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.

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 fresh look at how ocean waves and sea ice interact.

Because of their capacity to alter floe size distribution and concentration and consequently to influence atmosphere-ocean fluxes, there is a compelling justification and demand to include waves in ice/ocean models and earth system models. Similarly, global wave forecasting models like WAVEWATCH III® need better parametrizations to capture the effects of a sea ice cover such as the marginal ice zone on incoming wave energy. Most parametrizations of wave propagation in sea ice assume without question that the frequency-dependent attenuation which is observed to occur with distance x travelled is exponential, i.e. A = A0 e-αx This is the solution of the simple first-order linear ordinary differential equation dA/dx = - αA, which follows from an Airy wave mode ansatz [Formula: see text] Yet, in point of fact, it now appears that exponential decay may not be observed consistently and a more general equation of the type dA/dx = - αAn is proposed to allow for a broader range of attenuation behaviours should this be necessary to fit data.This article is part of the theme issue 'Modelling of sea-ice phenomena'.

Antarctic ice shelf disintegration triggered by sea ice loss and ocean swell.

Understanding the causes of recent catastrophic ice shelf disintegrations is a crucial step towards improving coupled models of the Antarctic Ice Sheet and predicting its future state and contribution to sea-level rise. An overlooked climate-related causal factor is regional sea ice loss. Here we show that for the disintegration events observed (the collapse of the Larsen A and B and Wilkins ice shelves), the increased seasonal absence of a protective sea ice buffer enabled increased flexure of vulnerable outer ice shelf margins by ocean swells that probably weakened them to the point of calving. This outer-margin calving triggered wider-scale disintegration of ice shelves compromised by multiple factors in preceding years, with key prerequisites being extensive flooding and outer-margin fracturing. Wave-induced flexure is particularly effective in outermost ice shelf regions thinned by bottom crevassing. Our analysis of satellite and ocean-wave data and modelling of combined ice shelf, sea ice and wave properties highlights the need for ice sheet models to account for sea ice and ocean waves.

Past, present and impendent hydroelastic challenges in the polar and subpolar seas.

Current and emergent advances are examined on the topic of hydroelasticity theory applied to natural sea ice responding to the action of ocean surface waves and swell, with attention focused on methods that portray sea ice more faithfully as opposed to those that oversimplify interactions with a poor imitation of reality. A succession of authors have confronted and solved by various means the demanding applied mathematics associated with ocean waves (i) entering a vast sea-ice plate, (ii) travelling between plates of different thickness, (iii) impinging on a pressure ridge, (iv) affecting a single ice floe with arbitrarily specified physical and material properties, and (v) many such features or mixtures thereof. The next step is to embed simplified versions of these developments in an oceanic general circulation model for forecasting purposes. While targeted on specific sea-ice situations, many of the reported results are equally applicable to the interaction of waves with very large floating structures, such as pontoons, floating airports and mobile offshore bases.