CR3.4 | Ice shelves and tidewater glaciers - dynamics, interactions, observations, modelling
EDI
Ice shelves and tidewater glaciers - dynamics, interactions, observations, modelling
Co-organized by OS2
Convener: Nicolas Jourdain | Co-conveners: Inga Monika Koszalka, Rachel Carr, Peter Washam
Orals
| Mon, 24 Apr, 14:00–17:50 (CEST)
 
Room L3, Tue, 25 Apr, 08:30–12:20 (CEST)
 
Room L3
Posters on site
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
Hall X5
Posters virtual
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
vHall CR/OS
Orals |
Mon, 14:00
Tue, 14:00
Tue, 14:00
Ice shelves and tidewater glaciers are sensitive elements of the climate system. Sandwiched between atmosphere and ocean, they are vulnerable to changes in either. The recent disintegration of ice shelves such as Larsen B and Wilkins on the Antarctic Peninsula, current thinning of the ice shelves in the Amundsen Sea sector of West Antarctica, and the recent accelerations of many of Greenland's tidewater glaciers provide evidence of the rapidity with which those systems can respond. Changes in marine-terminating outlets appear to be intimately linked with acceleration and thinning of the ice sheets inland of the grounding line, with immediate consequences for global sea level. Studies of the dynamics and structure of the ice sheets' marine termini and their interactions with atmosphere and ocean are the key to improving our understanding of their response to climate forcing and of their buttressing role for ice streams. The main themes of this session are the dynamics of ice shelves and tidewater glaciers and their interaction with the ocean, atmosphere and the inland ice, including grounding line dynamics. The session includes studies on related processes such as calving, ice fracture, rifting and mass balance, as well as theoretical descriptions of mechanical and thermodynamic processes. We seek contributions both from numerical modelling of ice shelves and tidewater glaciers, including their oceanic and atmospheric environments, and from observational studies of those systems, including glaciological and oceanographic field measurements, as well as remote sensing and laboratory studies.

Orals: Mon, 24 Apr | Room L3

Chairpersons: Rachel Carr, Inga Monika Koszalka, Peter Washam
14:00–14:05
Ice mechanics, ice-shelf damage and calving
14:05–14:15
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EGU23-9001
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ECS
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Virtual presentation
Wang Yongji and Ching-Yao Lai

Ice flows in response to stresses according to the flow law that involves ice viscosity. An accurate description of effective ice viscosity is essential for predicting the mass loss of the Antarctic Ice Sheet, yet measurement of ice viscosity is challenging at a continental scale. Lab experiments of polycrystalline ice shows that the effective viscosity of ice obeys a power-law relation with the strain rate, known as Glen’s flow law. However, it remains unclear how processes at ice-shelf scales impact the effective viscosity of glacial ice. Here, we leverage the availability of remote-sensing data and physics-informed deep learning to infer the effective ice viscosity and examine the rheology, i.e. flow law,  of glacial ice in Antarctic Ice Shelves. We find that the rheology of ice shelves differs substantially between the compression and extension zones. In the compression zone near the grounding line the rheology of ice closely obeys power laws with exponents in the range 1<n<3, consistent with prior laboratory experiments. In the extension zone, which comprises most of the total ice-shelf area, ice performs complex rheological behavior, deviating from laboratory findings. We also discover the areas where ice viscosity appears non-isotropic.

How to cite: Yongji, W. and Lai, C.-Y.: Accessing ice effective viscosity using physics-informed deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9001, https://doi.org/10.5194/egusphere-egu23-9001, 2023.

14:15–14:25
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EGU23-1190
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On-site presentation
Maryam Zarrinderakht, Thomas Zwinger, and Christian Schoof
Calving is a key mechanism that controls the length of floating ice shelves, and therefore their
buttressing effect on grounded ice. A fully process-based model for calving is currently still not
available in a form suitable for large-scale ice sheet models. Here we build on prior work that
treats crevasse growth in the run-up to calving as an example of linear elastic fracture growth.
Purely elastic behaviour is confined to short time intervals, much less than a single Maxwell
time (the ratio of viscosity to Young’s modulus) in duration: this is typically hours to a few days
for cold polar ice shelves, depending on temperature and state of stress. We explicitly recognize
that the elastic stresses occurring during fracture propagation act on an ice-mass subject to a
pre-stress created by long-term viscous deformation. By coupling a boundary element solver
for instantaneous elastic stress increments and the resulting fracture propagation with the
Elmer/Ice Stokes flow solver that computes the pre-stress and is able to model the long-term
evolution of the domain, we are able to show how viscous deformation end elastic fracture
mechanics interact. We show that viscous deformation is in general an essential part of calving,
and as a result, viscous deformation ultimately sets the time scale for calving. The geometric
changes resulting from that deformation are necessary to cause continued growth to calving
of fractures that initially propagate only part-way through the domain. We identify two distinct
modes of fracture propagation: either fractures propagate episodically, the crack lengthening in
each instance by a finite difference over short (elastic) time scales. Alternatively, fractures grow
gradually in such a way as to keep the viscous pre-stress near the crack tip from becoming
tensile, with elasticity playing a secondary role. Our results point to the purely instantaneous
stress-based calving laws that have become popular in large-scale ice sheet mechanics being
too simplistic.
  • Figure1: ice shelf geometry evolution and crevasse propagation
 
 

How to cite: Zarrinderakht, M., Zwinger, T., and Schoof, C.: A periodic visco-elastic model for crevasses propagation in marine ice shelves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1190, https://doi.org/10.5194/egusphere-egu23-1190, 2023.

14:25–14:35
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EGU23-8261
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ECS
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On-site presentation
Niall Coffey, Ching-Yao Lai, and Yongji Wang

Ice shelves, the floating extensions of ice sheets, can reduce the rate of sea level rise by buttressing the upstream grounded ice. However, calving, or the fracturing that creates icebergs, can cut out regions that were resisting flow, and allow for increased ice flux and thus sea level contribution. In this work, I focus on the transition from basal crevasses, or seawater-filled fractures on the bottom surface, to full thickness fractures called rifts. Using RACMO ice shelf surface temperatures and holding the ice-ocean interface at -2℃, I find good agreement between observed rifts on the Larsen C and Ross Ice Shelves and rifts predicted to evolve from basal crevasses through 2D Mode I Linear Elastic Fracture Mechanics (LEFM). I also explore the influence of ice shelf geometry in rift formation by solving the Shallow Shelf Approximation (SSA) equations for idealized ice shelves with COMSOL’s Finite Element Analysis software. Using the stress field outputs with LEFM’s rift initiation criteria, I find qualitative agreement in the rift orientation between the predicted unstable basal crevasses and the observed rifts on the left margin of Pine Island Ice Shelf.

How to cite: Coffey, N., Lai, C.-Y., and Wang, Y.: Rift Initiation via Unstable Basal Crevasses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8261, https://doi.org/10.5194/egusphere-egu23-8261, 2023.

14:35–14:45
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EGU23-16435
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On-site presentation
Poul Christoffersen, Seungbong Lee, Samuel Cook, and Martin Truffer

Flow and mass balance of the Greenland Ice Sheet are largely controlled by marine-terminating glaciers that deliver large quantities of ice into fjords and coastal seas. The interaction of these glaciers with the ocean is crucial because heat and circulation in fjords drive high rates of melting. However, the links between warm ambient fjord water, subaqueous melting and iceberg calving are poorly understood. Here, we report a detailed record of surface circulation in Ikerasak Fjord, West Greenland, by tracking the displacements of icebergs in radar imagery acquired with a terrestrial radar interferometer, which also produced a detailed record of iceberg calving from Store Glacier. With images captured every three minutes, we derived fjord circulation and calving rates with unusually high temporal resolution. In the first of three periods, we observed low-speed surface currents (<0.15 m/s) together with high calving activity (around 50 events per hour) as a response to the break-up of proglacial winter melange. We subsequently observed faster surface currents (up to 0.57 m/s) but much less calving (<20 icebergs per hour). Later, as currents intensified and a large eddy formed, we observed a combination of fast fjord circulation (around 0.4 m/s) and high calving activity (20-40 events per hour). The record shows that calving is a self-organised critical system, with small icebergs produced continuously in a critical state, whereas large icebergs were produced mostly when calving becomes super-critical. A super-critical state was reached when the melange broke up and later as the eddy formed in front of the glacier. In this state, we found stronger fjord circulation to drive more frequent calving events, while more frequent calving in general caused a higher flux of ice to the ocean.

How to cite: Christoffersen, P., Lee, S., Cook, S., and Truffer, M.: Currents, mélange and iceberg calving in Greenland fjords: new insights to a self-organised critical system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16435, https://doi.org/10.5194/egusphere-egu23-16435, 2023.

14:45–14:55
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EGU23-14118
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On-site presentation
Anne Mangeney, Pauline Bonnet, Vladislav Yastrebov, Olivier Castelnau, Alban Leroyer, Patrick Queutey, Martin Rueckamp, and Amandine Sergeant

One current concern in Climate Sciences is the estimation of the annual amount of ice lost by glaciers and the corresponding rate of sea level rise. Greenland ice sheet contribution is significant with about 30% to the global ice mass losses. The processes that control ablation at tidewater glacier termini, glacier retreat and calving are complex, setting the limits to the estimation of dynamic mass loss and the relation to glacier dynamics. It involves interactions between bedrock – glacier – icebergs – ice-mélange – water – atmosphere. Moreover, the capsize of cubic kilometer scale icebergs close to a glacier front can destabilize the glacier, generate tsunami waves, and induce mixing of the water column which can impact both the local fauna and flora.

 

We aim to improve the physical understanding of the response of glacier front to the force of a capsizing iceberg against the terminus. For this, we use a mechanical model of iceberg capsize against the mobile glacier interacting with the solid earth through a frictional contact and we constrain it with measured surface displacements and seismic waves that are recorded at teleseismic distances. Our strategy is to construct a solid dynamics model, using a finite element solver, involving a deformable glacier, basal contact and friction, and simplified iceberg-water interactions. We simulate the response of a visco-elastic near-grounded glacier to the capsize of an iceberg close to the terminus. The influence of the glacier geometry, the type of capsize, the ice properties and the basal friction on the glacier dynamic and the observed surface displacements are assessed. The surface displacements simulated with our model are then compared with measured displacements for well documented events. We show the surface and basal displacements of the glacier are significantly different in the case of to a top-out and a bottom-out (the two possible rotations) iceberg capsize.  This suggests different basal forces in both types of capsize, and thus probably a different signature in the seismic waves generated at the basal surface during capsize. To reproduce the vertical displacements of the glacier, our results suggest a higher hydrodynamic force on the glacier tongue than suggested in previous studies.

