Cross-front phytoplankton pigments and chemotaxonomic groups in the Indian sector of the Southern Ocean

This work describes the phytoplankton pigments and main taxonomic groups across major oceanographic fronts in the Indian Sector of the Southern Ocean. Seawater samples were collected in late summer of 2011, during an Indian Southern Ocean Expedition. Twenty five stations were occupied by RV Sagar Nidhi along two longitudinal transects (between 37°S and 60°S). High Performance Liquid Chromatography (HPLC) analysis was performed to identify and quantify phytoplankton pigments concentration and the CHEMTAX software was applied to determine the relative contribution of the main taxonomic groups to total chlorophyll a (phytoplankton biomass index). Our results showed that the spatial distribution of phytoplankton groups, identified by pigment data, was highly correlated with ocean surface thermal gradients. Subtropical, Subantarctic and Antarctic surface waters were, respectively, mainly associated with (i) prochlorophytes (zeaxanthin and divinyl-chlorophyll a as the major pigments), (ii) haptophytes (19′-butanoyloxyfucoxanthin and 19′-hexanoyloxyfucoxanthin as the major pigments), and (iii) diatoms (fucoxanthin as the major pigment). This study contributes to better understanding the distribution of phytoplankton and its association with physical gradients in an undersampled complex region of the Southern Ocean.