Fig. 4.

Amplitude of the sea ice volume seasonal cycle versus the ice production-entrainment feedback factor. The ice production-entrainment feedback factor γ_θ is defined as the ratio of the melting due to warm water entrainment to the initial ice formation⁵⁰. The values are estimated over 1990–2005 for a standardized perturbation corresponding to an increase of 10 cm of sea ice. For both observational and model datasets, the evaluation of γ_θ is performed on the basis of temperature and salinity profiles in the Southern Ocean, averaged over January–February for the period 1990–2005. Values are represented by five crosses corresponding to five sectors of the Southern Ocean¹¹¹. Results for NEMO-LIM¹¹², CCSM4¹¹³, and IPSL¹¹⁴ models are in colors. Estimates are given in black based on oceanic observations¹¹⁵ and the sea ice volume derived from a reanalysis¹¹⁶. For all datasets, the plain circles correspond to the average of γ_θ and of the amplitude of the ice volume seasonal cycle over all sectors, and ρ is the correlation coefficient between these two quantities