How to cite: Mangeney, A., Bonnet, P., Yastrebov, V., Castelnau, O., Leroyer, A., Queutey, P., Rueckamp, M., and Sergeant, A.: Modelling the source of glacial earthquakes: numerical modelling of the response of a tide-water glacier to the capsize of an instable iceberg, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14118, https://doi.org/10.5194/egusphere-egu23-14118, 2023.

14:55–15:05
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EGU23-11695
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ECS
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Virtual presentation
Adrien Wehrlé, Martin P Lüthi, Ana Nap, Andrea Kneib-Walter, Guillaume Jouvet, Hugo Rousseau, and Fabian Walter

Sermeq Kujalleq in Kangia (Jakobshavn Isbræ), Greenland is one of the most studied glaciers in the world mainly due to its recent retreat associated with extremely fast ice stream flow and high solid ice discharge. However, large limitations remain in the understanding of its short-term ice dynamics as the study of sub-daily variations, generally undetectable in spaceborne observations, requires high-rate field measurements that are challenging to acquire. Here, we present glacier surface velocities determined in Post-Processed Kinematic (PPK) mode from eight autonomous Global Navigation Satellite System (GNSS) stations deployed in July 2022 along the ice stream at a distance of 4 to 30 kilometers from the calving front. During this field campaign, we identified an 8-hour-long glacier speedup which was recorded at all GNSS stations and reached up to 11% of the pre-event velocity, followed by a 12-hour-long slowdown of similar magnitude. We further found the peak velocity was first measured at a GNSS station 16 kilometers away from the calving front, then recorded consecutively at each of the three other downstream GNSS stations with a positive time lag corresponding to a ~3 km/h wave propagation speed. At the station closest to the calving front, the timing of peak velocity corresponded to the occurrence of large-scale calving events. We further present line-of-sight glacier surface velocities measured along three shear margin transects with a terrestrial radar interferometer deployed simultaneously with the GNSS array. Across all profiles, we observed a widespread and simultaneous response of fast- and slow-moving ice suggesting a strong coupling between the main trunk and the shear margins of the ice stream.

How to cite: Wehrlé, A., Lüthi, M. P., Nap, A., Kneib-Walter, A., Jouvet, G., Rousseau, H., and Walter, F.: Calving response to the propagation of a speedup pulse through the ice stream of Sermeq Kujalleq in Kangia (Jakoshavn Isbræ), Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11695, https://doi.org/10.5194/egusphere-egu23-11695, 2023.

15:05–15:15
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EGU23-13326
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ECS
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On-site presentation
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Jakub Stocek, Robert Arthern, and Oliver Marsh

Ice loss from glaciers and ice sheets is the largest contributor to sea level rise. Damaged ice is central to the stability of the Antarctic Ice Sheet and calving of tabular icebergs from ice shelves accounts for more than half of all the ice lost from Antarctica each year. The processes driving calving and fracture are complex but not yet well understood. The aim of this talk is to present a physically based modelling of fracture.

The timing of calving is currently difficult to predict and is only included in some ice sheet models. Calving and cliff retreat rates are based on heuristic arguments or limited observations scaled up to the whole of Antarctica. There is no guarantee that current methods accurately capture the sea level contributions and physically based modelling is needed.

Recently, phase field models for fracture have gained a large following due to their ability to predict complex cracking phenomena such as crack branching and coalescence, or crack nucleation and have been applied to ice sheets for example by Clayton et al. (2022). We employ a phase field formulation of fracture for Maxwell viscoelastic materials capable of capturing the creep of glacial ice over longer periods as well as instantaneous elastic deformation.

In this talk we present different failure criteria and fracture driving forces used in phase field modelling and their impact on cliff retreat rates. We draw parallels with existing models and commonly used failure criteria and expand on the possibilities of using phase field modelling in large scale domains.


Clayton, T., Duddu, R., Siegert, M., Martínez-Pañeda, E. (2022). A stress-based poro-damage phase field model for hydrofracturing of creeping glaciers and ice shelves. Engineering Fracture Mechanics, 272, 108693.

How to cite: Stocek, J., Arthern, R., and Marsh, O.: Taxonomy of Cliff Failure Criteria: Phase Field Modelling and Parallels with Other Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13326, https://doi.org/10.5194/egusphere-egu23-13326, 2023.

15:15–15:25
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EGU23-12358
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ECS
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On-site presentation
Vjeran Visnjevic, Reinhard Drews, Guy Moss, and Clemens Schannwell

Ice shelves encircling the Antarctic perimeter buttress ice flow from the continent towards the ocean, and their evolution and integrity are governed by surface accumulation, basal melting, and ice dynamics. The disintegration of ice shelves, caused by future changes in the climate, leads to an increase in ice discharge towards the ocean and a consequent increase in global sea level – making their future stability important.

In this study we focus on the structure and composition of ice shelves. We model ice shelf stratigraphy for all ice shelves around Antarctica using a simplistic and observationally driven ice-dynamic forward model (validated on the Roi Baudouin Ice Shelf, Visnjevic et al., 2022), and map spatial variations in the percentage of locally accumulated ice on the ice shelf (local meteoric ice - LMI) compared to the ice inflowing from the continental ice sheet (continental meteoric ice - CMI). We investigate differences between LMI and CMI dominated ice shelves in the context of ice shelf stability, and discuss their susceptibility to future atmospheric and oceanic changes in climate. Expanding the analysis to the continental scale allows us to identify zones where future changes in climate might strongly impact ice shelf geometry and composition.

How to cite: Visnjevic, V., Drews, R., Moss, G., and Schannwell, C.: Mapping the ratio of meteoric and continental ice in Antarctic Ice Shelves as a metric for susceptibility to future climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12358, https://doi.org/10.5194/egusphere-egu23-12358, 2023.

15:25–15:45
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EGU23-15957
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solicited
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On-site presentation
Maaike Izeboud and Stef Lhermitte

The contribution of the Antarctic ice sheet to sea level rise remains uncertain due to the potential instability of ice shelves. Damage areas in the shear zone of an ice shelf are a first sign of mechanical weakening, which can lead to speed-up of the ice and additional damage development. This damage feedback can precondition ice shelves for disintegration and enhanced grounding line retreat but remains one of the least understood processes, mainly since we lack a quantification of damage and its changes on large spatiotemporal domains.

Recent efforts have resulted in a new, automated approach to detect damage. The NormalisEd Radon Transform Damage (NeRD) detection method allows to robustly detect damage features from multi-source, high-resolution satellite imagery. We have made both long-term (25 years) and short-term (annual) assessments from SAR images, based on both RAMP Radarsat (1997) and Sentinel-1 datasets (2015-2021).

We produce, for the first stime, damage state and damage change maps of Antarctic ice shelves. Over the past two decades we detect a general damage increase on ice shelves, most evident on fast flowing ice shelves in the West Antarctic (Thwaites, Pine Island, Crosson) and the Peninsula (Wilkins).  On short time scales the detected damage changes are governed by new damage development versus calving events, imposing fluctuations on its increase or decrease from year to year. A strong decrease in damage is observed on ice shelves that have retreated significantly, thereby removing all damaged parts. This gives attention to small, retreated ice shelves that are otherwise overlooked.  We furthermore detect areas with stable damage states across the Antarctic. We detect this for both initially intact and initially damaged ice shelves, showing that the amount of damage itself is no indication for damage-induced instability.

Our results provide new insights in Antarctic wide damage change, identifying regions that are (not) sensitive to a potential damage feedback and/or are vulnerable to retreat in combination with other forcings such as ocean warming or surface melt.  This large-scale damage change assessment is a first and important step in identifying ice shelf weakening and potential instability.

How to cite: Izeboud, M. and Lhermitte, S.: Long- and Short-term Damage Changes on Antarctic Ice Shelves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15957, https://doi.org/10.5194/egusphere-egu23-15957, 2023.

Coffee break
Chairpersons: Nicolas Jourdain, Peter Washam, Inga Monika Koszalka
Antarctic ice shelf changes and climate drivers
16:15–16:25
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EGU23-7332
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ECS
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Highlight
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On-site presentation
Celia A. Baumhoer, Andreas J. Dietz, and Claudia Kuenzer

The Antarctic ice sheet is fringed by ice shelves regulating the ice flow into the ocean. The fronts of these ice shelves are constantly moving and are sensitive indicators of glaciological and environmental change. Previously, Antarctic ice shelf front change was not observed regularly due to limited availability of satellite imagery and time-consuming manual front delineations. The era of freely available SAR satellite data and recent developments in image processing with artificial intelligence created new opportunities for monitoring ice shelf front dynamics on a regular basis. Here, we present the IceLines dataset providing continuous time series of calving front dynamics for 36 major Antarctic ice shelves since 2015. The dataset consists of over 19,000 front positions extracted from Sentinel-1 satellite data by using a convolutional neural network called HED-Unet. The automatically extracted front positions can deviate from manual delineated fronts due to fast ice, mélange and icebergs close to the front by 209±12 m (5.2 pixel) on dual polarized imagery and 432±21 m (8.8 pixel) for single-polarized imagery whereas the frontal movement can be determined with higher accuracies of 63±68 m (1.6 pixel) for dual and 107±126 m (2.7 pixel) for single polarized imagery. To minimize errors and enhance quick usability, automatic separation of unreliable front positions (still accessible) is applied for an easy analysis of the dataset. This contribution features the analysis of the IceLines dataset providing new insights into Antarctic calving front dynamics by investigating intra-annual calving front dynamics, changing advance rates of ice shelf fronts, recent calving events and overall calving front change.

How to cite: Baumhoer, C. A., Dietz, A. J., and Kuenzer, C.: Antarctic ice shelf front dynamics between 2015 and 2023, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7332, https://doi.org/10.5194/egusphere-egu23-7332, 2023.

16:25–16:35
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EGU23-7200
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ECS
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Highlight
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On-site presentation
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Bertie Miles and Robert Bingham

Pinning points form when floating ice shelves locally reground on bathymetric highs. The anchoring of ice shelves onto these pinning points buttresses ice flow from the interior of the ice sheet, meaning they play a vital role in the mass balance of the ice sheet. However, we do not know how the hundreds of pinning points that fringe the Antarctic coastline have changed over recent decades. By utilizing the historic Landsat satellite image archive, we show that there has been an acceleration in pinning point loss over the past 5 decades, and in doing so help resolve the timeline of the onset of widespread ice shelf thinning in Antarctica. Between 1974 and 1990, only ice shelves in isolated regions were thinning and unanchoring from their pinning points, with 11% of all mapped pinning points reducing in size. Pinning point loss spreads from these isolated regions in the 1990s, with the proportion of pinning points reducing in size across the ice sheet more than doubles to 23%, before further increasing to 35% between 2000 and 2022. Pinning point loss is concentrated along the western Antarctic Peninsula, West Antarctic and Wilkes Land coastlines, but we do also observe the rapid growth and break-up of some large ice rises outside of these regions. Continued acceleration in pinning point loss will reduce the buttressing potential of ice shelves and ultimately result in enhanced discharge of ice into the Southern Ocean and contribute to sea level rise.

