Circulation beneath the Filchner Ice Shelf, Antarctica, and its sensitivity to changes in the oceanic environment: a case-study

We investigate the sensitivity of the ocean circulation in the Filchner Trough to changes in the large-scale oceanic environment and its impact on the mass balance of the Filchner Ice Shelf, Antarctica. Three experiments with a three-dimensional ocean model describe (i) the current situation, (ii) a scenario with increased ocean temperatures, and (iii) a scenario with reduced sea-ice formation rates on the adjacent continental shelf. in the final discussion brief results of a combined scenario with increased ocean temperatures and reduced sea-ice formation are presented. The changes from the current situation affect the circulation in the Filchner Trough, and melting and freezing processes beneath the ice shelf. The latter affect the amount and properties of Ice Shelf Water (ISW), a component of Antarctic Bottom Water. Net basal melt rates provide an overall measure for the changes: while the control run yields 0.35 m a−1 net melting averaged over the Filchner Ice Shelf area, the warming scenario results in a more than twofold increase in ice-shelf mass loss. Reduced production of High Salinity ShelfWater due to smaller sea-ice formation rates in the second scenario leads, on the other hand, to a decrease in basal mass loss, because the deep cavity is less well ventilated than in the control run. ISW is cooled and the ice shelf is stabilized under this scenario, which is arguably the more likely development in the southern Weddell Sea.

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A recent update on the circulation and water masses around the Filchner and Ronne ice shelves in the southern Weddell Sea

10.5194/egusphere-egu2020-10194 ◽

2020 ◽

Author(s):

Markus Janout ◽

Hartmut Hellmer ◽

Tore Hattermann ◽

Svein Osterhus ◽

Lucrecia Stulic ◽

...

Keyword(s):

Sea Ice ◽

Ocean Circulation ◽

Large Scale ◽

Austral Summer ◽

Weddell Sea ◽

Shelf Water ◽

Ice Shelf ◽

Present Context ◽

The Stability ◽

Ice Production

The Filchner and Ronne ice sheets (FRIS) compose the second largest contiguous ice sheet on the Antarctic continent. Unlike at several other Antarctic glaciers, basal melt rates at FRIS are comparatively low, as cold and dense waters presently dominate the wide southern Weddell Sea (WS) continental shelf and effectively block out any significant inflow of warmer ocean waters. We revisited the southern WS shelf in austral summer 2018 during Polarstern expedition PS111 with detailed hydrographic and tracer measurements along both the Ronne and Filchner ice fronts. The hydrography along FRIS was characterized by near-freezing high salinity shelf water (HSSW) in front of Ronne, and a striking dominance of ice shelf water (ISW) in Filchner Trough. The cold (-2.2&#176;C) and fresher (34.6) ISW was formed by the interaction of Ronne-sourced HSSW with the ice shelf base. The strong dominance of ISW in Filchner Trough indicates a recently enhanced circulation below FRIS, likely fueled by enhanced sea ice production in the southwestern WS. We view these recent observations in a multidecadal (1973-present) context, contrast the two dominant circulation modes below FRIS, and discuss the importance of sea ice formation and large-scale sea level pressure patterns for the stability of the ocean circulation and basal melt rates underneath FRIS.

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The role of sea ice in the fresh-water budget of the Weddell Sea, Antarctica

Annals of Glaciology ◽

10.3189/172756401781818121 ◽

2001 ◽

Vol 33 ◽

pp. 419-424 ◽

Cited By ~ 19

Author(s):

R. Timmermann ◽

A. Beckmann ◽

H. H. Hellmer

Keyword(s):

