How do Climate Modes Shape the Chlorophyll-a Interannual Variability in the Tropical Atlantic?

Chlorophyll-a concentration (Chl-a) observed by satellite shows a marked seasonal and interannual variability in the tropical Atlantic. This study analyzes how the remotely sensed surface Chl-a responds to the leading boreal summer climate modes affecting the interannual tropical Atlantic variability over 1998-2018, corresponding to a positive Atlantic Multidecadal Oscillation phase. We show that the Atlantic Zonal Mode (AZM) and the North Tropical Atlantic Mode (NTAM) significantly drive the interannual surface Chl-a variability in the equatorial Atlantic, with different timings and contrasted zonal modulation of the cold tongue. The AZM involves remotely forced wave propagations favoring upwelling in the east and Chl-a modulation in the core of the cold tongue. Instead, the impact of the NTAM is mainly in the west, in response to locally forced pumping that modulates the western extension of the cold tongue. Such conditions can affect the marine food web, inducing significant variations for ecosystem functioning and fisheries.