Decadal oscillations in the ocean's largest oxygen-deficient zone - coral isotopes records & linear extension rates

The impact of global warming on the ocean’s oxygen-deficient zones (ODZs) is poorly known, in part due to a lack of data on past changes. We present monthly resolved records of coral skeleton-bound nitrogen isotopes (CS-δ15N) to reconstruct denitrification in the ODZ of the Eastern Tropical North Pacific (ETNP) over the last 80 years. The data record strong decadal variation in ETNP denitrification in phase with the Pacific Decadal Variability (PDV). Denitrification (and thus oxygen deficiency) is enhanced in the cold PDV phase, likely due to stronger upwelling, enhanced productivity, and thus greater oxygen demand in the thermocline. Prior findings of ODZ expansion were likely biased by this variability. ODZ's evolution in the next century will depend on how global warming influences these decadal changes.