Sea Ice ◽

Fresh Water ◽

Water Budget ◽

Ocean Model ◽

Weddell Sea ◽

Ice Formation ◽

Necessary Condition ◽

Ice Shelf ◽

Basal Melting ◽

Good Agreement

AbstractA coupled sea-ice-ocean model of the Weddell Sea, Antarctica, has been developed as part of the Bremerhaven Regional Ice-Ocean Simulations (BRIOS) project. It is based on the s-Coordinate Primitive Equation ocean Model (SPEM) and a dynamic-thermodynamic sea-ice model with viscous-plastic rheology which also provides the thermohaline forcing at the base of the Antarctic ice shelves. Model runs are forced with wind, cloudiness, temperature and precipitation fields of the European Centre for Medium-range Weather Forecasts and U.S. National Centers for Environmental Prediction re-analyses. Model results show good agreement with observations of ice extent, thickness and drift. Water-mass properties and the large-scale circulation are in good agreement with observations. Fresh-water fluxes from sea-ice formation as well as from ice-shelf basal melting and from precipitation are computed and compiled to the fresh-water budget of the Weddell Sea. Supporting estimates based on hydrographic observations, model results indicate that fresh-water loss due to sea-ice formation and export (34mSv) is roughly balanced by ice-shelf basal melting (9 mSv) and net precipitation (19 mSv). Furthermore, sea-ice formation appears to be a necessary condition for bottom-water production in the Weddell Sea.

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Atmospheric forcing of coastal polynyas in the south-western Weddell Sea

Antarctic Science ◽

10.1017/s0954102014000893 ◽

2015 ◽

Vol 27 (4) ◽

pp. 388-402 ◽

Cited By ~ 13

Author(s):

Verena Haid ◽

Ralph Timmermann ◽

Lars Ebner ◽

Günther Heinemann

Keyword(s):

Sea Ice ◽

Large Scale ◽

Reanalysis Data ◽

Ocean Model ◽

Weddell Sea ◽

Small Scale ◽

Atmospheric Conditions ◽

Atmospheric Forcing ◽

The South ◽

Ice Production

AbstractThe development of coastal polynyas, areas of enhanced heat flux and sea ice production strongly depend on atmospheric conditions. In Antarctica, measurements are scarce and models are essential for the investigation of polynyas. A robust quantification of polynya exchange processes in simulations relies on a realistic representation of atmospheric conditions in the forcing dataset. The sensitivity of simulated coastal polynyas in the south-western Weddell Sea to the atmospheric forcing is investigated with the Finite-Element Sea ice-Ocean Model (FESOM) using daily NCEP/NCAR reanalysis data (NCEP), 6 hourly Global Model Europe (GME) data and two different hourly datasets from the high-resolution Consortium for Small-Scale Modelling (COSMO) model. Results are compared for April to August in 2007–09. The two coarse-scale datasets often produce the extremes of the data range, while the finer-scale forcings yield results closer to the median. The GME experiment features the strongest winds and, therefore, the greatest polynya activity, especially over the eastern continental shelf. This results in higher volume and export of High Salinity Shelf Water than in the NCEP and COSMO runs. The largest discrepancies between simulations occur for 2008, probably due to differing representations of the ENSO pattern at high southern latitudes. The results suggest that the large-scale wind field is of primary importance for polynya development.

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Tidal influences on a future evolution of the Filchner–Ronne Ice Shelf cavity in the Weddell Sea, Antarctica

The Cryosphere ◽

10.5194/tc-12-453-2018 ◽

2018 ◽

Vol 12 (2) ◽

pp. 453-476 ◽

Cited By ~ 18

Author(s):

Rachael D. Mueller ◽

Tore Hattermann ◽

Susan L. Howard ◽

Laurie Padman

Keyword(s):

