Articles | Volume 19, issue 10
https://doi.org/10.5194/tc-19-5135-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-19-5135-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
28 Oct 2025
Research article |
| 28 Oct 2025
| 28 Oct 2025
Sub-grid parameterization of iceberg drag in a coupled iceberg–ocean model
Paul T. Summers
CORRESPONDING AUTHOR
Department of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
Department Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, USA
Rebecca H. Jackson
Department Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, USA
Department of Earth and Climate Sciences, Tufts University, Medford, Massachusetts, USA
Alexander A. Robel
Department of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
Related authors
Andrew O. Hoffman, Paul T. Summers, Jenny Suckale, Knut Christianson, Ginny Catania, and Howard Conway
EGUsphere, https://doi.org/10.5194/egusphere-2025-1239, https://doi.org/10.5194/egusphere-2025-1239, 2025
Short summary
Short summary
In Antarctica, fast-flowing ice streams drive most ice loss. Radar data from Conway Ice Ridge reveal that the van der Veen and Mercer Ice Streams were wider ~3000 years ago and narrowed progressively. Numerical modeling demonstrates that small thickness changes can rapidly alter shear-margin locations. These findings offer crucial insights into Late Holocene Ice Sheet readvance.
Vincent Verjans, Alexander A. Robel, Lizz Ultee, Helene Seroussi, Andrew F. Thompson, Lars Ackermann, Youngmin Choi, and Uta Krebs-Kanzow
The Cryosphere, 19, 3749–3783, https://doi.org/10.5194/tc-19-3749-2025, https://doi.org/10.5194/tc-19-3749-2025, 2025
Short summary
Short summary
This study examines how random variations in climate may influence future ice loss from the Greenland ice sheet. We find that random climate variations are important for predicting future ice loss from the entire Greenland ice sheet over the next 20–30 years but relatively unimportant after that period. Thus, uncertainty in sea level projections from the effect of climate variability on Greenland may play a role in coastal decision-making about sea level rise over the next few decades.
Madeline S. Mamer, Alexander A. Robel, Chris C. K. Lai, Earle Wilson, and Peter Washam
The Cryosphere, 19, 3227–3251, https://doi.org/10.5194/tc-19-3227-2025, https://doi.org/10.5194/tc-19-3227-2025, 2025
Short summary
Short summary
In this work, we simulate estuary-like seawater intrusions into the subglacial hydrologic system for marine outlet glaciers. We find the largest controls on seawater intrusion are the subglacial space geometry and meltwater discharge velocity. Further, we highlight the importance of extending ocean-forced ice loss to grounded portions of the ice sheet, which is currently not represented in models coupling ice sheets to ocean dynamics.
Samuel T. Kodama, Tamara Pico, Alexander A. Robel, John Erich Christian, Natalya Gomez, Casey Vigilia, Evelyn Powell, Jessica Gagliardi, Slawek Tulaczyk, and Terrence Blackburn
The Cryosphere, 19, 2935–2948, https://doi.org/10.5194/tc-19-2935-2025, https://doi.org/10.5194/tc-19-2935-2025, 2025
Short summary
Short summary
We predicted how sea level changed in the Ross Sea (Antarctica) due to glacial isostatic adjustment, or solid Earth ice sheet interactions, over the last deglaciation (20 000 years ago to present) and calculated how these changes in bathymetry impacted ice stream stability. Glacial isostatic adjustment shifts stability from where ice reached its maximum 20 000 years ago, at the continental shelf edge, to the modern grounding line today, reinforcing ice-age climate endmembers.
Ziad Rashed, Alexander A. Robel, and Hélène Seroussi
The Cryosphere, 19, 1775–1788, https://doi.org/10.5194/tc-19-1775-2025, https://doi.org/10.5194/tc-19-1775-2025, 2025
Short summary
Short summary
Sermeq Kujalleq, Greenland's largest glacier, has significantly retreated since the late 1990s in response to warming ocean temperatures. Using a large-ensemble approach, our simulations show that the retreat is mainly initiated by the arrival of warm water but sustained and accelerated by the glacier's position over deeper bed troughs and vigorous calving. We highlight the need for models of ice mélange to project glacier behavior under rapid calving regimes.
