A conceptual model for the temporal spectrum of oceanic oxygen variability

Changes in dissolved O₂ observed across the world oceans in recent decades have been interpreted as a response of marine biogeochemistry to climate change. Little is known however about the spectrum of oceanic O ₂ variability. Using an idealized model, we illustrate how fluctuations in ocean circulation and biological respiration lead to low-frequency variability of thermocline oxygen. Because the ventilation of the thermocline naturally integrates the effects of anomalous respiration and advection over decadal timescales, short-lived O₂ perturbations are strongly damped, producing a red spectrum, even in a randomly varying oceanic environment. This background red spectrum of O₂ suggests a new interpretation of the ubiquitous strength of decadal oxygen variability and provides a null hypothesis for the detection of climate change influence on oceanic oxygen. We find a statistically significant spectral peak at a 15-20 year timescale in the subpolar North Pacific, but the mechanisms connecting to climate variability remain uncertain.