Ocean Circulation ◽

Three Dimensional ◽

Ocean Model ◽

Tidal Currents ◽

Weddell Sea ◽

Ice Shelf ◽

Ice Streams ◽

Future Evolution ◽

History Of ◽

Basal Melting

Abstract. Recent modeling studies of ocean circulation in the southern Weddell Sea, Antarctica, project an increase over this century of ocean heat into the cavity beneath Filchner–Ronne Ice Shelf (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS ice draft. The corresponding change in cavity shape will affect advective pathways and the spatial distribution of tidal currents, which play important roles in basal melting under FRIS. These feedbacks between heat flux, basal melting, and tides will affect the evolution of FRIS under the influence of a changing climate. We explore these feedbacks with a three-dimensional ocean model of the southern Weddell Sea that is forced by thermodynamic exchange beneath the ice shelf and tides along the open boundaries. Our results show regionally dependent feedbacks that, in some areas, substantially modify the melt rates near the grounding lines of buttressed ice streams that flow into FRIS. These feedbacks are introduced by variations in meltwater production as well as the circulation of this meltwater within the FRIS cavity; they are influenced locally by sensitivity of tidal currents to water column thickness (wct) and non-locally by changes in circulation pathways that transport an integrated history of mixing and meltwater entrainment along flow paths. Our results highlight the importance of including explicit tidal forcing in models of future mass loss from FRIS and from the adjacent grounded ice sheet as individual ice-stream grounding zones experience different responses to warming of the ocean inflow.

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The Ronne polynya of 1997/98: observations of air-ice-ocean interaction

Annals of Glaciology ◽

10.3189/172756401781818725 ◽

2001 ◽

Vol 33 ◽

pp. 425-429 ◽

Cited By ~ 23

Author(s):

S. F. Ackley ◽

C. A. Geiger ◽

J. C. King ◽

E. C. Hunke ◽

J. Comiso

Keyword(s):

Solar Radiation ◽

Sea Ice ◽

Satellite Imagery ◽

Southern Oscillation ◽

Open Water ◽

Weddell Sea ◽

Ice Formation ◽

Late Winter ◽

Wind Fields ◽

Ice Shelf

AbstractThe Ronne polynya formed in the Weddell Sea, Antarctica, during the period November 1997−February 1998 to an extent not seen previously in the 25 years of all-weather satellite observations. The vessel HMS Endurance traversed the polynya region and took sea-ice, physical oceanographic and meteorological measurements during January and early February 1998. These observations, together with satellite imagery and weather records, were analyzed to determine the causes of the anomalous condition observed and to provide comparisons for numerical modeling experiments. The polynya area, analyzed from satellite imagery, showed a linear, nearly constant, increase with time from mid-November 1997 through February 1998. It had a maximum open-water area of 3 × 105 km2 and extended 500 km north of the Ronne Ice Shelf (at 76° S) to 70° S. The ice and snow structure of floes at the northern edge of the polynya showed the ice there had formed in the previous mid- to late winter (October 1997 or earlier) and had been advected there either from the eastern Weddell Sea or from the front of the Ronne Ice Shelf. Analyses of the wind fields showed anomalous spring-summer wind fields in the polynya year, with a strong southerly to southwesterly component compared to the mean easterly winds typical of summer conditions. These southerly wind conditions, in both magnitude and direction, therefore account for the drift of ice northward. The predominant summer easterly winds usually fill the southern Weddell Sea with ice from the east, and the high-albedo surfaces reflect the solar radiation, preventing warming of the surface ocean waters and consequent sea-ice melt. Instead, high incident solar radiation from November 1997 to February 1998 was absorbed by the open water, rather than being reflected, thereby both melting ice and preventing ice formation, and thereby sustaining the polynya. We conclude that open-water-albedo feedback is necessary to allow the observed polynya formation, since similar drift conditions prevail in winter (arising from southerly winds also) and usually result in extensive new ice formation in front of the Ronne Ice Shelf. The strong southerly winds therefore have quite opposing seasonal effects, leading to high ice production in winter as usually found, and extensive open water if they occur in spring and summer, as seen in this atypical event in 1997/98. In this case, the atypical southerly winds may be associated with an El Niño-Southern Oscillation (ENSO)-induced atmospheric circulation pattern.

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Investigating the climate variability in the Totten area using NEMO-LIM regional model.

10.5194/egusphere-egu2020-8075 ◽

2020 ◽

Author(s):

Guillian Van Achter ◽

Charles Pelletier ◽

Thierry Fichefet

Keyword(s):

