Characterizing compound physical and biogeochemical extremes in the California Current Large Marine Ecosystem

Natalie M. Freeman , Gaëlle Hervieux , Michael A. Alexander , Michael Jacox, Dillon J. Amaya , James D. Scott , Antonietta Capotondi 

Discrete environmental stressors, such as prolonged periods of extreme temperature or low oxygen, threaten the functioning of marine ecosystems. While considerable attention has been given to studying extremes occurring in isolation, our understanding of such events co-occurring in the water column–referred to as multi-stressor events or compound extremes–is still limited, despite their potentially synergistic effects on individual species. We use a historical ocean model simulation with biogeochemistry to characterize the frequency, intensity, and duration of multi-stressor events (temperature, chlorophyll, and oxygen) in the California Current Large Marine Ecosystem (CCLME) from 1996–2019. We highlight key spatiotemporal patterns of compound physical and biogeochemical extremes in the context of large-scale climate variability, particularly ENSO. Marine heatwaves and low chlorophyll extremes are generally associated with strong El Niño events, while nearshore shallow hypoxia extremes are generally associated with La Niña events. Marine heatwave-low chlorophyll extremes are the most common compound extreme in nearshore waters, while triple extremes are relatively rare, as conditions favoring warm and low productivity anomalies tend to also favor high oxygen anomalies. Results from this study advance our understanding of where and when multi-stressor events tend to occur in the CCLME, highlighting spatiotemporal characteristics that suggest potential sources of predictability, which could be leveraged in the ecosystem-based management of living marine resources.