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CR7.1

EDI
Coupled modelling in the polar regions

In recent decades, the climate in the polar regions has undergone dramatic changes. Quantifying the individual contributions of Earth system components (cryosphere, ocean, atmosphere, and land) to the observed changes is challenging due to feedback between the components. Examples include (but are not limited to) ice shelf-ocean interactions (through basal melting and cavity geometry evolution) and elevation feedbacks (through surface mass balance). Hence, studies based on individual components of the Earth System have limited capacity to represent all relevant processes. This session aims to provide a platform for sharing coupled modelling experiences incorporating the cryosphere in the polar regions.

Before obtaining scientific outcomes, design decisions must be made in the development of coupled models. Adopting existing coupling technologies or implementing new, concurrent or sequential parallelism, bringing component source codes together or maintaining independence, choosing the level of temporal synchronicity between components operating on different timescales, are all examples of choices to be made.
We solicit both technical and scientific contributions from modelling studies in which feedback and emergent properties between the cryosphere and other Earth System components in polar regions are investigated, better understood, and possibly even quantified. In addition to application of coupled modelling to real world domains, contributions are also invited from idealised studies and intercomparisons, such as the Marine Ice Sheet-Ocean Intercomparison Project (MISOMIP).

Co-organized by OS1
Convener: Konstanze Haubner | Co-conveners: Rupert Gladstone, Yoshihiro Nakayama, Chen ZhaoECSECS
Presentations
| Fri, 27 May, 08:30–09:58 (CEST)
 
Room N2

Fri, 27 May, 08:30–10:00

Chairpersons: Konstanze Haubner, Yoshihiro Nakayama

08:30–08:36
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EGU22-13099
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On-site presentation
Thomas Zwinger et al.

In recent years, subglacial hydrological models as well as till deformation models have been coupled to ice-flow models in order to determine mechanical basal conditions underneath ice sheets and glaciers. These models, nevertheless, often ignore the thermo-dynamical aspects, in particular, not including the influence of permafrost in proximity to or underneath glaciers. Here we present a thermo-mechanically coupled ice-sheet bedrock model. The latter includes components of saturated aquifer water transport, soil deformation, salinity transport and – most important – energy balance including phase change of the solvent. Using synthetic flow-line setups we present studies of ice-sheet fronts, advancing either over existing permafrost or largely unfrozen soils. We investigate the heat- and meltwater-transfer between the ice-body and its substrate and discuss their impact on ice-dynamics. As the results suggest that in certain situations the water balance further demands the existence of a hydrological system between ice and bedrock, we currently work to include this third model component in form of a subglacial hydrological model. All model components are implemented in the Finite Element software Elmer, which renders their mutual coupling relatively easy, yet, numerically demanding.

How to cite: Zwinger, T., Cohen, D., Gladstone, R., and Råback, P.: Modelling the thermal and mechanical interaction of an ice-sheet with a partly frozen bedrock, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13099, https://doi.org/10.5194/egusphere-egu22-13099, 2022.

08:36–08:42
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EGU22-10275
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On-site presentation
Qin Zhou et al.

Coupled ice sheet - ocean models are increasingly being developed and applied to important questions pertaining to processes at the Greenland and Antarctic Ice Sheet margins, and the wider implications of such processes. In particular, ice sheet - ocean interactions have a strong control on ice sheet stability and sea level contribution. One of the challenges of such coupled modelling activities is the timescale discrepancy between ice and ocean dynamics, which, combined with the high cost of ocean models, can limit the timeframe that can be modelled. Here we present an "accelerated oceanic forcing'' approach to the ocean side of the coupling, in which the rates of change passed from ice model to ocean model components are increased by a constant factor and the period for which the  ocean model is run is correspondingly decreased. The ice sheet change over a coupling interval is thus compressed into  a shorter period over which the ocean model is run, based on the assumption that the ocean response time frame is shorter than  the compressed run period. We demonstrate the viability of this approach in an idealised setup based on the Marine Ice Sheet-Ocean Model Intercomparison Project, using the open-source Framework for Ice Sheet-Ocean Coupling (FISOC) combining two different ocean models (FVCOM and ROMS) and the ice-sheet model Elmer/Ice. We also demonstrate that the mean cavity residence time computed from the stand-alone ocean simulations can guide the selection of a suitable enhanced forcing factor for the coupled simulations. 

