Mushy-layer growth and convection, with application to sea ice

• Published in: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
• Main Authors: Wells, Andrew J., Hitchen, Joseph R., Parkinson, James R. G.
• Other Authors: NERC, European Union FP7, Royal Society International Exchanges
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 2019
• Subjects: Sea ice
• Online Access: http://dx.doi.org/10.1098/rsta.2018.0165; https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2018.0165; https://royalsocietypublishing.org/doi/full-xml/10.1098/rsta.2018.0165

Sea ice is a reactive porous medium of ice crystals and liquid brine, which is an example of a mushy layer. The phase behaviour of sea ice controls the evolving material properties and fluid transport through the porous ice, with consequences for ice growth, brine drainage from the ice to provide buoyancy fluxes for the polar oceans, and sea-ice biogeochemistry. We review work on the growth of mushy layers and convective flows driven by density gradients in the interstitial fluid. After introducing the fundamentals of mushy-layer theory, we discuss the effective thermal properties, including the impact of salt transport on mushy-layer growth. We present a simplified model for diffusively controlled growth of mushy layers with modest cooling versus the solutal freezing-point depression. For growth from a cold isothermal boundary, salt diffusion modifies mushy-layer growth by around 5–20% depending on the far-field temperature and salinity. We also review work on the onset, spatial localization and nonlinear development of convective flows in mushy layers, highlighting recent work on transient solidification and models of nonlinear convection with dissolved solid-free brine channels. Finally, future research opportunities are identified, motivated by geophysical observations of ice growth. This article is part of the theme issue ‘The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets’.