Atma does no karmas. Jeev (Body, mind) does Karma. Now these Karmas done by the jeev, decide (or have impact) on next life.
But the only connection between the body of current life and the body of next life is Atma. So, does the Atma carries the first life's karma with it to the next body? Or is it that "someone" is maintaining a separate record of all karmas done by everyone?