How to cite: Miles, B. and Bingham, R.: Un-pinning of Antarctic ice shelves over the past 5 decades, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7200, https://doi.org/10.5194/egusphere-egu23-7200, 2023.

16:35–16:45
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EGU23-9993
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ECS
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On-site presentation
Karla Boxall, Frazer D. W. Christie, Ian C. Willis, Jan Wuite, and Thomas Nagler

Ice flow of the Antarctic Ice Sheet has experienced multi-annual acceleration in response to increased rates of ice thinning and retreat. Despite the well-documented seasonality of ice flow in Arctic and Alpine regions, little to no observations exist of seasonal ice-flow variability in Antarctica, due largely to a lack of systematic, high temporal-resolution satellite imagery. Accordingly, the mechanisms driving any such seasonality remain similarly undetermined. Such information is critical for understanding, modelling, and ultimately refining projections of the ongoing and future contribution of Antarctica to global sea-levels.

Here, we use high spatial- and temporal- (6/12-daily) resolution Copernicus Sentinel-1a/b synthetic aperture radar (SAR) observations spanning 2014 to 2020 to provide evidence for seasonal flow variability of land ice feeding George VI Ice Shelf (GVIIS), Antarctic Peninsula. Between 2014 and 2020, the flow of glaciers draining to GVIIS from Palmer Land and Alexander Island increased during the austral summertime (December – February) by ~15% relative to baseline rates of flow. This speedup is corroborated by independent observations of ice flow as imaged by the Landsat 8 Operational Land Imager.

To identify the likely drivers of this seasonality, we carry out statistical time-series analyses on an array of remotely sensed and reanalysis datasets of potential environmental forcing mechanisms. We find that both surface and oceanic forcing act as statistically significant precursors to summertime ice-flow acceleration. Ultimately, these findings imply that seasonality may be present elsewhere in Antarctica where comparable forcing mechanisms exist.

How to cite: Boxall, K., Christie, F. D. W., Willis, I. C., Wuite, J., and Nagler, T.: Seasonal land-ice-flow variability and its drivers in the Antarctic Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9993, https://doi.org/10.5194/egusphere-egu23-9993, 2023.

16:45–16:55
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EGU23-5472
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ECS
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On-site presentation
Benjamin Wallis, Anna Hogg, J. Melchior van Wessem, Benjamin Davison, Michiel van den Broeke, and Michael Meredith

In Antarctica changes to ice dynamics dominate the ice sheet’s contribution to rising sea-levels. The Antarctic Peninsula (AP), has undergone the greatest atmospheric warming of any southern hemisphere terrestrial area in the 20th century. Over the last three decades, the AP has experienced significant change; floating ice shelves have collapsed and retreated, and the loss of ice shelf buttressing strength has led to an acceleration in ice speed and dynamic thinning of the grounded ice. On the west coast warming ocean water at depth has been linked to glacier terminus retreat, acceleration, and grounding line retreat.

In this study, we use feature tracking of Sentinel-1 synthetic aperture radar (SAR) imagery to measure ice speed of the Antarctic Peninsula’s west coast tidewater glaciers from 2014-2022 at 6-12 day temporal resolution.

Our results show widespread patterns of increased summertime ice speed over a study area of 105 tidewater glaciers. We observe average seasonal speed variability of 12.4 ± 4.2 %, with maximum speed change of 22.3 ± 3.2 % on glaciers with the most pronounced seasonality. We also measure ice dynamic changes on inter-annual timescales on the west AP coast in this period. We study one example, Cadman Glacier, in detail, which has increased speed by 1025 ± 83 m/yr (41.6%) from October 2018 to November 2019. This increased flow speed has been maintained until at least May 2022 causing terminus retreat, increased ice discharge, and dynamic thinning of grounded ice by 20.3 ± 2.1 m/yr.

We investigate forcing mechanisms which may cause the seasonal and long-term dynamic variability we observe using a regional climate model, ocean temperature reanalysis data and remote sensing observations of terminus position. We find that summertime speed increases may be explained by a combination of perennial firn aquifer modulated meltwater runoff and seasonal patterns of terminus position change, revealing that these glaciers can respond to forcings on seasonal timescales. For the longer-term speed change, we find that the large acceleration of Cadman glacier is coincident with a period of anomalously high ocean temperatures on the west AP shelf.

How to cite: Wallis, B., Hogg, A., van Wessem, J. M., Davison, B., van den Broeke, M., and Meredith, M.: Ocean and atmospheric forcing of ice dynamic variability of west Antarctic Peninsula glaciers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5472, https://doi.org/10.5194/egusphere-egu23-5472, 2023.

16:55–17:05
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EGU23-11256
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ECS
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Virtual presentation
Thorsten Seehaus, Christian Sommer, Philipp Malz, Thomas Dethinne, Francisco Navarro, and Kaian Shahateet

Some of the highest specific mass change rates in Antarctica are reported for the Antarctic Peninsula. However, the existing estimates for the northern Antarctic Peninsula (<70°S) are either spatially limited or are affected by considerable uncertainties. Within this study, the first assessment of the geodetic mass balance throughout the ice sheet of the northern Antarctic Peninsula is carried out employing bi-static SAR data from the TanDEM-X satellite mission. Repeat coverages from austral-winters 2013 and 2017 are employed. An overall coverage of 96.4% of the study area by surface elevation change measurements is revealed. The spatial distribution of the surface elevation and mass changes points out, that the former ice shelf tributary glaciers of the Prince-Gustav-Channel, Larsen-A&B, and Wordie ice shelves are the hotpots of ice loss in the study area, and highlights the long-lasting dynamic glacier adjustments after the ice shelf break-up events. The highest mass change rate is revealed for the Airy-Seller-Fleming glacier system and the highest average surface elevation change rate is observed at Drygalski Glacier. The comparison of the ice mass budget with anomalies in the climatic mass balance indicates, that for wide parts of the southern section of the study area the mass changes can be partly attributed to changes in the climatic mass balance. The previously reported connection between mid-ocean warming along the southern section of the west coast and increased frontal glacier recession does not repeat in the pattern of the observed glacier mass losses, excluding Wordie Bay.

How to cite: Seehaus, T., Sommer, C., Malz, P., Dethinne, T., Navarro, F., and Shahateet, K.: Mass balance of the northern Antarctic Peninsula Ice Sheet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11256, https://doi.org/10.5194/egusphere-egu23-11256, 2023.

17:05–17:15
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EGU23-3165
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ECS
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On-site presentation
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Frazer Christie, Toby Benham, Christine Batchelor, Wolfgang Rack, Aleksandr Montelli, and Julian Dowdeswell

The disintegration of the eastern Antarctic Peninsula’s Larsen A and B ice shelves has been attributed to atmosphere and ocean warming, and increased mass losses from the glaciers once restrained by these ice shelves have increased Antarctica’s total contribution to sea-level rise. Abrupt recessions in ice-shelf frontal position presaged the break-up of Larsen A and B, yet, in the ~20 years since these events, documented knowledge of frontal change along the entire ~1,400-km-long eastern Antarctic Peninsula is limited. Here, we show that 85% of the seaward ice-shelf perimeter fringing this coastline underwent uninterrupted advance between the early 2000s and 2019, in contrast to the two previous decades. We attribute this advance to enhanced ocean-wave dampening, ice-shelf buttressing and the absence of sea-surface slope-induced gravitational ice-shelf flow. These phenomena were, in turn, enabled by increased near-shore sea ice driven by a Weddell Sea-wide intensification of cyclonic surface winds around 2002. Collectively, our observations demonstrate that sea-ice change can either safeguard from, or set in motion, the final rifting and calving of even large Antarctic ice shelves.

How to cite: Christie, F., Benham, T., Batchelor, C., Rack, W., Montelli, A., and Dowdeswell, J.: Antarctic ice-shelf advance driven by anomalous atmospheric and sea-ice circulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3165, https://doi.org/10.5194/egusphere-egu23-3165, 2023.

17:15–17:25
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EGU23-8902
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ECS
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On-site presentation
Alessandro SIlvano, Paul Holland, Kaitlin Naugthen, Oana Dragomir, Pierre Dutrieux, Adrian Jenkins, Yidongfang Si, Andrew Stewart, Beatriz Peña Molino, Gregor Janzing, Tiago Dotto, and Alberto Naveira Garabato

Warm ocean waters drive rapid ice-shelf melting in the Amundsen Sea. The ocean heat transport toward the ice shelves is associated with the Amundsen Undercurrent, a near-bottom current that flows eastward along the shelf break and transports warm waters onto the continental shelf via troughs. Here we use a regional ice-ocean model to show that, on decadal time scales, the undercurrent's variability is baroclinic (depth-dependent). Decadal ocean surface cooling in the tropical Pacific results in cyclonic wind anomalies over the Amundsen Sea. These wind anomalies drive a westward perturbation of the shelf-break surface flow and an eastward anomaly (strengthening) of the undercurrent, leading to increased ice-shelf melting. This contrasts with shorter time scales, for which surface current and undercurrent covary, a barotropic (depth-independent) behavior previously assumed to apply at all time scales. This suggests that interior ocean processes mediate the decadal ice-shelf response in the Amundsen Sea to climate forcing.

How to cite: SIlvano, A., Holland, P., Naugthen, K., Dragomir, O., Dutrieux, P., Jenkins, A., Si, Y., Stewart, A., Peña Molino, B., Janzing, G., Dotto, T., and Naveira Garabato, A.: Baroclinic Ocean Response to Climate Forcing Regulates Decadal Variability of Ice-Shelf Melting in the Amundsen Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8902, https://doi.org/10.5194/egusphere-egu23-8902, 2023.

