The 33-year-old Cairo, who agreed Tuesday to an $850,000, one-year contract, played 82 games for the New York Yankees and St. Louis Cardinals last season and has been with four other major-league teams,
beginning with the Toronto Blue Jays in 1996. He batted .253 in 2007 while starting 27 games combined at second base, shortstop, first base, third base and left field.
"Miguel strengthens our bench by giving us another player, along with Willie Bloomquist, who can cover all four infield spots and, in a pinch, the corners of the outfield," Seattle general manager Bill Bavasi said, adding the move makes manager John McLaren's job easier.
"This should allow Mac more flexibility to use Miguel or Willie earlier in a game, if he wants, and still be covered late," he said.
Cairo can earn $150,000 in performance bonuses: $50,000 each for 300, 400 and 475 plate appearances.
His decision to sign with the Mariners follows Bavasi's declaration five weeks ago that Lopez must improve in 2008. Lopez struggled with focus last season and was eventually benched after signing a $6 million deal.
This is the third consecutive spring training that the 24-year-old Lopez will have a veteran pushing him for his job. In 2006, Seattle signed 36-year-old Fernando Vina. Last spring, Rey Ordonez was in camp after years out of baseball. But those signings were both minor-league deals with invitations to spring training.
Cairo now has a spot on Seattle's 40-man roster.
"We need improved offense at second base. ... Whether we get someone else or take Jose and make him better, we have to get better there," Bavasi said in late November.
"He's a young kid finding his way still," he said. "From my point of view, it is more a focus issue than anything else."