Meghana Ranganathan, Alexander A. Robel, Alexander Huth, and Ravindra Duddu
The Cryosphere, 19, 1599–1619, https://doi.org/10.5194/tc-19-1599-2025, https://doi.org/10.5194/tc-19-1599-2025, 2025
Short summary
Short summary
The rate of ice loss from ice sheets is controlled by the flow of ice from the center of the ice sheet and by the internal fracturing of the ice. These processes are coupled; fractures reduce the viscosity of ice and enable more rapid flow, and rapid flow causes the fracturing of ice. We present a simplified way of representing damage that is applicable to long-timescale flow estimates. Using this model, we find that including fracturing in an ice sheet simulation can increase the loss of ice by 13–29 %.
Andrew O. Hoffman, Paul T. Summers, Jenny Suckale, Knut Christianson, Ginny Catania, and Howard Conway
EGUsphere, https://doi.org/10.5194/egusphere-2025-1239, https://doi.org/10.5194/egusphere-2025-1239, 2025
Short summary
Short summary
In Antarctica, fast-flowing ice streams drive most ice loss. Radar data from Conway Ice Ridge reveal that the van der Veen and Mercer Ice Streams were wider ~3000 years ago and narrowed progressively. Numerical modeling demonstrates that small thickness changes can rapidly alter shear-margin locations. These findings offer crucial insights into Late Holocene Ice Sheet readvance.
Jason M. Amundson, Alexander A. Robel, Justin C. Burton, and Kavinda Nissanka
The Cryosphere, 19, 19–35, https://doi.org/10.5194/tc-19-19-2025, https://doi.org/10.5194/tc-19-19-2025, 2025
Short summary
Short summary
Some fjords contain dense packs of icebergs referred to as ice mélange. Ice mélange can affect the stability of marine-terminating glaciers by resisting the calving of new icebergs and by modifying fjord currents and water properties. We have developed the first numerical model of ice mélange that captures its granular nature and that is suitable for long-timescale simulations. The model is capable of explaining why some glaciers are more strongly influenced by ice mélange than others.
Alexander A. Robel, Vincent Verjans, and Aminat A. Ambelorun
The Cryosphere, 18, 2613–2623, https://doi.org/10.5194/tc-18-2613-2024, https://doi.org/10.5194/tc-18-2613-2024, 2024
Short summary
Short summary
The average size of many glaciers and ice sheets changes when noise is added to the system. The reasons for this drift in glacier state is intrinsic to the dynamics of how ice flows and the bumpiness of the Earth's surface. We argue that not including noise in projections of ice sheet evolution over coming decades and centuries is a pervasive source of bias in these computer models, and so realistic variability in glacier and climate processes must be included in models.
Lizz Ultee, Alexander A. Robel, and Stefano Castruccio
Geosci. Model Dev., 17, 1041–1057, https://doi.org/10.5194/gmd-17-1041-2024, https://doi.org/10.5194/gmd-17-1041-2024, 2024
Short summary
Short summary
The surface mass balance (SMB) of an ice sheet describes the net gain or loss of mass from ice sheets (such as those in Greenland and Antarctica) through interaction with the atmosphere. We developed a statistical method to generate a wide range of SMB fields that reflect the best understanding of SMB processes. Efficiently sampling the variability of SMB will help us understand sources of uncertainty in ice sheet model projections.
Vincent Verjans, Alexander A. Robel, Helene Seroussi, Lizz Ultee, and Andrew F. Thompson
Geosci. Model Dev., 15, 8269–8293, https://doi.org/10.5194/gmd-15-8269-2022, https://doi.org/10.5194/gmd-15-8269-2022, 2022
Short summary
Short summary
We describe the development of the first large-scale ice sheet model that accounts for stochasticity in a range of processes. Stochasticity allows the impacts of inherently uncertain processes on ice sheets to be represented. This includes climatic uncertainty, as the climate is inherently chaotic. Furthermore, stochastic capabilities also encompass poorly constrained glaciological processes that display strong variability at fine spatiotemporal scales. We present the model and test experiments.
