The left-handed-hitting outfielder played six games with the Yankees in May, going 1-for-8 with one run and one walk while playing mostly as a defensive replacement.
He was Rookie of the Year for the International League in 2015 after hitting .300 with 77 runs, 64 RBIs and 13 stolen bases in 129 games. Gamel was selected by the Yankees in the 10th round of the 2010 MLB Draft out of Bishop Kenny High School in Jacksonville, Fla.
The Mariners gave up a pair of young right-handed pitchers, Jio Orozco and Juan De Paula.
De Paula, 18, was 1-2 with a 3.