Representation of basal melting at the grounding line in ice flow
models

Seroussi, Hélène; Morlighem, Mathieu

doi:10.5194/tc-2018-117

Cited by 14 publications

(30 citation statements)

References 19 publications

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“…Our experimentation revealed that the use of sub-grid melting increases the ability of glacier grounding lines to retreat, leading to faster ice loss. Although the numerical veracity of this approach has been questioned 57 , we have previously found little evidence for a grid-size dependency in using this scheme 19 and find instead that it enables simulated mass loss under warmer-than-present palaeoclimate scenarios that is more closely in agreement with proxy reconstructions that when sub-grid melting is omitted 56 . In support of this approach are recent observations confirming that oceanic water intrudes into the grounding zone of marine-terminating Antarctic glaciers in some areas 58 , carrying with it heat available for melting of ice.…”

Section: Methodsmentioning

confidence: 86%

Global environmental consequences of twenty-first-century ice-sheet melt

Golledge

Keller

Gomez

et al. 2019

Nature

367

369

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Section: Methodsmentioning

confidence: 86%

Global environmental consequences of twenty-first-century ice-sheet melt

Golledge

Keller

Gomez

et al. 2019

Nature

367

369

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“…The grounding line position is determined using hydrostatic equilibrium, with sub-cell treatment of the friction and a modified 30 driving stress (Cornford et al, 2016). The melt rate is applied only for fully-floating cells (as in (Seroussi and Morlighem, 2018)) and is composed of a base rate and the anomalies specified in the individual experiments. The base melt rate is time varying and designed to prevent ice shelf thickening but permit thinning where flux divergence in the shelf is positive.…”

Section: A2 Bisi-lbl: Bisiclesmentioning

confidence: 99%

“…The grounding line position is determined using hydrostatic equilibrium, with sub-element parameterization of the friction (Seroussi et al, 2014). The melt rate is applied only for full-floating elements (Seroussi and Morlighem, 2018) and is initialized using mean rates of ocean estimates over the 2004-2015 period (Schodlok et al, 2016), that are kept constant with time. The surface mass balance is from RACMO2.1 1979-2010 mean (Lenaerts et al, 2012).…”

Section: A7 Issm-jpl: Ice Sheet System Model -Jplmentioning

confidence: 99%

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Projecting Antarctica's contribution to future sea level rise from basal ice-shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)

Levermann¹

2019

Preprint

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Abstract. The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty that arises from large uncertainty in the external forcing that future warming may exert onto the ice sheet. While ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean, the approach is neglecting a number of processes such as surface mass balance related contributions and mechanisms. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any dampening or self-amplifying processes. This is particularly relevant in situations where an instability is dominating the ice loss. Results obtained here are thus relevant in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014), but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP-5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP-5 models in relation to the global mean surface warming) and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 is 9.6 mm with a likely range between 5.2 mm and 20.3 mm compared to the observed sea-level contribution from Antarctica of 7.4 mm with a standard deviation of 3.7 mm (Shepherd et al., 2018). For the so-called business-as-usual warming path, RCP-8.5, we obtain a median contribution of the Antarctic ice sheet to global mean sea-level rise within the 21st century of 17 cm with a likely range (66-percentile around the mean) between 9 cm and 36 cm and a very likely range (90-percentile around the mean) between 6 cm and 59 cm. For the RCP-2.6 warming path which will keep the global mean temperature below two degrees of global warming and is thus consistent with the Paris Climate Agreement yields a median of 13 cm of global mean sea-level contribution. The likely range for the RCP-2.6 scenario is between 7 cm and 25 cm and the very likely range is between 5 cm and 39 cm. The structural uncertainties in the method do not allow an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario, separately. The rate of sea level contribution is highest under the RCP-8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade with a likely range between 2 cm/dec and 8 cm/dec and a very likely range between 1 cm/dec and 13 cm/dec.

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“…This is determined in MALI by evaluating the hydrostatic ice floatation criterion at the center of each grid cell. Note that because of the dual grid implementation used in MALI (Hoffman et al, ), this convention leads to treatment of melting near the grounding line in a fashion similar to, but not identical to, the SEM1 melt parameterization described by Seroussi and Morlighem ().…”

Section: Methodsmentioning

confidence: 99%

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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Representation of basal melting at the grounding line in ice flow models

Cited by 14 publications

References 19 publications

Global environmental consequences of twenty-first-century ice-sheet melt

Global environmental consequences of twenty-first-century ice-sheet melt

Projecting Antarctica's contribution to future sea level rise from basal ice-shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)

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

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