Implications of Ocean Oxygen Availability from Particulate Organic Carbon-to-Oxygen Respiration Quotient

One of the main uncertainties in predicting future ocean oxygen levels is the response and feedback of biological respiration demand. Currently, respiration is considered directly proportional to carbon export – a relationship based on the assumption that there is a static ratio of oxygen and carbon consumption for marine organic matter (i.e., the respiration quotient, r-O2:C). Relatively small changes in the respiration quotient produce large changes in oxygen minimum zones with strong feedbacks on primary productivity through the nitrogen inventory. We measured the respiration quotient along a meridional transect in the Eastern Pacific Ocean. Because r-O2:C has rarely been measured in the ocean, this result conveys a large uncertainty for future deoxygenation. We present direct measurements of r-O2:C ranged from 0.73 to 1.54 with a positive temperature relationship with a mean of 1.15. A similar positive temperature dependence was revealed using an independent inverse model constrained by the global database of dissolved nutrients, oxygen and carbon. Although previously unrecognized, the biological control of the oxidation state of carbon in marine organic matter is a fundamental driver of ocean biogeochemistry.