A Case Study on Phytoplankton Blooms Triggered by Tropical Cyclone Emeraude in the Central Indian Ocean

Abstract

Phytoplankton blooms occurred in the Central Indian Ocean after tropical cyclone (TC) Emeraude with an elliptic track in March 2016. Here, the ecological responses of the upper ocean layer were first researched based on remote sensing, reanalysis data and Argo data. The results show that two clockwise cyclonic eddies with a vorticity of 0.22 s–1 appeared on the southern equatorial current after the TC. Chlorophyll-a (Chl-a) blooms were found in the two eddies after the TC. The Chl-a concentration in the center of the cyclonic eddies reached 0.5 mg∙m–3. The deepened mixed layer, weakened thermocline, and thinned barrier layer facilitated the uplift of nutrients from the deep sea to the upper layer. Additionally, the sufficient photosynthetically available radiation (PAR) over the two eddies reached 50 Einstein m–2∙day–1 after March 24, thereby providing favorable conditions for the Chl-a blooms that occurred on March 26 in Box A and March 28 in Box B. This study contributes to assessments of the ecological impacts of ocean eddies in the Central Indian Ocean after TCs.

Keywords

• chl-a
• cyclonic eddies
• upwelling
• tropical cyclone