17:25–17:45
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EGU23-10142
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ECS
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solicited
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On-site presentation
Gemma O'Connor, Paul Holland, Eric Steig, Pierre Dutrieux, and Greg Hakim

Ice loss in the Amundsen Sea Embayment is occurring primarily via exposure to warm ocean water, which varies in response to local wind variability. There is evidence that glacier retreat in this region was initiated in the mid-20th century, however the perturbation that may have triggered retreat remains unknown, leaving the climatic mechanisms driving retreat highly uncertain. A leading hypothesis is that a large atmospheric circulation anomaly in the Amundsen Sea occurred in the 1940s, driving a strong oceanic ice-shelf melting perturbation. However, the characteristics and drivers of this 1940s event remain poorly constrained, and the expected occurrence of such events in a natural climate has not yet been evaluated. We investigate this hypothesis using paleoclimate reconstructions and climate model simulations. The reconstructions show that a large multi-year westerly wind anomaly occurred from ~1938-1942, likely as a combined response to the very large El Niño event from 1940-1942 and variability sourced from outside the tropical Pacific starting years earlier. In climate model simulations we find evidence that events of similar magnitude and duration are unusual but may have occurred tens to hundreds of times throughout the Holocene. Our results suggest that the strong westerly event in the 1940s is unlikely to be exceptional enough to initiate glacier retreat on its own; naturally driven climatic/oceanic trends preceding the event or perhaps anthropogenically driven trends following the event are needed to explain retreat. Our analyses provide novel constraints on the significance of the 1940s westerly event in the Amundsen Sea and highlight outstanding uncertainties in our understanding of the mechanisms driving glacier retreat. 

How to cite: O'Connor, G., Holland, P., Steig, E., Dutrieux, P., and Hakim, G.: Drivers and rarity of the strong 1940s westerly wind event in the Amundsen Sea, West Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10142, https://doi.org/10.5194/egusphere-egu23-10142, 2023.

17:45–17:50

Orals: Tue, 25 Apr | Room L3

Chairpersons: Peter Washam, Rachel Carr, Nicolas Jourdain
08:30–08:35
Ice shelves and ice tongues, from Antarctica to Greenland
08:35–08:45
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EGU23-16400
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On-site presentation
Stef Lhermitte, Bert Wouters, and HiRISE Team

Ice shelf instability is a key uncertainty in future sea level rise projections, as several small-scale processes leading to ice shelf collapse remain poorly quantified. Historical large scale ice shelf collapses, like the Conger Ice Shelf collapse in March 2022, therefore, provide unique insights in the processes leading to ice shelf instability.

In this study, we assess the long- and short-term changes on Conger Ice Shelf in historical satellite records (Landsat, Sentinel, MODIS, ICESat) and model output of ocean and climate conditions (HYCOM, RACMO, IMAU-FDM and ERA-5). Based on both observations and model output we determine the role of known ice shelf instability processes like hydrofracturing, basal melting and damage changes. Moreover, we evaluate the role of extreme weather and ocean conditions in the sudden Conger Ice Shelf collapse.

The longer satellite record shows that Conger Ice Shelf has been weakening for years and then collapsed in two abrupt events (2 and 15 of March 2022). The long-term weakening is the result of damage processes and calving events due to extreme ocean/weather conditions that gradually abate the ice shelf. The abrupt Conger Ice Shelf collapse, however, coincides with extreme atmospheric and ocean conditions (e.g., ocean slope and wave conditions) that trigger the weakened ice shelf into a sudden collapse. Our results show that the known ice shelf instability processes like hydrofracturing and basal melting do not play a key role in the abrupt Conger Ice Shelf collapse, but that gradual weakening followed by extreme weather and ocean conditions triggered the ice shelf collapse.

Our results stress the importance of separating ice shelf weakening from ice shelf collapse in studies of ice shelf stability. Moreover, they imply that extreme weather and oceanic conditions need to be to considered when assessing the future vulnerability of Antarctic ice shelves to collapse.

How to cite: Lhermitte, S., Wouters, B., and Team, H.: The triggers for Conger Ice Shelf demise: long-term weakening vs. short-term collapse, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16400, https://doi.org/10.5194/egusphere-egu23-16400, 2023.

08:45–08:55
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EGU23-2492
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On-site presentation
What Determines the Shape of a Pine-Island-Like Ice Shelf?
(withdrawn)
Yoshihiro Nakayama, Toshiki Hirata, Daniel Goldberg, and Chad Greene
08:55–09:05
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EGU23-8124
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On-site presentation
Paul Holland, Suzanne Bevan, and Adrian Luckman

The accelerating ice loss from Thwaites Glacier is making a substantial contribution to global sea-level rise, and could add tens of centimetres to sea level over the coming centuries. This ice loss is associated with rapid thinning and disintegration of the floating sections of Thwaites Glacier, and retreat of its grounding line. In this study, we use a high-resolution ocean model and a series of Digital Elevation Models of the floating part of Thwaites Glacier from 2011 to 2022 to simulate the evolution of sub-ice melting during this rapid retreat.

The results show that the ice evolution induces a strong geometrical feedback onto melting. The ice thinning and retreat provide a larger melting area, thicker and better-connected sub-ice water column, and steeper ice base. This leads to stronger sub-ice ocean currents, increasing melting by ~50% without any change in forcing from wider ocean conditions. This geometrical feedback over just 12 years is stronger than the melting changes expected from century-scale changes in ocean conditions and subglacial meltwater input. The strength of this feedback implies that greenhouse gas emissions policy may have a very weak influence over future ocean-driven ice loss from Thwaites Glacier.

How to cite: Holland, P., Bevan, S., and Luckman, A.: Strong ocean melting feedback during the recent retreat of Thwaites Glacier, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8124, https://doi.org/10.5194/egusphere-egu23-8124, 2023.

09:05–09:15
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EGU23-7613
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ECS
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On-site presentation
Maria Osińska

A 3D modelling of glacial bay hydrodynamics has been performed in Admiralty Bay (AB), King George Island, Antarctica, using Delft3D Flow model with tides and density gradients as its drivers. It was conducted in multiple scenarios of varied glacial input - a baseline case without meltwater added, and scenarios with meltwater input divided into two modes: drained through entire glacial front and with glacial input solely added to the surface layers of the ocean. Each mode was further divided into three cases dependent on the volume of  freshwater added, with estimated small, medium and large volume input case per each mode. Through these seven studied scenarios a character of glacial impact on overall glacial bay flow patterns, water level changes and salinity was shown. Results revealed general circulation pattern in AB, consisting of two cyclonic circulation cells that control water exchange between the bay and the ocean. Cells are separated by a boundary area, located approximately 7 km from the bay’s opening, dividing Admiralty Bay into waters primarily driven by the ocean, and inner waters significantly influenced by glacial input. This pattern is consistent in all studied cases, however its intensity and specific location is controlled by the volume of glacial input and tidal phases. Although water level changes have been found to be overall predominantly driven by tides, areas within the boundary and top 50-60 m of the water column are substantially influenced by glacial forcing, regardless of the scenario mode. Salinity distribution showed strong water column stratification, classifying AB as a salt-wedge estuary. Gathered results have been confronted with abundant in situ measurements consisting of ADCP probing validating water flow velocities and CTD+ profile measurements consistently carried out in 31 locations in AB, throughout three-year long period. Modelled calculations compared with measurement dataset allowed an estimation of summerly glacial inflow volume into AB from adjacent twenty tidewater glaciers. These values contrasted with CTD+ data from different seasons permitted assessment of glacial input volume variability during the course of the year. Altogether results of the study give first in this scale and detail image of seasonally changing impact of glaciers on Antarctic bay waters.

How to cite: Osińska, M.: Features and extent of meltwater impact on glacial bay’s flow pattern, water level and salinity revealed through multi-scenario 3D modelling and in situ measurements in Admiralty Bay, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7613, https://doi.org/10.5194/egusphere-egu23-7613, 2023.

09:15–09:25
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EGU23-13003
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On-site presentation
Michael Wolovick, Angelika Humbert, Thomas Kleiner, Martin Rückamp, and Ralph Timmermann

The Filchner-Ronne sector of Antarctica contains a number of deep-bedded ice streams and glaciers potentially vulnerable to the Marine Ice Sheet Instability (MISI).  Previous work has shown that, in a warming climate, the ocean circulation in the cavity underneath the Filchner-Ronne Ice Shelf (FRIS) could switch from its present cold state to an alternate warm mode, in which intrusions of Circumpolar Deep Water (CDW) cause high basal melt rates near the deep grounding lines of potentially vulnerable glaciers.  However, less work has been done on modeling the response of the ice sheet and ice shelf system to such a mode switch in the cavity circulation.  Here, we use the Ice-sheet and Sea-level System Model (ISSM) to simulate the response of the Filchner-Ronne sector of Antarctica over multi-centennial timescales to changes in basal melt rate caused by a mode switch in the cavity circulation.  We force ISSM with both melt rates directly calculated by the cavity-resolving Finite-Element Sea ice-Ocean Model (FESOM) and with parameterized melt rate forcing derived from CMIP6 global models.  We find that parameterized melt rates in high-emissions scenarios cause rapid grounding line retreat at almost all of the major glaciers and ice streams feeding the FRIS beginning in the 22nd century, followed by ice shelf collapse and rapid sea level rise in the 23rd.  Using FESOM simulated melt rates the destabilization of the FRIS sector proceeds more slowly. During the 22nd century retreat is concentrated in specific ice streams, reflecting the more heterogeneous distribution of melt rate in the ocean model as opposed to the parameterized forcing.  In the 23rd century retreat becomes more widespread, culminating in ice shelf collapse and rapid sea level rise in the 24th and 25th centuries.  

How to cite: Wolovick, M., Humbert, A., Kleiner, T., Rückamp, M., and Timmermann, R.: Timescales for Ice Shelf Collapse and MISI Initiation in the Filchner-Ronne Sector, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13003, https://doi.org/10.5194/egusphere-egu23-13003, 2023.

09:25–09:35
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EGU23-15930
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ECS
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On-site presentation
Joanna Zanker, Emma Young, Ivan Haigh, Paul Holland, and Paul Brickle

Mass loss from marine-terminating glaciers in high-latitude fjords is increasing globally, contributing to sea-level rise. It is widely cited that oceanic melting of these glaciers is enhanced by turbulent plumes rising in contact with the submarine face. Increasing evidence suggests fjord-wide horizontal circulation also enhances melting outside of plumes. The influence of buoyancy-driven outflow arising from submarine plumes on fjord-wide circulation is complex and subject to fjord geometry.  There are many studies of fjord systems in Greenland and Antarctica, but relatively little is known about fjords on sub-Antarctic islands such as South Georgia. This study uses observations and a new high-resolution model of Cumberland Bay, South Georgia, to study the interactions between fjord geometry and buoyancy-driven outflow on the circulation regime. We examine how this varies seasonally and the implications for glacier retreat. Cumberland Bay is a fjord system with two arms, each with a large marine-terminating glacier at the head. These glaciers have shown contrasting retreat rates over the past century.   In the shallower fjord arm (~70 m) the plume reaches the surface year-round, whereas in the deeper fjord arm (~160 m) the plume terminates sub-surface for ~3 months of the year. The addition of a shallow submarine sill in the deeper fjord arm leads to warmer and fresher water properties in the inner basin by blocking colder, higher salinity waters at depth. This change in water properties results in the plume reaching the surface year-round and the strength of the circulation outside of the plume is increased by recirculation of the buoyancy-driven outflow bouncing off the sill. The increase in temperature and energetic fjord-wide circulation both increases the plume-driven melt by as much as 2 m per day, and the potential for melt outside of the plume. Our results give the first detailed description of the oceanography of Cumberland Bay and highlight the importance of the interaction between fjord geometry and buoyancy-driven outflow influencing the rate of glacier retreat. 

