Surface freshening of the Southern Ocean driven by meltwater discharge from the Antarctic ice sheet has been shown to influence global climate dynamics. However, most climate models fail to account for spatially and temporally varying freshwater inputs from ice sheets, introducing significant uncertainty into climate projections. We present the first historically calibrated projections of Antarctic freshwater fluxes (sub-shelf melting, calving, and surface meltwater runoff) to 2300 that can be used to force climate models lacking interactive ice sheets. Our findings indicate substantial changes in the magnitude and partitioning of Antarctic freshwater discharge over the coming decades and centuries, particularly under very-high warming scenarios, driven by the progressive collapse of the West Antarctic ice shelves. We project a shift in the form and location of Antarctic freshwater sources, as liquid sub-shelf melting increases under the two climate scenarios considered, and surface meltwater runoff could potentially become a dominant contributor under extreme atmospheric warming.
How to cite: Coulon, V., De Rydt, J., Gregov, T., Qin, Q., and Pattyn, F.: Future Freshwater Fluxes From the Antarctic Ice Sheet, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5701, https://doi.org/10.5194/egusphere-egu25-5701, 2025.
The stability of marine-terminating glaciers at the grounding line is critical for understanding the future of the West Antarctic Ice Sheet and its contribution to sea-level rise. While warm water intrusions are well-known drivers of ice-shelf melting, the role of shore-parallel ambient currents remains underexplored. Using a high-resolution, idealized MITgcm setup, we model a grounding zone cavity to investigate how along-shelf ambient currents influence circulation and melting patterns. Our results reveal that even modest ambient currents disrupt classical buoyancy-driven circulation by introducing Ekman layers and geostrophic flows that redistribute heat and salt. Positive along-shelf gradients amplify melting throughout the cavity, while negative gradients reduce melt rates, except near the grounding line. This dynamic interplay between ice-shelf and ambient currents significantly influences melt patterns and grounding-line stability. These findings emphasize the necessity of incorporating realistic three-dimensional ocean dynamics, including tides and residual circulation, into grounding-zone models. By linking shore-parallel flows, tides, and stratified ocean dynamics with melting processes, this study provides new insights into the retreat of Thwaites Glacier and underscores the critical role of small-scale ocean variability in ice-ocean interactions.
How to cite: Mondal, M., Holland, D. M., Nicholls, K. W., and Holland, P. R.: Effects of Ambient Currents on Melting at the Grounding Line , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7173, https://doi.org/10.5194/egusphere-egu25-7173, 2025.
Increased ice loss from the West Antarctic Ice Sheet plays a significant role in determining future sea level rise. Much of this loss originates from within the Amundsen Sea sector, where the floating components of ice sheets, the ice shelves, are expected to melt more rapidly over the coming century. This increased melting is caused by warm waters entering the continental shelf and melting these ice shelves from below. While models project an increase in ocean warming over the coming century, the causes behind this warming are little understood. In this study, we untangle how climate change will affect ocean warming in the future by comparing ocean warming under high emissions to pre-industrial simulations. An anthropogenic signal in ocean warming first emerges between 2013 and 2018 in the simulations and continues to strengthen under high emissions forcing. We then compare the effects of stronger winds shifted southwards (wind forcing) against the impacts of a warmer, wetter atmosphere (thermodynamic forcing). We find that the thermodynamic changes are primarily responsible for the predicted Amundsen Sea warming. Under a warmer and wetter climate, the ice shelves experience an increase in the poleward flow of warmer waters at depth, leading to more melting.
How to cite: Turner, K., Naughten, K., Holland, P., and Naveira Garabato, A.: Modelled centennial ocean warming in the Amundsen Sea driven by thermodynamic atmospheric changes, not winds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7100, https://doi.org/10.5194/egusphere-egu25-7100, 2025.
How to cite: Silvano, A., Castagno, P., and Nihashi, S.: What is happening in the Ross Sea? , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4501, https://doi.org/10.5194/egusphere-egu25-4501, 2025.
Ocean temperatures on the continental shelf in the Ross Sea and beneath the Ross Ice Shelf have remained cold in recent decades, despite climate-related warming trends in nearby regions, such as the Amundsen Sea. The Ross Sea is an important area for water mass transformation and the formation of Antarctic Bottom Water, an essential water mass in the global overturning circulation. Inflows of Circumpolar Deep Water (CDW) and outflows of High Salinity Shelf Water and Antarctic Bottom Water across the continental shelf break and beneath the Ross Ice Shelf, particularly in the west, are strongly modulated by tides. We find that tidal forcing modifies the cross-shelf circulation and regulates the inflow of warm CDW and sub-ice shelf warming, with associated impacts on basal melt rates.
Using a regional ocean model configuration (NEMO) at 1/4° resolution, which includes both the Amundsen and the Ross seas, we explore the influence of tides on potential future warming in the Ross Sea and continental shelf with four simulations as follows. The model is run with two different climate conditions: firstly, the control simulation is forced by repeat normal year atmospheric forcings, and secondly, a future 2300 climate scenario simulation is forced with air temperature +10°C and precipitation increased by a factor of two. We assess the sensitivity of both the control simulation and the 2300 climate scenario to tidal forcing by running each simulation firstly with only surface tidal forcing (no tides) and then with both surface tidal forcing and tidal harmonic forcing at the model domain lateral boundaries (tidal forcing). Under 2300 temperature and precipitation conditions, in the simulation with no tides, the Ross Ice Shelf cavity warms rapidly to temperatures of over 1°C during a 20 year period, with a rapid increase in basal melt rates. This is followed by a slower cooling period with a stabilisation of basal melt rates, leading to the cavity being filled with cold, fresh water by the end of the simulation period. In the simulation with tidal forcing, the cavity warms more gradually and remains warm, at temperatures at or above 0°C, with an associated increase in basal melt rates, for the duration of the simulation period. The tidal modulation leads to more gradual warming of the Ross Ice Shelf cavity and prevents a rapid transition of the cavity from cold to warm and from warm to fresh, as we see in the simulation without tides. This work suggests that tides are an important process to be included when modelling future climate projections.
