The council and the city manager or either of them, and any officer or officers formally authorized by them shall have power to make investigations into the city's affairs, to subpoena witnesses, administer oaths, and to compel the production of books and papers. The council may at any time provide for an examination or audit of the accounts of any officer or department of the city government. The accounts of the city shall be audited by the state public examiner or a certified public accountant at least once each year.