How to cite: Zanker, J., Young, E., Haigh, I., Holland, P., and Brickle, P.: Variability in circulation in Cumberland Bay, South Georgia, and implications for glacier retreat, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15930, https://doi.org/10.5194/egusphere-egu23-15930, 2023.

09:35–09:45
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EGU23-16803
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ECS
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Virtual presentation
Yikai Zhu, Chunxia Zhou, and Dongyu Zhu

Ice losses from the Greenland Ice Sheet (GrIS) have expanded rapidly in recent decades. The Ryder Glacier (RG) is one of the major marine-terminating outlet glaciers located on the northwestern GrIS. Paying attention to its dynamic changes is of great significance to the study of the mass balance in the whole GrIS. We utilize the Double Differential Synthetic Aperture Radar Interferometry (DDInSAR) to detect the change of grounding line (GL) position in RG from 1992 to 2021. It is found that the GL has retreated significantly (1-8 km) during this period and its rate on the eastern and western flanks is nearly eight times different. To explore the reasons for the retreat, we combine the ice-shelf thickness variation, surface and bed topography, and potential subglacial drainage-pathway to discover that the basal melt governs the severe migration in RG. The uneven melting dominates the asymmetric retreat on the eastern and western flanks, which is caused by the disparity of ocean heat near the GL at different depths and the bed topography slope. The higher the ocean heat and the greater the slope are, the more intense the basal melt is, leading to further GL retreat and threatening the stability of the ice shelf. The experimental results also demonstrate that RG may continue to retreat, with a more drastic change in the west, in the coming decades.

How to cite: Zhu, Y., Zhou, C., and Zhu, D.: Rapid Grounding Line Retreat of Ryder Glacier, Northern Greenland, from 1992 to 2021, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16803, https://doi.org/10.5194/egusphere-egu23-16803, 2023.

09:45–10:05
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EGU23-7094
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solicited
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On-site presentation
Angelika Humbert, Veit Helm, Niklas Neckel, Ole Zeising, Martin Rückamp, Khan Shfaqat Abbas, Loebel Erik, Dietmar Gross, Rabea Sondershaus, and Ralf Müller

The largest floating tongue of Greenland’s ice sheet, Nioghalvfjerdsbrae, has so far been relatively stable with respect to areal retreat. Curiously, it experienced significant less thinning and ice flow acceleration than its neighbour Zacharias Isbrae. Draining more than 6% of the ice sheet, Nioghalvfjerdsbrae might become a large contributor to sea level rise in the future. Therefore, the stability of the floating tongue is a focus of this study. We employ a suite of observational methods to detect recent changes. We found that the calving style has changed at the southern part of the eastern calving front from normal tongue-type calving to a crack evolution initiated at frontal ice rises reaching 5-7km and progressing further upstream compared to 2010. The calving front area is further weakened by a substantial increase of a zone of fragments and open water at the tongue’s southern margin, leading to the formation of a narrow ice bridge. These geometric and mechanical changes are a precursor of instability of the floating tongue. We complement our study by numerical ice flow simulations to estimate the impact of future break-up or disintegration events on the ice discharge. These idealised scenarios reveal that a loss of the south-eastern area would lead to 1% of increase of ice discharge at the grounding line, while a sudden collapse of the frontal area (46% of the floating tongue area) will enhance the ice discharge by 8.3% due to loss in buttressing.

Humbert, A., Helm, V., Neckel, N., Zeising, O., Rückamp, M., Khan, S. A., Loebel, E., Gross, D., Sondershaus, R., and Müller, R.: Precursor of disintegration of Greenland's largest floating ice tongue, The Cryosphere Discuss. [preprint], https://doi.org/10.5194/tc-2022-171, in review, 2022

How to cite: Humbert, A., Helm, V., Neckel, N., Zeising, O., Rückamp, M., Shfaqat Abbas, K., Erik, L., Gross, D., Sondershaus, R., and Müller, R.: Precursor of disintegration of Greenland's largest floating ice tongue, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7094, https://doi.org/10.5194/egusphere-egu23-7094, 2023.

Coffee break
Chairpersons: Inga Monika Koszalka, Nicolas Jourdain, Rachel Carr
Tidewater glaciers, ice tongues and fjords
10:45–10:55
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EGU23-4949
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ECS
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On-site presentation
Jonathan Wiskandt, Inga Monika Koszalka, and Johan Nilsson

The oceanic forcing of basal melt remains a major source of uncertainty in climate ice sheet modelling.
Several factors such as ice and fjord geometry, ambient water properties and subglacial discharge in-
fluence the submarine melt processes. We use a high resolution, non-hydrostatic configuration of the
Massachusetts Institute of Technology general circulation model (MITgcm, see Wiskandt et al., 2022)
to investigate the dependence of basal melt rates and melt driven circulation in the Sherard Osborn
Fjord (SOF) under the floating ice tongue of Ryder Glacier (RG), northwest Greenland, on the fjords
bathymetry in connection with variable subglacial discharge. In SOF, a sill in front of the floating ice
shields the cavity underneath the ice from warm Atlantic water (AW) penetrating towards the grounding
line, providing an effective shielding of the glacier from oceanic thermal forcing. The volume flux of the
AW inflow is controlled by the sill height and the melt water outflow. The outflow volume flux is in turn
dependent on basal melting, subglacial discharge and the mixing of the two with the AW. For sufficiently
strong outflow, hydraulic control at the sill crest can limit the available glacier–ward flux and therefore
the available oceanic thermal forcing for basal melting creating a stabilizing feedback. In this study
we investigate the sensitivity of the AW inflow into an idealized fjord to the presence of a sill, variable
sill height and seasonal forcing from subglacial discharge. The model results are compared to theory of
hydraulic control (Nilsson et al., 2022).

References
Nilsson, J., van Dongen, E., Jakobsson, M., O’Regan, M., and Stranne, C. (2022).
Hydraulic suppression of basal glacier melt in sill fjords. EGUsphere, 2022:1–33.
Wiskandt, J., Koszalka, I. M., and Nilsson, J. (2022). Basal melt rates and ocean
circulation under the Ryder Glacier ice tongue and their response to climate warming: a high resolution
modelling study. EGUsphere, 2022:1–29.

How to cite: Wiskandt, J., Koszalka, I. M., and Nilsson, J.: Hydraulic control of the submarine glacier melt in Greenlandic sill fjords, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4949, https://doi.org/10.5194/egusphere-egu23-4949, 2023.

10:55–11:15
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EGU23-14665
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ECS
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solicited
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Virtual presentation
Claire Parrott, Stephanie Waterman, Paul Myers, Maya Bhatia, Erin Bertrand, Andrew Hamilton, David Burgess, Terry Noah, Eric Brossier, and David Didier

Tidewater glaciers, numerous in the Canadian Arctic Archipelago (CAA), are an important and dynamic source of freshwater to the Arctic freshwater system, with glacial inputs modifying ocean structure, stimulating vertical mixing, enhancing biogeochemical delivery near-terminus, as well as contributing to regional freshwater budgets, storage, transport and export. Despite their abundance, we lack important knowledge regarding glacier-ocean systems across the CAA, and these systems are often omitted in regional studies of freshwater transport or storage.

In this study, we examine the nature and spatial extent of glacial meltwater influence on freshwater dynamics in Jones Sound, a tidewater glacier-rich region in the CAA. Our goals are to better understand the influences of glacier inputs on upper ocean water column structure and mixing processes near the glacier terminus, as well as the role of tidewater glaciers in the regional oceanic freshwater system. We use summertime,  near-shore  in situ observations at both glacierized and non-glacierized sites, collected using the sailing yacht Vagabond and local vessels operated by community members from Ausuittuq (Grise Fiord, NU) over a 4-year timespan. This novel dataset provides fjord-scale and interannual resolution of water column properties from glacier terminus to open ocean. Further, we employ a high-resolution regional model (Nucleus for European Modelling of the Ocean (NEMO) framework of the Arctic and Northern Hemisphere Atlantic at 1/12 degree resolution) to examine regional freshwater transport and storage.

In this presentation we will present results detailing notable year-to-year and site-to-site variation in upper ocean structure at the glacierized sites.  These results suggest that there is important spatial and temporal variability of the influences of glacially-sourced freshwater to Jones Sound that should be considered in near-shore ocean functioning and the regional freshwater budget.

How to cite: Parrott, C., Waterman, S., Myers, P., Bhatia, M., Bertrand, E., Hamilton, A., Burgess, D., Noah, T., Brossier, E., and Didier, D.: Exploring the variability of freshwater inputs from tidewater glacier-ocean systems in the Canadian Arctic Archipelago, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14665, https://doi.org/10.5194/egusphere-egu23-14665, 2023.

11:15–11:25
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EGU23-5510
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ECS
|
On-site presentation
José Manuel Muñoz Hermosilla, Eva De Andrés, Kaian Shahateet, Jaime Otero, and Francisco J. Navarro

Frontal ablation is responsible for a large fraction of the mass loss from marine-terminating glaciers. The main contributors to frontal ablation are iceberg calving and submarine melting, being calving the largest one. However, submarine melting, in addition to its direct contribution to mass loss, also promotes calving through the changes induced in the stress field at the glacier terminus, so both processes should be jointly analysed. Among the factors influencing submarine melting, the formation of a buoyant plume due to the emergence of fresh subglacial water at the glacier grounding line plays a key role. 

In this study we use Elmer/Ice, an open-source, parallel, finite-element software which solves the full-Stokes system, to develop a 3D glacier dynamics model including calving and subglacial hydrology coupled with a line-plume model fed by the subglacial discharge that accounts for the submarine melting at the calving front. The ice flow model provides the calving front position at every time-step. 

We apply this model to the Hansbreen–Hansbukta glacier–fjord system in Southern Spitsbergen, Svalbard, where a large set of data are available for both glacier and fjord. The evolution of the modelled front positions are in agreement in terms of advance and retreatment with those observed from time-lapse images of the glacier front, and, in general, the modelled is always ahead of the observed due to an underestimation of calving.

How to cite: Muñoz Hermosilla, J. M., De Andrés, E., Shahateet, K., Otero, J., and Navarro, F. J.: A 3D glacier dynamics-line plume model to estimate the frontal ablation of Hansbreen, Svalbard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5510, https://doi.org/10.5194/egusphere-egu23-5510, 2023.