How to cite: Mountford, A. S., Jenkins, A., Bull, C. Y. S., Jourdain, N. C., and Mathiot, P.: The role of tidal modulation on potential future warming behaviour in the Ross Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18881, https://doi.org/10.5194/egusphere-egu25-18881, 2025.
We present a 1000 km transect of Autonomous phase-sensitive Radio Echo Sounding (ApRES) measurements of ice thickness, basal reflection strength, basal melting, and ice-column deformation across the Ross Ice Shelf (RIS). Measurements were gathered across 32 repeat measurement sites and over five austral summers (2015-2020) connecting the grounding line with the distant ice shelf front. ApRES identifies varying basal reflection strength revealing a variety of basal conditions influenced by ice flow and by ice-ocean interaction at the ice base. Reflection strength is lower across the central RIS, characterised by higher strengths from major glaciers and ice streams and lower strengths in shear margins and suture zones. Strong reflections in the near-front and near-grounding line regions correspond with higher basal melt rates, up to 0.47 ± 0.02 m a-1 in the north. Melting from atmospherically warmed surface water is shown to extend 150-170 km south of the RIS front. Melt rates up to 0.29 ± 0.03 m a-1 and 0.15 ± 0.03 m a-1 are observed near the grounding lines of the Whillans and Kamb Ice Stream, respectively. Our surface-based observations generally agree with the basal melt pattern provided by satellite-based methods but provide a distinctly smoother pattern.
How to cite: Rack, W., Price, D., Snodgrass, J., Purdie, H., Hulbe, C., Wild, C. T., Stevens, C., Marsh, O. J., Ryan, M., McDonald, A., Gragg, K., and Forbes, M.: Basal reflectance and melt rates across the Ross Ice Shelf, Antarctica, from grounding line to ice shelf front, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13619, https://doi.org/10.5194/egusphere-egu25-13619, 2025.
Models are reported to overestimate basal melting under warm water ice shelves. Hence, ice-ocean heat exchange and its parameterisation are investigated using an ice-ocean boundary current model (IOBCM). Using the simplified case of a horizontal ice-ocean interface (IOI), we demonstrate how parameterizations in z-coordinate ocean models can significantly overestimate melt rates in boundary layers over dynamically stable pycnoclines when far-field ocean currents are weak.
We propose a simple physics-based parameterisation framework for this specific case. Two case studies are presented: 1) a horizontal IOI with uniform far-field currents; and 2) a sloped IOI with density-driven, sheared currents. We use this parameterisation framework to formulate a hybrid model for the general case of density-driven currents under ice shelves. The hybrid model is a combination of the classic plume model for dynamically unstable regimes and the parameterized version of the IOBCM for dynamically stable regimes. In the hybrid model, for stable regimes, the melt rate as well as its response to warming are significantly reduced when compared with the regime-independent treatment in the classic plume model.
Our findings highlight the importance of careful consideration of the ocean stratification and flow conditions when parameterizing ice-ocean interactions, especially in regions with weak currents and stable stratification.
How to cite: T. Pillai, J. and Jenkins, A.: Ice shelf Basal Melt Parameterisations for Ice-Ocean Boundary Layers over Dynamically Stable Pycnoclines: Case studies using a Boundary Current Model , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11731, https://doi.org/10.5194/egusphere-egu25-11731, 2025.
Modeling of the interactions between the Southern Ocean, sea ice, and ice shelves can provide insights into understanding the future sea level rising and climate changes, yet the interactions in the Southern Ocean are complex due to the coupled ocean-sea ice-ice shelf system. Considering the complexity of the Southern Ocean, the development of a high-resolution coupled circumpolar ocean-sea ice-ice shelf model could provide insights into the complex processes in the Southern Ocean. The Massachusetts Institute of Technology General Circulation Model (MITgcm), including a sea ice component and an ice shelf component, has been applied to the Southern Ocean to derive estimates of the oceanic state, sea ice evolution, and ice shelf basal fluxes. This Coupled Southern Ocean-Sea Ice-Ice Shelf Model (SOSIM v1.0) uses version c66m of the MITgcm, and the ocean, sea ice, and ice shelf components share the same horizontal grid layout (the Arakawa C grid). The sea ice model in the MITgcm is a viscous-plastic dynamic and zero-layer thermodynamic model, with the so-called zero-layer thermodynamics assuming one layer of ice underneath one layer of snow. The ice-shelf model is used to represent the static and thermodynamically active ice shelves located in the south of the model domain. In this study, the configuration of SOSIM v1.0 is documented, and the simulated features from SOSIM v1.0 are evaluated.
How to cite: Liu, C., wang, Z., Han, X., Leng, H., and Cheng, C.: The Development of the Coupled Southern Ocean-Sea Ice-Ice Shelf Model (SOSIM v1.0), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-325, https://doi.org/10.5194/egusphere-egu25-325, 2025.
