-advance for the Whillans Ice Stream (Fried et al, 2014).…”

Section: Post-lgm Grounding Line Positionmentioning

confidence: 99%

Did Holocene climate changes drive West Antarctic grounding line retreat and re-advance?

Neuhaus¹,

Tulaczyk²,

Stansell³

et al. 2020

Preprint

View full text Add to dashboard Cite

Abstract. Knowledge of past ice sheet configurations is useful for informing projections of future ice sheet dynamics and for calibrating ice sheet models. The topology of grounding line retreat in the Ross Sea Sector of Antarctica has been much debated, but it has generally been assumed that the modern ice sheet is as small as it has been for more than 100,000 years (Conway et al., 1999; Lee et al., 2017; Lowry et al., 2019; McKay et al., 2016; Scherer et al., 1998). Recent findings suggest that the West Antarctic Ice Sheet (WAIS) grounding line retreated beyond its current location earlier in the Holocene and subsequently re-advanced to reach its modern position (Bradley et al., 2015; Kingslake et al., 2018). Here, we further constrain the post-LGM grounding line retreat and re-advance in the Ross Sea Sector using a two-phase model of radiocarbon input and decay in subglacial sediments from six sub-ice sampling locations. In addition, we reinterpret high basal temperature gradients, measured previously at three sites in this region (Engelhardt, 2004), which we explain as resulting from recent ice shelf re-grounding accompanying grounding line re-advance. At one location – Subglacial Lake Whillans (SLW) – for which a sediment porewater chemistry profile is known, we estimate the grounding line re-advance by simulating ionic diffusion. Collectively, our analyses indicate that the grounding line retreated over SLW ca. 4000 years ago, and over sites on Whillans Ice Stream (WIS), Kamb Ice Stream (KIS), and Bindschadler Ice Stream (BIS) ca. 4500, ca. 2000, and ca. 2000 years ago respectively. The grounding line only recently re-advanced back over those sites ca. 1000, ca. 1100, ca. 500, and ca. 500 years ago for SLW, WIS, KIS, and BIS respectively. The timing of grounding line retreat coincided with a warm period in the mid- to late-Holocene. Conversely, grounding line re-advance is coincident with climate cooling in the last 1000–2000 years. Our estimates for the timing of grounding line retreat and re-advance are also consistent with relatively low carbon-to-nitrogen ratios measured in our subglacial sediment samples (suggesting a marine source of organic matter) and with the lack of grounding-zone wedges in front of modern grounding lines. Based on these results, we propose that the Siple Coast grounding line motions in the mid- to late-Holocene were driven by relatively modest changes in regional climate, rather than by ice sheet dynamics and glacioisostatic rebound, as hypothesized previously (Kingslake et al., 2018).

show abstract

Mechanical analysis of pinning points in the Ross Ice Shelf, Antarctica

Cited by 29 publications

References 57 publications

Mechanics and dynamics of pinning points on the Shirase Coast, West Antarctica

Mechanics and dynamics of pinning points on the Shirase Coast, West Antarctica

Holocene Formation of Henry Ice Rise, West Antarctica, Inferred From Ice‐Penetrating Radar

Did Holocene climate changes drive West Antarctic grounding line retreat and re-advance?

Contact Info

Product

Resources

About