How to cite: Zhou, Q., Zhao, C., Gladstone, R., Hattermann, T., Gwyther, D., and Galton-Fenzi, B.: Accelerated oceanic forcing in coupled ice sheet-ocean modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10275, https://doi.org/10.5194/egusphere-egu22-10275, 2022.

08:42–08:48
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EGU22-80
Yoshihiro Nakayama et al.

Ice shelf melt rates near grounding lines are a few orders of magnitude higher than other locations. This intense melting close to
the grounding zone is crucial as it induces ice shelf thinning, further acceleration of ice flow, and grounded ice loss. However,
little is revealed about ice and ocean processes determining peak ice shelf melt rates close to the grounding line because (1) ocean
modelers apply a constant cavity geometry, (2) ice modelers typically assume some parameterizations for determining ice shelf melt rates,
and (3) ice-ocean coupled simulations typically require long model integration, necessitating coarse resolution, and they are not able to
resolve small-scale processes near grounding zones. Here, we develop an idealized high-resolution Pine-Island-like model configuration (250
m, 500m, and 1km horizontal and 10 m vertical grid spacings) and conduct ice-ocean coupled simulation for 20 years after 60 years of
initialization. We show that ice slope and ice shelf melt rate close to the grounding zone increases with higher grid resolution but ice
shelf geometry converges towards the highest resolution solution. We are also able to simulate the formation of sub-ice shelf channels by
applying seasonally varying oceanic conditions. We also present our preliminary results of ice-ocean coupled realistic Pine Island
simulation using unprecedentedly high horizontal and vertical resolution  (200m horizontal and 10 m vertical grid spacings). This is
a step towards understanding the ice-ocean interacting mechanisms determining ice shelf shape and melt rate, which is crucial for
improved projections of future Antarctic ice loss.

How to cite: Nakayama, Y., Hirata, T., and Goldberg, D.: What determines the ice shelf shape? , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-80, https://doi.org/10.5194/egusphere-egu22-80, 2022.

08:48–08:54
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EGU22-1125
Daniel Goldberg and Paul Holland

Dynamically coupled ice sheet-ocean models are beginning to be used to study the response of the Antarctic Ice Sheet to fluctuations in ocean temperatures. However, initialising a coupled ice-ocean model for realistic settings is challenging and can introduce nonphysical transients. The extent to which such transients can affect model evolution and projection is unclear. Here, we use a synchronously-coupled model of ice-ocean dynamics to investigate the evolution of Pope, Smith and Kohler Glaciers, West Antarctica, over the next half-century. Two methods of coupled initialisation are used: in one, the ice-sheet model is constrained to fit observed velocities in its initial state; in the other, the model is constrained with both velocities and grounded thinning rates over a 4-year period while forced with simulated ocean melt rates. For each method, two climate scenarios are considered -- one where ocean conditions during this initialisation period persist indefinitely, and one where the ocean is in a permanent ``warm'' state -- as well as two ice-sheet basal sliding laws. At first, the model runs initialised with thinning rates exhibit volume loss much closer to observed values than those initialised with velocity only, but after 1-2 decades the forcing primarily determines rates of retreat. This ``crossover’’ timescale is expected to vary by glacier, however. Under the ``warm’’ scenario, grounding line retreat of ~30 km is simulated for Smith and Kohler, but it is questionable whether this will continue due to narrowing of submarine troughs and limiting of heat transport by controlling obstacles.

