I've been working really hard for a while now on a race of creatures called Nordic mountain Valkyrie Dragons. They are large: around 7'ft tall, and 9'ft from nose to tail tip, and I'm trying to come up with a kind of blood that they might have. I don't want to use red, iron-based blood, as it wont really fit with the backstory I've given them, but I also want to have the blood be based on a metal that would actually function.

They live in a cold and mountainous area, so whatever kind of blood it is, it needs to be efficient in keeping them warm to whatever reach it can. On top of this, it needs to be able to function with relatively low oxygen levels, as they tend to live at very high altitudes. I am NOT just looking for color.

I have searched everywhere and found nothing, so I would really appreciate some help.

Icefish style: clear blood.

The icefish has no hemoglobin or other oxygen carrying pigment. Oxygen dissolves directly in the blood.

https://www.popsci.com/science/article/2013-04/weird-fish-has-clear-blood

The ocellated icefish, for example, has clear blood. It's not very
well understood how or why this is. The red color of most blood is
given by hemoglobin, a protein that carries oxygen along through the
bloodstream to the organs that need it.

The ocellated icefish ("ocellated" refers to the eye-like spots that
make up the fish's coloration) does not have any hemoglobin. Its
circulatory system gets along without it: oxygen, rather than being
transported by the hemoglobin, is fully dissolved in the plasma (the
main liquid element of blood). At those cold temperatures, oxygen
dissolves into plasma more easily, and the muscles of the fish's
circulatory system are able to absorb oxygen directly from the plasma.

That's all helped along by the fact that the ocellated icefish has an
extremely strong circulatory system. It's got a much larger and
stronger heart than most other fish, and pumps blood through its body
at a rate five times greater than the average fish.

Clear blood dragons need it cold and they need to stay cold; the colder the better. The warmer it is, the less oxygen dissolves in plasma and the less they can deliver to muscles and organs. Maybe you can rig some way in which they can dump excess heat into their breath weapon, leaving their bodies colder?

Also, the icefish is kind of sluggish. Your dragons could accumulate an oxygen store in myoglobin - that does not circulate but is part of the muscles. Oxygen stored in myoglobin is how whales can pull off their deep dives. That oxygen storage would enable a one time burst of activity on the part of the dragon.

Scandium

1. It's rare and there isn't really any data to indicate that it wouldn't work.


2. It oxidizes faster than iron, so it is ideal for lower oxygen levels.


3. It's yellow when oxidized, and white or silvery when not oxidized.


4. It is generally considered to be non-toxic

PS. The metal that carries the oxygen around in the blood doesn't constitute a large enough fraction of the blood to have an effect on how well the fluid transfers heat. At the end of the day, all blood is mostly water, which is good at carrying heat. As far as keeping them warm, it's more about insulation and good circulation than anything else.

Look to nature

Well, hemoglobin is iron based, but hemocyanin is copper based and is used by many animals.

The Ocellated Ice Fish does not use metal hemoglobin or hemocyanin It depends upon the oxygen that simply dissolves in the blood plasma.

I suppose Cobalt and Nickel are also likely metals that bridge the gap between Iron and Copper and perhaps could be reasonable substitutes. Heavier elements are less viable due to relative scarcity if nothing else.