Modelling wave-ice interactions in three dimensions in the marginal ice zone

This study concerns wave-ice interactions in the marginal ice zone (MIZ). We compare idealized simulations using two recent three-dimensional formulations for wave-ice interactions for flexible ice floes, with selected parametrizations for the scattering of ocean surface waves due to individual ice floes. These parametrizations are implemented in a modern version of the wave model WAVEWATCH III® (hereafter, WW3) as source terms in the action balance equation. The comparisons consist of simple hypothetical experiments to identify characteristics of the wave-ice parametrizations. Comparisons show that the two new wave-ice formulations give attenuation of wave heights that can be less intense in the direction of propagation than those of other considered formulations. Within the wave energy spectrum, the one-dimensional attenuation extends over the entire frequency domain to the high-frequency limit. Within the MIZ beyond the ice edge, there is evidence for a 'roll-over' effect in the simulations of attenuation. These new formulations can potentially improve previous parametrizations in simulations of wave scattering and attenuation within the MIZ. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

Wind waves in sea ice of the western Arctic and a global coupled wave-ice model

The retreat of Arctic sea ice is enabling increased ocean wave activity at the sea ice edge, yet the interactions between surface waves and sea ice are not fully understood. Here, we examine in situ observations of wave spectra spanning 2012-2021 in the western Arctic marginal ice zone (MIZ). Swells exceeding 30 cm are rarely observed beyond 100 km inside the MIZ. However, local wind waves are observed in patches of open water amid partial ice cover during the summer. These local waves remain fetch-limited between ice floes with heights less than 1 m. To investigate these waves at climate scales, we conduct experiments varying wave attenuation and generation in ice with a global model including coupled interactions between waves and sea ice. A weak high-frequency attenuation rate is required to simulate the local waves in observations. The choices of attenuation scheme and wind input in ice have a remarkable impact on the extent of wave activity across ice-covered oceans, particularly in the Antarctic. As well as demonstrating the need for stronger constraints on wave attenuation, our results suggest that further attention should be directed towards locally generated wind waves and their role in sea ice evolution. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

A model study of convergent dynamics in the marginal ice zone

With the increasing resolution of operational forecasting models, the marginal ice zone (MIZ), the area where waves and sea ice interact, can now be better represented. However, the proper mechanics of wave propagation and attenuation in ice, and especially their influence on sea ice dynamics, still remain poorly understood and constrained in models. Observations have shown exponential wave energy decrease with distance in sea ice, particularly strong at higher frequencies. Some of this energy is transferred to the ice, breaking it into smaller floes and weakening it, as well as exerting a stress on the ice similar to winds and currents. In this article, we present a one-dimensional, fully integrated wave and ice model that has been developed to test different parameterizations of wave-ice interactions. The response of the ice cover to the wind and wave radiative stresses is investigated for a variety of wind, wave and ice conditions at different scales. Results of sensitivity analyses reveal the complex interplay between wave attenuation and rheological parameters and suggest that the compressive strength of the MIZ may be better represented by a Mohr-Coulomb parameterization with a nonlinear dependence on thickness. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

Marginal ice zone dynamics: history, definitions and research perspectives

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'.

Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks

The marginal ice zone (MIZ) is the dynamic interface between the open ocean and sea ice-covered ocean. It is characterized by interactions between surface gravity waves and granular ice covers consisting of relatively small, thin chunks of sea ice known as floes. This structure gives the MIZ markedly different properties to the thicker, quasi-continuous ice cover of the inner pack that waves do not reach, strongly influencing various atmosphere-ocean fluxes, especially the heat flux. The MIZ is a significant component of contemporary sea ice covers in both the Antarctic, where the ice cover is surrounded by the Southern Ocean and its fierce storms, and the Arctic, where the MIZ now occupies vast expanses in areas that were perennial only a decade or two ago. The trend towards the MIZ is set to accelerate, as it reinforces positive feedbacks weakening the ice cover. Therefore, understanding the complex, multiple-scale dynamics of the MIZ is essential to understanding how sea ice is evolving and to predicting its future. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