Coupled ice sheet and ocean models are vital for projecting the dynamics of the Antarctic Ice Sheet and for predicting future sea level rise. The Filchner-Ronne sector of Antarctica contains a number of deep-bedded ice streams and glaciers potentially vulnerable to the Marine Ice Sheet Instability. Previous work has shown that, in a warming climate, a mode switch in circulation could bring intrusions of warm Circumpolar Deep Water (CDW) that would increase basal melt rates near the deep grounding lines of these vulnerable glaciers. Furthermore, the adjacent Weddell Sea is an important site of global deep water formation that is heavily dependent on the export of Ice Shelf Water. Here, we develop a new ice-ocean coupling framework for linking the global Finite volumE Sea ice Ocean Model (FESOM-2) with the Ice-sheet and Sea-level System Model (ISSM), and we apply this framework to model the Filchner-Ronne sector of Antarctica and the adjacent Weddell Sea. We use adaptive mesh resolution for FESOM-2 ranging from 100 km elements in the far field down to 3 km in the Weddell Sea and the sub-ice cavity. Our ice sheet model resolution varies from 10 km down to ~300 m, with basal friction taken from an inversion fit to present-day surface velocities. We use offline coupling with a timestep of 1 year. We develop an adaptive filtering technique for the transmission of melt rates from the ocean model to the ice model that effectively removes numerical artifacts caused by the z-coordinate representation of the ice base in the ocean model while preserving true structure in the melt rate field. For the adaptation of the ocean model to the updated ice geometry, we develop an iterative horizontal-vertical extrapolation procedure for ocean tracers and a minimal smoothing procedure for ocean velocities to ensure that the ocean model can restart in a manner that is both realistic and numerically stable. Using this coupling architecture, we are able to directly restart the ocean model after the geometry change without requiring either a cold start or a spinup period with reduced timesteps and increased viscosity. We then simulate the evolution of the coupled ice-ocean system, including a moving calving front, over the next century under a range of climate forcing scenarios. We find that the projected mode switch to warm conditions in the Filchner-Ronne cavity happens earlier in our coupled model than in previous projections, with warm CDW first entering the Filchner cavity in ~2035 under SSP585 forcing, followed by ice shelf thinning, grounding line retreat, and grounded ice mass loss in the ensuing decades. By comparison, previous projections in strongly warming scenarios showed the CDW entering the cavity in 2050-2075. These results emphasize the rapid changes in the cryosphere and the Southern Ocean that could arise from continued anthropogenic warming, and the importance of coupled modeling for fully understanding the dynamics of the ice-ocean system.
How to cite: Wolovick, M., Wekerle, C., Humbert, A., Timmermann, R., Rückamp, M., and Kleiner, T.: Coupled Ice Sheet-Ocean Modeling of the Filchner-Ronne sector using ISSM and FESOM-2, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15530, https://doi.org/10.5194/egusphere-egu25-15530, 2025.
Processes at the ice-ocean boundary are key in driving the rapid mass loss of the Greenland ice sheet. However, quantifying and understanding these processes remains challenging, particularly those occurring at the ice terminus beneath the fjord's water surface. Critical mechanisms include the melting of the submerged ice front by ocean water (oceanic melt), which influences the geometry of the glacier terminus and thus the glacier mass loss, and the outflow of subglacial meltwater. Subglacial meltwater can enforce a circulation cell within the fjord, drawing warm ocean water at depth towards the glacier front and enhancing oceanic melt. This circulation generates highly variable and opposing currents across different depths and over time. The harsh and highly dynamic environment makes direct observation and quantification of these circulations extremely difficult. Consequently, our understanding of key mechanisms is limited, restricting our ability to predict the future behaviour of the Greenland ice sheet. To bridge this knowledge gap, more comprehensive observations of circulation patterns near the calving front are crucial to improve our knowledge about the processes in the fjords.
This study exploits a unique time-series of terrestrial radar interferometry (TRI) acquisitions, complemented by fjord measurements, to investigate the tidewater outlet glacier Eqalorutsit Kangilliit Sermiat (EKaS) in South Greenland. A novel approach is applied to this dataset for inferring three-dimensional underwater fjord circulation with high temporal (minute-scale) and spatial (meter-scale) resolution over continuous periods lasting several weeks. An automated iceberg tracking method is employed to analyse the movement of icebergs of various sizes within the approximately 300 m deep fjord over time. TRI-derived elevation models are used to determine the above-water shapes of icebergs and estimate their submerged draft below the waterline. By linking the movements of icebergs with their draft, this study is able to extract the general water circulation patterns in the fjord at different depths, as icebergs of varying sizes are influenced by currents at distinct water layers. These findings are combined with fjord stratification data obtained from CTD profiles, providing a comprehensive understanding of the fjord's circulation dynamics.
The results of the inverted fjord circulation can later be compared with modelled fjord water circulation and combined with observations of glacier dynamics and calving derived from TRI acquisitions to obtain a comprehensive image of the “hidden” interplay between glacier and fjord circulation acting below the waterline. The findings are essential for understanding and predicting the role of oceanic forcing for the Greenland ice sheet mass loss and for assessing the implications for biodiversity within fjords in a changing climate.
How to cite: Kneib-Walter, A., Slater, D., Dachauer, A., and Vieli, A.: Unveiling the 3-dimensional fjord water circulation from iceberg tracking at a calving glacier in Greenland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11117, https://doi.org/10.5194/egusphere-egu25-11117, 2025.
