Does anyone know if this affects submarine performance enough that the crews get special training to go here?

I don't know about that but I do know another factoid: Apparently Australian ocean research vessels (or is it navy? stales?) aren't allowed to go further south than a certain latitude because that's the point at which the water becomes cold very suddenly (possibly one of the fronts mentioned above), and the hulls of their boats will crack. How's that for cool?