scholarly journals Tidal Modulation of Antarctic Ice Shelf Melting

2020 ◽  
Author(s):  
Ole Richter ◽  
David E. Gwyther ◽  
Matt A. King ◽  
Benjamin K. Galton-Fenzi
Keyword(s):  
Boundary Layer ◽  
Continental Shelf ◽  
Friction Velocity ◽  
Cold Water ◽  
Singular Spectrum Analysis ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Basal Melting ◽  
The Impact

Abstract. Tides influence basal melting of individual Antarctic ice shelves, but their net impact on Antarctic-wide ice-ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas by means of a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the total basal mass loss by 57 Gt/yr (4 %), while decreasing continental shelf temperatures by 0.04 °C, indicating a slightly more efficient conversion of ocean heat into ice shelf melting. Regional variations can be larger, with melt rate modulations exceeding 500 % and temperatures changing by more than 0.5 °C, highlighting the importance of capturing tides for robust modelling of glacier systems and coastal oceans. Tide-induced changes around the Antarctic Peninsula have a dipolar distribution with decreased ocean temperatures and reduced melting towards the Bellingshausen Sea and warming along the continental shelf break on the Weddell Sea side. This warming extends under the Ronne Ice Shelf, which also features one of the highest increases in area-averaged basal melting (150 %) when tides are included. Further, by means of a singular spectrum analysis, we explore the processes that cause variations in melting and its drivers in the boundary layer over periods of up to one month. At most places friction velocity varies at tidal timescales (one day or faster), while thermal driving changes at slower rates (longer than one day). In some key regions under the large cold-water ice shelves, however, thermal driving varies faster than friction velocity and this can not be explained by tidal modulations in boundary layer exchange rates alone. Our results suggest that large scale ocean models aiming to predict accurate ice shelf melt rates will need to explicitly resolve tides.

scholarly journals Tidal Modulation of Antarctic Ice Shelf Melting

2021 ◽  
Author(s):  
Ole Richter ◽  
David E. Gwyther ◽  
Matt A. King ◽  
Ben K. Galton-Fenzi
Keyword(s):  
Boundary Layer ◽  
Continental Shelf ◽  
Friction Velocity ◽  
Cold Water ◽  
Singular Spectrum Analysis ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Basal Melting ◽  
The Impact

<p>Tides influence basal melting of individual Antarctic ice shelves, but their net impact on Antarctic-wide ice-ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas by means of a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the total basal mass loss by 57 Gt/yr (4 %), while decreasing continental shelf temperatures by 0.04 °C, indicating a slightly more efficient conversion of ocean heat into ice shelf melting. Regional variations can be larger, with melt rate modulations exceeding 500 % and temperatures changing by more than 0.5 °C, highlighting the importance of capturing tides for robust modelling of glacier systems and coastal oceans. Tide-induced changes around the Antarctic Peninsula have a dipolar distribution with decreased ocean temperatures and reduced melting towards the Bellingshausen Sea and warming along the continental shelf break on the Weddell Sea side. This warming extends under the Ronne Ice Shelf, which also features one of the highest increases in area-averaged basal melting (128 %) when tides are included. Further, by means of a singular spectrum analysis, we explore the processes that cause variations in melting and its drivers in the boundary layer over periods of up to one month. At most places friction velocity varies at tidal timescales (one day or faster), while thermal driving changes at slower rates (longer than one day). In some key regions under the large cold-water ice shelves, however, thermal driving varies faster than friction velocity and this can not be explained by tidal modulations in boundary layer exchange rates alone. Our results suggest that large scale ocean models aiming to predict accurate ice shelf melt rates will need to explicitly resolve tides.</p>

scholarly journals Viscous and elastic buoyancy stresses as drivers of ice-shelf calving

