Bathymetric Controls on Calving Processes at Pine Island Glacier

Arndt, Jan Erik; Larter, Robert D; Friedl, Peter; Gohl, Karsten; Höppner, Kathrin

doi:10.5194/tc-2017-262

Cited by 9 publications

(18 citation statements)

References 32 publications

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“…For PIG, this damage evolution started near the grounding line in 1999 as has been previously documented (7), but satellite imagery in our study shows how the initial damage has rapidly evolved since 2016 into tearing apart of the southern shear zone of the PIG ice shelf (Movies S1 and S2), whereas the northern shear zone remained largely intact after the unprecedented retreat and disconnection from the northern PIG ice shelf in 2015 (6). For TG, the damage started with the gradual disintegration of the shear zone between its glacier tongue and the eastern ice shelf and the subsequent removal of a large part of the TG glacier tongue as described by ref.…”

Section: Damage Evolutionsupporting

confidence: 78%

Damage accelerates ice shelf instability and mass loss in Amundsen Sea Embayment

Lhermitte

Sun

Shuman

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

137

132

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Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are among the fastest changing outlet glaciers in West Antarctica with large consequences for global sea level. Yet, assessing how much and how fast both glaciers will weaken if these changes continue remains a major uncertainty as many of the processes that control their ice shelf weakening and grounding line retreat are not well understood. Here, we combine multisource satellite imagery with modeling to uncover the rapid development of damage areas in the shear zones of Pine Island and Thwaites ice shelves. These damage areas consist of highly crevassed areas and open fractures and are first signs that the shear zones of both ice shelves have structurally weakened over the past decade. Idealized model results reveal moreover that the damage initiates a feedback process where initial ice shelf weakening triggers the development of damage in their shear zones, which results in further speedup, shearing, and weakening, hence promoting additional damage development. This damage feedback potentially preconditions these ice shelves for disintegration and enhances grounding line retreat. The results of this study suggest that damage feedback processes are key to future ice shelf stability, grounding line retreat, and sea level contributions from Antarctica. Moreover, they underline the need for incorporating these feedback processes, which are currently not accounted for in most ice sheet models, to improve sea level rise projections.

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Section: Damage Evolutionsupporting

confidence: 78%

Damage accelerates ice shelf instability and mass loss in Amundsen Sea Embayment

Lhermitte

Sun

Shuman

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

137

132

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“…These areas with low surface slopes are atypical when compared with other bathymetric highs in the area, which have rugged surface morphologies characterised by bedrock grooves and channels (Fig. 2, 4d) (Nitsche et al, 2013;Arndt et al, 2018;Kirkham et al, 2019). Instead, the low slope values are similar to those derived for the base of the troughs in front of Thwaites Ice Shelf (Fig.…”

Section: Bathymetric Highs and Ridgesmentioning

confidence: 50%

“…3b), which are in line with modern ice-velocity vectors (Mouginot et al, 2019) but oblique to the orientation of crag-and-tails in the troughs. A similar interpretation was made for the lineated surface of a former pinning point of the Pine Island Ice Shelf (PIIS) that has been recently exposed by ice-shelf calving events (Arndt et al, 2018), although that feature was not planed off to form a flat-topped high but rather has a stepped and rugged surface morphology https://doi.org/10.5194/tc-2020-25 Preprint. Discussion started: 3 February 2020 c Author(s) 2020.…”

Section: Bathymetric Highs and Ridgesmentioning

confidence: 59%

“…3a) or the moderate-relief areas of lineated terrain with fewer bathymetric highs in eastern Pine Island Bay (Fig. 2a) (Nitsche et al, 2013;Arndt et al, 2018;Kirkham et al, 2019). The continuity and orientation of the trough and ridge relates to the structure of basement rocks on the inner shelf.…”

Section: Implications From the New Bathymetric And Geomorphological Datamentioning

confidence: 99%

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Revealing the former bed of Thwaites Glacier using sea-floor bathymetry

