The Seattle Mariners acquired All-Star first baseman Yonder Alonso from the Oakland Athletics on Sunday in exchange for minor league outfielder Boog Powell.Alonso, 30, was hitting .266 with 22 home runs, 49 RBIs, a .369 on-base percentage, .527 slugging mark and a .896 OPS in 100 games with Oakland this season.The 2017 American League All-Star has set career highs in home runs, on-base percentage, slugging and OPS. Alonso's previous career high for homers in a single season was nine in 2012 with the San Diego Padres."I can't thank the Oakland A's enough for the opportunity they gave me," Alonso told reporters after the announcement. "They believed in me and helped me mature and recharge my career."Alonso said he was initially stunned when informed of the deal."Surprised but excited, going to a team that is one game out of the playoffs," Alonso said. "I get to play some meaningful baseball, which will be probably the first time in my career I'll be able to do that. I'm ecstatic."In parts of eight major league seasons with Cincinnati (2010-11), San Diego (2012-15) and Oakland (2016-17), Alonso has combined to hit .269 with 61 home runs, 288 RBIs and a .339 on-base percentage in 762 games.Powell, 24, hit .194 (7-for-36) with two RBIs in 23 games over three stints with Seattle this season as he made his major league debut. He spent the majority of the season with Triple-A Tacoma, batting .340 with six home runs and 33 RBIs in 58 games.The Mariners also acquired right-handed pitcher Ryan Garton and catcher Mike Marjama from the Tampa Bay Rays in exchange for left-hander Anthony Misiewicz, infielder Luis Rengifo and a player to be named later.Garton, 27, made his major league debut with Tampa Bay in 2016. In parts of two big-league seasons (2016-2017) he is 1-3 with a 5.26 ERA and one save in 44 relief appearances. For Triple-A Durham, he is 2-0 with a 1.64 ERA and four saves in 24 games, including one start.Marjama, 28, spent the season with Durham, hitting .274 with nine home runs and 51 RBIs in 72 games.Misiewicz, 20, went 8-5 with a 4.75 ERA in 23 starts combined between High-A Modesto and Double-A Arkansas this season.Rengifo, 20, hit .250 with 11 homers and 44 RBIs in 102 games with Class A Clinton this season.In addition, Seattle designated catcher Tuffy Gosewisch for assignment.Gosewisch, 33, spent the majority of the season at Triple-A, but also appeared in 11 games with Seattle, hitting .071 (2-for-28).