Fig. Main reservoirs and fluxes (in unit 1012 mol/yr) of the modern global oxygen (O2 specifically) cycle. Four main reservoirs, i.e., terrestiral biosphere, marine biosphere, lithosphere, and atmosphere are shown in the figure. Note that the brown bald mountain in the left side of this figure also represents a part of lithosphere. Main fluxes between these reservoirs are shown in colored arrows, where the green arrows are related to the terrestrial biosphere, blue arrows are related to the marine biosphere, black arrows are related to the lithosphere, purple arrow is related to the space (not a reservoir, but also contributes to the atmosphere oxygen level). [1] The value of photosynthesis or net primary productivity (NPP) can be estimated through the variation in the abundance and isotopic composition of atmospheric oxygen[2][3] The rate of organic carbon burial can be derived by estimating the flux of volcanic and hydrothermal carbon.[4][5]