Effects of Tropical Cyclone (TC) Hellen on the north-westward movement of chlorophyll in the northern Mozambique Channel

An intense tropical cyclone (TC), TC Hellen, occurred in the northern Mozambique Channel on March 27, 2014, and moved from the east coast of the African continent to the northern Madagascar island. TC Hellen dramatically altered the marine environment in the northern Mozambique Channel, resulting in a significant chlorophyll-a (Chl-a) bloom. A giant surface Chl-a northwest-ward movement from the northwest coast of Madagascar Island was first observed after the passage of TC Hellen in the northern Mozambique Channel. The dynamic mechanisms of these phenomenon were studied by satellite remote sensing, multisource reanalysis data, and Argo float data. The results show that transient northwestward-moving eddies, upwelling, and winds had important effects on the Chl-a bloom and its northwestward movement. Ekman transport driven by coastal southeasterly winds entrained waters with high Chl-a concentrations to the northwest, while TC Hellen enhanced cyclonic eddy upwelling and uplifted nutrient-rich deep water to the upper ocean. This vertical mixing and upwelling in turn triggered the Chl-a bloom in the offshore surface layer. This study provides insight into the reflection of phytoplankton dynamics by TCs in the northern Mozambique Channel.