The Transient Response of Ice Shelf Melting to Ocean Change

Holland, Paul R.

doi:10.1175/jpo-d-17-0071.1

Cited by 26 publications

(35 citation statements)

References 35 publications

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“…As the period of variability decreases below 5 years, we expect delays to become increasingly trivial. This expectation is consistent with Holland (2017), who showed that for small, warm ice shelves (similar to Thwaites Ice Shelf), ocean temperature variability below 5-year periodicity has a complex interaction with subshelf melting that tends to cancel out the effects of warm and cold phases of variability, at least for idealized model configurations. This is because water mass residence times are long enough relative to the period of variability to preclude complete cavity flushing between alternating warm and cold phases.…”

Section: Role Of Variability Periodsupporting

confidence: 90%

Effect of Subshelf Melt Variability on Sea Level Rise Contribution From Thwaites Glacier, Antarctica

et al. 2019

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Modeling and observations suggest that Thwaites Glacier, West Antarctica, has begun unstable retreat. Concurrently, oceanographic observations have revealed substantial multiyear variability in the temperature of the ocean water driving retreat through melting of the ice shelf that restrains inland glacier flow. Using an ensemble of 72 ice‐sheet model simulations that include an idealized representation of ocean temperature variability, we find that variable ice‐shelf melting causes delays in grounding line retreat, mass loss, and sea level contribution relative to steady forcing. Modeled delays are up to 43 years after 500 years of simulation, corresponding to a 10% reduction in glacier mass loss. Delays are primarily caused by asymmetric melt forcing in the presence of variability. For the “warm cavity” conditions beneath Thwaites Ice Shelf, increases in access of warm, deeper water are unable to raise water temperatures in the cavity by much, whereas increases in access of significantly colder, shallow water reduce cavity water temperatures substantially. This leads to lowered mean melt rates under variable ocean temperature forcing. Additionally, about one quarter of the mass loss delay is caused by a nonlinear ice dynamic response to varying ice‐shelf thinning rate, which is amplified during the initial phases of unstable, bed‐topography‐driven retreat. Mass loss rates under variability differ by up to 50% from ensemble mean values at any given time. Our results underscore the need for taking climate variability into account when modeling ice sheet evolution and for continued efforts toward the coupling of ice sheet models to ocean and climate models.

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Section: Role Of Variability Periodsupporting

confidence: 90%

Effect of Subshelf Melt Variability on Sea Level Rise Contribution From Thwaites Glacier, Antarctica

et al. 2019

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“…An ice influx of 2 × 10 5 m 2 a −1 per unit width is prescribed at the “southern” boundary with a fixed calving front at 300 km, and no‐slip conditions at the “east”‐“west” boundaries. The “northern” ocean boundary is restored to temperature and salinity profiles representative of conditions observed in the Amundsen Sea (Figure b, De Rydt et al, ; Holland, ). The boundary restoring occurs over a width of 10 km with a time scale increasing linearly from 1 day to 10 days on the inner edge.…”

Section: Methodsmentioning

confidence: 89%

“…Holland () considers the transient response of ice shelf melting to variable ocean forcing. For ocean oscillations slower than the ocean cavity residence time, melting anomalies adhere to the equilibrium response derived from steady simulations and transient ocean history is unimportant.…”

Section: Introductionmentioning

confidence: 99%

The Response of Ice Sheets to Climate Variability

Snow

Goldberg

Holland

et al. 2017

Geophysical Research Letters

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West Antarctic Ice Sheet loss is a significant contributor to sea level rise. While the ice loss is thought to be triggered by fluctuations in oceanic heat at the ice shelf bases, ice sheet response to ocean variability remains poorly understood. Using a synchronously coupled ice‐ocean model permitting grounding line migration, this study evaluates the response of an ice sheet to periodic variations in ocean forcing. Resulting oscillations in grounded ice volume amplitude is shown to grow as a nonlinear function of ocean forcing period. This implies that slower oscillations in climatic forcing are disproportionately important to ice sheets. The ice shelf residence time offers a critical time scale, above which the ice response amplitude is a linear function of ocean forcing period and below which it is quadratic. These results highlight the sensitivity of West Antarctic ice streams to perturbations in heat fluxes occurring at decadal time scales.

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“…they do not account for ocean circulation timescales (e.g. water residence time in ice-shelf cavities, Holland, 2017). None of the parameterisations account for the Coriolis effect or for bathymetric features (e.g.…”

Section: Ocean Melting From Ocean-dependent Sub-shelf Parameterisationsmentioning

confidence: 99%

Assessment of sub-shelf melting parameterisations using the ocean–ice-sheet coupled model NEMO(v3.6)–Elmer/Ice(v8.3)

et al. 2019

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Abstract. Oceanic melting beneath ice shelves is the main driver of the current mass loss of the Antarctic ice sheet and is mostly parameterised in stand-alone ice-sheet modelling. Parameterisations are crude representations of reality, and their response to ocean warming has not been compared to 3-D ocean–ice-sheet coupled models. Here, we assess various melting parameterisations ranging from simple scalings with far-field thermal driving to emulators of box and plume models, using a new coupling framework combining the ocean model NEMO and the ice-sheet model Elmer/Ice. We define six idealised one-century scenarios for the far-field ocean ranging from cold to warm, and representative of potential futures for typical Antarctic ice shelves. The scenarios are used to constrain an idealised geometry of the Pine Island glacier representative of a relatively small cavity. Melt rates and sea-level contributions obtained with the parameterised stand-alone ice-sheet model are compared to the coupled model results. The plume parameterisations give good results for cold scenarios but fail and underestimate sea level contribution by tens of percent for warm(ing) scenarios, which may be improved by adapting its empirical scaling. The box parameterisation with five boxes compares fairly well to the coupled results for almost all scenarios, but further work is needed to grasp the correct number of boxes. For simple scalings, the comparison to the coupled framework shows that a quadratic as opposed to linear dependency on thermal forcing is required. In addition, the quadratic dependency is improved when melting depends on both local and non-local, i.e. averaged over the ice shelf, thermal forcing. The results of both the box and the two quadratic parameterisations fall within or close to the coupled model uncertainty. All parameterisations overestimate melting for thin ice shelves while underestimating melting in deep water near the grounding line. Further work is therefore needed to assess the validity of these melting parameteriations in more realistic set-ups.

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The Transient Response of Ice Shelf Melting to Ocean Change

Cited by 26 publications

References 35 publications

Effect of Subshelf Melt Variability on Sea Level Rise Contribution From Thwaites Glacier, Antarctica

Effect of Subshelf Melt Variability on Sea Level Rise Contribution From Thwaites Glacier, Antarctica

The Response of Ice Sheets to Climate Variability

Assessment of sub-shelf melting parameterisations using the ocean–ice-sheet coupled model NEMO(v3.6)–Elmer/Ice(v8.3)

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