The strength of the biological soft tissue pump in the ocean critically depends on how much organic carbon is produced via photosynthesis and how efficiently the carbon is transferred to the ocean interior. For a given amount of limiting nutrient, phosphate, soft tissue pump would be strengthened if the carbon (C) to phosphorus (P) ratio of sinking organic matter increases as the remineralization length scale of C increases. Here, we present a new data compilation of particle flux stoichiometry and show that C:P of sinking particulate organic matter (POM) in the ocean twilight zone is systematically higher than the Redfield C:P and the C:P ratio of surface suspended POM. We further demonstrate using a physics-biology coupled global ocean model combined with a theory from first principles that an increase in C:P flux ratio in the ocean’s twilight zone can lead to considerable variability in atmospheric pCO₂.