2020 ◽  
Vol 66 (258) ◽  
pp. 643-657 ◽  
Author(s):  
Cyrille Mosbeux ◽  
Till J. W. Wagner ◽  
Maya K. Becker ◽  
Helen A. Fricker
Keyword(s):  
Ice Sheet ◽  
Elastic Model ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Bending Stresses ◽  
Iceberg Calving ◽  
Basal Melting ◽  
The Antarctic ◽  
The Impact ◽  
Maximum Stresses

AbstractThe Antarctic Ice Sheet loses mass via its ice shelves predominantly through two processes: basal melting and iceberg calving. Iceberg calving is episodic and infrequent, and not well parameterized in ice-sheet models. Here, we investigate the impact of hydrostatic forces on calving. We develop two-dimensional elastic and viscous numerical frameworks to model the ‘footloose’ calving mechanism. This mechanism is triggered by submerged ice protrusions at the ice front, which induce unbalanced buoyancy forces that can lead to fracturing. We compare the results to identify the different roles that viscous and elastic deformations play in setting the rate and magnitude of calving events. Our results show that, although the bending stresses in both frameworks share some characteristics, their differences have important implications for modeling the calving process. In particular, the elastic model predicts that maximum stresses arise farther from the ice front than in the viscous model, leading to larger calving events. We also find that the elastic model would likely lead to more frequent events than the viscous one. Our work provides a theoretical framework for the development of a better understanding of the physical processes that govern glacier and ice-shelf calving cycles.

Bathymetry and acoustic facies beneath the former Larsen-A and Prince Gustav ice shelves, north-west Weddell Sea

2001 ◽  
Vol 13 (3) ◽  
pp. 312-322 ◽  
Author(s):  
Carol J. Pudsey ◽  
Jeffrey Evans ◽  
Eugene W. Domack ◽  
Peter Morris ◽  
Rodolfo A. Del Valle
Keyword(s):  
Continental Shelf ◽  
Weddell Sea ◽  
Shelf Edge ◽  
Ice Shelf ◽  
Ice Shelves ◽  
North West ◽  
Preliminary Results ◽  
The Past ◽  
Acoustic Facies ◽  
Marine Mud

We present preliminary results of the first detailied surveys of the former Larsen-A Ice Shelf, Larsen Inlet and southern Prince Gustav Channel, where disintegration of small ice shelves in the past ten years has exposed the seafloor. Glacial troughs in the Larsen-A area, Larsen Inlet and Prince Gustav Channel reach 900–1100 m depth and have hummocky floors. Farther south-east, the continental shelf is shallower (400–500 m) and its surface is fluted to smooth, with the density of iceberg furrowing increasing towards the shelf edge. Acoustic profiles show a drape of transparent sediment 4–8 m thick in Prince Gustav Channel, thinning southwards. In cores, this drape corresponds to diatom-bearing marine and glacial-marine mud. In the Larsen-A area and Larsen Inlet, acoustically opaque sediment includes proximal ice shelf glaciomarine gravelly and sandy muds, and firm to stiff diamicts probably deposited subglacilly. These are overlain by thin (up to 1.3 m) glaciomarine muds, locally with distinctive diatom ooze laminae.

scholarly journals Explicit and parametrised representation of under ice shelf seas in a z<sup>*</sup> coordinate ocean model

2017 ◽  
Author(s):  
Pierre Mathiot ◽  
Adrian Jenkins ◽  
Christopher Harris ◽  
Gurvan Madec
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Weddell Sea ◽  
Depth Range ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Antarctic Continental Shelf ◽  
Shelf Seas ◽  
Ocean Properties ◽  
The Antarctic

