"Low oxygen" refers to a situation where there is not enough oxygen available in a particular environment or for a living organism to breathe. Full definition
The influence of climate change was evident in areas with either extreme incidents of oxygen depletion or longer - than - normal trends of low oxygen levels. (scientificamerican.com)
The two most common causes of low oxygen are heart failure and anemia. (2ndchance.info)
Low oxygen conditions slow decay rates, resulting in much of the carbon accumulating in the soil. (fs.fed.us)