Humans have colonized the subsurface oceans of Europa - building large cities embedded in the icy crust, hanging beneath it, and resting on the rocky seafloor. These colonists mine metals for construction from the mantle and harvest local fauna for food - but where do they get their air?
- Europa has a thin oxygen exosphere.
- The ocean is mostly water, and it's salty.
- The seafloor is in contact with a rocky mantle composed of mafic rock.
- Hydrothermal vents produced by tidal heating are common, and they release Earth-analogous minerals into the water.
- The ocean is enriched in oxygen due to radiolysis and crustal ice circulation.
- Fusion technology exists, so fusion-associated helium isotopes are available
- Resource can be imported or mined off-world but only if no cheaper alternatives exist
What resources would be most efficient to draw on in order to create air breathable for whole lifetimes inside the colonies? Oxygen seems abundant, but assuming many of the submarines on this world will be pressurized, colonists won't want to risk oxygen toxicity. Thus, other gases need to be mixed in.
What resources can be drawn on most efficiently and combined to make breathable air?
One starting point might be looking at breathing gases.
CLARIFYING EDIT: Oxygen is abundant, as evidenced by the list of resources above. I'm looking for an answer that specifies how to achieve a healthy atmosphere beyond just getting oxygen because just oxygen is poisonous. How can other complimentary gases be harvested?