Uhh... because it is a parameter of the planet's state space. The glacial-intrglacial cycle is a planetary phenomenon. That makes "external" mean "not of the Earth".
Salinity is NOT a direct function of temperature.
But not all of it and, so what?
I agree changes in major ocean circulation will have an enormous impact. But you STILL haven't explained what is causing it to change.
Do you ever read what you've written" When the Atlantic moves heat to the Arctic the planet warms because the Atlantic moves heat to the Arctic. If you're trying to say that the AMOC causes the planet AS A WHOLE to warm, then you need to do a GREAT deal more explaining.
I find it interesting that you reject positive feedback from CO2 coming out of solution from a warming ocean but accept feedback from glaciation-caused albedo changes. The same comment about global affects applies here as well. Unless you are depending entirely on albedo changes, you have yet to describe a single function related to external influences. And you just stated that the glaciation takes place AFTER the AMOC has collapsed. WHAT DO YOU BELIEVE CAUSES THE AMOC TO COLLAPSE?