Abstract
AbstractThe first stage of sea-ice formation is often grease ice, a mixture of sea water and frazil ice crystals. Over time, grease ice typically congeals first to pancake ice floes and then to a solid sea-ice cover. Grease ice is commonly not explicitly simulated in basin-scale sea-ice ocean models, though it affects oceanic heat loss and ice growth and is expected to play a greater role in a more seasonally ice-covered Arctic Ocean. We present an approach to simulate the grease-ice layer with, as basic properties, the surface being at the freezing point, a frazil ice volume fraction of 25%, and a negligible change in the surface heat flux compared to open water. The latter governs grease-ice production, and a gradual transition to solid sea ice follows, with ∼50% of the grease ice solidifying within 24 hours. The new parameterization delays lead closing by solid ice formation, enhances oceanic heat loss in fall and winter, and produces a grease-ice layer that is variable in space and time. Results indicate a 10-30% increase in mean winter Arctic Ocean heat loss compared to a standard simulation, with instant lead closing leading to significantly enhanced ice growth.
Highlights
The present generation of basin-scale sea-ice ocean models incorporate a number of essential processes of the coupled polar air–ice–ocean systems
For some modelling purposes it might be desirable to keep computational costs as low as possible, which in the most extreme case would not allow for an explicitly simulated and advected grease-ice category. In this case we suggest carefully adjusting the sequence in which frazil ice solidifies in the model and calculating the heat exchange with the ocean in order to ensure that, to first order, grease enables the same heat flux as open water
We find that grease-ice growth, peaking in late August, dips in September, when the interior Arctic solid pack ice becomes compact and significant amounts of frazil ice are only formed in the marginal ice zone (MIZ), which migrates south during fall
Summary
The present generation of basin-scale sea-ice ocean models incorporate a number of essential processes of the coupled polar air–ice–ocean systems. Observations of grease and frazil ice have been obtained from laboratory investigations (Daly and Colbeck, 1986; Martin and Kauffman, 1981; Smedsrud, 2001). These have, for instance, partly been used in polynya modelling (Biggs and others, 2000). We suggest using recent laboratory experiments (de la Rosa and others, 2011) as a guide to the transition from grease ice to pancake ice, i.e. solid sea ice. Detailed numerical studies involving frazil ice dynamics exist (Omstedt, 1985; Svensson and Omstedt, 1998; Kämpf and Backhaus, 1999; Smedsrud, 2002), using grid resolutions as fine as 1–10 m. Smedsrud and Martin: Grease-ice modelling but when we use the term basin-scale model here, we think of a model with a horizontal resolution larger than 10 km
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
