It was announced last week that Mertesacker would be leaving the post at the end of the season.
Arteta said ahead of tonight's Carabao Cup semifinal first-leg against Chelsea: "Well it’s been 15 years at the club.
"We were teammates, we were friends, we were captains together, and we shared an incredible project together in different roles, him as an academy director and me as a manager, so I enjoy every minute of it.
"I think he’s someone that I think transmits the values of this football club, its ambition and everything that is related to it in the best manner.
"So very thankful, we had a great time together and for sure, as well, he’s made that decision and I wish him the best of luck, for the next one, next chapter, because I’m sure he’s going to be a success.