"Extreme Surfer" is a single stamp that you can buy through Stampin Up'! I am trying to build up my stock of kids/teenager stamps. These 2 cards I CASEd from a fellow SU demo - Belinda Neil. The stamp itself is a solid image so I did a lot of sponging to get the ocean effect.
The 2nd "Extreme Surfer" card background effect was achieved by swiping "Pear Pizzazz" ink pad across the "Certainly Celery" cardstock. I did the same thing on the "Not Quite Navy" card with the "Not Quite Navy" ink pad. This technique gives a great background if you don't have a background stamp to suit in your stash.