Search

Landfast ice is sea ice that is attached to the coastline via its tensile strength, grounding to the ocean floor from pressure ridges in the Stamukhi region, or anchoring on offshore islands. Fast ice is a platform used by local communities for hunting, traveling and a place for oil and gas drilling and scientific observation. Previous work shows that adding tensile strength to sea ice in regions of shallow bathymetry in order to simulate represent landfast ice in models improves the simulation of the halocline and thermohaline circulation by changing the location of new ice formation and brine rejection at the edge of landfast ice in coastal polynya. However, the impact of fast ice presence or absence in coastal regions with deeper bathymetry (e.g. Kara Sea) on the Arctic hydrography remains unknown. In this contribution, we compare the simulated hydrography in the full Arctic with and without landfast ice parameterization that allows for a landfast ice cover in deep coastal region through lateral anchoring with land --- something not resolved in coarse ice-ocean models. Results show a fresher upper ocean signal when landfast ice is present --- because of the isolating effect of stable ice cover --- that is advected eastward from the Kara Sea to the Makarov Basin (north of the Laptev Sea) via Vilkitsky Strait, suggesting a proper landfast ice simulation in the Kara Sea influences the hydrography in the Arctic and the circulation of Atlantic and Pacific water below the halocline.

Simulating sea ice drift and deformation in the Arctic Ocean is still a challenge because of the multiscale interaction of sea ice floes that compose the Arctic Sea ice cover. The Sea Ice Rheology Experiment (SIREx) is a model intercomparison project of the Forum of Arctic Modeling and Observational Synthesis (FAMOS). In SIREx, skill metrics are designed to evaluate different recently suggested approaches for modeling linear kinematic features (LKFs) to provide guidance for modeling small‐scale deformation. These LKFs are narrow bands of localized deformation that can be observed in satellite images and also form in high resolution sea ice simulations. In this contribution, spatial and temporal properties of LKFs are assessed in 36 simulations of state‐of‐the‐art sea ice models and compared to deformation features derived from the RADARSAT Geophysical Processor System. All simulations produce LKFs, but only very few models realistically simulate at least some statistics of LKF properties such as densities, lengths, or growth rates. All SIREx models overestimate the angle of fracture between conjugate pairs of LKFs and LKF lifetimes pointing to inaccurate model physics. The temporal and spatial resolution of a simulation and the spatial resolution of atmospheric boundary condition affect simulated LKFs as much as the model's sea ice rheology and numerics. Only in very high resolution simulations (≤2 km) the concentration and thickness anomalies along LKFs are large enough to affect air‐ice‐ocean interaction processes., Plain Language Summary: Winds and ocean currents continuously move and deform the sea ice cover of the Arctic Ocean. The deformation eventually breaks an initially closed ice cover into many individual floes, piles up floes, and creates open water. The distribution of ice floes and open water between them is important for climate research, because ice reflects more light and energy back to the atmosphere than open water, so that less ice and more open water leads to warmer oceans. Current climate models cannot simulate sea ice as individual floes. Instead, a variety of methods is used to represent the movement and deformation of the sea ice cover. The Sea Ice Rheology Experiment (SIREx) compares these different methods and assesses the deformation of sea ice in 36 numerical simulations. We identify and track deformation features in the ice cover, which are distinct narrow areas where the ice is breaking or piling up. Comparing specific spatial and temporal properties of these features, for example, the different amounts of fractured ice in specific regions, or the duration of individual deformation events, to satellite observations provides information about the realism of the simulations. From this comparison, we can learn how to improve sea ice models for more realistic simulations of sea ice deformation., Key Points: All models simulate linear kinematic features (LKFs), but none accurately reproduces all LKF statistics. Resolved LKFs are affected strongest by spatial and temporal resolution of model grid and atmospheric forcing and rheology. Accurate scaling of deformation rates is a proxy only for realistic LKF numbers but not for any other LKF static., DOE, HYCOM NOPP, Innovation Fund Denmark and the Horizon 2020 Framework Programme of the European Union, National centre for Climate Research, SALIENSEAS, ERA4CS, German Helmholtz Climate Initiative REKLIM (Regional Climate Change), Gouvernement du Canada, Natural Sciences and Engineering Research Council of Canada (NSERC) http://dx.doi.org/10.13039/501100000038, Environment and Climate Change Canada Grants & Contributions program, Office of Naval Research Arctic and Global Prediction program, U.S. Department of Energy Regional and Global Model Analysis program, National Science Foundation Arctic System Science program, Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659, https://zenodo.org/communities/sirex

Arctic sea ice plays a critical role in the climate system. Therefore it needs to be modeled accurately to make precise climate predictions of the current anthropogenic climate change. Most of today’s climate models simulate sea ice motion using a viscous-plastic (VP) rheology with an elliptical yield curve and a normal flow rule [1]. This rheology gives accurate predictions at low resolution but features discrepancies at high resolution when compared to observations. Observations show that narrow lines of deformation dominate the pattern of sea ice motion. Models using the VP rheology feature these fracture lines but overestimate the intersection angles between them [2]. To understand and solve these differences, we study the creation of fracture angles using idealized compression experiments. We test several yield curves and flow rules and investigate their effect on the angles between fracture lines. The results show that: first, the fracture angle depends on the shape of the yield curve as well as the flow rule, in agreement with Roscoe’s angle [3]; second, the elliptical yield curve with normal flow rule cannot create angles lower than 30° in uniaxial compression; finally, implementing a non-normal flow rule can lead to fracture angles as low as 22°. Results also show that sea ice dynamics in models disagree with sea ice observed granular behavior. With the new knowledge gained from these idealized experiments, we can now define new VP rheologies for more accurate sea ice modeling, e.g., with Mohr-Coulomb or teardrop yield curves. REFERENCES: [1] Hibler III WD: A dynamic thermodynamic sea ice model, Journal of physical oceanography. Jul;9(4):815-46, 1979. [2] Hutter, N. and Losch, M.: Feature-based comparison of sea ice deformation in lead-permitting sea ice simulations, The Cryosphere, 14, 93–113, https://doi.org/10.5194/tc-14-93-2020, 2020. [3] Roscoe, K. H.: The Influence of Strains in Soil Mechanics, Géotechnique, 20, 2, 129-170, 1970.

Sea ice is regarded as a clear indicator of climate change in the Arctic Ocean. Landfast ice is immobile or nearly immobile sea ice in coastal regions that affects the transfer of heat, moisture, and momentum between the atmosphere and the ocean. As an extension of the land for travel and hunting, landfast ice also determines the construction of ice roads and Arctic shipping routes in the summertime. Despite the important role of landfast ice in the climate system, landfast ice is not simulated very well by current sea ice models and needs to be parameterized, for example, by a grounding scheme. Comparing landfast ice in two sea-ice simulations with different grid resolutions indicates that a higher resolution model better presents landfast ice in deep water regions, where a grounding scheme fails. The better representation of coastline details, which serve as pinning points for sea ice arches in the high-resolution model, is thought to improve the representation of landfast ice. Based on this hypothesis, a new parameterization of lateral drag as a function of sea ice thickness, drift velocity, and coastline length is presented. The results suggest that a combination of lateral drag parameterization and grounding (parameterized by basal stress) is required to simulate fast ice in most regions successfully. This work may lead to a versatile landfast ice parameterization for sea ice models in both shallow and deep coastal areas in the Arctic.