The interaction between glacier fronts and ocean waters is one of the key uncertainties for projecting future ice mass loss. Direct observations at glacier fronts are sparse, but studies indicate that the magnitude and timing of freshwater fluxes are crucial in determining fjord circulation, ice frontal melt and ecosystem habitability. In particular, wintertime dynamics are severely understudied due to inaccessible conditions, leading to a bias towards summer observations.
Using a novel uncrewed aerial vehicle, we conducted multiple measurements in late winter in South Greenland. Here, we present our in-situ observations of temperature and salinity acquired at the front of a marine-terminating glacier and in surrounding fjords. Our observations indicate the existence of an anomalously fresh pool of water by the glacier front, suggesting that meltwater generated at the bed of the glacier discharges during winter. The results suggest that during winter, warm Atlantic water and nutrients are entrained at the glacier front, leading to enhanced frontal melt and increased nutrient levels. Our findings have implications for understanding the heat exchange between glacier fronts and ocean waters, glacier frontal melt rates, ocean mixing and currents, and biological production.
How to cite: Karlsson, N. B., Hansen, K., How, P., Poulsen, E., Mortensen, J., and Rysgaard, S.: Unique In-situ Measurements from Greenland Fjord Show Winter Freshening by Subglacial Melt, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10170, https://doi.org/10.5194/egusphere-egu25-10170, 2025.
Greenland’s glacial fjords are the sites of climatically important exchanges of heat, freshwater, and nutrients between the North Atlantic Ocean and the Greenland ice sheet, as well as hosting productive ecosystems integral to local communities. Though both glacial inputs and ocean exchanges are modulated by seasonal and interannual variability, observational studies of the complex interactions that take place in these fjords often necessarily rely on data from a single field campaign, amounting to a summer snapshot of fjord conditions.
We have sustained a long-term monitoring program in Sermilik Fjord, a major glacial fjord in southeast Greenland, since 2008, collecting ocean temperature and salinity profiles almost annually, supplemented by ongoing mooring records that cover the full period from 2008-2023. This exceptional data set, at times augmented by the collection of complementary data such as velocity measurements and noble gas, nutrient, and dissolved oxygen concentrations, has given us a more robust understanding of the fjord circulation and water mass transformations. This in turn can be leveraged to help us address a range of questions within this complex system.
We apply this foundational knowledge of Sermilik Fjord to interpret the cycling of mercury in the fjord from full water column measurements of mercury concentrations from summer 2021. We use a water mass analysis to show that the exported glacially-modified waters are depleted in inorganic mercury (HgII) relative to ambient ocean waters. We propose that sediments initially suspended in glacier meltwaters scavenge particle-reactive HgII and are subsequently buried, making the fjord a net sink of oceanic mercury.
How to cite: Lindeman, M., Straneo, F., Holte, J., and Roth, A.: Leveraging sustained monitoring of a southeast Greenland glacial fjord to understand ice-ocean and biogeochemical interactions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13605, https://doi.org/10.5194/egusphere-egu25-13605, 2025.
The Greenland Ice Sheet (GrIS) is undergoing accelerated melt and dynamic shifts that influence sediment export, with critical implications for regional biogeochemical cycles and cryospheric processes. However, direct observations of sediment export variability remain limited. To address this gap, we analyzed sediment cores from three glacier-fed fjords in Disko Bay, encompassing diverse catchment areas and glacier dynamics. The spatial extent of sediment packages and ice-rafted debris (IRD) within the cores was assessed, alongside decadal-scale sedimentation rates. These rates were integrated with sedimentary facies analyses and subbottom profiling.
By examining sedimentation rate variations with respect to glacier retreat histories, velocity data, and meltwater flux estimates, we identify contrasting behavior in sediment export amongst the fjords and catchments. The findings highlight the differential roles of glacier dynamics, catchment size, land or marine-terminating glacier fjord type, and meltwater contributions in modulating sedimentation patterns. Furthermore, several hyperpycnal deposits are present that could be the result of glacier outburst floods. We discuss their potential role in supplying sediment to the fjord and the challenges they introduce when trying to establish climate effects. This study underscores the importance of sediment production and mobilization processes from the GrIS and emphasizes the need for regional sediment export assessments to refine predictions of future discharge scenarios.
These results link sedimentary processes to ice sheet dynamics, offering a framework to evaluate processes controlling sediment fluxes in response to ongoing ice sheet retreat and climate change.
How to cite: Delaney, I., Gevers, M., Perchanok, F., Bollen, M., Pierce, E., Wellner, J., Toucanne, S., Liu, P., Overeem, I., Bomou, B., Carlson, B., and Jaccard, S.: Insights from Sediment Export Variability in Three Glacier-Fed Fjords in Disko Bay Kalaallit Nunaat (Greenland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7295, https://doi.org/10.5194/egusphere-egu25-7295, 2025.
Interactions between ice masses and the ocean are key couplings in the global climate system. In many cases these interactions occur through glacial fjords, which are long, deep, and narrow troughs connecting the open ocean to marine-terminating glaciers. By controlling the fluxes of ocean heat towards the ice sheet and ice sheet freshwater towards the ocean, glacial fjords play an important role in modulating ice sheet mass loss and the impacts of freshwater on ocean circulation. Yet, these dynamics occur at small scales that are challenging to resolve in earth system models and so are they often ignored, represented in an ad-hoc manner, or studied using expensive high-resolution models that are limited in scope.
