Climate Response to Increasing Antarctic Iceberg and Ice Shelf Melt

Mackie, Shona; Smith, Inga J.; Ridley, Jeff; Stevens, David P.; Langhorne, Patricia J.

doi:10.1175/jcli-d-19-0881.1

Cited by 24 publications

(21 citation statements)

References 74 publications

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“…(2020), we imposed the meltwater fluxes in regions of observed ice shelf melting rather than a spatially uniform flux. However, all freshwater enters at the surface and directly on the shelf, while in nature, freshwater discharge from the AIS occurs through basal melting at the grounding lines in the subsurface ocean and through iceberg calving (a mechanism that can deliver fresh water away from the shelf) (Rignot et al., 2013; Deeporter et al., 2013; Stern et al., 2016; Mackie et al., 2020). Additionally, we did not include any temporal variability or vertical structure in the meltwater perturbations.…”

Section: Discussionmentioning

confidence: 99%

“…The subsurface ocean warms as a consequence of the reduced vertical heat transport (Bronselaer et al., 2018). Robust responses to increased Antarctic meltwater have been documented in modeling studies utilizing diverse methods for applying the meltwater forcing, differing background climatological states, and differing model resolutions (Bintanja et al., 2013; Bronselaer et al., 2018; Fogwill et al., 2015; Lago & England, 2019; Ma & Wu, 2011; Mackie et al., 2020; Menviel et al., 2010; Moorman et al., 2020; Pauling et al., 2016; Purich et al., 2018; Sadai et al., 2020; Snow et al., 2016; Stouffer et al., 2007; Swart & Fyfe, 2013; Swingedouw et al., 2009). Common responses reported in all of the studies cited above include a strong cooling of surface air temperature (SAT) and sea surface temperature (SST), expansion and thickening of Antarctic sea ice, reduced Antarctic Bottom Water (AABW) formation, increased subsurface heat content, and shifts in global wind and precipitation patterns (Bronselaer et al., 2018; Ma & Wu, 2011; Mackie et al., 2020; Stouffer et al., 2007; Swingedouw et al., 2009).…”

Section: Introductionmentioning

confidence: 99%

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Importance of the Antarctic Slope Current in the Southern Ocean Response to Ice Sheet Melt and Wind Stress Change

et al. 2022

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We use two coupled climate models, GFDL‐CM4 and GFDL‐ESM4, to investigate the physical response of the Southern Ocean to changes in surface wind stress, Antarctic meltwater, and the combined forcing of the two in a pre‐industrial control simulation. The meltwater cools the ocean surface in all regions except the Weddell Sea, where the wind stress warms the near‐surface layer. The limited sensitivity of the Weddell Sea surface layer to the meltwater is due to the spatial distribution of the meltwater fluxes, regional bathymetry, and large‐scale circulation patterns. The meltwater forcing dominates the Antarctic shelf response and the models yield strikingly different responses along West Antarctica. The disagreement is attributable to the mean‐state representation and meltwater‐driven acceleration of the Antarctic Slope Current (ASC). In CM4, the meltwater is efficiently trapped on the shelf by a well resolved, strong, and accelerating ASC which isolates the West Antarctic shelf from warm offshore waters, leading to strong subsurface cooling. In ESM4, a weaker and diffuse ASC allows more meltwater to escape to the open ocean, the West Antarctic shelf does not become isolated, and instead strong subsurface warming occurs. The CM4 results suggest a possible negative feedback mechanism that acts to limit future melting, while the ESM4 results suggest a possible positive feedback mechanism that acts to accelerate melt. Our results demonstrate the strong influence the ASC has on governing changes along the shelf, highlighting the importance of coupling interactive ice sheet models to ocean models that can resolve these dynamical processes.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Importance of the Antarctic Slope Current in the Southern Ocean Response to Ice Sheet Melt and Wind Stress Change

et al. 2022

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“…The fate and impact of the meltwater-rich water depends greatly on the depth at which it achieves neutral buoyancy and leaves the region flowing along density surfaces. If the relatively fresh meltwater-rich water rises, it could offset the brine rejected by sea ice formation and reduce occurrences of deep convection and bottom-water formation 7,8 . The relatively warm meltwaterrich water may also melt the sea ice in front of the ice shelf [9][10][11] .…”

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confidence: 99%

“…The relatively warm meltwaterrich water may also melt the sea ice in front of the ice shelf [9][10][11] . The resulting polynya would allow air-sea heat exchange and feedback onto ice-shelf basal melt by influencing the upper-ocean heat content 1,8,12 . The outflow of meltwater may boost the overturning circulation resulting in an enhanced heat flux into the ice cavity [13][14][15][16] .…”

mentioning

confidence: 99%

Winter seal-based observations reveal glacial meltwater surfacing in the southeastern Amundsen Sea

