The extent and thickness of the Arctic sea ice cover has decreased dramatically in the past few decades with minima in sea ice extent in September 2005 and 2007. These minima have not been predicted by climate models used for the Intergovernmental Panel on Climate Change AR4 report, suggesting that the sea ice component of climate models should more realistically represent the processes controlling the sea ice mass balance. One of the processes poorly represented in sea ice models is the formation and evolution of melt ponds. Melt ponds accumulate on the surface of sea ice from snow and sea ice melt and their presence reduces the albedo of the ice cover, leading to further melt, figure 1. Melt ponds thus contribute to the well-known albedo feedback effect. Towards the end of the melt season melt ponds cover up to 50% of the sea ice surface. Within the ASBO project we have developed a model of the evolution of melt ponds on Arctic sea ice (Flocco and Feltham, 2007).

We have now then incorporated this theory into the Los Alamos CICE sea ice model, which has required us to include the refreezing of melt ponds (Flocco et al., submitted), see figure 1.

Results show that the presence, or otherwise, of a representation of melt ponds has a significant effect on the predicted sea ice thickness and extent, see figure 2. We also present a sensitivity study to uncertainty in the sea ice permeability, number of thickness categories in the model representation, and pond albedo.

For references, see publications.

Figure 1 shows the impact of the inclusion of our pond routine into CICE and figure 2 shows the aggregated pond area distribution in the Arctic.

Melt ponds on Arctic sea ice at the Surface Heat Budget of the Arctic (SHEBA) field experiment, August 14, 1998. The ponds in this image are approximately 5 m wide and 0.5 m deep.

Figure 1: Average fractional pond area for July over the years 1980-2001 using the CICE sea ice model with the Flocco et al. [submitted] melt pond scheme.

Figure 2: Seasonal cycle of domain-averaged sea ice thickness (left) and ice concentration (right) averaged over the years 1980-2001. The "CPOM" run is the CICE model with the Flocco et al. [submitted] melt pond scheme, the "CICE" run is the CICE run with an ad hoc, tuned melt pond scheme, and "no ponds" is a run using the CICE scheme with no ponds present.