What happened to Admiral Morrow?

I understand by this film he was replaced by Cartwright, and the novelization gives some hint that he resigned in connection with the events of the previous movie. Can anyone shed any light on this?

I'm imagining it goes like this: once Kirk's encounter with the Klingons sparks a diplomatic incident (not to mention the court martialling of a Starfleet Admiral) then anything about Genesis and the events surrounding it basically gets blown out in the open. Presumably given there is an inquiry into quite why a vessel on a purely peaceful scientific mission gets destroyed by Klingons along with all hands but one, and those same Klingons murder a scientist, and to establish the facts behind what Kirk did and why. This is certainly going to bring up Morrow's role in the decision to only send a single science vessel to Genesis without even any backup/escort from an additional starship (a reasonable decision except in hindsight- it was a precautionary measure to ensure as few people "needed to know" as possible and no-one expected the details to be leaked to the Klingons) and it was only the Enterprise being in the vicinity without authorization that salvaged the situation at all. The inquiry clears Morrow of negligence, but by this time public opinion is already against him given that not only has a vessel been lost and a scientist killed, but that such a dangerous secret could have all too nearly been revealed to the Klingons. This is possibly also weighing on his conscience. So, Morrow takes the honourable course, and resigns.