An improved single-column model representation of ocean mixing associated with summertime leads: Results from a SHEBA case study

[1] Ice/ocean mixed layer model simulations are run for a SHEBA field project case study from 5 July–8 August 1998. Observations indicate that during this time, calm winds occurred and coincided with a rapid warming and freshening of the surface of a lead near the SHEBA camp. A subsequent storm mixed down this warm, fresh water. Single-column model simulations of this event are performed to isolate properties of the ocean system which must be accounted for to improve the representation of mixing in summertime leads. A traditional method of simulating the ice/ocean system in which a single ocean mixed layer calculation is forced with fluxes aggregated over the ice and open water portions of the domain is compared with simulations in which separate mixed layer calculations are done for the lead and under-ice ocean systems. It is found that not only are multiple ocean mixed layer calculations needed to improve the simulations but the surface of the lead must be realistically embedded within the ice cover. When stable conditions occur, the lead surface remains isolated from the under-ice system. Using this method considerably improves simulated lead vertical temperature and salinity profiles, allowing the lead surface to freshen to 20 ppt and reach temperatures greater than 1.4 C above freezing. This modifies the ice mass budgets, increasing lateral melt rates, open water formation, and the amount of absorbed solar radiation. This has implications for the accurate simulation of climate change and variability due to its effects on the albedo feedback mechanism.