Here, we propose a means of capturing glacial fjord dynamics at negligible computational expense in the form of a new "reduced physics" model (FjordRPM) that resembles a "1.5-dimensional" or box model. We describe the make-up of the model and show that it accurately captures glacial fjord circulation when compared with simulations in a full general circulation model (MITgcm). We conclude by considering applications for the model, including furthering the understanding of fjord circulation, the production of ocean temperature boundary conditions for ice sheet models and freshwater boundary conditions for ocean models, and the potential to act as a bridge between ice sheet and ocean in earth system models.
How to cite: Slater, D., Johnstone, E., Mas e Braga, M., Fraser, N., Cowton, T., and Inall, M.: Efficient simulation of glacial fjord dynamics using a new reduced physics model (FjordRPM), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9654, https://doi.org/10.5194/egusphere-egu25-9654, 2025.
Greenland fjords connect and modulate exchanges between its outlet glaciers and the open ocean. Subglacial meltwater and icebergs discharged from the ice sheet cause convection and mixing inside the fjord, upwelling warmer waters from depth and cooling down the upper layers. As a result of these processes, the water temperatures that effectively melt outlet-glacier termini are different than what is observed close to the fjord mouths and on the continental shelf. Data coverage to study such processes, however, is limited in both space and time, and a Greenland-wide assessment of fjord behaviour using general circulation models is computationally prohibitive. To tackle these issues, we use the Fjord Reduced-Physics Model (FjordRPM) to simulate 37 fjords around Greenland forced by available observations between 2016 and 2020. Its low computational cost enables large-ensemble analyses (i.e., 27000 simulations in total for this study) to explore the effects of icebergs, exchanges between the fjord and the continental shelf, and meltwater plumes.
We show that, while fjords cool down at the surface under increased icebergs, the effect of fjord-shelf exchanges and the meltwater plume are less straightforward. The depth where the plume reaches neutral buoyancy will determine which water masses are mixed, which might either warm or cool the fjord. The intensity of exchanges between the fjord and the shelf will affect the fjord stratification, therefore affecting the plume’s role in mixing water masses and homogenising the water column. Finally, we match our simulations to available observations to find the best-fitting model parameters, and highlight that, although there is a high variability in the best-fit model parameters between fjords and between years for a given fjord, values for the model parameters tested follow known statistical distributions, which can be used to refine prescribed model-parameter ranges. Although fjord systems are highly complex and the effects of different processes are not linear, a reduced-physics model can elucidate how fjords modulate ice-sheet-ocean exchanges at a Greenland-wide scale, provided observations are available to force the model.
How to cite: Mas e Braga, M., Cowton, T., Slater, D., Inall, M., Johnstone, E., and Fraser, N.: Drivers of glacial fjord-shelf temperature differences in the reduced-physics model FjordRPM, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3758, https://doi.org/10.5194/egusphere-egu25-3758, 2025.
Iceberg calving is a complex process often followed by the capsize of the newborn iceberg because of the torque created by the buoyancy and gravity forces. In the case of kilometer-scale icebergs, calving/capsize events can trigger seismic waves (glacial earthquakes) recorded hundreds of kilometers away by global seismic networks. These recordings contain information on the seismic source such as the calved-iceberg volume as well as the contact force applied by the iceberg on the glacier, the glacier dynamical response but also water waves and flow following the capsize.
To obtain an accurate estimation of the iceberg volume, it is necessary to couple seismic inversion of glacial earthquakes with numerical modeling of the capsize [Sergeant 2019]. Therefore, based on our previous work, we use a Computational Fluid Dynamics (CFD) model to simulate the fluid-structure interaction between the ocean and an iceberg capsizing against a glacier terminus. The model reproduces with great accuracy lab experiments (rotation kinematics, effect of calving type, hydrodynamic pressure, etc).
In this talk, we will focus on field-scale simulations. We will show that the forces applied on the glacier terminus due to the hydrodynamic pressure and to the iceberg-glacier contact appear to have similar amplitudes, are of opposite signs, and depend on the iceberg geometry. We also give a first estimation of the glacier deformation under the action of these forces. Our CFD simulations make it possible to compute the water velocity field in which values exceed 10 m/s close to the 200-meters-high-iceberg capsize.
Sergeant, A. et al. (2019) ‘Monitoring Greenland ice sheet buoyancy-driven calving discharge using glacial earthquakes’, Annals of Glaciology, 60(79), pp. 75–95. doi:10.1017/aog.2019.7.
How to cite: De Pinho Dias, N., C. Burton, J., Leroyer, A., Mangeney, A., and Castelnau, O.: On the forces at play during kilometer-scale iceberg calving: insight from numerical simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6688, https://doi.org/10.5194/egusphere-egu25-6688, 2025.
Representing ice-shelf and ocean interactions in Earth system models (ESMs) has been challenging due to their coarse resolution and static ice shelf cavity geometries. Additionally, coupling techniques often struggle to conserve mass and energy across components. We have recently implemented new algorithms in the ocean component of the Energy Exascale Earth System Model to enable dynamic ice-ocean interactions within Antarctica’s ice-shelf cavities. These include a thin subglacial film below grounded ice, subglacial runoff into ice-shelf cavities, and ice shelf-ocean fluxes computed in the ESM’s coupler. Together, these three approaches will enable representation of dynamic ice-sheet and ice-shelf geometry as well as continuity between the subglacial hydrological system while conserving mass and energy. Here, we present ocean simulations that explore the capabilities separately and report progress toward integrating both. We explore the thin-film capability in an idealized ice-shelf cavity at 2 km resolution modeled on the ISOMIP+ domain and the coupling capability in a global domain containing all Antarctic ice shelves at 12 km resolution. All simulations feature active ice-shelf thermodynamics. In the idealized simulations, we compare ice-ocean boundary layer properties and ice-shelf melt distributions from simulations with continuous dynamics between grounded and floating ocean model regions to those with fixed grounding line representations. We explore the model’s ability to simulate grounding-line migration due to both large ice-sheet thickness changes and tidal motion. We show that with our thin-film approach, subglacial runoff can mix with ocean waters below grounded ice before crossing the grounding line. In the global simulations, we demonstrate the ability to prescribe both fixed and dynamic ice-shelf thickness and outline the next steps for integrating the thin-film approach in this configuration.
