Upwelling Dynamics and Phytoplankton Variability in the Indian Ocean

The Indian Ocean hosts a complex system of coastal and open-ocean upwelling driven primarily by the seasonal reversal of monsoon winds, large-scale ocean-atmosphere oscillations and mesoscale circulation features. During the southwest monsoon (June–September), strong southwesterly winds induce offshore Ekman transport along the eastern African and Arabian‐Peninsula coasts, as well as off western India, bringing cold, nutrient-rich subsurface waters to the surface. Conversely, during the southeast monsoon (December–February), upwelling intensifies along the southern coasts of Indonesia, particularly Java and Sumatra, under northeasterly wind forcing. These processes fertilise surface waters, triggering phytoplankton blooms characterised by elevated chlorophyll-a concentrations. Interannual variability is modulated by the Indian Ocean Dipole and remote El Niño–Southern Oscillation teleconnections, which alter wind stress, thermocline depth and stratification. Decadal trends linked to basin-wide warming and shifts in atmospheric circulation are shifting the timing and intensity of blooms, with clear implications for regional fisheries, carbon sequestration and boundary-layer climate feedbacks.

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Upwelling Dynamics and Phytoplankton Variability in the Indian Ocean publication trend

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Technical terms

Upwelling: The process by which deep, cold, nutrient-rich water rises to the ocean surface, often driven by wind-induced Ekman transport.

Ekman transport: The net motion of surface water at 90° to the wind direction, resulting from the balance between wind stress and the Coriolis force.

Chlorophyll-a: A pigment found in phytoplankton; its concentration serves as a proxy for primary productivity in surface waters.

Thermocline: A subsurface ocean layer characterised by a rapid temperature gradient, separating warmer surface water from colder, deeper layers.

Indian Ocean Dipole (IOD): A climate mode defined by an east–west gradient in sea surface temperature across the tropical Indian Ocean that influences regional wind and precipitation patterns.

Mesoscale eddy: An oceanic circulation feature, typically 10–200 km in diameter, that can trap and transport water masses, altering local stratification and nutrient distributions.

References

1. Long-term shift and recent early onset of chlorophyll-a bloom and coastal upwelling along the southern coast of Java. Frontiers in Climate (2023).
2. On Investigating the Dynamical Factors Modulating Surface Chlorophyll-a Variability along the South Java Coast. Remote Sensing (2022).
3. Satellite-Observed Multi-Scale Variability of Sea Surface Chlorophyll-a Concentration along the South Coast of the Sumatra-Java Islands. Remote Sensing (2021).