Fields that are necessary for an exact restart should be added to the restart file. These are binary files that are read by the ice model for initial conditions for almost all types of runs. There are two subroutines in ice_history.F called restartfile and dumpfile that read and write these files. The actual reading of the unformatted file is done by subroutine ice_read in module ice_read_write.F. New fields should be added to the end of the restart file to allow backwards compatibility, i.e. older versions of the model should be able to read the new restart file. There is code in restartfile that checks for the end of the file. Currently, the salt flux is the last field in the file. If this field is present, it is read in, if not, it is set to zero. An exact restart test should be done after modifying the restart file. This test is automated in the CSIM and CCSM scripts. Adding more fields to the restart file should only be done if required by physics changes. It needs to be done carefully, considering the need for backwards compatibility.