Abstract. Ice shelf/ocean interactions are a major source of fresh water on the Antarctic continental shelf and have a strong impact on ocean properties, ocean circulation and sea ice. However, climate models based on the ocean/sea ice model NEMO currently do not include these interactions in any detail. The capability of explicitly simulating the circulation beneath ice shelves is introduced in the non-linear free surface model NEMO. Its implementation into the NEMO framework and its assessment in an idealised and realistic circum-Antarctic configuration is described in this study. Compared with the current prescription of ice shelf melting (i.e. at the surface) inclusion of open sub-ice-shelf leads to a decrease sea ice thickness along the coast, a weakening of the ocean stratification on the shelf, a decrease in salinity of HSSW on the Ross and Weddell Sea shelves and an increase in the strength of the gyres that circulate within the over-deepened basins on the West Antarctic continental shelf. Mimicking the under ice shelf seas overturning circulation by introducing the meltwater over the depth range of the ice shelf base, rather than at the surface is also tested. It yields similar improvements in the simulated ocean properties and circulation over the Antarctic continental shelf than the explicit ice shelf cavity representation. With the ice shelf cavities opened, the widely-used “3 equations” ice shelf melting formulation enables an interactive computation of melting that has been assessed. Comparison with observational estimates of ice shelf melting indicates realistic results for most ice shelves. However, melting rates for Amery, Getz and George VI ice shelves are considerably overestimated.

scholarly journals Impact of ice-shelf basal melting on inland ice-sheet thickness: a model study

2012 ◽  
Vol 53 (60) ◽  
pp. 129-135 ◽  
Author(s):  
Jürgen Determann ◽  
Malte Thoma ◽  
Klaus Grosfeld ◽  
Sylvia Massmann
Keyword(s):  
Mass Loss ◽  
Sea Level ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Ice Volume ◽  
Basal Melting ◽  
The Impact

AbstractIce flow from the ice sheets to the ocean contains the maximum potential contributing to future eustatic sea-level rise. In Antarctica most mass fluxes occur via the extended ice-shelf regions covering more than half the Antarctic coastline. The most extended ice shelves are the Filchner–Ronne and Ross Ice Shelves, which contribute ~30% to the total mass loss caused by basal melting. Basal melt rates here show small to moderate average amplitudes of <0.5ma–1. By comparison, the smaller but most vulnerable ice shelves in the Amundsen and Bellinghausen Seas show much higher melt rates (up to 30 ma–1), but overall basal mass loss is comparably small due to the small size of the ice shelves. The pivotal question for both characteristic ice-shelf regions, however, is the impact of ocean melting, and, coevally, change in ice-shelf thickness, on the flow dynamics of the hinterland ice masses. In theory, ice-shelf back-pressure acts to stabilize the ice sheet, and thus the ice volume stored above sea level. We use the three-dimensional (3-D) thermomechanical ice-flow model RIMBAY to investigate the ice flow in a regularly shaped model domain, including ice-sheet, ice-shelf and open-ocean regions. By using melting scenarios for perturbation studies, we find a hysteresis-like behaviour. The experiments show that the system regains its initial state when perturbations are switched off. Average basal melt rates of up to 2 ma–1 as well as spatially variable melting calculated by our 3-D ocean model ROMBAX act as basal boundary conditions in time-dependent model studies. Changes in ice volume and grounding-line position are monitored after 1000 years of modelling and reveal mass losses of up to 40 Gt a–1.

scholarly journals Modeling the Influence of the Weddell Polynya on the Filchner–Ronne Ice Shelf Cavity

2019 ◽  
Vol 32 (16) ◽  
pp. 5289-5303 ◽  
Author(s):  
Kaitlin A. Naughten ◽  
Adrian Jenkins ◽  
Paul R. Holland ◽  
Ruth I. Mugford ◽  
Keith W. Nicholls ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Deep Convection ◽  
Ocean Model ◽  
Shelf Break ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Warm Deep Water ◽  
Regional Ocean Model ◽  
Ocean Models ◽  
Basal Melting

