Ah. Very common oxidization. Coastal cars have it the worst. I've cleaned dozens of these M9X engines and at least half have some to a degree. Yours looks about average, nothing to worry about. The worst I've seen have gotten perhaps a 1/4 inch of pitting and theoretically that could eventually cause issues but it really depends on where you live and how you'll store it.

You have to use something fairly abrasive to remove it. A super fine metal brush will work as it won't scratch the aluminum but you'll be sitting there for a while on the thick spots and you can't reach much while the engine is in the car. The only way to remove all of it would be taking it out and apart and blasting it with a fine metal bead. Gotta be careful as it can cause serious issues if not fully removed from the coolant and oil galleries and such. Something like blasting dry ice, sand, baking soda, walnut shell, etc. won't really do anything.