Phytoplankton play a pivotal role in the marine food web and the global carbon cycle, contributing approximately 50% of global carbon fixation. Phytoplankton production in the low-latitude North Atlantic has long been recognized as low to moderate and thus not received substantial attention in their carbon sequestration potential. Nevertheless, sporadic surges in chlorophyll concentrations have been detected by satellites in these regions, yet their causes and contributions to annual primary production and carbon export remain poorly understood. Using satellite observations of sea surface temperature (SST) and chlorophyll, we show that episodic phytoplankton blooms in low-latitude North Atlantic often occur after abrupt drops in SST. To further discern the underlying causes and quantify the contributions of these episodic events to annual carbon sequestration, we employ a one-dimensional nutrient-chlorophyll-phytoplankton-zooplankton-detritus model. The model is calibrated by satellite and biogeochemical-Argo data to reproduce the climatological seasonal variability of surface chlorophyll and deep chlorophyll maxima (DCM) of low-latitude North Atlantic. A series of model experiments are conducted to isolate the roles of surface entrainment of nutrients versus the upward lifting of DCM in triggering surface chlorophyll enhancement. Their impacts on annual primary production and carbon export are also quantified and implications for carbon sequestration are discussed.

episodic phytoplankton blooms, low-latitude North Atlantic, carbon