ABSTRACT Open-ocean polynyas in the Weddell Sea of Antarctica are the product of deep convection, which transports Warm Deep Water (WDW) to the surface and melts sea ice or prevents its formation. These polynyas occur only rarely in the observational record but are a near-permanent feature of many climate and ocean simulations. A question not previously considered is the degree to which the Weddell polynya affects the nearby Filchner–Ronne Ice Shelf (FRIS) cavity. Here we assess these effects using regional ocean model simulations of the Weddell Sea and FRIS, where deep convection is imposed with varying area, location, and duration. In these simulations, the idealized Weddell polynyas consistently cause an increase in WDW transport onto the continental shelf as a result of density changes above the shelf break. This leads to saltier, denser source waters for the FRIS cavity, which then experiences stronger circulation and increased ice shelf basal melting. It takes approximately 14 years for melt rates to return to normal after the deep convection ceases. Weddell polynyas similar to those seen in observations have a modest impact on FRIS melt rates, which is within the range of simulated interannual variability. However, polynyas that are larger or closer to the shelf break, such as those seen in many ocean models, trigger a stronger response. These results suggest that ocean models with excessive Weddell Sea convection may not be suitable boundary conditions for regional models of the Antarctic continental shelf and ice shelf cavities.

scholarly journals Explicit representation and parametrised impacts of under ice shelf seas in the <i>z</i><sup>∗</sup> coordinate ocean model NEMO 3.6

2017 ◽  
Vol 10 (7) ◽  
pp. 2849-2874 ◽  
Author(s):  
Pierre Mathiot ◽  
Adrian Jenkins ◽  
Christopher Harris ◽  
Gurvan Madec
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Weddell Sea ◽  
Surface Model ◽  
Depth Range ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Antarctic Continental Shelf ◽  
Ocean Properties ◽  
The Antarctic

Abstract. Ice-shelf–ocean interactions are a major source of freshwater on the Antarctic continental shelf and have a strong impact on ocean properties, ocean circulation and sea ice. However, climate models based on the ocean–sea ice model NEMO (Nucleus for European Modelling of the Ocean) currently do not include these interactions in any detail. The capability of explicitly simulating the circulation beneath ice shelves is introduced in the non-linear free surface model NEMO. Its implementation into the NEMO framework and its assessment in an idealised and realistic circum-Antarctic configuration is described in this study. Compared with the current prescription of ice shelf melting (i.e. at the surface), inclusion of open sub-ice-shelf cavities leads to a decrease in sea ice thickness along the coast, a weakening of the ocean stratification on the shelf, a decrease in salinity of high-salinity shelf water on the Ross and Weddell sea shelves and an increase in the strength of the gyres that circulate within the over-deepened basins on the West Antarctic continental shelf. Mimicking the overturning circulation under the ice shelves by introducing a prescribed meltwater flux over the depth range of the ice shelf base, rather than at the surface, is also assessed. It yields similar improvements in the simulated ocean properties and circulation over the Antarctic continental shelf to those from the explicit ice shelf cavity representation. With the ice shelf cavities opened, the widely used three equation ice shelf melting formulation, which enables an interactive computation of melting, is tested. Comparison with observational estimates of ice shelf melting indicates realistic results for most ice shelves. However, melting rates for the Amery, Getz and George VI ice shelves are considerably overestimated.

scholarly journals The Impact of Overturning and Horizontal Circulation in Pine Island Trough on Ice Shelf Melt in the Eastern Amundsen Sea

2019 ◽  
Vol 49 (1) ◽  
pp. 63-83 ◽  
Author(s):  
Benjamin G. M. Webber ◽  
Karen J. Heywood ◽  
David P. Stevens ◽  
Karen M. Assmann
Keyword(s):  
Continental Shelf ◽  
Ocean Circulation ◽  
Circulation Model ◽  
Shelf Break ◽  
Ekman Pumping ◽  
Overturning Circulation ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Basal Melting ◽  
The Impact

AbstractThe ice shelves around the Amundsen Sea are rapidly melting as a result of the circulation of relatively warm ocean water into their cavities. However, little is known about the processes that determine the variability of this circulation. Here we use an ocean circulation model to diagnose the relative importance of horizontal and vertical (overturning) circulation within Pine Island Trough, leading to Pine Island and Thwaites ice shelves. We show that melt rates and southward Circumpolar Deep Water (CDW) transports covary over large parts of the continental shelf at interannual to decadal time scales. The dominant external forcing mechanism for this variability is Ekman pumping and suction on the continental shelf and at the shelf break, in agreement with previous studies. At the continental shelf break, the southward transport of CDW and heat is predominantly barotropic. Farther south within Pine Island Trough, northward and southward barotropic heat transports largely cancel, and the majority of the net southward temperature transport is facilitated by baroclinic and overturning circulations. The overturning circulation is related to water mass transformation and buoyancy gain on the shelf that is primarily facilitated by freshwater input from basal melting.