Zheng

Heywood

Webber

et al. 2021

Commun Earth Environ

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Determining the injection of glacial meltwater into polar oceans is crucial for quantifying the climate system response to ice sheet mass loss. However, meltwater is poorly observed and its pathways poorly known, especially in winter. Here we present winter meltwater distribution near Pine Island Glacier using data collected by tagged seals, revealing a highly variable meltwater distribution with two meltwater-rich layers in the upper 250 m and at around 450 m, connected by scattered meltwater-rich columns. We show that the hydrographic signature of meltwater is clearest in winter, when its presence can be unambiguously mapped. We argue that the buoyant meltwater provides near-surface heat that helps to maintain polynyas close to ice shelves. The meltwater feedback onto polynyas and air-sea heat fluxes demonstrates that although the processes determining the distribution of meltwater are small-scale, they are important to represent in Earth system models.

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“…Melting of ice at the periphery drives global overturning circulation through the stratification of the water column and production of sea ice (Bintanja 1.2. ANTARCTIC GLACIOLOGY 5 et al, 2015a;Mackie et al, 2020;Bronselaer et al, 2018). The ice sheet also plays a primary role in regulation of Southern Ocean ecosystems and global biogeochemical cycles (Vizcaino, 2014).…”

Section: Antarctic Glaciology 121 Antarcticamentioning

confidence: 99%

Future Evolution of the Amundsen Sea Embayment, West Antarctica: Exploring the Modelled Ice Stream Sensitivity to Numerical Representation

Alevropoulos-Borrill¹

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<p>The Amundsen Sea Embayment (ASE) is among the most dynamic catchments in Antarctica. With a recent history of increasing mass loss, and the potential to raise global sea levels by 1.2 m, the evolution of ice streams in the ASE in response to a changing climate must be understood. Sub-ice shelf (IS) basal melting of ASE ice streams is projected to increase in the future in response to climate change, which could initiate unstable retreat in the region. Ice sheet models are used to numerically represent ice flow and simulate future evolution of ice sheets in response to climate. Representation of processes, boundary conditions, model initialisation and the input datasets are at the discretion of model users. However, numerical representation impacts the modelled behaviour of ice streams and can lead to uncertainty in future projections. Understanding the interplay between uncertainty in external forcing and internal ice sheet model configuration is important for constraining future estimates of ASE sea level contribution. This thesis explores the future evolution of ASE ice streams with a focus on the sensitivity of ice streams to IS melting and the role of numerical representation in altering the sensitivity of ice streams to future forcing. Here, century scale simulations are performed on a regional ASE domain with the high resolution adaptive mesh refinement model, BISICLES. BISICLES captures both shear-dominated flow of grounded ice and longitudinal stress-dominated flow of floating ice, while resolving the grounding line to 250 m, meaning the fast evolving ice streams in the ASE are well represented. Experiments use perturbations of IS melting to force the ice sheet over 200 years. Different representations of subglacial rheology (sliding law), calving front position, geometry product, choice of ice sheet model and parameterization of IS melting are explored for simulations with varying future IS melt rates. Following a multi-decadal period of elevated IS melting, a sustained reduction in melting to below present-day rates can limit the total mass loss from the ASE and drive regrowth of ice streams through grounding line advance. Pine Island Glacier (PIG) is more sensitive to the choice of sliding law than to the migration of a calving front, however, sliding law and ice front are most important during application of positive forcing. Thwaites Glacier is less sensitive to the sliding law than PIG, but is more sensitive to the bed geometry product used, particularly in inducing acceleration consistent with observations. Differences in the parameterization of IS melt over the 21 st century leads to a doubling in projected mass loss for a single future climate scenario. The results of a model comparison demonstrate the choice of ice flow model is less important than the model initialisation, which amplifies model differences in response to perturbed IS melting. The exploration presented here into the role of numerical representation provides context for the interpretation of existing ASE simulations and also helps clarify which model configuration(s) are best able to reduce sea-level projection uncertainty.</p>

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Climate Response to Increasing Antarctic Iceberg and Ice Shelf Melt

Cited by 24 publications

References 74 publications

Importance of the Antarctic Slope Current in the Southern Ocean Response to Ice Sheet Melt and Wind Stress Change

Importance of the Antarctic Slope Current in the Southern Ocean Response to Ice Sheet Melt and Wind Stress Change

Winter seal-based observations reveal glacial meltwater surfacing in the southeastern Amundsen Sea

Future Evolution of the Amundsen Sea Embayment, West Antarctica: Exploring the Modelled Ice Stream Sensitivity to Numerical Representation

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