Sea-ice Evolution in Arctic Summer – SEAS

The extent of sea ice during summer in the Arctic Ocean is among the most sensitive indicators of the ongoing climate change. The Arctic sea ice is known to have a key role in determining the planet albedo, which is the ratio of reflected over incoming solar radiation.

During the last summer (2012) satellites have recorded an exceptional reduction of the Arctic sea-ice pack to an extent that none of the available large-scale numerical Global Climate models could predict [Schiermeier, Nature 489, 185-186 (2012)] (see Figure 1). The observed ice loss has lead scietists to question their quantitative understanding of the dynamical and thermodynamical processes involved in the summer season melting and with it to reconsider several of the simplifying assumptions on which the current large-scale computer models are based. Approximations in large-scale models are unavoidable. The range of spatial and temporal scales involved, extending over several decades, cannot be encompassed by any of the existing supercomputers. Therefore models relies on ad-hoc approximations, called parametrizations, derived from physical understanding or field measurements.

Features related to water ponds forming over melted ice are too small to be directly accounted for in large-scale sea ice and global climate models. How does the heat transfer occur in the ponds and how does that affect the large-scale sea ice mass balance? How does the melt progresses on the bottom and on the lateral walls of the ponds? How does the surface topography of the ponds, their surface and depth evolve in the course of the summer season? All the above questionshave been overlooked in the present models. Melt ponds and the surface topography are the key contributor, at the most important time of the year, to the surface albedo of the Arctic Ocean [Eicken et al., 2004], which is a key factor for the global climate. The present goal in sea ice climate science is to physically improve the models in order to refine their predictive power.

This ANR JCJC project addresses the problem of the growth process of ice melt ponds in the Arctic during the summer season by focusing on the small-scale (~ few meters) mechanisms controlling the evolution of the basin topography of a single melt pond. In particular we study the phenomenology of the thermal convective flow in the pond, which is know to be highly turbulent, and its interaction with the phase-change mechanisms at the pond boundaries.

The goal of the present project is to reach a sound understanding on how fluid dynamics and phase-change processes contribute in determing the pond growth in order to provide useful guidelines for parametrizations in large-scale ice models.

The proposed research is based on numerical simulations. We plan to develop a
computational-fluid dynamics code based on the Lattice Boltzmann Equation algorithm, capable to describe both the turbulent convective dynamics of melted water, with its inherent salt content, and the ice phase change in realistic conditions.

The project will be carried out in the Laboratoire de Mécanique de Lille (LML) by three young permanent assistant professors, Enrico Calzavarini, Silvia Hirata and Stefano Berti, who are specialized in computational fluid dynamics, turbulent mixing, convective flows, transport phenomena through fluid and porous media. This team will collaborate closely with a young CNRS researcher, Martin Vancoppenolle, based at LOCEAN laboratory from Université Paris 6. M. Vancopenolle is a geophysicist specialized in the modelling and development of large-scale sea ice models. This team will also rely on the support of two external collaborators specialized in sea ice observations (Dr. Vivier also from LOCEAN laboratory, responsible for ANR project OPTIMISM) and on simultation models for Global Climate reasearch (Dr. Fichefet from TECLIM laboratory, Université Catholique de Louvain, Belgium).