In the tropical Pacific, year-to-year changes in chlorophyll, a proxy for the phytoplankton base of ocean food webs, is dominated by the El Niño–Southern Oscillation. El Niño, triggered by westerly wind anomalies and subsequent redistributions of upper ocean heat content, can sharply reduce the regional supply of nutrients, limiting phytoplankton growth. GFDL’s new Earth System Model (ESM4.1) captures not only the onset and extent of chlorophyll anomalies during El Niño events, but also a pronounced post-El Niño “chlorophyll rebound” that produces positive equatorial Pacific chlorophyll anomalies in the summer following El Niño events.

A new study, led by AOS Postdoc Hyung-Gyu Lim, a CIMES researcher, explores the pattern correlation of ENSO-driven chlorophyll anomalies and representation of the post El-Niño chlorophyll rebound in ESM2M and ESM4.1. The researchers then diagnose oceanic and atmospheric drivers underlying the post El-Niño chlorophyll rebound, taking advantage of ESM4.1's inclusion of dynamic feedbacks between climate conditions, dust emissions, and dust-iron deposition. GFDL's John Dunne, Charlie Stock, Paul Ginoux, Jasmin John and John Krasting are among the paper's co-authors.