Abstract:Sea ice in the marginal ice zone (MIZ) consists of relatively small floes with a wide size span. In response to oceanic and atmospheric forcing, it behaves as an approximately two-dimensional, highly polydisperse granular material. The established viscous-plastic rheologies used in continuum sea ice models are not suitable for the MIZ; the collisional rheology, in which sea ice is treated as a granular gas, captures only one aspect of the granular behaviour, typical for a narrow range of conditions when dynami… Show more
“…However, in [23] Boutin et al assumed that the recovery time scale of ice strength after a fragmentation event is the same as for brittle fracture in the pack ice, but wave break-up is likely to create a larger number of cracks in the sea ice and may have a longer-lasting effect. Another limitation of their approach is that it neglects the impact of floe-floe interactions on internal stress, which can be significant [54].…”
We evaluate marginal ice zone (MIZ) extent in a wave–ice 25 km-resolution coupled model, compared with pan-Arctic wave-affected sea-ice regions derived from ICESat-2 altimetry over the period December 2018–May 2020. By using a definition of the MIZ based on the monthly maximum of the wave height, we suggest metrics to evaluate the model taking into account the sparse coverage of ICESat-2. The model produces MIZ extents comparable to observations, especially in winter. A sensitivity study highlights the need for strong wave attenuation in thick, compact ice but weaker attenuation as sea ice forms, as the model underestimates the MIZ extent in autumn. This underestimation may be due to limited wave growth in partially covered ice, overestimated sea-ice concentration or the absence of other processes affecting floe size. We discuss our results in the context of other definitions of the MIZ based on floe size and sea-ice concentration, as well as the potential impact of wave-induced fragmentation on ice dynamics, found to be minor at the climate scales investigated here.
This article is part of the theme issue ‘Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks’.
“…However, in [23] Boutin et al assumed that the recovery time scale of ice strength after a fragmentation event is the same as for brittle fracture in the pack ice, but wave break-up is likely to create a larger number of cracks in the sea ice and may have a longer-lasting effect. Another limitation of their approach is that it neglects the impact of floe-floe interactions on internal stress, which can be significant [54].…”
We evaluate marginal ice zone (MIZ) extent in a wave–ice 25 km-resolution coupled model, compared with pan-Arctic wave-affected sea-ice regions derived from ICESat-2 altimetry over the period December 2018–May 2020. By using a definition of the MIZ based on the monthly maximum of the wave height, we suggest metrics to evaluate the model taking into account the sparse coverage of ICESat-2. The model produces MIZ extents comparable to observations, especially in winter. A sensitivity study highlights the need for strong wave attenuation in thick, compact ice but weaker attenuation as sea ice forms, as the model underestimates the MIZ extent in autumn. This underestimation may be due to limited wave growth in partially covered ice, overestimated sea-ice concentration or the absence of other processes affecting floe size. We discuss our results in the context of other definitions of the MIZ based on floe size and sea-ice concentration, as well as the potential impact of wave-induced fragmentation on ice dynamics, found to be minor at the climate scales investigated here.
This article is part of the theme issue ‘Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks’.
“…(3) Sea ice becomes more susceptible to change, for example by (a) melting more rapidly [25,32,71], (b) consolidating more effectively [27,77], (c) being more mobile [78][79][80][81], (d) altering the attenuation and transmission of wave energy [22][23][24], (4) The sea ice cover changes, triggering local coupled feedbacks, and:…”
Section: Floe Size Distribution Impactsmentioning
confidence: 99%
“…A chief rationale for studying the FSD in coupled models and in observations is the possibility of climate-scale feedbacks triggered by FSD changes. One of the most-studied feedbacks is related to wave-induced fracture, summarized in figure 3 in the case of continuous, level ice An episodic wave event reaches the MIZ.Floes flexed by high-amplitude waves fail and are broken into smaller pieces.Sea ice becomes more susceptible to change, for example by melting more rapidly [25,32,71],consolidating more effectively [27,77],being more mobile [78–81],altering the attenuation and transmission of wave energy [22–24],The sea ice cover changes, triggering local coupled feedbacks, and: Waves energize through increased fetch [82], reaching areas they previously could not, restarting the feedback process.Changes to sea ice or wave properties allow for sea ice expansion, reducing wave energies and insulating a location against future wave events.Figure 3A summer floe-size-related positive feedback process in the MIZ. (1) A high-amplitude wave event reaches sea ice in the MIZ.…”
Marginal ice zones (MIZs) are qualitatively distinct sea-ice-covered areas that play a critical role in the interaction between the polar oceans and the broader Earth system. MIZ regions have high spatial and temporal variability in oceanic, atmospheric and ecological conditions. The salient qualitative feature of MIZs is their composition as a mosaic of individual floes that range in horizontal extent from centimetres to tens of kilometres. Thus the floe size distribution (FSD) can be used to quantitatively identify and describe them. Here, the history of FSD observations and theory, and the processes (particularly the impact of ocean waves) that determine floe sizes and size distribution, are reviewed. Coupled wave-FSD feedbacks are explored using a stochastic model for thermodynamic wave-sea-ice interactions in the MIZ, and some of the key open questions in this rapidly growing field are discussed.
This article is part of the theme issue ‘Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks’.
“…Even though there were very few other rheology models suitable to the MIZ, research aimed at finding constitutive relations for granular materials remained fairly active. Herman [18], in this issue, presents a review of collisional rheologies and more generally granular effects in the MIZ. She also carries out thorough sensitivity analyses of the friction coefficient as a function of FSD for a dense granular flow rheology using a discrete-element modelling (DEM) approach.…”
Section: (A) Rheologymentioning
confidence: 99%
“…Unfortunately, there were only very few attempts to derive such rheology and there is virtually no existing dataset so far that would inform and validate such a rheology. In this issue, Agnieszka Herman provides a review and a contemporary view on how to derive a physically adequate rheology for the MIZ [18]. Here, in §3a, I will instead describe the most commonly used sea ice rheology for geophysical applications, and discuss how it could be modified in order to become applicable to sea ice in all conditions, including the MIZ.…”
Despite enormous scientific and technological progress in numerical weather and climate prediction, sea ice still remains unreliably predicted by models, both in short-term forecasting and climate projection applications. The total ice extent in both hemispheres is tied to the location of the ice edge, and consequently to what happens in the portion of the ice cover immediately adjacent to the open ocean that is called the marginal ice zone (MIZ). There is mounting evidence that processes occurring in the MIZ might play an important role in the polar climate of both hemispheres, yet some key physical processes are still missing in models. As sea ice models developed for climate studies are increasingly used for operational forecasting, the missing physics also impede short-term sea ice prediction skills. This paper is a mini-review that provides a historical perspective on how MIZ research has progressed since the 1970s, with a focus on the fundamental importance of the interactions between sea ice and surface gravity waves on sea ice dynamics. Completeness is not achieved, as the body of literature is huge, scattered and rapidly growing, but the intention is to inform future collaborative research efforts to improve our understanding and predictive capabilities of sea ice dynamics in the MIZ.
This article is part of the theme issue ‘Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks’.
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