According to a major league source, the Sox are not expected to part with a prospect of significance in the deal. Because Carp is out of options and requires a spot on the 40-man roster, his trade market was somewhat limited after the Mariners designated him for assignment last week. Carp is expected to join a roster competition that already features veteran Lyle Overbay  and others with more limited big league experience — including Matt Hamilton, Mitch Maier and Daniel Nava — in competition for a spot on the Sox bench to serve as a left-handed alternate to Mike Napoli  at first base and Jonny Gomes in left field.
Though Carp struggled in 2012, hitting .213/.312/.341/.654 in 59 games for Seattle, in 173 big league games, Carp has hit .255/.327/.413/.740 with 18 homers in 608 plate appearances. However, he’s just two years removed from an impressive season during which he hit .276/.326/.466/.791 with 12 homers and a 125 OPS+ in 79 games with Seattle. The contrast between those two seasons suggested a potential buy-low opportunity for the Sox on a player who, at 26, should have his best years ahead of him.
Given that Gomes has had pronounced career splits throughout his career, enjoying much more success against lefties than righties, and that there are questions about the degree to which Napoli’s hip condition will permit him to stay on the field (perhaps requiring that he receive regular days off even assuming he avoids the DL), the Sox have made little secret of the fact that they would like to find a left-handed hitter who can partner with both players to sustain productive lineups. That said, somewhat surprisingly, Carp has enjoyed more early-career success against left-handers — .300/.341/.462/.802 — than right-handers — .241/.323/.398/.721. In parts of nine minor league seasons, Carp has a career line of .276/.366/.465/.832.
One evaluator characterized Carp as a solid defender in both first base and left field, with his range being a tick below average. Still, he’s sufficiently competent at both positions to offer value through his versatility.
By no means is Carp guaranteed a big league roster spot. He will enter camp in competition with Overbay (who signed a minor league deal), Hamilton, Maier and Daniel Nava, who was getting some work at first base this spring (though it’s worth noting that Nava, like Mauro Gomez, has minor league options, and so is now most likely to open the years as a depth option in the minors). The Sox will use the next five-plus weeks to evaluate Carp and determine whether he represents the best candidate for the bench. If not, then at the end of spring training, he’d be exposed to waivers and likely taken by another team.
Still, the Sox are clearly intrigued about Carp’s upside, particularly given that the primary cost of landing him was cash. And while he’s out of options, Carp wouldn’t be eligible for salary arbitration until after this season, and he wouldn’t be eligible for free agency until after the 2016 campaign.
The team scouted him as a player who has consistently demonstrated power, the ability to control the strike zone, the ability to work deep into counts who fits the team’s roster needs. As such, he represents a potential buy-low acquisition, particularly given the possibility of enjoying a performance uptick in a favorable home hitting environment (Fenway Park ), as opposed to the offense-suppressing home of Safeco Field  in Seattle.
For his part, Overbay said that while he didn’t know until this morning that a deal for Carp had been finalized, he “had a feeling that could happen,” and the 35-year-old said that he’s prepared to compete for a roster spot.
In order to clear a spot on the 40-man roster for Carp, the Sox placed outfielder Ryan Kalish  on the 60-day disabled list. Kalish, who underwent surgery in late January on the labrum in his right shoulder, is expected to need four to six months of rehab before he is able to start playing in minor league games.
Rob Bradford contributed to this report.