MLBTR reports that the Pirates have traded right-handed reliever Chris Resop to Oakland for minor league right-hander Zach Thornton. Resop is eligible for arbitration and was considered a non-tender possibility. Thornton was a 23rd round draft pick in 2010 out of the University of Oregon. So far in his career he's pitched entirely in relief, with a 3.29 ERA and 1.21 WHIP. He spent nearly all of 2012 in the California League, where he posted an ERA of 4.53 (remember, it's a hitter-friendly league) and a 11.7 strikeouts per nine innings. He throws with a three-quarters motion that probably accounts for most of his success. His fastball starts off in the low 90s but can drop into the 80s. Baseball America has described his breaking ball as "nothing special." He has not made any top prospect lists.
MLBTR also reports that, a few days after designating utility player Yamaico Navarro for assignment, the Pirates have traded him to the Orioles for right-handed pitcher Jhondaniel Medina. A 19-year-old Venezuelan, Medina pitched in the Dominican Summer League in 2010-11, then spent last year in the Gulf Coast League, with the exception of one relief appearance in the New York-Penn League. In the GCL, Medina posted a 3.72 ERA, 1.09 WHIP, and good BB/9 (3.3) and K/9 (9.2) rates. Medina is listed at 5'11, 158, so he's probably a longshot to establish himself as a prospect. He currently throws 89-91 with secondary pitches that need to improve.
UPDATE by Charlie: Thornton certainly has nice strikeout numbers, but he was 24 last year and was a late-round pick. He's also never started, so it looks like the A's regarded him as an organizational player from the beginning. Add in the three-quarters motion (guys who have unusual arm angles and put up good numbers in the low minors but don't have great stuff don't usually see their success translate to the higher levels), and it looks highly unlikely that he's a prospect. All this indicates that the Pirates intended to non-tender Resop, and they made this deal so that they'd get something for him.
In any case, the Pirates aren't going to leave the bullpen like it is now. They'll surely be active on the free agent market. And that's fine. The bullpen is the one area where the Pirates can use the free agent market to reliably improve. That they're not willing to settle on Resop may well turn out to be a good thing.