Decadal Prediction of Hypoxia along the US West Coast

Coastal hypoxia events along the US West Coast are strongly influenced by changes in local upwelling winds. However, the long-term statistics of coastal hypoxia are affected by changes in the oxygen content of the subsurface water masses that feed the main upwelling. To diagnose how subsurface circulation dynamics impact long-term changes in the oxygen of coastal upwelling water masses, we combine the ECMWF Ocean Reanalysis System 3 (ORAS3) with an oxygen proxy model on isopycnal 26.5. We show that this oxygen proxy tracks the observed decadal fluctuations of subsurface oxygen in the long-term records of the California Current, Oregon Shelf, and Gulf of Alaska. In this model, these low-frequency changes in oxygen originate in the subtropical gyre and propagate downstream into the coastal upwelling system through the mean gyre circulation. We exploit these propagation dynamics to develop a decadal prediction model of coastal hypoxia. Although more analyses are needed to establish the robustness of this forecast model, the current sign of the anomalies in the gyre predicts strong hypoxic conditions by 2020.