Sea Ice ◽

Ocean Circulation ◽

Ice Sheet ◽

Regional Model ◽

East Antarctica ◽

Shelf Area ◽

Ice Shelf ◽

Ice Shelves ◽

Landfast Ice ◽

The Impact

The Totten ice shelf drains over 570 000 km&#178; of East Antarctica. Most of the ice sheet that drains through the Totten ice-shelf is from Aurora Subglacial Basin and is marine based making the region potentially vulnerable to rapid ice sheet colapse. Understanding how the changes in ocean circulation and properties are causing increased basal melt of Antarctic ice shelves is crucial for predicting future sea level rise. In the context of the The PARAMOUR project (decadal predictability and variability of polar climate: the role of atmosphere-ocean-cryosphere multiscale interaction), we use a high resolution NEMO-LIM 3.6 regional model to investigate the variability and the predictability of the coupled climate system over the Totten area in East Antarctica. In this poster, we will present our on-going work about the impact of landfast ice over the variability of the system. Landfast ice is sea ice that is fastened to the coastline, to the sea floor along shoals or to grouded icebergs. Current sea ice models are unable to represent very crudely the formation, maintenance and decay of coastal landfast ice. We applyed several parameterization for modeling landfast ice over the Totten ice shelf area.

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Seasonal control of Petermann Gletscher ice-shelf melt by the ocean's response to sea-ice cover in Nares Strait

Journal of Glaciology ◽

10.1017/jog.2016.140 ◽

2017 ◽

Vol 63 (238) ◽

pp. 324-330 ◽

Cited By ~ 13

Author(s):

E. L. SHROYER ◽

L. PADMAN ◽

R. M. SAMELSON ◽

A. MÜNCHOW ◽

L. A. STEARNS

Keyword(s):

Sea Ice ◽

Mass Loss ◽

Ocean Circulation ◽

Greenland Ice Sheet ◽

Ice Shelf ◽

Near Surface ◽

Eastern Side ◽

Nares Strait ◽

Landfast Sea Ice ◽

Basal Melting

AbstractPetermann Gletscher drains ~4% of the Greenland ice sheet (GrIS) area, with ~80% of its mass loss occurring by basal melting of its ice shelf. We use a high-resolution coupled ocean and sea-ice model with a thermodynamic glacial ice shelf to diagnose ocean-controlled seasonality in basal melting of the Petermann ice shelf. Basal melt rates increase by ~20% in summer due to a seasonal shift in ocean circulation within Nares Strait that is associated with the transition from landfast sea ice to mobile sea ice. Under landfast ice, cold near-surface waters are maintained on the eastern side of the strait and within Petermann Fjord, reducing basal melt and insulating the ice shelf. Under mobile sea ice, warm waters are upwelled on the eastern side of the strait and, mediated by local instabilities and eddies, enter Petermann Fjord, enhancing basal melt down to depths of 200 m. The transition between these states occurs rapidly, and seasonal changes within Nares Strait are conveyed into the fjord within the same season. These results suggest that long-term changes in the length of the landfast sea-ice season will substantially alter the structure of Petermann ice shelf and its contribution to GrIS mass loss.

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Predicting ocean-induced ice-shelf melt rates using a machine learning image segmentation approach

10.5194/tc-2021-396 ◽

2022 ◽

Author(s):

Sebastian Harry Reid Rosier ◽

Christopher Bull ◽

G. Hilmar Gudmundsson

Keyword(s):

Deep Learning ◽

Ocean Circulation ◽

Large Scale ◽

Ice Sheet ◽

Ground Truth ◽

Ocean Model ◽

Ice Shelf ◽

Computational Expense ◽

Shelf Slope ◽

Wide Range

Abstract. Through their role in buttressing upstream ice flow, Antarctic ice shelves play an important part in regulating future sea level change. Reduction in ice-shelf buttressing caused by increased ocean-induced melt along their undersides is now understood to be one of the key drivers of ice loss from the Antarctic Ice Sheet. However, despite the importance of this forcing mechanism most ice-sheet simulations currently rely on simple melt-parametrisations of this ocean-driven process, since a fully coupled ice-ocean modelling framework is prohibitively computationally expensive. Here, we provide an alternative approach that is able to capture the greatly improved physical description of this process provided by large-scale ocean-circulation models over currently employed melt-parameterisations but with trivial computational expense. We introduce a new approach that brings together deep learning and physical modelling to develop a deep neural network framework, MELTNET, that can emulate ocean model predictions of sub-ice shelf melt rates. We train MELTNET on synthetic geometries, using the NEMO ocean model as a ground-truth in lieu of observations to provide melt rates both for training and to evaluate the performance of the trained network. We show that MELTNET can accurately predict melt rates for a wide range of complex synthetic geometries and outperforms more traditional parameterisations for > 95 % of geometries tested. Furthermore, we find MELTNET's melt rate estimates show sensitivity to established physical relationships such as a changes in thermal forcing and ice shelf slope. This study demonstrates the potential for a deep learning framework to calculate melt rates with almost no computational expense, that could in the future be used in conjunction with an ice sheet model to provide predictions for large-scale ice sheet models.