John Erich Christian, Alexander A. Robel, and Ginny Catania
The Cryosphere, 16, 2725–2743, https://doi.org/10.5194/tc-16-2725-2022, https://doi.org/10.5194/tc-16-2725-2022, 2022
Short summary
Short summary
Marine-terminating glaciers have recently retreated dramatically, but the role of anthropogenic forcing remains uncertain. We use idealized model simulations to develop a framework for assessing the probability of rapid retreat in the context of natural climate variability. Our analyses show that century-scale anthropogenic trends can substantially increase the probability of retreats. This provides a roadmap for future work to formally assess the role of human activity in recent glacier change.
Alexander A. Robel, Earle Wilson, and Helene Seroussi
The Cryosphere, 16, 451–469, https://doi.org/10.5194/tc-16-451-2022, https://doi.org/10.5194/tc-16-451-2022, 2022
Short summary
Short summary
Warm seawater may intrude as a thin layer below glaciers in contact with the ocean. Mathematical theory predicts that this intrusion may extend over distances of kilometers under realistic conditions. Computer models demonstrate that if this warm seawater causes melting of a glacier bottom, it can cause rates of glacier ice loss and sea level rise to be up to 2 times faster in response to potential future ocean warming.
Cited articles
Abib, N., Sutherland, D. A., Peterson, R., Catania, G., Nash, J. D., Shroyer, E. L., Stearns, L. A., and Bartholomaus, T. C.: Ice mélange melt changes observed water column stratification at a tidewater glacier in Greenland, The Cryosphere, 18, 4817–4829, https://doi.org/10.5194/tc-18-4817-2024, 2024. a
Adcroft, A., Hill, C., and Marshall, J.: Representation of topography by shaved cells in a height coordinate ocean model, Monthly Weather Review, 125, 2293–2315, https://doi.org/10.1175/1520-0493(1997)125<2293:ROTBSC>2.0.CO;2, 1997. a, b
Amundson, J. M., Fahnestock, M., Truffer, M., Brown, J., Lüthi, M. P., and Motyka, R. J.: Ice mélange dynamics and implications for terminus stability, Jakobshavn Isbræ, Greenland, Journal of Geophysical Research: Earth Surface, 115, 1–12, https://doi.org/10.1029/2009JF001405, 2010. a, b
Amundson, J. M., Robel, A. A., Burton, J. C., and Nissanka, K.: A quasi-one-dimensional ice mélange flow model based on continuum descriptions of granular materials, The Cryosphere, 19, 19–35, https://doi.org/10.5194/tc-19-19-2025, 2025. a, b, c
Carroll, D., Sutherland, D. A., Shroyer, E. L., Nash, J. D., Catania, G. A., and Stearns, L. A.: Subglacial discharge‐driven renewal of tidewater glacier fjords, Journal of Geophysical Research: Oceans, 122, 6611–6629, https://doi.org/10.1002/2017JC012962, 2017. a
Cenedese, C. and Straneo, F.: Icebergs Melting, Annual Review of Fluid Mechanics, 55, 377–402, https://doi.org/10.1146/annurev-fluid-032522-100734, 2023. a
Cowton, T., Slater, D., Sole, A., Goldberg, D., and Nienow, P.: Modeling the impact of glacial runoff on fjord circulation and submarine melt rate using a new subgrid‐scale parameterization for glacial plumes, Journal of Geophysical Research: Oceans, 120, 796–812, https://doi.org/10.1002/2014JC010324, 2015. a, b, c
FitzMaurice, A., Cenedese, C., and Straneo, F.: Nonlinear response of iceberg side melting to ocean currents, Geophysical Research Letters, 44, 5637–5644, https://doi.org/10.1002/2017GL073585, 2017. a, b