Hogan

Larter

Graham

et al. 2020

Preprint

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Abstract. The geometry of the sea floor beyond Thwaites Glacier (TG) is a major control on the routing of warm ocean waters towards the ice stream’s grounding zone, which has led to increased mass loss through sub-ice-shelf melting and resulting accelerated ice flow. Nearshore topographic highs act as pinning points for the Thwaites Ice Shelf and potentially provide barriers to warm water incursions. To date, few vessels have been able to access this area due to persistent sea-ice and iceberg cover. This critical data gap was addressed in 2019 during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project, with more than 2000 km2 of new multibeam echo-sounder data (MBES) were acquired offshore TG. Here, these data along with legacy MBES datasets are compiled to produce a set of standalone bathymetric grids for the inner Amundsen Sea shelf beyond both Pine Island and Thwaites glaciers. At TG, the bathymetry is dominated by a > 1200 m deep, structurally-controlled trough and discontinuous ridge, on which the Eastern Ice Shelf is pinned. The geometry and composition of the ridge varies spatially with some parts having distinctive flat-topped morphologies produced as their tops were planed-off by erosion at the base of the seaward-moving Thwaites Ice Shelf, suggesting a positive feedback mechanism for ice-shelf ungrounding. Knowing that this offshore area is a former bed for TG, we applied a novel spectral approach to investigate bed roughness and find that derived power spectra can be approximated using an inverse-square law, a result that is consistent with spectra for bed profiles from the modern TG. Using existing ice-flow theory, we also make a first assessment of the form drag (basal drag contribution) for ice flow over this topography. Ice flowing over the sea-floor troughs and ridges would have been affected by similarly high basal drag to that acting in the grounding zone today. We show that the sea-floor bathymetry is an analogue for extant bed areas of TG and that more can be gleaned from these 3D bathymetric datasets regarding the likely spatial variability of bed roughness and bed composition types underneath TG. Comparisons with existing regional bathymetric compilations for the area show that high-frequency (finer than 5 km) bathymetric variability beyond Antarctic ice shelves can only be resolved by observations such as MBES and that without these data calculations of the capacity of bathymetric troughs, and thus oceanic heat flux, may be significantly underestimated. This work meets the requirements of recent numerical ice-sheet and ocean modelling studies that have recognised the need for accurate and high-resolution bathymetry to determine warm water routing to the grounding zone and, ultimately, for predicting glacier retreat behaviour.

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“…Perhaps the most prominent of these extreme changes is the retreat of the floating ice shelves that fringe the Antarctic continent. Ice shelf retreat has been observed to occur gradually, i.e., over a period of years to decades (MacGregor et al, 2012;Arndt et al, 2018), and also abruptly, i.e., over a period of weeks to months (Scambos et al, 2000;Banwell et al, 2013). Although ice shelves themselves do not contribute to sea level rise, they do act to buttress grounded ice (Rignot et al, 2004;Scambos et al, 2004;Goldberg et al, 2009;Gudmundsson, 2013).…”

Section: Introductionmentioning

confidence: 99%

Ice shelf rift propagation: stability, three dimensional effects, and the role of marginal weakening

Lipovsky¹

2019

Preprint

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Abstract. Understanding the processes that govern ice shelf extent are of fundamental importance to improved estimates of future sea level rise. In present-day Antarctica, ice shelf extent is most commonly determined by the propagation of through-cutting fractures called ice shelf rifts. Here, I present the first three-dimensional analysis of ice shelf rift propagation. I present a linear elastic fracture mechanical (LEFM) description of rift propagation. The model predicts that rifts may be stabilized when buoyant flexure results in contact at the tops of the near-tip rift walls. This stabilizing tendency may be overcome, however, by processes that act in the ice shelf margins. In particular, both marginal weakening and the advection of rifts into an ice tongue are shown to be processes that may trigger rift propagation. Marginal shear stress is shown to be the determining factor that governs these types of rift instability. I furthermore show that rift stability is closely related to the transition from uniaxial to biaxial extension known as the compressive arch. Although the partial contact of rift walls is fundamentally a three-dimensional process, I demonstrate that it may be parameterized within more numerically efficient two-dimensional calculations. This study provides a step towards a description of calving physics that is based in fracture mechanics.

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Bathymetric Controls on Calving Processes at Pine Island Glacier

Cited by 9 publications

References 32 publications

Damage accelerates ice shelf instability and mass loss in Amundsen Sea Embayment

Damage accelerates ice shelf instability and mass loss in Amundsen Sea Embayment

Revealing the former bed of Thwaites Glacier using sea-floor bathymetry

Ice shelf rift propagation: stability, three dimensional effects, and the role of marginal weakening

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