Shifting of phytoplankton community in the frontal regions of Indian Ocean sector of the Southern Ocean using in situ and satellite data

Abstract. The phytoplankton pigment indices were used to characterize the spatial succession of the community composition in the frontal regions of the subtropical front (STF), sub-Antarctic front (SAF), and polar front (PF) in the Indian Ocean sector of the Southern Ocean during austral summer 2013. Diagnostic indices revealed that the flagellates were dominant in STF (51%) and progressively declined toward SAF (39%) and PF (11%). Similarly, the prokaryotes were highest in STF (43%) and decreased to SAF (32%) and PF (28%). In contrast, the diatoms were gradually increased from STF (6%) to SAF (29%) and PF (61%). The variability of flagellates and diatoms from the STF to PF is attributed to the variability of photosynthetically available radiation, sea surface temperature, and sea surface wind speed. The in-situ pigment indices were then compared to the NASA Ocean Biogeochemical model that shows the similar patterns of frontal community distribution except their magnitude. Similarly, the satellite retrieved phytoplankton biomass (chlorophyll a) was checked for its consistency after comparing with the in-situ observations and the result shows underestimation of satellite measured values. The result suggests that the conjunctive analysis of in-situ, satellite, and model archive is suitable to study the impact of climate variability on the structure of marine ecosystems.

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