How to cite: Asay-Davis, X., Begeman, C., Engwirda, D., Hager, A., Hillebrand, T., Hoffman, M., Nolan, A., Price, S., Vaňková, I., and Wolfe, J.: Dynamic ice sheet-ocean interactions in the Energy Exascale Earth System Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13400, https://doi.org/10.5194/egusphere-egu25-13400, 2025.
The Amundsen Sea sector in West Antarctica has undergone dramatic changes recently, with increased ice loss, widespread thinning and retreating grounding lines. This has led to concerns about the future stability of the region and of the wider ice sheet, which could raise global mean sea level by several meters. Mass loss is predominantly driven by basal melting at the coast, where vulnerable ice shelves are exposed to warm ocean waters. However, internal ice dynamics also plays a huge role in how the ice sheet responds to ocean-induced melting. To understand the ice sheet evolution, we must consider changes in both the ice and ocean systems and how they affect each other.
Here we show preliminary results from a new coupled ice-ocean model of the Amundsen Sea sector. The model domain spans from the Abbot basin to the Getz basin, including the major Pine Island and Thwaites glaciers, and includes the continental shelf, break and open ocean. We use the ice-flow model Úa to produce a present-day configuration of the ice sheet, through a two-stage optimisation procedure involving observations of ice velocities and thickness changes. This is coupled offline to the MIT general circulation model, which includes both sea ice and ice shelf thermodynamics, and is forced with historical atmospheric conditions. The coupled model has been validated using both ice and ocean observations and will now be run using projected conditions. This new model will help us to better understand the complex interplay between ice dynamics and ocean conditions in the Amundsen Sea sector and what impact this will have in future scenarios.
How to cite: Reed, B., Naughten, K., Turner, K., and De Rydt, J.: A new coupled ice-ocean model of the Amundsen Sea sector, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17223, https://doi.org/10.5194/egusphere-egu25-17223, 2025.
The West Antarctic Ice Sheet is rapidly losing mass due to ocean-driven ice shelf melt, contributing to sea level rise. This ice shelf melt is typically studied using either global climate models without open ice shelf cavities or regional models with ice shelf cavities. We will present updates on development work with a ¼° circumpolar Antarctic NEMO configuration that extends from the continent to 50 degrees south to allow for interaction between regions and which includes sea ice, icebergs, and open ice shelf cavities with BedMachinev3 bathymetry. While experiments forced by ERA5 atmospheric conditions are stable over the observational period (1979-now), there is a tendency for reduction of stratification in the water column in the Weddell Sea, making it prone to destabilization when forced with historical conditions and resulting in excess deep convection. We will present results from testing of the sensitivity to excess Weddell Sea deep convection in the model configuration, leading to a set of sea ice parameter combinations that appear to reduce convection, while maintaining desired ice shelf cavity properties. We will also discuss some explorations into mixing representations within ice shelf cavities. Moving forward, we plan to use this configuration to study attribution questions of ocean-driven melt of the West Antarctic Ice Sheet.
How to cite: Rogalla, B., Naughten, K., Holland, P., Mathiot, P., Jourdain, N., and Kittel, C.: Developments within an Antarctic ocean model configuration: balancing regional characteristics with circumpolar modelling challenges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16538, https://doi.org/10.5194/egusphere-egu25-16538, 2025.
Ice shelves buttress the grounded ice sheet, slowing its flow into the ocean. Mass loss from these ice shelves occurs primarily through ocean-induced basal melting, with the highest melt rates concentrated within basal channels—elongated, kilometre-wide zones of relatively thinner ice. While some models suggest that basal channels could mitigate overall ice shelf melt rates, channels have also been linked to basal and surface crevassing, leaving their cumulative impact on ice shelf stability a topic of ongoing debate. However, due to their relatively small spatial scale and the limitations of previous satellite datasets, our understanding of how channelised melting evolves over time remains limited.
In this study, we present a novel approach to integrate CryoSat-2 radar altimetry data to calculate ice shelf basal melt rates, demonstrated here as a case study over Pine Island Glacier (PIG) ice shelf. Our method generates monthly Digital Elevation Models and melt maps with a 250m spatial resolution. Using these data, we show that near the grounding line basal melting preferentially melts the channels western flank 50% more than its eastern flank. We also find that the main channelised geometries on PIG are inherited from upstream of the grounding line and that channels play a role in forming ice shelf pinning points, potentially impacting the stability of the ice shelf. These observations further highlight the impact of channelised melting under ice shelves, emphasising the need to investigate them further and to consider their impacts on datasets and models that do not resolve them.
How to cite: Lowery, K., Dutrieux, P., Holland, P., Hogg, A., Gourmelen, N., and Wallis, B.: Basal Channels on Pine Island Glacier with CryoSat-2: their formation, melt evolution and impact on buttressing., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-306, https://doi.org/10.5194/egusphere-egu25-306, 2025.
