Seasonal evolution of chlorophyll in the Indian sector of the Southern Ocean: Analyses of Bio-Argo measurements

To better understand the impact of climate change on the Southern Ocean (SO) biogeochemistry, we must know the evolution of the seasonal cycle of biological properties. Here we present the first estimate of the seasonal evolution of chlorophyll-a (Chl-a) along oceanic fronts in the Indian sector of SO using Bio-Argo float observations. The present study is based on data collected using three such floats deployed in the frontal zones. The high productivity is usually attributed to the upwelling of nutrient-enriched subsurface water, the supply of dissolved iron to the ocean surface and their horizontal advection. Our analysis shows that the seasonal evolution of Chl-a is similar in all the three frontal regions, namely Sub-Tropical front (STF), Sub-Antarctic Front (SAF) and Polar Front (PF). We also found that shoaling of the Mixed Layer Depth (MLD) above the critical depth, owing to an increase in light exposure during spring, triggers the initiation of the spring bloom.