A look beneath the ice shelves of western Dronning Maud Land, East Antarctica: subglacial topography linked to ice shelf stability

2020 ◽  
Author(s):  
Hannes Eisermann ◽  
Graeme Eagles ◽  
Antonia Ruppel ◽  
Emma C. Smith ◽  
Wilfried Jokat
Keyword(s):  
Sea Level ◽  
Reference Points ◽  
Magnetic Data ◽  
Airborne Gravity ◽  
Thermocline Depth ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Warm Deep Water ◽  
Dronning Maud Land ◽  
Basal Melting

<p>Antarctica’s ice shelves play a key role in stabilizing their related ice sheets. The ice shelves of western Dronning Maud Land – including the Ekström, Atka, Jelbart, Fimbul and Vigrid ice shelves – currently buttress a catchment that comprises an ice volume equivalent to 0.95 meters of sea level. Any future increase in ice shelf mass loss, with basal melting likely being the main cause, will inevitably accelerate ice sheet drainage and contribute to global sea level rise. Since basal melting largely depends on ice-ocean interactions, it is crucial to attain reliable and consistent bathymetry models to estimate water and heat exchange beneath these ice shelves. We have constructed bathymetry models for an area of about 63,000 km<sup>2</sup> beneath the ice shelves of western Dronning Maud Land by inverting airborne gravity data, tied to radar, seismic, and offshore depth reference points. New high-resolution airborne magnetic data across the ice shelves point to Jurassic intrusions and seaward-dipping reflectors originating from Gondwana breakup; enabling us to consider geological density variations as part of the bathymetry modelling process. Our bathymetric models reveal deep glacial troughs beneath the ice shelves, and sills close to the continental shelf breaks which currently limit the possible entry of Warm Deep Water from the Southern Ocean. The present-day average thermocline depth is comparable to the average depths of saddles along the sills, which present gateways into the sub-ice cavities. This leads us to suggest a high sensitivity for these ice shelves to changes in ocean temperature and especially thermocline depth in the future. Once a significant amount of warm water overtops the sills, the deep troughs will allow for fast access to the grounding line, after which it seems there may be little to stop basal melting from rapidly eroding the ice shelves of western Dronning Maud Land.</p>

scholarly journals Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Masahiro Minowa ◽  
Shin Sugiyama ◽  
Masato Ito ◽  
Shiori Yamane ◽  
Shigeru Aoki
Keyword(s):  
Freezing Point ◽  
East Antarctica ◽  
Ice Shelf ◽  
Rate Estimate ◽  
Ice Shelves ◽  
Plume Water ◽  
Warm Deep Water ◽  
Glacier Ice ◽  
Basal Melting

AbstractBasal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302–12 m-thick ocean cavity beneath 234–412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65–0.95°C, leading to a mean basal melt rate estimate of 1.42 m a−1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

scholarly journals An improved bathymetry compilation for the Bellingshausen Sea, Antarctica, to inform ice-sheet and ocean models

2010 ◽  
Vol 4 (4) ◽  
pp. 2079-2101 ◽  
Author(s):  
A. G. C. Graham ◽  
F. O. Nitsche ◽  
R. D. Larter
Keyword(s):  
Ocean Circulation ◽  
Ice Sheet ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Sea Floor ◽  
Bellingshausen Sea ◽  
Warm Deep Water ◽  
Basal Melting

Abstract. The southern Bellingshausen Sea (SBS) is a rapidly-changing part of West Antarctica, where oceanic and atmospheric warming has led to the recent basal melting and break-up of the Wilkins ice shelf, the dynamic thinning of fringing glaciers, and sea-ice reduction. Accurate sea-floor morphology is vital for understanding the continued effects of each process upon changes within Antarctica's ice sheets. Here we present a new bathymetric grid for the SBS compiled from shipborne echo-sounder, spot-sounding and sub-ice measurements. The 1-km grid is the most detailed compilation for the SBS to-date, revealing large cross-shelf troughs, shallow banks, and deep inner-shelf basins that continue inland of coastal ice shelves. The troughs now serve as pathways which allow warm deep water to access the ice fronts in the SBS. Our dataset highlights areas still lacking bathymetric constraint, as well as regions for further investigation, including the likely routes of palaeo-ice streams. The new compilation is a major improvement upon previous grids and will be a key dataset for incorporating into simulations of ocean circulation, ice-sheet change and history. It will also serve forecasts of ice stability and future sea-level contributions from ice loss in West Antarctica, required for the next IPCC assessment report in 2013.