11:25–11:35
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EGU23-13220
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ECS
|
On-site presentation
Donald Slater and Fiamma Straneo

The retreat and acceleration of Greenland's marine-terminating glaciers since the 1990s is responsible for approximately half of Greenland's sea level contribution over the same period. A warming ocean, and the associated increase in submarine melting of calving fronts, is understood to be the most likely driver of this retreat. Yet atmospheric variability can also affect submarine melting by modulating subglacial discharge, which plays a role in driving fjord circulation and enhancing the transfer of heat from ocean to ice. The relative importance of atmospheric and oceanic sources of variability in submarine melting have, however, not been quantified.

We use atmospheric and oceanic reanalyses to estimate submarine melt rate at Greenland's marine-terminating glaciers since 1979, finding that in southeast Greenland the ocean has driven the majority of variability in submarine melt, while in northwest Greenland it is the atmosphere that has played the greater role. A simple two-stage glacier model is then used to map submarine melting onto dynamic mass loss, suggesting that although submarine melting is intuitively an ocean process, a warming atmosphere has amplified the impact of the ocean on the Greenland ice sheet.

How to cite: Slater, D. and Straneo, F.: Submarine melting of glaciers in Greenland amplified by atmospheric warming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13220, https://doi.org/10.5194/egusphere-egu23-13220, 2023.

11:35–11:45
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EGU23-17325
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On-site presentation
Tom Cowton, Donald Slater, and Mark Inall

Greenland’s glacial fjords modulate the exchange of heat and freshwater between the ice sheet and ocean, with the ocean properties adjacent to tidewater glaciers influencing the rate of submarine glacier melting and the properties of glacially modified waters exported to the shelf. Here we use a numerical plume model in conjunction with observations from close to 14 glaciers in northwest Greenland to assess the impact of subglacial-runoff-driven plumes on near-glacier ocean properties. We find that at depths where plumes most commonly find neutral buoyancy (~75-300m), intruded plume waters frequently make up the largest component of the near-glacier water composition. These plume waters register predominantly as a warm anomaly relative to waters of equivalent density on the shelf, and will thus serve to increase submarine melting at intermediate depths. Our findings demonstrate the key role played by plumes in driving water modification in Greenland’s fjords, the importance of accounting for this process when studying ice-sheet/ocean interactions, and the potential for simple models to capture these impacts across a range of settings.

How to cite: Cowton, T., Slater, D., and Inall, M.: Glacial plumes drive widespread subsurface warming in northwest Greenland’s fjords, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17325, https://doi.org/10.5194/egusphere-egu23-17325, 2023.

11:45–11:55
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EGU23-7295
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ECS
|
Virtual presentation
Jan-Hendrik Malles, Fabien Maussion, Lizz Ultee, Will Kochtitzky, Luke Copland, Paul Myers, and Ben Marzeion

Marine-terminating glaciers cover roughly one-third of the Northern Hemisphere's glacierized area (outside the Greenland ice sheet) and their direct freshwater export to the oceans has the potential to change not only global mean sea level (GMSL), but also local and regional ocean circulation patterns. Due to the interrelation of surface and frontal mass budgets, the dynamics of marine-terminating  glaciers are distinct from those of land-terminating glaciers forced only by the atmosphere. Here, were present recent advances in large-scale modeling of marine-terminating glaciers in the Open Global Glacier Model (OGGM). These include an enhanced representation of frontal processes and an independent calibration of surface and frontal mass balance. Further, we do a first investigation of coupling effects with an ocean general circulation model (Nucleus for European Modelling of the Ocean; NEMO). Including an explicit treatment of frontal processes (but so far ignoring future changes in ocean climate), we find that the spread between different emission scenarios at the end of the 21st century is reduced. Cumulative GMSL rise contribution projected for Northern Hemisphere glaciers is reduced by ca. 8 % in 2100, while the reduction for marine-terminating glaciers is ca. 23 %. Utilizing temperature and salinity output of NEMO, configured for the Arctic and Northern Hemisphere Atlantic (NEMO-ANHA4), to force a newly implemented submarine melt parameterization in OGGM, we estimate that 12 (6 - 22) % of the total frontal ablation was caused by submarine melt between 2010 and 2020. Finally, we explore differences in the ocean model’s output between runs that include the freshwater forcing from northern hemisphere glaciers and those that do not. The two main findings considering NEMO runs that include the freshwater forcing derived from OGGM output compared to those that do not are: i) an increased heat transport into Baffin Bay, and ii) changes in the pathways of Atlantic water to the Arctic Ocean, with less transport into the Barents Sea and more through Fram Strait.

How to cite: Malles, J.-H., Maussion, F., Ultee, L., Kochtitzky, W., Copland, L., Myers, P., and Marzeion, B.: Simulating northern hemisphere glacier – ocean interactions using the Open Global Glacier Model and the Nucleus for European Modelling of the Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7295, https://doi.org/10.5194/egusphere-egu23-7295, 2023.

11:55–12:05
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EGU23-10704
|
On-site presentation
Maya Bhatia, Stephanie Waterman, Erin Bertrand, Paul Myers, Andrew Hamilton, Terry Noah, David Burgess, Eric Brossier, France Pinczon du Sel, Claire Parrott, Patrick White, Patrick Williams, Megan Roberts, Maria Cavaco, Jenifer Spence, and Ana Heras Duran

Tidewater glaciers are defining coastal features in Canadian high Arctic marine systems. Rapid Arctic climate warming is dramatically altering the nature of these coastlines and adjacent waters through changing atmospheric forcing, a lengthening open-water season, and accelerating glacier retreat. These changes have a broad range of impacts enhancing glacier meltwater discharge, shifting coastal biological productivity patterns, and changing upper ocean freshwater variability and circulation. For the community of Aujuittuq (Grise Fiord), Canada’s northernmost community and ‘the place that never thaws’, these impacts have critical implications for local infrastructure, travel safety and food security. Over the last decade, Aujuittuq community members have noted significant recession of glaciers, as well as changes in the fjords surrounding their home and hunting grounds. To better understand these changes, for the last several years, we have been collaborating with the community to collect year-round marine observations in Jones Sound, home of the Inuit of Aujuittuq. Our observations span the nearshore coastal zone to the open Sound, comparing glacierized and non-glacierized fjords and multiple glaciers of varying type (land-terminating, tidewater), grounding line depth, and size draining surrounding ice caps. In total these observations represent over 400 casts measuring water column temperature, salinity, turbidity, dissolved oxygen, and chlorophyll a, with paired bottle samples characterizing carbon, nutrient, metal, and phytoplankton community composition and activity to elucidate how these properties evolve with distance from the shore. In 2022, we worked with 12 local youth, adults, and elders to make these observations. Our efforts aim to establish a long-term, community-led monitoring program centered around the co-consideration of Indigenous and scientific knowledge to understand ongoing change in high Arctic coastal environments. Results from this study substantially further our holistic understanding of glacier-ocean impacts in the sparsely sampled Canadian Arctic Archipelago and beyond, while also providing data critical to accurate future projections of high-latitude marine change in regions that are a hotspot for tidewater glacial retreat and meltwater runoff to the ocean.

How to cite: Bhatia, M., Waterman, S., Bertrand, E., Myers, P., Hamilton, A., Noah, T., Burgess, D., Brossier, E., Pinczon du Sel, F., Parrott, C., White, P., Williams, P., Roberts, M., Cavaco, M., Spence, J., and Heras Duran, A.: Community-based monitoring to understand changing tidewater glacier-ocean interactions in the Canadian Arctic Archipelago, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10704, https://doi.org/10.5194/egusphere-egu23-10704, 2023.

12:05–12:15
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EGU23-8393
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ECS
|
On-site presentation
|
Eliot Jager, Fabien Gillet-Chaulet, Nicolas Champollion, and Romain Millan

The uncertainty of the future contribution to sea level rise of the Antarctic and Greenland polar ice sheet remains important, as shown by the latest multi-model intercomparison (ISMIP6). We can summarise three main sources of uncertainties that are related to the ice flow model, the atmospheric and oceanic forcing and final to the Shared Socioeconomic Pathways (SSP). Results for the Greenland Ice Sheet (Goelzer and al., 2020) show that the model uncertainty explains a similar part of the ensemble spread (40 mm of sea-level rise by 2100) compared to the atmospheric forcing uncertainty (36 mm) or the SSP uncertainty (48 mm) and two times more than the ensemble spread due to the oceanic forcing uncertainty (19 mm). 

Uncertainties in ice flow models are mainly due to different assumptions in numerical models and parameterisation, as well as model initialisation (spin-up, data assimilation). Here, we investigate the sensitivity of a single ice flow model (Elmer/Ice) to different sources of uncertainties for Upernavik Isstrøm, a tidewater glacier in the North-West sector of Greenland. To achieve this goal, we have identified potential sources of uncertainties: parameters related to the initialization of the model by inverse method (ice stiffness, friction law, regularization, input observations), those related to the dynamics (ice flow law, friction law) and finally those related to the forcing (sensitivity to the ocean, global climate model, regional climate model, SSP). To evaluate their influence we run a 200-member ensemble that samples these different sources of uncertainty. Each member is initialised to a state close to 1985 and evaluated during a historical simulation from 1985 to 2015 where the front positions are forced using observations (Wood et al., 2021). We then use the ISMIP6 protocol where the front position is parametrized as a function of ocean temperature and runoff to perform projections to 2100.

We then evaluate the sensitivity of this ensemble to our different sources of uncertainty using Sobol indices. Based on this novel approach, we define several metrics that allow us to score individual ensemble members using a comprehensive record of ice velocity, surface elevation and mass loss over the period 1985-2015. We then evaluate the possibility of reducing the uncertainty in Upernavik Isstrøm's contribution to sea level rise using these scores. 

How to cite: Jager, E., Gillet-Chaulet, F., Champollion, N., and Millan, R.: Constraining the overall future projection of Upernavik Isstrøm by observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8393, https://doi.org/10.5194/egusphere-egu23-8393, 2023.

12:15–12:20
5-minute discussion

Posters on site: Tue, 25 Apr, 14:00–15:45 | Hall X5

Chairpersons: Nicolas Jourdain, Inga Monika Koszalka, Rachel Carr
X5.259
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EGU23-4541
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ECS
Mattia Poinelli, Michael Schodlok, Eric Larour, Miren Vizcaino, and Riccardo Riva

The ongoing ablation of Antarctic ice shelves - to a large extent due to enhanced melting at the grounding line - is known to accelerate the outflow of upstream glaciers into the world oceans, rising the global sea level. A better understanding of ocean heat intrusion under the ice base is therefore essential to accurately estimate basal melt and the consequent impact on ice sheet dynamics. Observations also show that most ice shelves are crossed by full-thickness ice rifts. Nevertheless, their impact on ocean circulation around and below ice shelves has been largely unexplored as ocean models are commonly characterized by resolutions that are too coarse to resolve km-sized features in the ice draft. In this work, we investigate ocean circulation under rifted ice-shelves using the Massachusetts Institute of Technology ocean general circulation model. We find that the rift presence modulates oceanic heat transport toward the grounding line with potential repercussion in the dynamics of the most vulnerable portions of the ice shelf.

