Climate change has led to increases in the intensity and frequency of marine heatwaves (MHWs). However, the impact of MHWs on phytoplankton at the global scale remains unclear. The metaheuristic superlearner proposed in this research indicates that the occurrence of MHWs weakens the Fe limitation of phytoplankton growth, leading to intensified phytoplankton blooms. The shock transmission effect analysis further reveals the interactions among sea surface temperature (SST), iceberg melting, Fe, ammonium (