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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 20^th 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.

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.

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.

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.

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.

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.

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.

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 22^nd century, followed by ice shelf collapse and rapid sea level rise in the 23^rd.  Using FESOM simulated melt rates the destabilization of the FRIS sector proceeds more slowly. During the 22^nd 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 23^rd century retreat becomes more widespread, culminating in ice shelf collapse and rapid sea level rise in the 24^th and 25^th 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.