How to cite: Goldberg, D. and Holland, P.: The relative impacts of initialisation and climate forcing in coupled ice sheet-ocean modelling: application to Pope, Smith and Kohler glaciers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1125, https://doi.org/10.5194/egusphere-egu22-1125, 2022.

08:54–09:04
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EGU22-12129
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ECS
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solicited
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Virtual presentation
Kaitlin Naughten et al.

A potentially irreversible threshold in Antarctic ice shelf melting would be crossed if the ocean cavity beneath the large Filchner-Ronne Ice Shelf were to become flooded with warm water from the deep ocean. Previous studies have identified this possibility, but there is great uncertainty as to how easily it could occur. Here, we show, using a coupled ice sheet-ocean model forced by climate change scenarios, that any increase in ice shelf melting is likely to be preceded by an extended period of reduced melting. Climate change weakens the circulation beneath the ice shelf, leading to colder water and reduced melting. Warm water begins to intrude into the cavity when global mean surface temperatures rise by approximately 7°C above pre-industrial, which is unlikely to occur this century. However, this result should not be considered evidence that the region is unconditionally stable. Unless global temperatures plateau, increased melting will eventually prevail.

How to cite: Naughten, K., De Rydt, J., Rosier, S., Jenkins, A., Holland, P., and Ridley, J.: Two-timescale response of the Filchner-Ronne Ice Shelf to climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12129, https://doi.org/10.5194/egusphere-egu22-12129, 2022.

09:04–09:10
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EGU22-12248
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Virtual presentation
Jan De Rydt and Kaitlin Naughten

Glaciers in the Pacific sector of West Antarctica are losing mass at an accelerating rate. Superimposed on this long-term trend are interannual variations in mass balance that result from a combination of internal ice dynamics and variability in ocean-induced ice shelf melt rates. We explore the relative importance of these internal and external drivers of change, using a newly developed coupling between the 3D ocean model MITgcm, and the SSA ice flow model Úa. For present-day ocean conditions, we simulate persistent retreat of the Pine Island, Thwaites, Smith and Kohler grounding lines between 2020 and 2150. We demonstrate complex changes in ice shelf melt rates caused by the evolving cavity geometries.

How to cite: De Rydt, J. and Naughten, K.: Coupled ice-ocean modelling of the Amundsen Sea glaciers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12248, https://doi.org/10.5194/egusphere-egu22-12248, 2022.

09:10–09:16
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EGU22-9710
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ECS
Jim Jordan et al.

Increased warm water intrusions would cause mass loss in East Antarctica within 200 years

The East Antarctic Ice Sheet (EAIS) is the single largest potential contributor to future global mean sea level rise, containing 52.2 m of sea level equivalent. Current observations put the mass balance of the EAIS to be approximately stable (albeit with some margin of error), although future climatic conditions have the potential to change this. A warming climate is expected to have both a positive effect on ice sheet mass balance via increased precipitation and a negative effect via increased ice discharge over the grounding line, a process enhanced by ocean driven melting of floating ice reducing the buttressing effect of ice shelves. In addition to a general increase in the ocean temperature surrounding the EAIS there is the potential that future climatic shifts may increase the incidence of intrusions of warm Circumpolar Deep Water (CDW) onto the continental shelf, further increasing basal melting.

Here we show, by using a numerical ice-sheet model, simulations of the future EAIS under different  future climate scenarios, both with and without increased CDW intrusions. We find that without increased CDW intrusions the EAIS will have a negative contribution to sea level rise, with increased precipitation more than compensating increased ice discharge. If melting becomes predominately driven by CDW, however, our simulations find the EAIS to have a positive contribution to sea level rise. All simulations, both those with increased CDW forcing and those without, show an overall reduction in floating ice as well as a reduction in grounded ice area.

How to cite: Jordan, J., Gudmundsson, H., Jenkins, A., Miles, B., Stokes, C., and Jamieson, S.: Increased warm water intrusions would cause mass loss in East Antarctica within 200 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9710, https://doi.org/10.5194/egusphere-egu22-9710, 2022.