Gladish, C. V., Holland, D. M., Rosing-Asvid, A., Behrens, J. W., and Boje, J.: Oceanic boundary conditions for Jakobshavn Glacier, Part I: Variability and renewal of Ilulissat Icefjord waters, 2001-14, Journal of Physical Oceanography, 45, 3–32, https://doi.org/10.1175/JPO-D-14-0044.1, 2015. a
Hughes, K. G.: Pathways, Form Drag, and Turbulence in Simulations of an Ocean Flowing Through an Ice Mélange, Journal of Geophysical Research: Oceans, 127, 1–17, https://doi.org/10.1029/2021JC018228, 2022. a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z, aa, ab, ac, ad, ae, af, ag, ah, ai, aj, ak, al, am
Jackett, D. R. and Mcdougall, T. J.: Minimal Adjustment of Hydrographic Profiles to Achieve Static Stability, Journal of Atmospheric and Oceanic Technology, 12, 381–389, https://doi.org/10.1175/1520-0426(1995)012<0381:MAOHPT>2.0.CO;2, 1995. a
Jackson, R. H. and Straneo, F.: Heat, Salt, and Freshwater Budgets for a Glacial Fjord in Greenland, Journal of Physical Oceanography, 46, 2735–2768, https://doi.org/10.1175/JPO-D-15-0134.1, 2016. a
Jain, L., Slater, D., and Nienow, P.: Modelling ocean melt of ice mélange at Greenland's marine-terminating glaciers, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-4081, 2025. a, b, c
Klymak, J. M., Legg, S. M., and Pinkel, R.: High-mode stationary waves in stratified flow over large obstacles, Journal of Fluid Mechanics, 644, 321–336, https://doi.org/10.1017/S0022112009992503, 2010. a, b
Klymak, J. M., Balwada, D., Garabato, A. N., and Abernathey, R.: Parameterizing nonpropagating form drag over rough bathymetry, Journal of Physical Oceanography, 51, 1489–1501, https://doi.org/10.1175/JPO-D-20-0112.1, 2021. a
Moon, T., Sutherland, D. A., Carroll, D., Felikson, D., Kehrl, L., and Straneo, F.: Subsurface iceberg melt key to Greenland fjord freshwater budget, Nature Geoscience, 11, 49–54, https://doi.org/10.1038/s41561-017-0018-z, 2018. a, b
Morlighem, M., Wood, M., Seroussi, H., Choi, Y., and Rignot, E.: Modeling the response of northwest Greenland to enhanced ocean thermal forcing and subglacial discharge, The Cryosphere, 13, 723–734, https://doi.org/10.5194/tc-13-723-2019, 2019. a
Moyer, A. N., Sutherland, D. A., Nienow, P. W., and Sole, A. J.: Seasonal Variations in Iceberg Freshwater Flux in Sermilik Fjord, Southeast Greenland From Sentinel‐2 Imagery, Geophysical Research Letters, 46, 8903–8912, https://doi.org/10.1029/2019GL082309, 2019. a, b
Otosaka, I. N., Shepherd, A., Ivins, E. R., Schlegel, N.-J., Amory, C., van den Broeke, M. R., Horwath, M., Joughin, I., King, M. D., Krinner, G., Nowicki, S., Payne, A. J., Rignot, E., Scambos, T., Simon, K. M., Smith, B. E., Sørensen, L. S., Velicogna, I., Whitehouse, P. L., A, G., Agosta, C., Ahlstrøm, A. P., Blazquez, A., Colgan, W., Engdahl, M. E., Fettweis, X., Forsberg, R., Gallée, H., Gardner, A., Gilbert, L., Gourmelen, N., Groh, A., Gunter, B. C., Harig, C., Helm, V., Khan, S. A., Kittel, C., Konrad, H., Langen, P. L., Lecavalier, B. S., Liang, C.-C., Loomis, B. D., McMillan, M., Melini, D., Mernild, S. H., Mottram, R., Mouginot, J., Nilsson, J., Noël, B., Pattle, M. E., Peltier, W. R., Pie, N., Roca, M., Sasgen, I., Save, H. V., Seo, K.-W., Scheuchl, B., Schrama, E. J. O., Schröder, L., Simonsen, S. B., Slater, T., Spada, G., Sutterley, T. C., Vishwakarma, B. D., van Wessem, J. M., Wiese, D., van der Wal, W., and Wouters, B.: Mass balance of the Greenland and Antarctic ice sheets from 1992 to 2020, Earth System Science Data, 15, 1597–1616, https://doi.org/10.5194/essd-15-1597-2023, 2023. a
Robel, A. A.: Thinning sea ice weakens buttressing force of iceberg mélange and promotes calving, Nature Communications, 8, 14596, https://doi.org/10.1038/ncomms14596, 2017. a, b, c