Marginal ice zone dynamics

For the best part of my entire career, I have focused on the marginal ice zone, abbreviated to MIZ by most sea ice scientists. Defined perfunctorily by the National Snow & Ice Data Center as the part of the seasonal ice zone where waves, swells and other open ocean processes affect the sea ice, the MIZ habitually extends from the ice edge some 100-200 km into the ice pack with morphology that varies dramatically spatially and with time. In general, the Antarctic MIZ is wider than MIZs in the Arctic, recognizing that increases in the ferocity and incidence of storms and the durability of ice due to global climate change are already affecting the physical attributes of each MIZ. I provide here a somewhat historically tailored preamble to a unique compilation of up-to-the-minute MIZ research in this theme issue that includes the nexus between contemporary theoretical, modelling and experimental projects. A prognosticative synopsis of these projects is also included later in the volume, framed in the context of the ongoing ontogenesis of the research field. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

A prognosticative synopsis of contemporary marginal ice zone research

Commentary narrated in this theme issue is recast to contextualize the diverse themes presented into a forward-looking conversation that synthesizes, debates opportunities for multidisciplinary advances and highlights topics that deserve enduring sharpened attention. Research oriented towards foundational elements of the marginal ice zone that relates to three unifying topic subclasses-namely (i) wave propagation through sea ice, (ii) floe size distributions and (iii) ice dynamics and break-up-and is encapsulated in mini-reviews provided by Thomson, Horvat and Dumont is revisited to distill it into a blueprint for the future guided by the cutting-edge, present-day knowledge documented herein by leading practitioners in the field. Six threads are signalled as imperative for prospective research, each with a bearing on Arctic and Antarctic sea-ice canopies in which the propensity for marginal ice zones to coexist with pack ice is greater as a result of global climate change reducing sea-ice resilience while increasing the prevalence and forcefulness of injurious storm winds and waves. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

Marginal ice zone dynamics: future research perspectives and pathways

Perspectives are discussed on future directions for the field of marginal ice zone (MIZ) dynamics, based on the extraordinary progress made over the past decade in its theory, modelling and observations. Research themes are proposed that would shift the field's focus towards the broader implications of MIZ dynamics in the climate system. In particular, pathways are recommended for research that highlights the impacts of trends in the MIZ on the responses of Arctic and Antarctic sea ice to climate change. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

Granular effects in sea ice rheology in the marginal ice zone

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 dynamics is dominated by binary floe collisions. This paper reviews rheology models and concepts from research on granular materials relevant for MIZ dynamics (average stress as a result of 'microscopic' interactions of grains; [Formula: see text] and collisional rheologies). Idealized discrete-element simulations are used to illustrate granular effects and strong influence of the floe size distribution on strain-stress relationships in sheared sea ice, demonstrating the need for an MIZ rheology model capturing the whole range of 'regimes', from quasi-static/dense flow in the inner MIZ to the inertial flow in the outer MIZ. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

Improving Resource Management for Unattended Observation of the Marginal Ice Zone Using Autonomous Underwater Gliders

We present control policies for use with a modified autonomous underwater glider that are intended to enable remote launch/recovery and long-range unattended survey of the Arctic's marginal ice zone (MIZ). This region of the Arctic is poorly characterized but critical to the dynamics of ice advance and retreat. Due to the high cost of operating support vessels in the Arctic, the proposed glider architecture minimizes external infrastructure requirements for navigation and mission updates to brief and infrequent satellite updates on the order of once per day. This is possible through intelligent power management in combination with hybrid propulsion, adaptive velocity control, and dynamic depth band selection based on real-time environmental state estimation. We examine the energy savings, range improvements, decreased communication requirements, and temporal consistency that can be attained with the proposed glider architecture and control policies based on preliminary field data, and we discuss a future MIZ survey mission concept in the Arctic. Although the sensing and control policies presented here focus on under ice missions with an unattended underwater glider, they are hardware independent and are transferable to other robotic vehicle classes, including in aerial and space domains.

