Quantifying changes in oceanic aerobic respiration is essential for understanding marine deoxygenation. Here we use an Earth system model to investigate if and to what extent oxygen utilization rate (OUR) can be used to track the temporal change of true respiration ($R_\mathrm{true}$). $R_\mathrm{true}$ results from the degradation of particulate and dissolved organic matter in the model ocean, acting as ground truth to evaluate the accuracy of OUR. Results show that in thermocline and intermediate waters of the North Atlantic Subtropical Gyre (200m-1000m), vertically integrated OUR and $R_\mathrm{true}$ both decrease by 0.2 $\mathrm{mol O_{2}/m^{2}/yr}$ from 1850 to 2100 under global warming. However, in the mesopelagic Tropical South Atlantic, integrated OUR increases by 0.2 $\mathrm{mol O_{2}/m^{2}/yr}$, while the $R_\mathrm{true}$ integral decreases by 0.3 $\mathrm{mol O_{2}/m^{2}/yr}$. A possible reason for the diverging OUR and $R_\mathrm{true}$ is ocean mixing, which affects water mass composition and maps remote respiration changes to the study region.