scholarly journals Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

2016 ◽  
Vol 10 (6) ◽  
pp. 2623-2635 ◽  
Author(s):  
Lionel Favier ◽  
Frank Pattyn ◽  
Sophie Berger ◽  
Reinhard Drews
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Outlet Glacier ◽  
Ice Shelves ◽  
Dronning Maud Land

Abstract. The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice-shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennium. Overall, the sub-ice-shelf melting substantially impacts the sea-level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the transition of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrated that the onset of the marine ice-sheet retreat and subsequent promontory transition into ice rise is controlled by small pinning points, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and they play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning increases the sea-level rise by 10 %, while omitting the same pinning point in data assimilation decreases it by 10 %, but the more striking effect is in the promontory transition time, advanced by two centuries for unpinning and delayed by almost half a millennium when the pinning point is missing in data assimilation. Pinning points exert a subtle influence on ice dynamics at the kilometre scale, which calls for a better knowledge of the Antarctic margins.

Two ice shelf populations revealed in new gravity- derived bathymetry for the Thwaites, Crosson and Dotson ice shelves

2020 ◽  
Author(s):  
Tom Jordan ◽  
David Porter ◽  
Kirsty Tinto ◽  
Romain Millan ◽  
Atsuhiro Muto ◽  
...  
Keyword(s):  
Critical Role ◽  
Ice Sheet ◽  
Blind Spot ◽  
Airborne Gravity ◽  
Ice Shelf ◽  
Ice Shelves ◽  
West Antarctic ◽  
Glacier System ◽  
Cavity Thickness ◽  
Basal Melting

<p>Ice shelf buttressing plays a critical role in the long-term stability of ice sheets. The underlying bathymetry and cavity thickness therefore is a key to accurate models of future ice sheet evolution. However, direct observation of sub-ice shelf bathymetry is time consuming, logistically risky, and in some areas simply not possible, meaning there is a blind-spot in our understanding of this key system. Here we use airborne gravity anomaly data to provide new estimates of sub-ice shelf bathymetry outboard of the rapidly changing West Antarctic Thwaites Glacier, and beneath the adjacent Dotson and Crosson Ice Shelves. These regions are of especial interest as the low-lying inland reverse slope of the Thwaites glacier system makes it vulnerable to collapse through marine ice sheet instability, with rapid grounding-line retreat observed since 1993 suggesting this process may be underway. Our results confirm a major marine channel > 800 m deep extends to the front of Thwaites Glacier, while the adjacent ice shelves are underlain by more complex bathymetry. Comparison of our new bathymetry with ice shelf draft reveals that ice shelves formed since 1993 comprise a distinct population where the draft conforms closely to the underlying bathymetry, unlike the older ice shelves which show a more uniform depth of the ice base. This indicates that despite rapid basal melting in some areas, these “new” ice shelves are not yet in equilibrium with the underlying ocean system. We propose qualitative models of how this transient ice-shelf configuration may have developed, but further investigation is required to constrain the longevity and full impact of these newly recognised systems.</p>

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 Spatial and temporal variations in basal melting at Nivlisen ice shelf, East Antarctica, derived from phase-sensitive radars

2019 ◽  
Author(s):  
Katrin Lindbäck ◽  
Geir Moholdt ◽  
Keith W. Nicholls ◽  
Tore Hattermann ◽  
Bhanu Pratap ◽  
...  
Keyword(s):  
Deep Ocean ◽  
Temporal Variations ◽  
East Antarctica ◽  
Spatial And Temporal Variations ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Deep Ocean Water ◽  
Dronning Maud Land ◽  
Phase Sensitive ◽  
Basal Melting

Abstract. Thinning rates of ice shelves vary widely around Antarctica and basal melting is a major component in ice shelf mass loss. In this study, we present records of basal melting, at unique spatial and temporal resolution for East Antarctica, derived from autonomous phase-sensitive radars. These records show spatial and temporal variations of ice shelf basal melting in 2017 and 2018 at Nivlisen, central Dronning Maud Land. The annually averaged melt rates are in general moderate (~ 0.8 m yr-1). Radar profiling of the ice-shelf shows variable ice thickness from smooth beds to basal crevasses and channels. The highest melt rates (3.9 m yr-1) were observed close to a grounded feature near the ice shelf front. Daily time-varying measurements reveal a seasonal melt signal 4 km from the ice shelf front, at an ice draft of 130 m, where the highest daily melt rates occurred in summer (up to 5.6 m yr-1). This seasonality indicates that summer-warmed ocean surface water was pushed by wind beneath the ice shelf front. We observed a different melt regime 35 km into the ice-shelf cavity, at an ice draft of 280 m, with considerably lower melt rates (annual average of 0.4 m yr-1) and no seasonality. We conclude that warm deep ocean water at present has limited effect on the basal melting of Nivlisen. On the other hand, a warming in surface waters, as a result of diminishing sea-ice cover has the potential to increase basal melting near the ice-shelf front. Many ice shelves like Nivlisen are stabilized by pinning points at their ice fronts and these areas may be vulnerable to future change.

