How Accurately Should We Model Ice Shelf Melt Rates?

Goldberg, David M.; Gourmelen, Noël; Kimura, Satoshi; Millan, Romain; Snow, Kate

doi:10.1029/2018gl080383

Cited by 64 publications

(132 citation statements)

References 67 publications

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“…Numerous modeling studies have demonstrated that ice shelf basal melting is a critical factor in driving ice sheet retreat (e.g. Arthern & Williams, ; Cornford et al, ; DeConto & Pollard, ; Favier et al, ; Goldberg et al, ; Joughin et al, ), with basal melting near the grounding zone and in the new sub‐ice shelf cavities created as melting ice shelves go afloat being particularly important (Arthern & Williams, ; Reese et al, ; R. T. Walker et al, ). Thus, realistic representations of the magnitude and distribution of ice shelf basal melting in global climate models is essential for forecasting 21st century sea level rise.…”

Section: Introductionmentioning

confidence: 99%

“…Numerous modeling studies have demonstrated that ice shelf basal melting is a critical factor in driving ice sheet retreat (e.g. Arthern & Williams, 2017;Cornford et al, 2015;DeConto & Pollard, 2016;Favier et al, 2014;Goldberg et al, 2019;Joughin et al, 2014), with basal melting near the grounding zone and in the new sub-ice shelf cavities created as melting ice shelves go afloat being particularly important (Arthern & Williams, 2017;Reese et al, 2018;R. T. Walker et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

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Turbulence Observations Beneath Larsen C Ice Shelf, Antarctica

Davis

Nicholls

2019

JGR Oceans

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Increased ocean‐driven basal melting beneath Antarctic ice shelves causes grounded ice to flow into the ocean at an accelerated rate, with consequences for global sea level. The turbulent transfer of heat through the ice shelf‐ocean boundary layer is critical in setting the basal melt rate, yet the processes controlling this transfer are poorly understood and inadequately represented in global climate models. This creates large uncertainties in predictions of future sea level rise. Using a hot‐water drilled access hole, two turbulence instrument clusters (TICs) were deployed 2.5 and 13.5 m beneath Larsen C ice shelf in December 2011. Both instruments returned a yearlong record of turbulent velocity fluctuations, providing a unique opportunity to explore the turbulent processes within the ice shelf‐ocean boundary layer. Although the scaling between the turbulent kinetic energy (TKE) dissipation rate and mean flow speed varies with distance from the ice shelf base, at both TICs the TKE dissipation rate is balanced entirely by the rate of shear production. The freshwater released by basal melting plays no role in the TKE balance. When the upper TIC is within the log‐layer, we derive an under‐ice drag coefficient of 0.0022 and a roughness length of 0.44 mm, indicating that the ice base is smooth. Finally, we demonstrate that although the canonical three‐equation melt rate parameterization can accurately predict the melt rate for this example of smooth ice underlain by a cold, tidally forced boundary layer, the law of the wall assumption employed by the parameterization does not hold at low flow speeds.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Turbulence Observations Beneath Larsen C Ice Shelf, Antarctica

Davis

Nicholls

2019

JGR Oceans

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“…Ocean tides also affect sub–ice shelf ocean currents, ocean mixing, and, consequently, ice shelf basal melting (Gwyther et al, ; Jourdain et al, ; MacAyeal, ; Makinson & Nicholls, ; Makinson, ; Makinson et al, ; Mueller et al, , ). Excess basal melting can result in ice shelf thinning that reduces the back stress on ice flow (i.e., reduces “buttressing”), causing increases in ice flow speed (Dupont & Alley, ; Goldberg et al, ; Pritchard et al, ; Reese et al, ). Additionally, coupled ice sheet and ocean models that fail to capture the tidal contribution to basal melting may incorrectly tune parameterizations of basal melting, modifying the sensitivity of basal melting to future ocean conditions (Dinniman et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…Ice sheet dynamics are highly sensitive to reduced buttressing caused by increased melting near the grounding line, the location where the ice shelf first goes afloat (Goldberg et al, ; Reese et al, ; Seroussi & Morlighem, ). Below most of the area of large ice shelves, tidal currents that contribute to melting can be evaluated from an ocean model that assumes that the ice shelf is in local hydrostatic equilibrium (Padman et al, ).…”

Section: Introductionmentioning

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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“…Recent studies have highlighted a lack of sub‐ice‐shelf bathymetry as a “major limitation” (Pattyn et al, 2017) for future projections of Antarctic mass balance. Improved bathymetric mapping allows determination of water access pathways and calculation of spatially and temporally variable melt rates (e.g., Cochran et al, 2014; Goldberg et al, 2019; Milillo et al, 2019; Morlighem et al, 2020; Pattyn et al, 2017; Tinto et al, 2019). In addition, sub‐ice‐shelf bathymetry also provides information about ice dynamic history.…”

Section: Introductionmentioning

confidence: 99%

Detailed Seismic Bathymetry Beneath Ekström Ice Shelf, Antarctica: Implications for Glacial History and Ice‐Ocean Interaction

Smith

Hattermann

Kuhn

et al. 2020

Geophysical Research Letters

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The shape of ice shelf cavities are a major source of uncertainty in understanding ice-ocean interactions. This limits assessments of the response of the Antarctic ice sheets to climate change. Here we use vibroseis seismic reflection surveys to map the bathymetry beneath the Ekström Ice Shelf, Dronning Maud Land. The new bathymetry reveals an inland-sloping trough, reaching depths of 1,100 m below sea level, near the current grounding line, which we attribute to erosion by palaeo-ice streams. The trough does not cross-cut the outer parts of the continental shelf. Conductivity-temperature-depth profiles within the ice shelf cavity reveal the presence of cold water at shallower depths and tidal mixing at the ice shelf margins. It is unknown if warm water can access the trough. The new bathymetry is thought to be representative of many ice shelves in Dronning Maud Land, which together regulate the ice loss from a substantial area of East Antarctica.Plain Language Summary Antarctica is surrounded by floating ice shelves, which play a crucial role in regulating the flow of ice from the continent into the oceans. The ice shelves are susceptible to melting from warm ocean waters beneath them. In order to better understand the melting, knowledge of the shape and depth of the ocean cavity beneath ice shelves is crucial. In this study, we present new measurements of the sea floor depth beneath Ekström Ice Shelf in East Antarctica. The measurements reveal a much deeper sea floor than previously known. We discuss the implications of this for access of warm ocean waters, which can melt the base of the ice shelf and discuss how the observed sea floor features were formed by historical ice flow regimes. Although Ekström Ice Shelf is relatively small, the geometry described here is thought to be representative of the topography beneath many ice shelves in this region, which together regulate the ice loss from a substantial area of East Antarctica.

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How Accurately Should We Model Ice Shelf Melt Rates?

Cited by 64 publications

References 67 publications

Turbulence Observations Beneath Larsen C Ice Shelf, Antarctica

Turbulence Observations Beneath Larsen C Ice Shelf, Antarctica

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

Detailed Seismic Bathymetry Beneath Ekström Ice Shelf, Antarctica: Implications for Glacial History and Ice‐Ocean Interaction

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