[2Much2Lose]

"In the rooms of her ice water mansions" is a beautifully poetic phrase because it has more than one possible interpretation, and all of the interpretations add to the richness of the imagery.

As the place where "Superior sings", it is the physical location, the home, of the lake itself, filled with icy water. Moreover, as Superior is the lake which never gives up its dead, it is also the home of the dead who will never leave the icy lake. Finally, it is a description of the shipwrecks at the bottom of the lakes, the eternal dwellings holding the lost dead. All of those images, and perhaps more, are evoked by the poetry of the line.

BTW, as a matter of historical record, the church bells rang once for each sailor, so the comma is necessary.