09:16–09:22
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EGU22-9317
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ECS
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On-site presentation
Konstanze Haubner et al.

Ice mass loss on Greenland and Antarctica is a major contributor to sea level change and will thereby profoundly impact the world's infrastructure (e.g. transport, roads, ground water, housing) over the next decades. In order to react and adjust now accordingly, precise estimates of sea level change are needed. Though, future changes in sea level are provided by Earth system models, which rarely include ice sheet models, or by standalone ice sheet models. Hence, feedbacks between ice and atmosphere-ocean are overseen. Local scale coupled models can help bridging this gap by estimating how feedbacks between the different Earth systems affect global sea level estimates.

Here, we present results from a coupled simulation of the ocean-sea ice model NEMO3.6-LIM3 (1/24° grid ~ less than 2 km grid spacing) and the ice sheet model BISICLES (on 0.5-4km spatial resolution). The coupling routine is done via python code including variable exchange, pre- and postprocessing, done offline every 3 months, following the setup described in Pelletier et al., 2021.

Simulated ice mass changes, grounding line position and ice velocity changes of this high-resolution coupling scheme (between 1993-2014) are compared to observations and results of uncoupled simulations. We further discuss which processes might be neglectable and which are the main drivers of ice velocity acceleration and changes in sub-shelf ocean circulation.

 

Pelletier, C., Fichefet, T., Goosse, H., Haubner, K., Helsen, S., Huot, P.-V., Kittel, C., Klein, F., Le clec'h, S., van Lipzig, N. P. M., Marchi, S., Massonnet, F., Mathiot, P., Moravveji, E., Moreno-Chamarro, E., Ortega, P., Pattyn, F., Souverijns, N., Van Achter, G., Vanden Broucke, S., Vanhulle, A., Verfaillie, D., and Zipf, L.: PARASO, a circum-Antarctic fully-coupled ice-sheet - ocean - sea-ice - atmosphere - land model involving f.ETISh1.7, NEMO3.6, LIM3.6, COSMO5.0 and CLM4.5, Geosci. Model Dev. Discuss. [preprint], https://doi.org/10.5194/gmd-2021-315, in review, 2021.

How to cite: Haubner, K., Van Achter, G., Pelletier, C., Zipf, L., and Pattyn, F.: Changes on Aurora basin, East Antarctica, in coupled and uncoupled ice-ocean simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9317, https://doi.org/10.5194/egusphere-egu22-9317, 2022.

09:22–09:28
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EGU22-4558
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ECS
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On-site presentation
Sylvain Marchi et al.

How well is the Antarctic climate over the last decades represented in climate models and how predictable is its future evolution? These questions delve into the specificities of the Antarctic climate, a system characterized by large natural fluctuations and complex interactions between the ice sheet, ocean, sea ice and atmosphere. The PARAMOUR project aims at improving our understanding of key processes which control the variability and predictability of the Antarctic climate at the decadal timescale. In this context, we introduce PARASO, a novel fully-coupled regional ocean - sea-ice - ice-sheet - atmosphere climate model over an Antarctic circumpolar domain covering the full Southern Ocean. The state-of-the-art models used are f.ETISh1.7 (ice sheet), NEMO3.6 (ocean), LIM3.6 (sea ice), COSMO5.0 (atmosphere) and CLM4.5 (land), which are run at a horizontal resolution close to 1/4°. One key feature of this tool resides in a novel two-way coupling interface for representing the ocean - ice-sheet interactions, through explicitly resolved ice-shelf cavities. We also consider the impact of atmospheric processes on the Antarctic ice sheet through surface mass exchanges between COSMO-CLM and f.ETISh. Our developments include a new surface tiling approach to combine open-ocean and sea-ice covered cells within COSMO. Using a 30 year-long run, we investigate the model performance and the interannual-to-decadal variability of the simulated Antarctic climate. The focus is on the interactions between the atmosphere, ocean and ice components at the regional scale and the links with larger spatial scales. Specific attention is paid to the mass balance of ice sheets and ice shelves, which influences both the ice sheet dynamics and the changes in the ocean and atmosphere. The system and its performance will be documented in this presentation together with some aspects of decadal variability from a 30-year integration forced with reanalyses (ERA5 and ORAS5). Early results of a 3-member retrospective forecast driven by EC-Earth will also be presented.