Climate change is impacting high-latitude fjord circulation with consequences for the transport of marine biota essential for supporting local ecosystems. Currently, little is understood about oceanographic variability in sub-Antarctic island fjords such as Cumberland Bay, the largest fjord on the island of South Georgia in the Southern Ocean. Cumberland Bay is split into two arms, West Bay and East Bay, and is a key spawning site for the ecologically and commercially important mackerel icefish. Through the use of a high-resolution three-dimensional hydrodynamic model, the seasonal cycle in Cumberland Bay is found to be driven by a combination of boundary forcing influencing shelf exchange and deep inflow, atmospheric forcing influencing near surface temperatures and flows and freshwater forcing via subglacial discharge driving upwelling and strong outflowThere is a complex three-dimensional flow structure with a high degree of variability on short timescales due to wind forcing. Using model flow fields to drive an individual-based model parameterised for larvae of the ecologically and commercially important mackerel icefish spawned in Cumberland Bay, we identify West Bay as a key retention zone. Successful retention of mackerel icefish larvae is found to be sensitive complex circulation patterns driven by winds, freshwater and fjord-shelf exchanges and to changes in physical processes linked to climate change such as meltwater runoff and föhn wind events. This study highlights the importance of oceanographic variability in influencing ecological processes in fjords in our changing climate.
How to cite: Zanker, J., Young, E., Brickle, P., and Haigh, I.: Sub-Antarctic fjord circulation and associated larval retention in a changing climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6042, https://doi.org/10.5194/egusphere-egu25-6042, 2025.
The interface between marine-terminating glaciers and fjord waters is a key part of the Greenland cryosphere and marine systems. The discharge of glacial meltwater interacts with fjord conditions by affecting water circulation, heat budget and ecosystem dynamics. Sediment-laden plumes are clear visual evidence of this interaction. The plumes occur when meltwater from a marine-terminating glacier is discharged into a fjord at depth. The meltwater then forms buoyant, sediment-laden plumes that reach the fjord water surface, making them detectable by satellite. Although the presence of plumes is well-documented, direct observational evidence is sparse, and only a few in-situ observations exist. More observations are needed to improve our understanding of the driving mechanisms of the plumes, including their spatiotemporal extent.
In this study, we apply Random Forest Classification to high-resolution optical imagery from Sentinel-2 to automatically map the extent of the plumes in front of glaciers in South Greenland. Based on surface reflectance, we estimate the suspended sediment concentration in the plumes, and we assess the performance of Random Forest compared to more commonly used regression methods.
Our results provide the basis for future work of constructing a comprehensive dataset of subglacial discharge plumes and sediment concentration for all marine-terminating glaciers across Greenland, offering new insights into their extent and properties.
How to cite: Deichmann, A. K., Bjørk, A. A., and Karlsson, N. B.: Mapping Subglacial Discharge Plumes and Estimating Suspended Sediment Concentrations in South Greenland Fjords, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9797, https://doi.org/10.5194/egusphere-egu25-9797, 2025.
We present the first direct observations of submarine melt rate and boundary layer characteristics made from an instrumentation platform mounted underwater into the terminus of Xeitl Sit’ (LeConte Glacier) in southeast Alaska. The instrumentation platform, called a Meltstake, is a remotely deployed robotic platform that drills into a near-vertical submarine ice face, allowing for prolonged stationary measurements in the ice’s reference frame. Three deployments of the Meltstakes were completed at 20 m, 45 m, and 50 m depths, with each deployment lasting approximately two hours. Observations were targeted in the ambient melt region away from the subglacial discharge plume, where the ocean velocity is generally assumed to be quiescent and driven by submarine melt plumes. However, flow along the glacier exhibits broadband variability in both speed and direction. Ocean temperature and salinity within 1 m of the boundary suggest the presence of ambient melt water mixing with fjord water, but no signatures of ambient melt plumes are clearly observed at the deployment locations. Submarine melt rate at the deployment locations is variable in time and exceeds 1-2 m/d. These observations provide an unprecedented look into the boundary layer dynamics driving submarine melt at a near-vertical ice face.
How to cite: Weiss, K., Nash, J., Wengrove, M., Osman, N., Pettit, E., Cohen, N., Nahorniak, J., Knox, T., Jensen, K., Ross, L., Zhao, K., Jackson, R., Sutherland, D., Waghorn, L., Ovall, B., and Skyllingstad, E.: The first successful deployment of an ice-mounted instrument platform to measure submarine melt rate and boundary layer flow at an active tidewater glacier , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21454, https://doi.org/10.5194/egusphere-egu25-21454, 2025.
Tsunamis are rare but potentially highly destructive natural phenomena, posing a serious threat to coastal environments and communities in many parts of the world. Historical catalogues tell that about 70% of the tsunamis worldwide are generated by submarine or coastal earthquakes, while the remaining 30% includes landslides, volcanic eruptions, atmospheric disturbances, and calving. Especially in light of the rapidly changing global climate conditions, calving is gaining increasing attention in the tsunami research community. This study aims at describing calving generation mechanism, focusing on observations and modelling. Unlike earthquake-generated tsunamis, the mechanisms behind iceberg calving and the resulting water displacement are poorly understood and more difficult to model. The dynamics and unpredictable nature of calving events make it essential to improve our understanding of how these tsunamis form and propagate. Data from the Italian MACMAP Project (A Multidisciplinary Analysis of Climate Change Indicators in the Mediterranean and Polar Regions) coordinated by the Istituto Nazionale di Geofisica e Vulcanologia (Italy) is used to achieve this goal. In fact, the project operates a meteo-hydrometric station at Wolstenholme Fjord, Greenland, which provides continuous measurements of crucial parameters such as instantaneous, minimum, and maximum sea level measures, which are useful for studying calving-induced tsunamis in the basin. To model the tsunami initial conditions, generated by the calving events, a paraboloid shape is employed, with crests surrounding the block of ice falling into water. This geometry has been chosen due to its ability to replicate the initial displacement patterns observed in calving dynamics as described in Hu (2022) and in Huang (2023). The simulations are carried out by means of the JAGURS software for different geometries of the ice body and in different locations based on potential sources observed in the study fjord. The available tide gauge time histories are used to validate the results of the numerical modeling, aiming at acquiring knowledge of the calving source and quantifying the detached ice mass.
