I dunno if hypoxic is the right term here as it’s usually taken to mean oxygen deprivation / insufficiency, which isn’t what’s happening here, as evidenced by organisms being adapted to the conditions.
The oxygen concentration is actually quite a bit higher in most hadal zones (> 150 µmol/kg [1]) than oxygen minimum zones that exist in the middle layers (< 45 µmol/kg [2]). It's definitely not a hypoxic environment relative to the rest of the ocean.