How to cite: Poinelli, M., Schodlok, M., Larour, E., Vizcaino, M., and Riva, R.: Can rifts alter ocean dynamics beneath ice shelves?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4541, https://doi.org/10.5194/egusphere-egu23-4541, 2023.

X5.260
|
EGU23-14409
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ECS
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Simon Schöll, Ronja Reese, and Ricarda Winkelmann

The accelerating loss of grounded ice in Antarctica at present is mainly caused by a thinning of the surrounding ice shelves and a subsequent reduction in buttressing. The adjacent ice streams speed-up due to the decrease in back-pressure from the weakened ice shelves. Most methods typically used to quantify the buttressing of ice shelves analyze the state at individual locations along the grounding line or within the shelf. Based on the stress-balance at the grounding line, we here present a method to quantify shelf-wide buttressing values in Antarctica. The Parallel Ice Sheet Model (PISM) and Úa are used in diagnostic as well as in transient experiments to compare the buttressing effect of major ice shelves in Antarctica. We show an increase in buttressing in more confined ice shelves and a decrease for higher basal melt rates. The buttressing decreases consistently across different ice shelves and idealized ocean warming scenarios. The newly-developed, shelf-wide buttressing metrics can be used to understand the role of ice shelves in changing climate conditions.

How to cite: Schöll, S., Reese, R., and Winkelmann, R.: Ice shelf buttressing – a comparison of Antarctic ice shelves in a transient evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14409, https://doi.org/10.5194/egusphere-egu23-14409, 2023.

X5.261
|
EGU23-4043
Taekyun Kim, Ji-Seok Hong, Jae-Hong Moon, and Emilia Kyung Jin

Mass loss from ice shelves occurs through ocean-driven melting regulated by dynamic and thermodynamic processes in sub-ice shelf cavities. However, the understanding of these oceanic processes is quite limited because of the scant observations under ice shelves. Here, a regional coupled sea-ice/ocean model that includes physical interactions between the ocean and the ice shelf is used as an alternative tool for exploring ocean-driven melting beneath the Nansen Ice Shelf (NIS), Terra Nova Bay (TNB), Antarctica.

We will first show the spatiotemporal variability signatures for different modes of ocean-driven melting at the base of the NIS. Our model includes detailed bathymetry and ice shelf base topography based on in-situ observation and has been run with and without tides. We have also investigated how tide and model geometries (i.e., cavity geometry) affect the water mass transformations and ice shelf melting/freezing regimes at the base of the ice shelf which significantly affect the ice shelf stability.

How to cite: Kim, T., Hong, J.-S., Moon, J.-H., and Jin, E. K.: Impacts of tide and cavity geometry on ocean-driven melting beneath the Nansen Ice Shelf, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4043, https://doi.org/10.5194/egusphere-egu23-4043, 2023.

X5.262
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EGU23-5617
Keith Nicholls and Irena Vankova

We deployed multiple phase-sensitive radars (ApRES) on Filchner-Ronne Ice Shelf (FRIS) to measure and characterize variability in its basal melt rate under present-day climatic conditions.
Sites along the western portion of the ice shelf show primarily seasonal variations, consistent with the propagation dynamics of seasonal dense water from the western FRIS front into the cavity.
Fifteen years of melt rate estimates from instruments moored beneath the ice at sites further from the western Ronne Ice Front are remarkably uniform in that melting is bounded between 0 and 1 m/a throughout the record. Here, inter-annual melt rate variability is expressed as a suppression or delay in the arrival of a seasonal melt rate minimum, which can be understood in terms of inter-annual stratification changes and variable inflow pathways towards the western Ronne sites.
Elsewhere in the cavity, along a direct flow pathway connecting the western FRIS front and the southwestern tip of Berkner Island, the lower frequency inter-annual signal is superimposed on a regular seasonal signal, with year-to-year melt rate variations as high as 1 m/a. Anomalously low summer sea-ice concentrations in front of the ice shelf, such as in 1998 and 2017, cause higher melting along this pathway with a year's delay.
Long term mean ApRES melt rates agree with estimates from satellite data over eastern FRIS. However, the satellite estimates overstate the area of active basal freezing in the western part of the ice shelf. The temporal melt rate variability from the satellite estimates dramatically overstates the range of variability at both seasonal and inter-annual time scales and only one site, on the eastern Ronne Ice Shelf, shows any correspondence between the in-situ and remotely derived inter-annual variability.

How to cite: Nicholls, K. and Vankova, I.: Ocean variability beneath the Filchner-Ronne Ice Shelf inferred from basal melt rate time series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5617, https://doi.org/10.5194/egusphere-egu23-5617, 2023.

X5.263
|
EGU23-15572
Simulating the evolution and impact of Fimbulisen basal channels in a coupled ice shelf -ocean model
(withdrawn)
Rupert Gladstone, Qin Zhou, Chen Zhao, Tore Hattermann, and Ashley Morris
X5.264
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EGU23-4728
Sue Cook, Keith W. Nicholls, Irena Vaňková, Sarah S. Thompson, and Craig L. Stewart

Ocean-driven melt at the base of floating ice shelves is a major mass loss process from the Antarctic ice sheet, and a key component in accurately predicting its contribution to future sea level rise. Observations of basal melt are important tools for testing and improving models of ice shelf-ocean interaction. While many of these observations come from satellite methods, field observations of melt are valuable for validating satellite-derived data products, and to provide higher-temporal resolution timeseries of melt.

The NECKLACE project aims to collate field measurements of ice shelf melt to create a standardised data product that can be used by glaciologists, oceanographers, and ice sheet modellers for testing and validation. Field measurements of melt can use a range of techniques, including range finding from under-ice moorings and surface radar instruments, but the most commonly used instrument in recent years is the Autonomous phase-sensitive Radio Echo Sounder (ApRES) due to its low cost and ease of deployment. The project will combine data contributions from multiple international teams to create a continent-wide, open-access database of timeseries of basal melt rates. The initial dataset will contain contributions from over 40 sites on 12 ice shelves. Beyond the collation of existing data, the project team also aims promote the collection of new field data by providing assistance with equipment procurement, set-up, and data processing. We hope that this data product can provide the basis for an ongoing monitoring network observing basal melt around Antarctica.

How to cite: Cook, S., Nicholls, K. W., Vaňková, I., Thompson, S. S., and Stewart, C. L.: NECKLACE: A circum-Antarctic dataset of basal melt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4728, https://doi.org/10.5194/egusphere-egu23-4728, 2023.

X5.265
|
EGU23-11569
Reinhard Drews, Falk Oraschewski, Mohammadreza Ershadi, Clara Henry, Vjeran Višnjević, Paul Bons, Inka Koch, Jonathan Hawkins, and Olaf Eisen

Ice shelves buttress ice flow from Antarctica’s interior and provide the interface for ice-ocean interactions. Here, we present a comprehensive dataset collected with autonomous phase-sensitive radio-echo sounders (ApRES) on the Ekström Ice Shelf in East Antarctica. The data include a one year time series of basal melt near the grounding zone and > 40 repeat and quad-polarimetric observations covering the entire ice shelf with the transition to grounded ice and multiple lateral shear zones. The inferred melt rates are put into context in terms of their seasonality and with respect to spatial patterns which were mapped in the internal ice stratigraphy. The polarimetric backscatter show signs of anisotropic ice fabric and spatial changes can be traced coherently from the grounding line to the ice-shelf front. We investigate those signatures in conjunction with the vertical strain rates inferred from ApRES and ice-flow modelling to learn more about ice-shelf rheology, particularly with respect to the stress exponent n.

How to cite: Drews, R., Oraschewski, F., Ershadi, M., Henry, C., Višnjević, V., Bons, P., Koch, I., Hawkins, J., and Eisen, O.: Basal melt rates and mechanical properties of the Ekström Ice Shelf, East Antarctica, inferred from repeat, quad-polarimetric radar data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11569, https://doi.org/10.5194/egusphere-egu23-11569, 2023.

X5.266
|
EGU23-5827
Sainan Sun and Gudmundur Hilmar Gudmundsson

From 2017 to 2020, three significant calving events took place on Pine Island Glacier, West Antarctica. Ice-shelf velocities changed over this period and the calving events have been suggested as possible drivers. However, satellite observations also show significant changes in the areal extent of fracture zones, especially in the marginal areas responsible for providing lateral support to the ice shelf. Here we conduct a model study to identify and quantify drivers of recent ice-flow changes of the Pine Island Ice Shelf. In agreement with recent studies, we find that the calving events caused significant velocity changes over the ice shelf. However, calving alone cannot explain observed velocity changes. Changes in the structural rigidity, i.e., ice damage, further significantly impacted ice flow. We suggest that ice damage evolution of the ice-shelf margins may have influenced recent calving events, and these two processes are linked.

How to cite: Sun, S. and Gudmundsson, G. H.: Processes driving the speedup of Pine Island Ice Shelf between 2017 and 2020, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5827, https://doi.org/10.5194/egusphere-egu23-5827, 2023.

X5.267
|
EGU23-15683
Peter Washam and the ITGC MELT Team

Here, we present detailed ice and ocean data from beneath Thwaites Eastern Ice Shelf, Antarctica, collected with the underwater vehicle Icefin as part of the ITGC MELT project. The observations are a subset of the full data set that focus on the ice-ocean interactions within several well-sampled terrace formations occupying the ice base. These terraces range from 0.50 to 6 m in height and up to 100 m in width. We present measurements of ocean conditions to within centimeters of the ice surface along flat terrace roofs and their steeply sloping sidewalls. The ocean observations are combined with ice base elevations and scaled morphological melt patterns in the ice to understand the dominant mechanisms driving ice-ocean interactions within these features. We then input these data into the three-equation melt parameterization to estimate spatial variability in melt rates within these topographic features. We test various parameterizations for ocean heat flux into the flat and sloped ice surfaces, and compare the results to melt rates sampled along a nearby terrace sidewall and roof with a phase sensitive radar. This work in progress aims to better understand how ocean conditions interact with ice slope on small scales to drive variable melting in warm, highly stratified environments. We expect regions beneath much of the ice shelves occupying West Antarctica to interact similarly with the underlying ocean to what we observe beneath Thwaites Glacier. Hence, our observations hold relevance for how ice sheet models parameterize ocean-driven melting in this type of melt-driven regime.