Channelized Antarctic ice shelf melting from high-resolution remote sensing

2020 ◽  
Author(s):  
Stef Lhermitte ◽  
Jeffrey Nederend ◽  
Bert Wouters
Keyword(s):  
High Resolution ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Simplified Approach ◽  
Elevation Data ◽  
Quantitative Understanding ◽  
Elevation Model ◽  
Basal Melting

&lt;p&gt;Antarctic mass loss is the largest source of uncertainty in current sea level rise projections. Ice shelf instability plays a key role in this uncertainty as ice shelves are the floating gatekeepers that surround 75% of Antarctica&amp;#8217;s coastline and that buttress the contribution of grounded ice to sea level rise. Although basal melting has been identified as one of the key processes for ice shelf instability, the quantitative understanding of this process and how much, how fast it weakens ice shelves is limited as it is determined by fine scale processes (e.g. channelized basal melting) that until recently were difficult to quantify. The recent availability of high-resolution, multi-source satellite imagery (e.g. stereoscopic DEMs from the Reference Elevation Model of Antarctica (REMA) or swath-processing of Cryosat-2), however, offers the opportunity to quantify the role of channelized melting on ice shelf instability across Antarctica.&lt;/p&gt;&lt;p&gt;In this study, we use REMA, Cryosat-2 and IceBridge elevation data to develop high-resolution indicators of basal melt across some major Antarctic ice shelves (Dotson, Pine Island, Larsen C). The methodology consists of processing time series of high-resolution REMA strips in a Lagrangian framework while accounting for tilt and tide corrections.&lt;/p&gt;&lt;p&gt;Comparison of different approaches (e.g. simplified REMA-only approach; combined REMA-Cryosat-2 approach, combined REMA-IceBridge approach) shows that the simplified approach can be applied easily to develop Antarctic wide estimates of basal melting across Antarctica, while the combined REMA-Cryosat-2 shows the highest accuracy. Results of this study, finally, show the potential of using REMA for developing high resolution basal melt products across Antarctica and providing insight in the spatial variability of basal melting due to channelized melting.&lt;/p&gt;

scholarly journals Dynamic influence of pinning points on marine ice-sheet stability: a numerical study in Dronning Maud Land, East Antarctica

2016 ◽  
Author(s):  
Lionel Favier ◽  
Frank Pattyn ◽  
Sophie Berger ◽  
Reinhard Drews
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Shelves ◽  
Grounding Line ◽  
Dronning Maud Land

Abstract. The East Antarctic ice sheet is likely more stable than its West Antarctic counterpart, because its bed is largely lying above sea level. However, the ice sheet in Dronning Maud Land, East Antarctica, contains marine sectors that are in contact with the ocean through overdeepened marine basins interspersed by (more stable) grounded ice promontories and ice rises, pinning and stabilising the ice shelves. In this paper, we use the ice-sheet model BISICLES to investigate the effect of sub-ice shelf melting, using a series of scenarios compliant with current values, on the ice-dynamic stability of the outlet glaciers between the Lazarev and Roi Baudouin ice shelves over the next millennia. Overall, the sub-ice shelf melting substantially impacts the sea level contribution. Locally, we predict a short-term rapid grounding-line retreat of the overdeepened outlet glacier Hansenbreen, which further induces the collapse of the bordering ice promontories into ice rises. Furthermore, our analysis demonstrates that the onset of the marine ice-sheet retreat and subsequent promontory collapse is controlled by small pinning points within the ice shelves, mostly uncharted in pan-Antarctic datasets. Pinning points have a twofold impact on marine ice sheets. They decrease the ice discharge by buttressing effect, and play a crucial role in initialising marine ice sheets through data assimilation, leading to errors in ice-shelf rheology when omitted. Our results show that unpinning has a small effect on the total amount of sea level rise but locally affects the timing of grounding-line migration, advancing the collapse of a promontory by hundreds of years. On the other hand, omitting the same pinning point in data assimilation decreases the sea level contribution by 10 % and delays the promontory collapse by almost a millennium. This very subtle influence of pinning points on ice dynamics acts on kilometre scale and calls for a better knowledge of the Antarctic margins that will improve sea-level predictions.

