327 / 2024-09-14 11:22:14
Maintenance of multi-year La Niña by phytoplankton feedback in the tropical Pacific
ENSO,La Nina diversity,biological feedback
Session 65 - Oceanic-atmospheric processes over the Indian and western Pacific Oceans
Abstract Accepted
The occurrence of multi-year La Niña (MLN) event shows an increasing trend over the historical period, causing adverse climate and ecological impacts. In the equatorial Pacific, the ocean ecosystem undergoes significant changes during MLN, particularly in surface chlorophyll, which serves as a proxy for primary production. Interestingly, the impacts of chlorophyll on the evolution and amplitude of MLN remain unknown. Here, using a hierarchy of ocean model experiments, we show that interannual variations in surface chlorophyll cause initial warming during the first year of MLN due to a chlorophyll-induced heating effect. Subsequently, this warming leads to enhanced meridional advection and vertical mixing, resulting in cooling anomalies in the western equatorial Pacific during the second year of MLN. This differential impact between the western basin and the eastern basin contributes to sustaining the cooling phase of MLN. Additionally, the effect of chlorophyll is further amplified by the presence of subsurface chlorophyll maximum during MLN. Given the potential phytoplankton feedback, chlorophyll may play a significant role in shaping the evolution of MLN, and its influence should be considered in future ENSO predictions.