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Tidal influences on a future evolution of the Filchner-Ronne Ice Shelf cavity in the Weddell Sea, Antarctica

10.5194/tc-2017-110 ◽

2017 ◽

Author(s):

Rachael D. Mueller ◽

Tore Hattermann ◽

Susan L. Howard ◽

Laurence Padman

Keyword(s):

Ocean Circulation ◽

Three Dimensional ◽

Ocean Model ◽

Tidal Currents ◽

Weddell Sea ◽

Ice Shelf ◽

Ice Streams ◽

Future Evolution ◽

History Of ◽

Basal Melting

Abstract. Recent modeling studies of ocean circulation in the southern Weddell Sea, Antarctica, project an increase over this century of ocean heat into the cavity beneath Filchner-Ronne Ice Shelf (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS ice draft. The corresponding change in cavity shape will affect advective pathways and the spatial distribution of tidal currents, which play important roles in basal melting under FRIS. These feedbacks between heat flux, basal melting, and tides will affect the evolution of FRIS under the influence of a changing climate. We explore these feedbacks with a three-dimensional ocean model of the southern Weddell Sea that is forced by thermodynamic exchange beneath the ice shelf and tides along the open boundaries. Our results show regionally-dependent feedbacks that, in some areas, substantially modify the melt rates near the grounding lines of buttressed ice streams that flow into FRIS. These feedbacks are introduced by variations in meltwater production as well as the circulation of this meltwater within the FRIS cavity; they are influenced locally by sensitivity of tidal currents to water column thickness and non-locally by changes in circulation pathways that transport an integrated history of mixing and meltwater entrainment along flow paths. Our results highlight the importance of including explicit tidal forcing in models of future mass loss from FRIS and from the adjacent grounded ice sheet as individual ice stream grounding zones experience different responses to warming of the ocean inflow.

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Assessment of the Finite VolumE Sea Ice Ocean Model (FESOM2.0), Part I: Description of selected key model elements and comparison to its predecessor version

10.5194/gmd-2018-329 ◽

2019 ◽

Cited By ~ 1

Author(s):

Patrick Scholz ◽

Dmitry Sidorenko ◽

Ozgur Gurses ◽

Sergey Danilov ◽

Nikolay Koldunov ◽

...

Keyword(s):

Sea Ice ◽

Finite Volume ◽

Ocean Circulation ◽

Large Scale ◽

Unstructured Mesh ◽

Vertical Mixing ◽

Circulation Model ◽

Ocean Model ◽

Arbitrary Lagrangian Eulerian ◽

Nonlinear Free Surface

Abstract. The evaluation and model element description of the second version of the unstructured-mesh Finite-volumE Sea ice–Ocean circulation Model (FESOM2.0) is presented. The model sensitivity to arbitrary Lagrangian Eulerian (ALE) linear and nonlinear free surface formulation, Gent McWilliams eddy parameterisation, isoneutral Redi diffusion and different vertical mixing schemes is documented. The hydrographic biases, large scale circulation, numerical performance and scalability of FESOM2.0 are compared with its predecessor FESOM1.4. FESOM2.0 shows biases with a magnitude comparable to FESOM1.4 and it simulates a more realistic AMOC. Compared to its predecessor FESOM2.0 provides clearly defined fluxes and a three times higher throughput in terms of simulated years per day (SYPD). It is thus the first mature global unstructured-mesh ocean model with computational efficiency comparable to state-of-the-art structured-mesh ocean models. Other key elements of the model and new development will be described in following-up papers.

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