The Red Sox have not made an official announcement yet, but they have completed a trade with the Cincinnati Reds that will bring Alex Gonzalez back to Boston. Here is how Gonzalez will help the Sox, in the short term and the long:

* Instantly, he will upgrade their defense on the left side of the infield. From Julio Lugo to Jed Lowrie to Nick Green -- coupled with Mike Lowell’s loss of range resulting from hip surgery -- the Red Sox’ defense on the left side has been a major problem. (They have more errors at the position than any other team in the American League.) Gonzalez will improve that considerably, particularly when he is paired with Kevin Youkilis. If and when the Sox employ Casey Kotchman as a defensive replacement at first, particularly late in games, their overall infield defense should be excellent.

* Lowell still has excellent hands at third, but the tandem of Gonzalez and Youkilis is far better in terms of range. The Sox’ best team now seems to have Youkilis at third, Gonzalez at short, and Lowell as the designated hitter. Over the winter and next spring, it will be interesting to see if the Sox entertain the idea of having Lowell make a transition to first base, particularly if his mobility does not improve.

* Gonzalez comes with a $6 million club option for next season, though, according to a baseball source, the Sox are unlikely to exercise it. Certainly, Jed Lowrie would have tremendous value as a utility man given his ability to play multiple positions and the fact that he is much better as a hitter from the right side. The free agent market for shortstops is quite thin, and the likelihood of a major deal at that position seems slim. The Sox have an obvious long-term need at the position, but Gonzalez could buy them another year -- through the 2010 season -- given some of the other issues they may encounter during the offseason.