Terrestrial biosphere exchange of oxygen and carbon dioxide

The ratio between oxygen (O2) and carbon dioxide (CO2) serves as a valuable tracer for understanding the carbon cycle. This thesis focuses on the O2:CO2 ratio exchanged by the biosphere, which is often assumed to be a constant value of 1.1. We provide insights and methodological recommendations for quantifying this ratio while exploring its spatial and temporal variability. By integrating observational data with modelling approaches, we identify the processes that govern biospheric O2:CO2 ratios and establish connections across different temporal and spatial scales. The findings presented in this thesis demonstrate that the biospheric O2:CO2 ratio is not a fixed value and should be re-evaluated based on the relevant spatial and temporal context when applied as a tracer for carbon balance assessments.