scholarly journals The Antarctic contribution to 21st century sea-level rise predicted by the UK Earth System Model with an interactive ice sheet

2021 ◽  
Author(s):  
Antony Siahaan ◽  
Robin Smith ◽  
Paul Holland ◽  
Adrian Jenkins ◽  
Jonathan M. Gregory ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
System Model ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Global Mean Sea Level ◽  
Basal Melting ◽  
The Antarctic ◽  
Global Mean

Abstract. The Antarctic Ice Sheet will play a crucial role in the evolution of global mean sea-level as the climate warms. An interactively coupled climate and ice sheet model is needed to understand the impacts of ice—climate feedbacks during this evolution. Here we use a two-way coupling between the U.K. Earth System Model and the BISICLES dynamic ice sheet model to investigate Antarctic ice—climate interactions under two climate change scenarios. We perform ensembles of SSP1-1.9 and SSP5-8.5 scenario simulations to 2100, which we believe are the first such simulations with a climate model with two-way coupling between both atmosphere and ocean models to dynamic models of the Greenland and Antarctic ice sheets. In SSP1-1.9 simulations, ice shelf basal melting and grounded ice mass loss are generally lower than present rates during the entire simulation period. In contrast, the responses to SSP5-8.5 forcing are strong. By the end of 21st century, these simulations feature order-of-magnitude increases in basal melting of the Ross and Filchner-Ronne ice shelves, caused by intrusions of warm ocean water masses. Due to the slow response of ice sheet drawdown, this strong melting does not cause a substantial increase in ice discharge during the simulations. The surface mass balance in SSP5-8.5 simulations shows a pattern of strong decrease on ice shelves, caused by increased melting, and strong increase on grounded ice, caused by increased snowfall. Despite strong surface and basal melting of the ice shelves, increased snowfall dominates the mass budget of the grounded ice, leading to an ensemble-mean Antarctic contribution to global mean sea level of a fall of 22 mm by 2100 in the SSP5-8.5 scenario. We hypothesise that this signal would revert to sea-level rise on longer timescales, caused by the ice sheet dynamic response to ice shelf thinning. These results demonstrate the need for fully coupled ice—climate models in reducing the substantial uncertainty in sea-level rise from the Antarctic Ice Sheet.

scholarly journals Bathymetric and oceanic controls on Abbot Ice Shelf thickness and stability

2014 ◽  
Vol 8 (3) ◽  
pp. 877-889 ◽  
Author(s):  
J. R. Cochran ◽  
S. S. Jacobs ◽  
K. J. Tinto ◽  
R. E. Bell
Keyword(s):  
Gravity Data ◽  
Ocean Surface ◽  
Airborne Gravity ◽  
Thermocline Depth ◽  
Data Sets ◽  
Surface Mixed Layer ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Ice Water

Abstract. Ice shelves play key roles in stabilizing Antarctica's ice sheets, maintaining its high albedo and returning freshwater to the Southern Ocean. Improved data sets of ice shelf draft and underlying bathymetry are important for assessing ocean–ice interactions and modeling ice response to climate change. The long, narrow Abbot Ice Shelf south of Thurston Island produces a large volume of meltwater, but is close to being in overall mass balance. Here we invert NASA Operation IceBridge (OIB) airborne gravity data over the Abbot region to obtain sub-ice bathymetry, and combine OIB elevation and ice thickness measurements to estimate ice draft. A series of asymmetric fault-bounded basins formed during rifting of Zealandia from Antarctica underlie the Abbot Ice Shelf west of 94° W and the Cosgrove Ice Shelf to the south. Sub-ice water column depths along OIB flight lines are sufficiently deep to allow warm deep and thermocline waters observed near the western Abbot ice front to circulate through much of the ice shelf cavity. An average ice shelf draft of ~200 m, 15% less than the Bedmap2 compilation, coincides with the summer transition between the ocean surface mixed layer and upper thermocline. Thick ice streams feeding the Abbot cross relatively stable grounding lines and are rapidly thinned by the warmest inflow. While the ice shelf is presently in equilibrium, the overall correspondence between draft distribution and thermocline depth indicates sensitivity to changes in characteristics of the ocean surface and deep waters.

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