Forecasting Wave impact as Arctic sea ice declines

Arctic sea ice has been declining dramatically in the last decades, and the Arctic Ocean is expected to be ice-free in summer by the end of the century. This decline has exposed large ocean areas to winds, resulting in large waves forming more frequently in the Arctic Ocean. These waves can propagate over tens to hundreds of kilometres in the sea ice, breaking it and accelerating its melt. These physical processes – the breaking of sea ice by waves and its effect on sea-ice melt and growth – are both missing in the models we use to predict the evolution of the climate. Their absence contributes to large uncertainties in climate models. The impact of waves on sea ice is also not accounted for in forecasts of the ocean and sea-ice conditions used by ships operating in ice-infested waters. In ForWArd, we want to assess the impact waves have on sea-ice evolution in the rougher and rougher Arctic Ocean. To do so, we will use a highly advanced model including sea ice, ocean, waves, and their interactions. We will first evaluate how well it represents the conditions in the Arctic Ocean compared to the few available observations. We will then use this model to investigate how the wave height and area of broken sea ice have evolved in the last three decades. Then, we will combine our model with conditions of the future Arctic Ocean provided by climate predictions to investigate how the importance of wave-ice interactions will evolve as sea ice declines in the 21st century. This “wave impact” estimated with our model will allow the polar science community to assess how uncertain their climate predictions without waves are. Ultimately, our model results and developments will set the groundwork for adding wave effects into ocean and sea-ice forecasts in the Arctic, making them more accurate and contributing to the safety of human activities in this region.

Arctic sea ice decline under climate change has allowed waves to form and grow more easily in the Arctic Ocean. These waves propagate into the sea ice over tens to hundreds of kilometres, fragmenting it into small floes. This area of broken ice, known as the Marginal Ice Zone (MIZ), is a highly complex region where many interactions occur between the ocean, sea ice, and atmosphere. The action of waves strongly affects these interactions, with rapid feedbacks on the sea ice. However, climate models do not account for these wave-ice interaction processes, which likely contributes to the strong biases in their estimation of modelled sea ice extent and volume and their inability to capture short-term sea ice extent variability. Given the lack of observations available, numerical models remain the best way to estimate how wave-ice interaction processes can impact Arctic sea ice, but most wave-ice coupled models are still prototypes. In ForWArd, we will use one of the most advanced of these models to assess this impact in the context of climate change. To this aim, we will use the latest observations to calibrate the modelled wave-affected area and produce a 30-year-long hindcast of the MIZ extent evolution to analyse how it responded to larger wave height, delayed refreezing, and thinner ice. Then, we will assess the relative importance of the wave-ice interactions suspected to affect sea ice in the MIZ using well-documented events. Finally, we will estimate how waves will contribute to sea ice extent and volume variability in the coming decades, as large areas of open water will remain open until late in the autumn. The flexibility of our setup will allow us to test the sensitivity of our results to model resolution and assumptions, giving invaluable insights into the biases induced by misrepresenting wave-ice interactions. ForWArd will also pave the way for the integration of wave effects in sea ice forecasts, a requirement for safer operations in ice-infested waters.