Seasonal Diversity of El Niño‐Induced Marine Heatwave Increases in the Bay of Bengal.

This study explored the characteristics of marine heatwaves (MHWs) and the related dynamics in Bay of Bengal (BOB) associated with El Niño events during 1982–2020. This showed that El Niño can induce more MHW days, which displays remarkable seasonality. The strong influences of El Niño were found in the southern BOB at its peak phase in winter and the following spring, characterized by an increase in MHW days by 106% in winter and 83% in spring. In the proceeding summer, its influences weakened and shifted to the central bay. The more MHW days during winter and spring are primarily caused by the enhanced solar radiation associated with El Niño and partly contributed by the thick barrier layer in winter. In contrast, besides atmospheric heating, the deepening thermocline in the central bay induced by equatorial and local winds also plays an important role in the increase in MHWs during summer. Plain Language Summary: Marine heatwaves (MHWs) are warmer‐than‐usual events that occur in the ocean and exert disastrous consequences on marine ecosystems, such as bleached coral reefs. Bay of Bengal (including Andaman Sea) is globally known for its most diverse coral reef species. However, the coral reef there is facing increasing bleaching threats in response to severe MHWs. This study found that El Niño can induce more MHW days in the bay, which shows a remarkable seasonality. The strong influences of El Niño were found in the southern BOB and Andaman Sea in winter and spring, characterized by an increase in MHW days by 106% and 83%, respectively. In the proceeding summer, similar but weaker influences appeared in the central bay. The enhanced MHW days during winter and spring were mainly caused by stronger solar radiation, and partly contributed by the thick barrier layer in winter. In summer, in addition to surface heating, the deepening thermocline in the central bay induced by equatorial and local winds also plays an important role. These results expanded our understanding of the dynamic mechanisms of MHWs under the influence of El Niño, which may contribute to the prediction of MHWs and their ecological impact assessment. Key Points: The increase in marine heatwaves (MHWs) by El Niño showed a strong seasonal diversity in the Bay of BengalMore MHW days in the southern bay and Andaman Sea in winter due to the enhanced solar radiation and thick barrier layerMore MHW days in the central bay in summer caused by the stronger surface heating and deepening thermocline [ABSTRACT FROM AUTHOR]