Among the debris in the Arctic Circle is a filming model of the USS Enterprise-E's front saucer section, originally created for the crash sequence in Star Trek: Nemesis (2002).
This marks the first mention of one of the four quadrants of the galaxy on Star Trek: Enterprise (2001), specifically the Delta Quadrant.
The often mentioned Tarkaleans, first named but not seen in Past Prologue (1993), make their first and only on screen appearance in this episode.
Reed's line about shooting the Borg drones with holographic bullets was an in-joke by the episode writers. In the holodeck scene in Star Trek: First Contact (1996), drones could indeed be killed by holographic bullets, assuming the holodeck safety protocols were turned off.