The Mariners also outrighted reliever Jeff Gray, but he was claimed off waivers by the Twins.
Additionally, the club reinstated center fielder Franklin Gutierrez and catcher Adam Moore off the 60-day disabled list, which puts them back on the 40-man roster.
Aardsma, 29, would have been owed at least $3.6 million in arbitration by the Mariners while not being able to pitch until midseason, so he understands why he was waived, and he didn't rule out a potential return.
"I loved my time in Seattle," Aardsma said. "I love the fans and thank [general manager] Jack Zduriencik for giving me the opportunity to have a job and become a closer. I want to thank all the fans in Seattle for their support.
"It's not fun [being released], but it's part of the job and this is going to be the next step. It doesn't mean I won't be back. This is one of those things we all knew was coming because of the situation. It doesn't close any doors, it just opens more."
Aardsma saved 69 games for Seattle in 2009-10, but missed all of last season after undergoing hip surgery in December and then Tommy John surgery in July after injuring his elbow during his comeback. He said doctors generally expect a one-year recovery period, and he expects to be fully Major League ready by June or July.
Aardsma made $4.5 million last year and had one season of arbitration eligibility remaining with the Mariners, who thus would have had to tender him an offer of at least 80 percent of his contract ($3.6 million) for the coming year, or could have waited until Nov. 23 to non-tender a contract. Instead, the club outrighted him and he cleared waivers on Monday.
Gray was arbitration eligible as well, so the club now has just four potential arbitration-eligible players remaining in relievers Brandon League and Shawn Kelley, left-handed starter Jason Vargas and infielder Luis Rodriguez.
League took over Aardsma's closer duties last season and posted a 2.79 ERA with 37 saves while making the American League All-Star team.
Aardsma could still be re-signed by the Mariners, but he is also free to negotiate with any of the other 29 clubs. Gray's contract is assumed by the Twins.
Aardsma pitched in 126 games in his two healthy seasons in Seattle, posting a 2.90 ERA in 121 innings after taking over the closer's role for the first time in his career. He was acquired from the Red Sox in a 2009 trade for Minor League reliever Fabian Williamson.
Aardsma previously pitched for the Giants, Cubs, White Sox and Red Sox, and has a career record of 13-15 with a 4.20 ERA in 254 relief appearances.
Gray, 29, was selected off waivers by the Mariners on May 13 after starting last season with the White Sox. He was 0-1 with a 4.89 ERA and one save for Seattle in 35 innings over 24 outings.
Gutierrez went on the 60-day disabled list at the end of the season after straining an oblique muscle on Sept. 6.
Moore went on the 60-day DL on April 8 after tearing the medial meniscus ligament in his right knee in the first week of the season. He's currently playing in the Arizona Fall League for the Peoria Javelinas.
The moves leave the Mariners with 37 players on their 40-man roster.