Ok, since the first thing that pops up in Armory is gear, I'll start there. You're over 540 by a considerable amount, and that's fine. However, you need to replace Seal of the Pantheon ASAP with either Essence of Gossamer (Hadronox, H AN) or The Black Heart (TotC Reg). If you can get through Naxx bosses, you can get through those relatively easy. Also, you'll want to pick up a new belt and bracers pretty quick too. Bracers you can get from the Herald in Heroic Old Kingdom, and the belt I use (But admittedly need to replace) is the Icebane Girdle. There's no def rating, but with the eternal belt buckle you get three gem slots on top of 129 stamina. In my opinion, you can keep those shoulders for better threat, and just through a tank enchant on them from Sons of Hodir for the stam and def rate. On to the talents.
I assume the 23/36/12 build is your tank build, which tells me you're using a two disease rotation. This can be ok as long as you open with DnD and ask your DPS for a bit of a head start to build aggro. The latter part's pretty important because you gotta get your diseases spread around. The downside of this build is you missed some pretty crucial tank talents. Taking the Icy Talons tree is fine if you don't have a shaman in your usual raid party, and the rune tap is ok as well. I presume the healers like the help. The way I'll accomplish this is by teling you what you didnt need (to free up points) and the ones you do need (put the free points there.) In blood, you have 2 points in Subversion and another two in spell deflection. Removing these will also remove Veteran of the Third War most likely. In Unholy, you have two points in Ravenous Dead. Removing these talents will give you 9 points to put into Frost, which is the easy mode, starter tank tree and in my opinion, more fun than the other trees. In frost, talents you'll want to drop are Chillblains (PVP talent) and Icy Reach unless you pull with Icy Touch. Gives you a total of 12 (14 if you drop IR) points, 5 of which should go into Killing Machine. Three more into Glacier Rot. One point into Death Chill (Crit Oblits are purdy, and it procs a LOT), and three into Blood of the North so that Pestilence makes death runes. If you drop Icy Reach as well, those two points need to go into Guile of the Gorefiend for threat bonuses and extended IBF.
Next, we'll talk glyphs. Your minor glyphs are fine, as are the top two majors (Disease and DnD). However, glyph of Icebound Fortitude is kinda worthless because you should already be seeing more improvement than the glyph provides due to your armor rating. Glyph of Dark Death might be something to look into (Add damage, and thus threat to RP dumps) or Glyph of Obliterate could work as well, with the added damage it gives. Hopefully, this wall-o-text has helped a bit! Happy tanking!
...Thoughts of a philosophical Death Knight...
If death is the inevitable end of life, is life the inevitable end of undeath?