It was the British themselves who wanted to end the war before winter as it would be impossible to conduct sophicated naval operations in such foul conditions so far from proper basing.
Whats more there were no more Royal Marines, all 3 commandos in the RM were deployed to the Falklands.
You're forgeting the reserves and that given the time recently discharged men would be recalled. Not up to the same standard of course but good enough to back up the regulars.