How to cite: Guglielmin, A., Armigliato, A., Danesi, S., Muscari, G., Salimbeni, S., and Zaniboni, F.: Calving induced tsunamis in the Wolstenholme Fjord (Greenland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16776, https://doi.org/10.5194/egusphere-egu25-16776, 2025.
50% of mass loss from the Greenland Ice Sheet in recent decades is due to calving from tidewater glaciers (TWG). However, the relationship between climate and calving remains uncertain. While calving parameters in glacier models can replicate observed glacier retreat, they need validation against longer-term records of ice margin advance and retreat. By contextualizing both the advance and retreat of a Greenlandic TWG, Kangiata Nunaata Sermia, KNS, over centennial to millennial timescales, we can minimize the impact of short-term climate variations and assess if modelled climate-glacier interactions are biased toward retreat due to processes operating over decadal timescales.
Our model is validated against a well-constrained millennial-scale record of advance and retreat from a fast-flowing TWG in southwest Greenland. Our key research questions are: How do calving laws perform when modelling the advance of a grounded Greenlandic TWG? And how do calving law tuning parameters relate to physical processes, such as climate and fjord geometry? By comparing four calving laws and exploring a physical basis for glacier-specific tunning, we aim to better constrain calving fronts in glacier models and improve the capacity for predictive calving modelling.
A previous Greenland wide study suggested that the von Mises law better replicates decadal retreat, but our results show it lacks sensitivity to advance and, to avoid numerical instability, requires transient tuning for retreat. We further investigate the sensitivity of other calving laws, including eigen calving, height-above-buoyancy, and crevasse-water-depth.
How to cite: Jones, D., Mair, D., Nias, I., Lea, J., and Morlinghem, M.: Modelling calving over the last 1000 years of a Greenlandic tidewater glacier during advance and retreat, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17684, https://doi.org/10.5194/egusphere-egu25-17684, 2025.
Freshwater fluxes entering fjords are important for ice-ocean interactions, circulation in Greenland's fjords, and the use of freshwater forcing in ocean modelling. We study the timing, source type, and magnitude of freshwater fluxes and their temporal and spatial variability using statistically downscaled output from regional climate models for the mass fluxes, process-based estimates of basal melt and observational data for solid ice discharge. For seven climatologically distinct regions, we estimate the absolute and relative contribution of runoff from the Greenland Ice Sheet, ice caps, and tundra, solid ice discharge and precipitation directly falling into fjords between 1940 and 2023. The relative contribution of freshwater sources varies between months and regions, with distinct differences between the runoff-dominated southwest, and the solid-ice-discharge-dominated southeast.
How to cite: Vries, A., van de Berg, W. J., Noël, B., Meire, L., and van den Broeke, M.: Seasonal and interannual variability of freshwater sources for Greenland's fjords, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2179, https://doi.org/10.5194/egusphere-egu25-2179, 2025.
The Atlantic Meridional Overturning Circulation (AMOC) plays a central role in climate by transporting and redistributing recently observed temperature increases to depth, thereby regulating the effective heat capacity of the ocean under global warming. The AMOC is projected to decline in response to climate change and there is broad agreement that the climate consequences of a potential shutdown of this vital ocean circulation are enormous. The Nordic Seas are a dominant contributor to the overturning circulation due to the production of dense waters north of the Greenland-Scotland Ridge which feed into the lower limb of the AMOC.
The objectives of ARCTIC-FLOW, an ESA Polar Cluster project, are: 1) to identify the main locations of surface water mass transformation into denser waters; 2) to provide new estimates of water mass transformation and overturning in order to understand the mechanisms driving surface density changes and their impact on the ocean circulation; 3) to investigate the temporal and spatial scales at which the main processes of water mass formations occur; and 4) to assess the impact of extreme freshening events, with the main focus on different regions of the Nordic Seas.
To achieve these objectives, we will construct a new 16-year time series of satellite-derived freshwater and density fluxes for the Arctic and sub-Arctic regions, obtained by combining SSS, SST and velocity fields from EO observation, along with information of the Mixed Layer Depth. We will then perform an in-depth analysis of a comprehensive set of in situ measurements in combination with results of model experiments and the new EO-derived time series.
In this talk we will present the project and the progress made in generating the new satellite product.
How to cite: Olmedo, E., Arias, M., Beszczynska-Möller, A., Gabarró, C., González-Gambau, V., Karcher, M., B. Karlsson, N., Kauker, F., Oliva, R., Onrubia, R., Piracha, A., Sabia, R., Munck Solgaard, A., Turiel, A., Umbert, M., and Wearing, M.: ARCTIC-FLOW: A new project for better understanding water mass formation processes in the Nordic Seas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18807, https://doi.org/10.5194/egusphere-egu25-18807, 2025.