How to cite: Washam, P. and the ITGC MELT Team: Direct observations of coupled interactions between near-ice ocean stratification and ice slope and morphology in basal terraces beneath Thwaites Glacier, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15683, https://doi.org/10.5194/egusphere-egu23-15683, 2023.

X5.268
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EGU23-11661
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ECS
Benjamin Davison, Anna Hogg, Richard Rigby, Sanne Veldhuijsen, Melchior van Wessem, Michiel van den Broeke, Paul Holland, Heather Selley, and Pierre Dutrieux

Mass loss from the West Antarctic Ice Sheet is dominated by glaciers draining into the Amundsen Sea Embayment (ASE). The majority of that mass loss is driven by decadal variations in submarine melt rates. However, periods of extremely high or low precipitation can compound or mitigate ocean-driven mass losses, yet the impact of anomalous precipitation on the mass balance of the ASE is poorly known. We present a 25-year (1996-2021) record of ASE input-output mass balance and evaluate how two periods of anomalous precipitation affected its sea level contribution. Since 1996, the ASE has lost 3331±424 Gt ice, contributing 9.2±1.2 mm to global sea level. Overall, surface mass balance changes contributed just 7.7 % to total mass loss; however, two anomalous precipitation events had a larger, albeit short-lived, impact on rates of mass change. During 2009-2013, persistently low snowfall, due to anomalously zonal circulation, led to an additional 51±4 Gt yr-1 mass loss in those years (contributing positively to the total loss of 195±4 Gt yr-1). Contrastingly, extreme precipitation in the winters of 2019 and 2020 decreased mass loss by 60±16 Gt yr-1 during those years (contributing negatively to the total loss of 107±15 Gt yr-1). These results demonstrate that extreme snowfall variability can have a substantial impact on the short-term sea level contribution from West Antarctica and show that mass changes do not necessarily scale with grounding line discharge anomalies.

How to cite: Davison, B., Hogg, A., Rigby, R., Veldhuijsen, S., van Wessem, M., van den Broeke, M., Holland, P., Selley, H., and Dutrieux, P.: Revisiting the impact of anomalous precipitation on the mass budget of the Amundsen Sea Embayment ice streams, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11661, https://doi.org/10.5194/egusphere-egu23-11661, 2023.

X5.269
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EGU23-3240
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ECS
Armin Dachauer and Andreas Vieli

In response to the general warming ocean-termination outlet glaciers of the Greenland ice sheet are generally thinning and retreating rapidly. However, the glacier system of Qajuuttap Sermia (also known as Eqalorutsit Kangilliit Sermiat), at the southwestern basin of the greenland ice sheet, shows a strongly contrasting and highly heterogenous dynamical behaviour. Detailed analysis of elevation changes (AeroDEM, GIMP, ArcticDEM) and front positions between the years 1985 and 2021 show slight but significant advance and thickening over at least the last 35 years, whereas its neighboring ocean- and land-terminating glaciers and more interestingly its three direct northwestern tributaries all show rapid thinning. The data indicates that effects of fjord geometry alone cannot explain this anomaly and we therefore further investigate potential reasons using operational continuous time series of solid ice flux (PROMICE) and surface mass balance from regional climate models (RACMO, MAR). 

How to cite: Dachauer, A. and Vieli, A.: Anomalous mass gain of a tidewater outlet glacier with rapidly thinning ice sheet margin in Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3240, https://doi.org/10.5194/egusphere-egu23-3240, 2023.

X5.270
|
EGU23-7096
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ECS
Enrico Ciracì, Eric Rignot, Bernd Scheuchl, Valentyn Tolpekin, Michael Wollersheim, Lu An, Pietro Milillo, Jose Luis Bueso-Bello, Paola Rizzoli, and Luigi Dini

Petermann Glacier (80.75N, 60.75W) terminates in one of the most extensive remaining ice tongues of the Greenland Ice Sheet. The glacier is grounded 600 meters below sea level on a downsloping bed and could significantly contribute to sea level rise during the 21st century. Recent observations showed an ongoing acceleration in ice flow and kilometric-scale grounding line retreat after decades of stable dynamic conditions. Warming of the ocean waters surrounding Greenland has been indicated as the main driver of this process. However, the melting regime of the glacier at the interface between ocean waters and grounded ice is not well known and needs to be investigated.

In this study, we achieve this goal by employing a time series of satellite radar interferometry data available between 2011 and 2022. We document grounding line migration using high-frequency observations from the Italian COSMO-Skymed constellation and the Finnish ICEYE constellation. Furthermore, we use time-tagged digital elevation models from the German TanDEM-X mission to assess the ice shelf basal melt regime in a Lagrangian framework.

InSAR observations reveal kilometer-size grounding line migrations - (2-6 km) grounding zones - during tidal cycles, with preferential seawater intrusions of 6 km along pre-existing subglacial channels. In addition, results from the Lagrangian approach indicate that the highest ice shelf melt rates occur at these locations, with values reaching peaks ranging from 60 to 80 meters per year.

Such high melt rates concentrated in kilometer-wide grounding zones contrast with the traditional plume model adopted by physical models with zero melt at a fixed grounding line. Their inclusion in physical models will increase the glacier's sensitivity to ocean warming and double the projections of sea level rise from the glacier.

This work was supported by a grant from NASA.

How to cite: Ciracì, E., Rignot, E., Scheuchl, B., Tolpekin, V., Wollersheim, M., An, L., Milillo, P., Bueso-Bello, J. L., Rizzoli, P., and Dini, L.: Decadal grounding line migration and ice shelf melt regime of Petermann Glacier, North-West Greenland, from high-resolution InSAR data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7096, https://doi.org/10.5194/egusphere-egu23-7096, 2023.

X5.271
|
EGU23-7811
Rachel Carr, Emily Hill, and Hilmar Gudmundsson

The Greenland Ice Sheet (GrIS) contributed to 10.6 mm to global sea level rise between 1992 and 2018, making it crucial to accurately forecast its near future ice losses. Here, we assess the relative importance of two major sources of uncertainty in GrIS ice loss, namely the choice of sliding law and SMB forecasts. To do this we use the ice flow model Úa to perform a series of model experiments using different formulations of the sliding law, and different projections of future surface mass balance (SMB). We conducted this work at three major Greenland outlet glaciers, to assess the variability in the importance of sliding laws and/or SMB forecasts between different types of glacier. Our results show that the choice of sliding law had a small impact on ice loss from our study glaciers, whereas the choice of SMB forecast produced major differences in sea level rise estimates.

How to cite: Carr, R., Hill, E., and Gudmundsson, H.: Impact of sliding laws and surface mass projections on Greenland outlet glacier dynamics at 100-year timescales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7811, https://doi.org/10.5194/egusphere-egu23-7811, 2023.

X5.272
|
EGU23-11610
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ECS
Andrea Kneib-Walter, Guillaume Jouvet, Adrien Wehrlé, Ana Nap, Fabian Walter, and Martin P. Lüthi

Outlet glaciers and ice streams transport ice from the ice sheets to the ocean, where the glaciers lose mass by iceberg calving. Sermeq Kujalleq (SKK, Jakobshavn Isbræ) is one of the largest and most dynamic ice streams of the Greenland Ice Sheet with ice flow velocities up to 40 m/day. With extensive fieldwork and detailed repeated UAV surveys we aim at understanding the complex processes occuring at the ice stream margins and at the calving front of SKK. Such processes are often neclected in numerical models inducing uncertainties in projections of the ice sheet evolution.

Within the framework of the COEBELI project we conducted drone photogrammetry surveys in July 2022 at SKK along other field measurements including in-situ GPS, GPRI, seismometers, and time-lapse imagery. Despite challenging weather conditions and constraints due to flying restrictions, we acquired 17 repeated flight surveys over the calving front of SKK during two weeks. As a result, we produced a large imagery data set, which was processed to infer high-resolution ortho-images and digital elevation models (DEM). Comparing the different products enables us to estimate changes in surface topography and ice dynamics. During the observation period several large calving events occurred allowing us to investigate the interaction between frontal processes and ice flow dynamics. With the very detailed data we can study crevasse opening, acceleration at the front, weaknesses in the ice and their origin, and the reaction of the glacier to large calving events.

How to cite: Kneib-Walter, A., Jouvet, G., Wehrlé, A., Nap, A., Walter, F., and Lüthi, M. P.: Frontal processes of Sermeq Kujalleq in West Greenland observed with repeated UAV surveys, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11610, https://doi.org/10.5194/egusphere-egu23-11610, 2023.

X5.273
|
EGU23-13097
|
ECS
Multi-decadal ice-flow acceleration in the Greenland Ice Sheet interior
(withdrawn)
Anja Løkkegaard, William Colgan, and Shfaqat Abbas Khan

Posters virtual: Tue, 25 Apr, 14:00–15:45 | vHall CR/OS

Chairpersons: Peter Washam, Inga Monika Koszalka, Nicolas Jourdain
vCO.1
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EGU23-1109
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ECS
|
Ole Zeising, Olaf Eisen, Sophie Berger, M. Reza Ershadi, Reinhard Drews, Tanja Fromm, Tore Hattermann, Veit Helm, Niklas Neckel, Frank Pattyn, and Daniel Steinhage

Ice–ocean interaction is crucial for the integrity of ice shelves and thus ice sheet stability. Warm ocean currents lead to enhanced basal melting of ice shelves, which is the dominant component of mass loss for the Antarctic Ice Sheet. Knowing the current melt rates and predicting those under future climate scenarios is thus of great importance. In the course of the ­MIMO-EIS (Monitoring melt where Ice Meets Ocean) Project, we deployed a continuously measuring ApRES (Autonomous phase-sensitive Radio-Echo Sounding) device in the center of Ekström Ice Shelf, recording an hourly time series since April 2020. The continuous time series reveals a seasonal onset of enhanced melt rates, abruptly increasing from <0.5 to 2 m/a in July/August. High melt rates with around weekly to bi-weekly fluctuations last until November/December. In addition, we performed annual point measurements to determine the spatial pattern of basal melt rates. The majority of these sites show yearly averaged melt rates of <0.5 m/a. These measurements allow the evaluation of future ocean-simulations and are in good agreement with satellite remote sensing estimates.

How to cite: Zeising, O., Eisen, O., Berger, S., Ershadi, M. R., Drews, R., Fromm, T., Hattermann, T., Helm, V., Neckel, N., Pattyn, F., and Steinhage, D.: Seasonal enhanced melting under Ekström Ice Shelf, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1109, https://doi.org/10.5194/egusphere-egu23-1109, 2023.