Lars Henrik Smedsrud - Grease and pancake ice growth - in lab and simulations

The first stage of sea ice formation is often grease ice, a mixture of sea water and frazil ice crystals. Over time grease ice congeals to a solid sea ice cover, often in the form of pancakes. Grease ice is usually not simulated in large-scale sea-ice ocean models, but impacts ocean heat loss and ice growth.

A set of laboratory experiments on frazil and grease ice in a turbulent flow is presented, showcasing the growth process and a frazil ice size spectrum. Existing 1D simulations illustrates how frazil ice crystals remain sub-surface and can aggregate with particles (sediments) in the water. A simple approach capturing basic grease ice properties for 3D climate models is presented and shows a 10-30% increase in mean winter Arctic Ocean heat loss compared to standard simulations. The grease ice layer is ‘hurdled’ towards existing floes and congeals as pancake ice. The onwards transition to a ‘normal’ congealed ice cover is assumed to take place over 24h when ∼50 % of the grease has formed solid ice, but new observations are needed to better resolve this transition. Grease ice also dampens waves and simulating this in wave models may be the focus of future research.