Aerial surveys for Antarctic minke whales (Balaenoptera bonaerensis) reveal sea ice dependent distribution patterns

This study investigates the distribution of Antarctic minke whales (AMW) in relation to sea ice concentration and variations therein. Information on AMW densities in the sea ice-covered parts of the Southern Ocean is required to contextualize abundance estimates obtained from circumpolar shipboard surveys in open waters, suggesting a 30% decline in AMW abundance. Conventional line-transect shipboard surveys for density estimation are impossible in ice-covered regions, therefore we used icebreaker-supported helicopter surveys to obtain information on AMW densities along gradients of 0%-100% of ice concentration. We conducted five helicopter surveys in the Southern Ocean, between 2006 and 2013. Distance sampling data, satellite-derived sea-ice data, and bathymetric parameters were used in generalized additive models (GAMs) to produce predictions on how the density of AMWs varied over space and time, and with environmental covariates. Ice concentration, distance to the ice edge and distance from the shelf break were found to describe the distribution of AMWs. Highest densities were predicted at the ice edge and through to medium ice concentrations. Medium densities were found up to 500 km into the ice edge in all concentrations of ice. Very low numbers of AMWs were found in the ice-free waters of the West Antarctic Peninsula (WAP). A consistent relationship between AMW distribution and sea ice concentration weakens the support for the hypothesis that varying numbers of AMWs in ice-covered waters were responsible for observed changes in estimated abundance. The potential decline in AMW abundance stresses the need for conservation measures and further studies into the AMW population status. Very low numbers of AMWs recorded in the ice-free waters along the WAP support the hypothesis that this species is strongly dependent on sea ice and that forecasted sea ice changes have the potential of heavily impacting AMWs.

Three-dimensional time-domain scattering of waves in the marginal ice zone

Three-dimensional scattering of ocean surface waves in the marginal ice zone (MIZ) is determined in the time domain. The solution is found using spectral analysis of the linear operator for the Boltzmann equation. The method to calculate the scattering kernel that arises in the Boltzmann model from the single-floe solution is also presented along with new identities for the far-field scattering, which can be used to validate the single-floe solution. The spectrum of the operator is computed, and it is shown to have a universal structure under a special non-dimensionalization. This universal structure implies that under a scaling wave scattering in the MIZ has similar properties for a large range of ice types and wave periods. A scattering theory solution using fast Fourier transforms is given to find the solution for directional incident wave packets. A numerical solution method is also given using the split-step method and this is used to validate the spectral solution. Numerical calculations of the evolution of a typical wave field are presented.This article is part of the theme issue 'Modelling of sea-ice phenomena'.

Modelling wave-induced sea ice break-up in the marginal ice zone

A model of ice floe break-up under ocean wave forcing in the marginal ice zone (MIZ) is proposed to investigate how floe size distribution (FSD) evolves under repeated wave break-up events. A three-dimensional linear model of ocean wave scattering by a finite array of compliant circular ice floes is coupled to a flexural failure model, which breaks a floe into two floes provided the two-dimensional stress field satisfies a break-up criterion. A closed-feedback loop algorithm is devised, which (i) solves the wave-scattering problem for a given FSD under time-harmonic plane wave forcing, (ii) computes the stress field in all the floes, (iii) fractures the floes satisfying the break-up criterion, and (iv) generates an updated FSD, initializing the geometry for the next iteration of the loop. The FSD after 50 break-up events is unimodal and near normal, or bimodal, suggesting waves alone do not govern the power law observed in some field studies. Multiple scattering is found to enhance break-up for long waves and thin ice, but to reduce break-up for short waves and thick ice. A break-up front marches forward in the latter regime, as wave-induced fracture weakens the ice cover, allowing waves to travel deeper into the MIZ.