This looks good, two comments:

• do we want to add -Wall to some machines files in order to not introduce more unused variables ? How "clean" are we at the moment ? (also, which compiler was used to find these?)
• I'm not sure I understand how this argcheck setting will be used. It would be nice to see an explanation:)

I used -Wall on gnu and cleaned up what was easy. There are some variables that are passed as arguments in subroutines that are not used, but I chose not to clean those up. There were other warning messages that also weren't reasonable to cleanup, like a return statement after an abort and before and output variable was set. -Wall did not reveal too many things. I thought about adding it to one of the machines, but decided not to. I think this is something we can run occasionally, but I don't think it's something we need to have on by default. @phil-blain, if you want to add it to one of your machines, that's fine :).

The argcheck parameter planning documentation is here,

https://github.com/CICE-Consortium/Icepack/files/9004010/Icepack_Package-2.pptx on slide 14.

The idea is that optional arguments checking could be turned off, done at "first call", or done at every call. We may add other options later. I agree some of this needs to be added to the user guide. I think we can do that as we make progress adding new optional arguments and seeing how that works out.