Compound High Temperature and Low Chlorophyll Extremes in the Ocean Over the Satellite Period

• Published in: Biogeosciences Vol. 18; no. 6; pp. 2119 - 2137
• Main Authors: Grix, Natacha Le, Zscheischler, Jakob, Laufkötter, Charlotte, Rousseaux, Cecile S, Frölicher, Thomas L
• Format: Journal Article
• Language: English
• Published: Goddard Space Flight Center Copernicus Publications for the European Geosciences Union 24.03.2021; Copernicus GmbH; Copernicus Publications
• Subjects: Biogeochemistry; Chlorophyll; Chlorophylls; Climate change; Climate variability; Datasets; Earth Resources And Remote Sensing; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; Global temperature changes; Global warming; Gyres; Heat waves; Heatwaves; Hemispheres; High temperature; Marine ecosystems; Marine organisms; Ocean; Ocean circulation; Oceanography; Oceans; Plankton; Productivity; Satellites; Sea level; Sea surface; Sea surface temperature; Seasonal variations; Southern Oscillation; Surface temperature; Time; Australia; United States > US; California; High Temperature; Low Chlorophyll; Satellite; Ocean
• ISSN: 1726-4170; 1726-4189; 1726-4189
• DOI: 10.5194/bg-18-2119-2021

Ocean extreme events severely impact marine organisms and ecosystems. Of particular concern are compoundevents, i.e., when conditions are extreme for multiple potential ocean ecosystem stressors such as temperature and chlorophyll.Yet, little is known about the occurrence, intensity and duration of such compound high temperature (aka marine heatwaves -MHWs) and low chlorophyll (LChl) extreme events, whether their distributions have changed in the past decades and what thepotential drivers are. Here we use satellite-based sea surface temperature and chlorophyll concentration estimates to provide a5first assessment of such compound extreme events. We reveal hotspots of compound MHW and LChl events in the equatorialPacific, along the boundaries of the subtropical gyres, in the northern Indian Ocean, and around Antarctica. In these regions,compound events that typically last one week occur three to seven times more often than expected under the assumption ofindependence between MHWs and LChl events. The occurrence of compound MHW and LChl events varies on seasonalto interannual timescales. At the seasonal timescale, most compound events occur in summer in both hemispheres. At the10interannual timescale, the frequency of compound MHW and LChl events is strongly modulated by large-scale modes of naturalclimate variability such as the El Niño-Southern Oscillation, whose positive phase is associated with increased compoundevent occurrence in the eastern equatorial Pacific and in the Indian Ocean by a factor of up to four. Our results provide a firstunderstanding of where, when and why compound MHW and LChl events occur. Further studies are needed to identify theexact physical and biological drivers of these potentially harmful events in the ocean and their evolution under global warming.