Quantifying ocean oxygen-to-carbon demand by chemical analyses and inverse models

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The marine carbon and oxygen cycles are intimately linked through the production and consumption of oxygen during photosynthesis and respiration. The amount of oxygen consumed per mole of respired organic carbon, the respiration quotient, is key for accurately predicting ocean oxygen concentrations and how ocean oxygen levels will respond to climate change. Despite this importance, the respiration quotient has rarely been measured directly. The aim of this research is to estimate the respiration quotient and its variability across ocean regions and depth. This will be done through an integration of direct chemical measurements of particulate organic matter collected from multiple ocean regions and indirectly by using an ocean circulation model to analyze a global database of dissolved oxygen and carbon concentration with a circulation model. In addition to advancing the understanding of the ocean oxygen cycle in the scientific community, this project will provide research training for researchers and students. The project will also improve awareness and understanding in the general public about possible future changes to marine oxygen concentrations.One of the main uncertainties in predicting current and future oxygen levels is the regulation of the biological respiration demand. The respiration quotient describes the amount of oxygen needed during the consumption of one mole of organic carbon and thus is a key link between the carbon and oxygen cycles. Here, we propose to measure the amount of oxygen consumed per mole of respired organic carbon, the respiration quotient, in particulate organic matter (POM) from the surface and thermocline using a newly developed chemical technique. Thus, we aim to obtain new direct chemical measurements of the respiration quotient across distinct oceanic regimes and depths. Subsequently, we propose to incorporate these observations into a seasonally-resolved inverse model using global hydrographic tracer concentration data. This combined approach will provide the first global-scale estimates (and uncertainties) of the mean and regional variability of the respiration quotient in the POM stock and export flux. Different parameterizations linking the respiration quotient to regions or environmental variables will be applied to test how they impact and replicate global oxygen concentrations and the extent of the oxygen minimum zones.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.