Can We Estimate Air-Sea Flux of Biological O2 From Total Dissolved Oxygen?

In this study, we compare mechanistic and empirical approaches to reconstruct the air-sea flux of biological oxygen (FO2bio_as ${\mathrm{F}}_{{\left[{\mathrm{O}}_{2}\right]}_{{\text{bio}}<^>{\_\text{as}}}}$) by parameterizing the physical oxygen saturation anomaly (Delta O-2[phy]) in order to separate the biological contribution from total oxygen. The first approach matches Delta O-2[phy] to the monthly climatology of the argon saturation anomaly from a global ocean circulation model's output. The second approach derives Delta O-2[phy] from an iterative mass balance model forced by satellite-based physical drivers of Delta O-2[phy] prior to the sampling day by assuming that air-sea interactions are the dominant factors driving the surface Delta O-2[phy]. The final approach leverages the machine-learning technique of Genetic Programming (GP) to search for the functional relationship between Delta O-2[phy] and biophysicochemical parameters. We compile simultaneous measurements of O-2/Ar and O-2 concentration from 14 cruises to train the GP algorithm and test the validity and applicability of our modeled Delta O-2[phy] and FO2bio_as ${\mathrm{F}}_{{\left[{\mathrm{O}}_{2}\right]}_{{\text{bio}}<^>{\_\text{as}}}}$. Among the approaches, the GP approach, which incorporates ship-based measurements and historical records of physical parameters from the reanalysis products, provides the most robust predictions (R-2 = 0.74 for Delta O-2[phy] and 0.72 for FO2bio_as ${\mathrm{F}}_{{\left[{\mathrm{O}}_{2}\right]}_{{\text{bio}}<^>{\_\text{as}}}}$; RMSE = 1.4% for Delta O-2[phy] and 7.1 mmol O-2 m(-2) d(-1) for FO2bio_as ${\mathrm{F}}_{{\left[{\mathrm{O}}_{2}\right]}_{{\text{bio}}<^>{\_\text{as}}}}$). We use the empirical formulation derived from GP approach to reconstruct regional, inter-annual, and decadal variability of FO2bio_as ${\mathrm{F}}_{{\left[{\mathrm{O}}_{2}\right]}_{{\text{bio}}<^>{\_\text{as}}}}$ based on historical oxygen records. Overall, our study represents a first attempt at deriving FO2bio_as ${\mathrm{F}}_{{\left[{\mathrm{O}}_{2}\right]}_{{\text{bio}}<^>{\_\text{as}}}}$ from snapshot measurements of oxygen, thereby paving the way toward using historical O-2 data and a rapidly growing number of O-2 measurements on autonomous platforms for independent insight into the biological pump.

Automated summary

In this study, the researchers compared mechanistic and empirical approaches to reconstruct the air-sea flux of biological oxygen by parameterizing the physical oxygen saturation anomaly. The study highlights the importance of using snapshot measurements of oxygen and historical oxygen data, and provides the most robust predictions.