Alessandra Ambrosio Flashes Booty, Packs on PDA With Buck Palmer

Alessandra Ambrosio and her man Buck Palmer are all over each other on their European vacay ... and, Buck's body is just about the only thing covering Alessandra's.

The model and her dude were in Ibiza on Friday ... taking a dip at Casa Jondal -- a top-tier resort on the island good enough for this supermodel and her jewelry designer better half.

AA put on a cheeky display ... going with a thong-style bikini -- while Buck showed off his strong chest and held Alessandra's hand.

The two glided through the water together ... much like they glided through this early part of their relationship -- which has been full of fun beach days and beautiful views, and we don't just mean Alessandra.

Ambrosio and Palmer have been doing some globetrotting together ... with Alessandra telling Us Weekly just a couple months ago they share a "passion for life."