What is "qflux" and why is it important for climate models?
Q= Ocean heat flux

Slab Ocean Model is the name when the atmospheric component of CESM is coupled with ocean mixed layer. When CESM is configured in the fully coupled way, there's no need for the Q flux computation.

GCMs coupled with ocean mixed layer (and thus a thermodynamical ocean instead of a dynamical ocean) computes Q flux to account for the exchange of heat with the ocean. 

See http://www.cesm.ucar.edu/models/atm-cam/docs/description/node28.html:


  The ocean mixed layer contains an internal heat source $ Q$ (also called a $ Q$ flux), whose values are generally specified by a CAM control run, representing seasonal deep water exchange and horizontal ocean heat transport. For example, using prescribed sea surface temperatures and sea ice distributions, the net surface energy flux over the ocean surface can be evaluated to yield the heat source $ Q$.