How to cite: Marchi, S., Pelletier, C., Fichefet, T., Goosse, H., Haubner, K., Helsen, S., Huot, P.-V., Kittel, C., Klein, F., van Lipzig, N. P. M., Massonnet, F., Mathiot, P., Moravveji, E., Moreno-Chamarro, E., Ortega, P., Pattyn, F., Souverijns, N., Van Achter, G., Vanden Broucke, S., Verfaillie, D., Le Clech, S., Vanhulle, A., and Zipf, L.: PARASO, a circum-Antarctic fully-coupled ice-sheet - ocean - sea-ice - atmosphere - land model involving f.ETISh1.7, NEMO3.6, LIM3.6, COSMO5.0 and CLM4.5, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4558, https://doi.org/10.5194/egusphere-egu22-4558, 2022.

09:28–09:34
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EGU22-12408
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ECS
Impact of coupling frequency on warm and cold cavities in coupled Antarctic ice-sheet model simulations
(withdrawn)
Lars Zipf et al.
09:34–09:40
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EGU22-2773
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ECS
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On-site presentation
Clara Burgard et al.

Ice shelves at the outskirts of the Antarctic ice sheet are thinning due to warm ocean water intruding into their cavities. Thinning reduces the ice shelves' buttressing potential, which means that the restraining force that they exert on the ice flowing across the grounding line is lower and more ice is discharged into the ocean. Taking into account ocean-induced melt, or basal melt, is therefore crucial for accurate sea-level projections. Still, its current representation in ice-sheet models is the main source of uncertainty associated with the Antarctic contribution to global sea-level rise in climate projections.

An increasing amount of high-resolution ocean models are now able to resolve the circulation in the cavities below the ice shelves. However, running such models on multi-centennial scales or in a large ensemble is computationally expensive, especially when coupled with ice-sheet models. Instead, several parameterisations of varying complexity have been developed in past decades to describe the link between hydrographic properties in front of the ice shelf and basal melt rates. Previous studies have shown that the performance of these parameterisations depends on the ice shelf and that individual adjustments and corrections are needed for each ice shelf when applying them on the circum-Antarctic scale.

In this study, we assess the potential of a range of existing basal melt parameterisations to emulate basal melt rates simulated by a cavity-resolving ocean model on the circum-Antarctic scale, without regional adjustments. To do so, we re-tune the parameters of the different parameterisations using an ensemble of simulations from the ocean model NEMO as our reference. We find that the quadratic dependence of melt to thermal forcing and the plume parameterisation yield the best compromise, in terms of integrated shelf melt rates and spatial melt rate patterns. Parameterisations based on the box model, however, yield basal melt rates further from the reference. Additionally to the newly tuned parameters, we also provide uncertainty estimates for the tuned parameters, for applications in large ensembles.

How to cite: Burgard, C., Jourdain, N. C., Reese, R., Jenkins, A., and Mathiot, P.: Assessing basal melt parameterisations for Antarctic ice shelves using a cavity-resolving ocean model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2773, https://doi.org/10.5194/egusphere-egu22-2773, 2022.

09:40–09:46
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EGU22-4608
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ECS
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On-site presentation
Lars Ackermann et al.

Icebergs play a crucial role in Earth's climate system. They transport large amounts of fresh water and alter ocean salinity, affect sea-ice formation, and can lead to abrupt climate changes in the past. Hence, a proper representation of icebergs in Earth system models (ESMs) is essential to improve the understanding of processes involved in abrupt climate changes. Despite their importance, icebergs are rarely represented in ESMs. Freshwater fluxes are often parameterized, neglecting the transport via ocean currents and the heat loss due to iceberg melting. Other models that use an interactive iceberg component are typically ocean-only models, do not represent ice sheets and the atmospheric component explicitly, or are models of intermediate complexity. One reason for this deficiency is the considerable computational costs related to iceberg modeling.

