All the methods to estimate the MLD have been developed for the mid- and low latitudes. We compared several methods of estimating the MLD (Holton and Talley, 2009; Thompson and Fine, 2003; Sereeze et al., 2000). We found that a modified version of the Holton and Talley (2009) gives the best results for the polar region. The Franklin Bay data provided us with a time series of over 500 CTD profiles (and MLDs) in the winter of 2003-2004 at a single location.
The relationship between the under ice oceanic fluxes and the variations of the MLD was examined for the region. A one-dimensional model developed by Prieur et al. 2010 is employed in order to calculate the oceanic fluxes (i.e. mass and buoyancy) using the mass balance in the ML. Emery (1976) examined the relationship between heat content of the surface layer in mid-latitude and vertical motion deduced from temperature fluctuations. He developed a so-called divergent heat budget equation (his eq. 8). Prieur et al. (2010) developed a similar approach for the Mediterranean Sea, but based on the mass budget of the ML instead of the heat budget. We are developing a similar approach for the Polar Mixed Layer based on the mass content (density) of the surface layer because the salt content controls the density at the temperatures found in the Arctic. The advantage of this simple model is that it can be used to characterize the ML using drifting and fixed profiler data. The model results at the fixed station during CASES show that the MLD deepens in the winter and early spring, the maximum is reached in April. Estimated surface flux by the model between days 20-100 has the same trend as the MLD (i.e. while buoyancy fluxes decreases, the MLD decreases). In general, as in the CASES 2003-2004 data, the CFL and the Malina cases, the estimated surface mass flux can explain the MLD variations: the MLD deepens when the estimated surface flux has decreasing (negative) trend (cooling) and shallows when the trend of surface flux is increasing (heating).