A novel method for predicting fracture in floating ice

Logan, Liz C.; Catania, G. A.; Lavier, L. L.; Choi, Eunseo

doi:10.3189/2013jog12j210

Cited by 15 publications

(15 citation statements)

References 66 publications

(144 reference statements)

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“…The long‐term strain rate yields a stress estimate of about 80 kPa. We add to this extensional stress the local extensional stress induced by the steady‐state curvature of the ice at the grounding zone site (GZ19), as in Logan et al (). This local extensional stress is estimated at 30 kPa using a radius of curvature from kinematic GPS profiles across the flexure zone (Siegfried, ).…”

Section: Discussionmentioning

confidence: 99%

Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

et al. 2020

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Mass loss from the Antarctic ice sheet is sensitive to conditions in ice shelf grounding zones, the transition between grounded and floating ice. To observe tidal dynamics in the grounding zone, we moored an ocean pressure sensor to Ross Ice Shelf, recording data for 54 days. In this region the ice shelf is brought out of hydrostatic equilibrium by the flexural rigidity of ice, yet we found that tidal pressure variations at a constant geopotential surface were similar within and outside of the grounding zone. This implies that the grounding zone ocean cavity was overpressurized at high tide and underpressurized at low tide by up to 10 kPa with respect to glaciostatic pressure at the ice shelf base. Phase lags between ocean pressure and vertical ice shelf motion were tens of minutes for diurnal and semidiurnal tides, an effect that has not been incorporated into ocean models of tidal currents below ice shelves. These tidal pressure variations may affect the production and export of meltwater in the subglacial environment and may increase basal crevasse heights in the grounding zone by several meters, according to linear elastic fracture mechanics. We find anomalously high tidal energy loss at the K 1 constituent in the grounding zone and hypothesize that this could be explained by seawater injection into the subglacial environment at high tide or internal tide generation through interactions with topography. These observations lay the foundation for improved representation of the grounding zone and its tidal dynamics in ocean circulation models of sub-ice shelf cavities.Plain Language Summary One of the challenges for sea level rise prediction is understanding how the Antarctic ice sheets and the Southern Ocean interact. Ocean tides are an important component of this interaction, influencing ice shelf melting and the flow rate of grounded ice toward the coast. We report new observations relevant to this interaction: tidally varying ocean pressures where the ice first goes afloat to become an ice shelf. These tidal ocean pressure variations influence tidal currents below the ice shelf, and we propose that they also push seawater beneath the ice inland of the ice shelf and extend fractures at the ice shelf base. This study identifies tidal processes that may affect melt and fracture near the inland edge of ice shelves, a highly sensitive zone for ice dynamics.

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Section: Discussionmentioning

confidence: 99%

Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

et al. 2020

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“…In fact, resolving the vertical dimension of fracturing is relevant in understanding fracture interaction and calving and needs to be specified in an expanded formulation of the fracture density. To give an example, tensile crevasse formation at the ice-shelf bottom triggered by vertical bending at the grounding line (Logan et al, 2013) cannot be captured by shallow approximation models. Contribution of such processes may be considered as boundary conditions, φ 0 , in future studies.…”

Section: Discussionmentioning

confidence: 99%

Fracture-induced softening for large-scale ice dynamics

Albrecht

Levermann

2014

The Cryosphere

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Abstract. Floating ice shelves can exert a retentive and hence stabilizing force onto the inland ice sheet of Antarctica. However, this effect has been observed to diminish by the dynamic effects of fracture processes within the protective ice shelves, leading to accelerated ice flow and hence to a sea-level contribution. In order to account for the macroscopic effect of fracture processes on large-scale viscous ice dynamics (i.e., ice-shelf scale) we apply a continuum representation of fractures and related fracture growth into the prognostic Parallel Ice Sheet Model (PISM) and compare the results to observations. To this end we introduce a higher order accuracy advection scheme for the transport of the two-dimensional fracture density across the regular computational grid. Dynamic coupling of fractures and ice flow is attained by a reduction of effective ice viscosity proportional to the inferred fracture density. This formulation implies the possibility of non-linear threshold behavior due to self-amplified fracturing in shear regions triggered by small variations in the fracture-initiation threshold. As a result of prognostic flow simulations, sharp across-flow velocity gradients appear in fracture-weakened regions. These modeled gradients compare well in magnitude and location with those in observed flow patterns. This model framework is in principle expandable to grounded ice streams and provides simple means of investigating climate-induced effects on fracturing (e.g., hydro fracturing) and hence on the ice flow. It further constitutes a physically sound basis for an enhanced fracture-based calving parameterization.

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“…Increases in basal water pressure with subglacial channel depth (such that ocean water does not penetrate the glacial hydrologic system) and the hydrostatic pressure imbalance at the terminus support a generally extensional flow regime that promotes buoyancy at the terminus (Murray et al, ). Buoyant flexure at the grounding line (Logan et al, ) likely supports basal crevasse formation (James et al, ; van der Veen, ). Basal crevasses can propagate upwards via tidal pumping to connect to existing surface crevasses and create large volume, full‐thickness, laterally extensive iceberg calving events (Amundson et al, ; Bassis & Jacobs, ; Fried et al, ; James et al, ; Murray, Selmes, et al, ).…”

Section: Controls On Outlet Glacier Dynamicsmentioning

confidence: 98%

Future Evolution of Greenland's Marine‐Terminating Outlet Glaciers

et al. 2020

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Mass loss from the Greenland ice sheet (GrIS) has increased over the last two decades in response to changes in global climate, motivating the scientific community to question how the GrIS will contribute to sea‐level rise on timescales that are relevant to coastal communities. Observations also indicate that the impact of a melting GrIS extends beyond sea‐level rise, including changes to ocean properties and circulation, nutrient and sediment cycling, and ecosystem function. Unfortunately, despite the rapid growth of interest in GrIS mass loss and its impacts, we still lack the ability to confidently predict the rate of future mass loss and the full impacts of this mass loss on the globe. Uncertainty in GrIS mass loss projections in part stems from the nonlinear response of the ice sheet to climate forcing, with many processes at play that influence how mass is lost. This is particularly true for outlet glaciers in Greenland that terminate in the ocean because their flow is strongly controlled by multiple processes that alter their boundary conditions at the ice‐atmosphere, ice‐ocean, and ice‐bed interfaces. Many of these processes change on a range of overlapping timescales and are challenging to observe, making them difficult to understand and thus missing in prognostic ice sheet/climate models. For example, recent (beginning in the late 1990s) mass loss via outlet glaciers has been attributed primarily to changing ice‐ocean interactions, driven by both oceanic and atmospheric warming, but the exact mechanisms controlling the onset of glacier retreat and the processes that regulate the amount of retreat remain uncertain. Here we review the progress in understanding GrIS outlet glacier sensitivity to climate change, how mass loss has changed over time, and how our understanding has evolved as observational capacity expanded. Although many processes are far better understood than they were even a decade ago, fundamental gaps in our understanding of certain processes remain. These gaps impede our ability to understand past changes in dynamics and to make more accurate mass loss projections under future climate change. As such, there is a pressing need for (1) improved, long‐term observations at the ice‐ocean and ice‐bed boundaries, (2) more observationally constrained numerical ice flow models that are coupled to atmosphere and ocean models, and (3) continued development of a collaborative and interdisciplinary scientific community.

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A novel method for predicting fracture in floating ice

Cited by 15 publications

References 66 publications

Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

Fracture-induced softening for large-scale ice dynamics

Future Evolution of Greenland's Marine‐Terminating Outlet Glaciers

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