Stability of Marine Organic Matter Respiration Stoichiometry

The amount of oxygen consumed during organic matter remineralization critically depends on how much organic carbon is remineralized per unit dissolved oxygen respired (respiratory quotient, RQ) but the global distribution and the mechanisms that control RQ are not well understood. Here we estimate RQ in the surface ocean by using two independent methods, one using satellite-derived macromolecular composition of phytoplankton and another using objectively gridded nutrient data. Both methods yield mean RQ of ~0.7 with small spatial variability consistent with previous estimates. This pattern is likely to be a result of phytoplankton protein content universally exceeding those of carbohydrates and lipids. At face value, the relative stability of RQ suggests that the remineralization stoichiometry will not affect the ongoing deoxygenation of the world ocean. However, the possibility remains that RQ may increase in the future (e.g., organic matter becoming more carbohydrate-dominated) and thus ameliorate deoxygenation.