'Serious failures,' said the navy commander
There was no indication that the punishments were connected with the sinking of the Kursk nuclear submarine during a naval exercise more than a year ago.
But the move came on the same day that Russian President Vladimir Putin said an official report showed it was still too early to say what caused the Kursk disaster - the worst of its kind in Russian naval history.
Naval commander Vladimir Kuroyedov was quoted by the Russian news agency Interfax as saying that the officers punished had been guilty of "serious failures in the organisation of the military training activities of the fleet".
Admiral Popov and Northern Fleet chief-of-staff, Vice-Admiral Mikhail Motsak, have been demoted, and officers from the Northern Fleet and the Russian Navy had been "sacked and received other disciplinary sanctions", he was quoted as saying.
The Kursk sank in the icy waters of the Barents Sea after two unexplained explosions.
Mr Putin said it was Russia's moral duty to recover the submarine and give a decent burial to those who had lost their lives.
A total of 69 bodies have been recovered from the vessel, which has been raised from the seabed and is now back in port.
The demotions and disciplinary action in the navy were announced almost immediately after the Prosecutor General, Vladimir Ustinov, briefed Mr Putin on the preliminary investigation into the Kursk disaster.
Mr Putin is reported to have criticized the navy's preparations for military exercises, which the Kursk was taking part in when it sank.