Here, we present the latest version of the Alfred Wegener Institute-Earth System Model (AWI-ESM) with interactive ice sheets and a Lagrangian iceberg model. The iceberg component runs as a submodel of the ocean–sea-ice model FESOM2 with an asynchronous coupling to enable computationally effective simulations with the iceberg-enhanced coupled model. Total execution times can be strongly reduced compared to a non-overlapping execution of the iceberg model with other components. Iceberg meltwater and the associated heat fluxes are coupled to the ocean. The ice sheet is dynamically coupled to the climate components. A new feature of this model setup is the ice sheet-iceberg coupling: Icebergs are drawn from a specific size distribution to match the calving output of the ice sheet model in regions of iceberg discharge. Therefore, discharge-related freshwater fluxes are represented more realistically than in other ESMs.

How to cite: Ackermann, L., Rackow, T., Himstedt, K., Gierz, P., Knorr, G., and Lohmann, G.: A comprehensive Earth System Model (AWI-ESM) with interactive ice sheets and icebergs: A step towards realistic freshwater fluxes for abrupt climate change scenarios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4608, https://doi.org/10.5194/egusphere-egu22-4608, 2022.

09:46–09:52
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EGU22-10657
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ECS
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Virtual presentation
Adam Garbo et al.

Icebergs calved from high-latitude glaciers and ice shelves pose a threat to vessels and offshore infrastructure at a time when Arctic shipping and offshore resource exploration are increasing. Knowledge of the location of potential ice hazards is therefore critical to ensure safe and efficient operations in this remote region. The Canadian Ice Service provides information to stakeholders on the observed and predicted distribution of icebergs in Canadian waters by combining iceberg observations with forecasts from the North American Ice Service (NAIS) iceberg drift model. The NAIS model estimates the forces acting on an iceberg to predict its future position and velocity and is widely used for the East Coast of Canada. However, the model is unproven for areas >60°N and suffers from insufficient validation due to a lack of reliable in-situ observations of iceberg drift. In this study, we use a newly compiled iceberg tracking beacon database to assess the skill of the NAIS iceberg model's predictions of iceberg drift and investigate sensitivity to morphology and environmental forcing (e.g., ocean currents, winds).

Hindcast simulations of the observed tracks of 44 icebergs over the period 2008-2019 were run using ocean currents from three ocean models (CECOM, GLORYS and RIOPS) and wind and wave inputs from the ERA5 reanalysis. Comparisons of several distance error metrics between observed and modelled drift tracks indicate that the NAIS model produces realistic simulations of iceberg drift in Baffin Bay. The root mean square error after the initial 24-hour hindcast period ranged from 18-22 km and increased at a daily rate of 11-13 km, which is comparable to operational forecasts elsewhere. Improved model performance was observed for longer (>250 m) and deeper-keeled (>100 m) icebergs, which appears to counteract the model’s tendency to overestimate drift by reducing the influence of stronger surface ocean currents acting on the iceberg. Ocean current direction, wind direction, and iceberg keel geometry were identified by a sensitivity analysis as the model parameters and environmental driving forces that have the greatest influence on modelled iceberg drift. These results emphasize the need for accurate environmental information and underscore the importance of properly representing the physical characteristics of icebergs in drift models.

How to cite: Garbo, A., Copland, L., Mueller, D., Tivy, A., and Lamontagne, P.: Validation of the North American Ice Service iceberg drift model using a novel database of in-situ iceberg drift observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10657, https://doi.org/10.5194/egusphere-egu22-10657, 2022.

09:52–09:58
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EGU22-2515
Antarctic iceberg distributions and calving rates
(withdrawn)
Olav Orheim et al.