Sanchez, R., Slater, D., and Straneo, F.: Delayed Freshwater Export from a Greenland Tidewater Glacial Fjord, Journal of Physical Oceanography, 53, 1291–1309, https://doi.org/10.1175/JPO-D-22-0137.1, 2023. a
Schild, K. M., Sutherland, D. A., Elosegui, P., and Duncan, D.: Measurements of Iceberg Melt Rates Using High‐Resolution GPS and Iceberg Surface Scans, Geophysical Research Letters, 48, 1–9, https://doi.org/10.1029/2020GL089765, 2021. a
Schlemm, T. and Levermann, A.: A simple parametrization of mélange buttressing for calving glaciers, The Cryosphere, 15, 531–545, https://doi.org/10.5194/tc-15-531-2021, 2021. a
Slater, D. A., Nienow, P. W., Cowton, T. R., Goldberg, D. N., and Sole, A. J.: Effect of near-terminus subglacial hydrology on tidewater glacier submarine melt rates, Geophysical Research Letters, 42, 2861–2868, https://doi.org/10.1002/2014GL062494, 2015. a, b
Slater, D. A., Felikson, D., Straneo, F., Goelzer, H., Little, C. M., Morlighem, M., Fettweis, X., and Nowicki, S.: Twenty-first century ocean forcing of the Greenland ice sheet for modelling of sea level contribution, The Cryosphere, 14, 985–1008, https://doi.org/10.5194/tc-14-985-2020, 2020. a, b
Slater, D. A., Johnstone, E., Mas e Braga, M., Fraser, N., Cowton, T., and Inall, M.: FjordRPM v1.0: a reduced-physics model for efficient simulation of glacial fjords, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-3934, 2025. a, b, c, d
Smagorinsky, J.: General circulation experiments with the primitive equations, Monthly Weather Review, 91, 99–164, https://doi.org/10.1175/1520-0493(1963)091<0099:GCEWTP>2.3.CO;2, 1963. a
Sulak, D. J., Sutherland, D. A., Enderlin, E. M., Stearns, L. A., and Hamilton, G. S.: Iceberg properties and distributions in three Greenlandic fjords using satellite imagery, Annals of Glaciology, 58, 92–106, https://doi.org/10.1017/aog.2017.5, 2017. a, b
Summers, P. T.: somonesummers/ICEBERG2: ICEBERG2, Zenodo [code], https://doi.org/10.5281/zenodo.14721712, 2025. a
Summers, P. T., Jackson, R. H., and Robel, A. A.: Sub-grid Parameterization of Iceberg Drag in a Coupled Ice-Ocean Model: Dataset and Plotting, Zenodo [data set], https://doi.org/10.5281/zenodo.15116445, 2025. a
Wood, M., Khazendar, A., Fenty, I., Mankoff, K., Nguyen, A. T., Schulz, K., Willis, J. K., and Zhang, H.: Decadal Evolution of Ice-Ocean Interactions at a Large East Greenland Glacier Resolved at Fjord Scale With Downscaled Ocean Models and Observations, Geophysical Research Letters, 51, e2023GL107983, https://doi.org/10.1029/2023GL107983, 2024. a
Wood, M., Fenty, I., Khazendar, A., and Willis, J. K.: Feedbacks Between Fjord Circulation, Mélange Melt, and the Subglacial Discharge Plume at Kangerlussuaq Glacier, East Greenland, Journal of Geophysical Research: Oceans, 130, https://doi.org/10.1029/2024JC021639, 2025. a, b
Short summary
We develop a method that allows numerical ocean models to include drag from icebergs, even for icebergs smaller than the model grid scale. This builds upon previous models that have either neglected iceberg drag or required higher resolution to model individual icebergs. We test our model against higher-resolution models, as well as models without iceberg drag, and show that including drag from icebergs is important for capturing realistic ocean circulation, temperature, and ice melt rates.
We develop a method that allows numerical ocean models to include drag from icebergs, even for...
