Record High Chl-aorophyll-a Concentration in the Southeastern Indian Ocean in 2023
Description
Satellite-derived Ocean colour observations revealed an unprecedented chlorophyll-a (Chl-a) bloom in the southeastern Indian Ocean (SEIO) during the austral spring (September–November) of 2023, with surface Chl-a concentrations reaching up to 0.78 mg m-3, the highest recorded in the past two decades. The SEIO, particularly the region spanning 90°E–110°E and 0°–10°S, is highly responsive to Indian Ocean Dipole (IOD) events due to their influence on ocean-atmosphere interactions that regulate nutrient availability and phytoplankton productivity. Chl-a concentrations during the 2023 positive IOD (pIOD) phase were 13% higher than those observed in 2019 (0.6 mg m⁻³), previously regarded as the strongest pIOD year, and approximately 75% above the climatological mean. While key atmospheric and ocean surface parameters such as winds, Walker circulation, sea surface temperature, and upwelling intensity showed similar anomalies in both 2019 and 2023, the subsurface thermocline structure in 2023 exhibited significant differences.