qtr_ice_top in sbcblk.F90
The equation providing qtr_ice_top in sbcblk.90 comes from Fichefet et Morales-Maqueda (1997) :
i0 = 0.18*(1-c) + 0.35*c
which comes from Greenfell et Maykut (1977). However, in Greenfell et Maykut (1977), this equation is the one for multi-year ice. For young ice, it becomes :
i0 = 0.43*(1-c) + 0.63*c
This other set of coefficients appear on page 459 right below equation (6).
I think we could use the ice age to modify those coefficients.