scholarly journals On the freshening of the northwestern Weddell Sea continental shelf

2010 ◽  
Vol 7 (6) ◽  
pp. 2013-2042 ◽  
Author(s):  
H. H. Hellmer ◽  
O. Huhn ◽  
D. Gomis ◽  
R. Timmermann
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Weddell Sea ◽  
Central Basin ◽  
Ice Shelf ◽  
Thermal Front ◽  
Ice Shelves ◽  
Deep Waters ◽  
Sea Ice Edge ◽  
The Antarctic

Abstract. We analysed hydrographic data from the northwestern Weddell Sea continental shelf of three austral winters (1989, 1997 and 2006) and two summers following the last winter cruise. During summer a thermal front exists at ~64° S separating cold southern waters from warm northern waters that have similar characteristics as the deep waters of the central basin of the Bransfield Strait. In winter, the whole continental shelf exhibits southern characteristics with high Neon (Ne) concentrations, indicating a significant input of glacial melt water. The comparison of the winter data at the tip of the Antarctic Peninsula, spanning a period of 17 years, shows a salinity decrease of 0.09 for the whole water column. We interpret this freshening as a reduction in salt input to the water masses being advected northward on the western Weddell Sea continental shelf. Possible causes for the reduced winter salinification are a southward retreat of the summer sea ice edge together with more precipitation in this sector. However, the latter might have happened in conjunction with an increase in ice shelf mass loss, counteracting an enhanced salt input due to sea ice formation in coastal areas formerly occupied by Larsen A and B ice shelves.

scholarly journals The Fate of the Southern Weddell Sea Continental Shelf in a Warming Climate

2017 ◽  
Vol 30 (12) ◽  
pp. 4337-4350 ◽  
Author(s):  
Hartmut H. Hellmer ◽  
Frank Kauker ◽  
Ralph Timmermann ◽  
Tore Hattermann
Keyword(s):  
Twentieth Century ◽  
Continental Shelf ◽  
Ice Sheet ◽  
Open Ocean ◽  
Weddell Sea ◽  
Warm Water ◽  
Atmospheric Forcing ◽  
Ice Shelf ◽  
Ice Shelves ◽  
A1b Scenario

Warm water of open ocean origin on the continental shelf of the Amundsen and Bellingshausen Seas causes the highest basal melt rates reported for Antarctic ice shelves with severe consequences for the ice shelf/ice sheet dynamics. Ice shelves fringing the broad continental shelf in the Weddell and Ross Seas melt at rates orders of magnitude smaller. However, simulations using coupled ice–ocean models forced with the atmospheric output of the HadCM3 SRES-A1B scenario run (CO2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years) show that the circulation in the southern Weddell Sea changes during the twenty-first century. Derivatives of Circumpolar Deep Water are directed southward underneath the Filchner–Ronne Ice Shelf, warming the cavity and dramatically increasing basal melting. To find out whether the open ocean will always continue to power the melting, the authors extend their simulations, applying twentieth-century atmospheric forcing, both alone and together with prescribed basal mass flux at the end of (or during) the SRES-A1B scenario run. The results identify a tipping point in the southern Weddell Sea: once warm water flushes the ice shelf cavity a positive meltwater feedback enhances the shelf circulation and the onshore transport of open ocean heat. The process is irreversible with a recurrence to twentieth-century atmospheric forcing and can only be halted through prescribing a return to twentieth-century basal melt rates. This finding might have strong implications for the stability of the Antarctic ice sheet.

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