Stability of Marine Organic Matter Respiration Stoichiometry

• Published in: Geophysical research letters Vol. 47; no. 1
• Main Authors: Tanioka, T., Matsumoto, K.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.01.2020
• Subjects: Bacteria; Carbohydrates; Carbon; Climate change; Decomposition; Deoxygenation; Dissolved oxygen; elemental stoichiometry; Global warming; Lipids; Macromolecules; Marine ecosystems; marine phytoplankton; Methods; Oceans; Organic carbon; Organic matter; organic matter respiration; Oxygen; oxygen cycle; Phytoplankton; Plankton; Proteins; Quotients; Redfield ratio; Remineralization; Respiratory quotient; Spatial variability; Spatial variations; Stability; Stoichiometry
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL085564

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. Plain Language Summary Most organic carbon produced by phytoplankton in the surface ocean is decomposed by bacteria using dissolved oxygen. This process is expected to accelerate under global warming leading to a significant loss of oxygen from the marine ecosystem. In order to accurately estimate the total amount of oxygen consumed during the decomposition of organic matter, we require information on how much organic carbon is respired per unit of oxygen consumed (respiratory quotient). Here we estimate respiratory quotient using two independent methods and demonstrate that the estimates agree in showing a nearly uniform value in large parts of the world ocean. We suggest that this is attributable to the fact that globally, the organic matter is largely made of protein which requires more oxygen than other molecules such as lipid and carbohydrate. Key Points A new global estimate of respiratory quotient (RQ) of organic matter is determined using two independent methods Global ocean respiration stoichiometry is stable, RQ ~0.7 with small spatial variability Stability of respiration stoichiometry is attributable to the dominance of proteins in phytoplankton biomass