I used to be able to use the opacity of a default shader to get rid of all 'black masked' areas, and make an area of a plane or sphere completely transparent. But this seems to have changed, unless I overlook something forgotten in the years since I got it to work. One could make nice ice remains hovering over water or ice. It shows alright in the preview, but doesn't render that way. Can't find my old example, but it's in the forum somewhere.
Check this out. It only works if you attach the glass shader, but underlying gets only 25% of the detail (due to default subdivision setting, so that's to be overcome), ánd the ice sheet gets transparent, which is not what I wanted.
It also shows the method to get shore foam off a landmass, btw.