Matteo Selci, Angelina Cordone, Bernardo Barosa, Alessia Bastianoni, Deborah Bastoni, Francesco Bolinesi, Rosaria Capuozzo, Martina Cascone, Davide Corso, Luciano di Iorio, Cristina Misic, Francesco Montemagno, Annarita Ricciardelli, Maria Saggiomo, Luca Tonietti, Olga Mangoni, Donato Giovannelli

The Antarctic Circumpolar Current (ACC) is the major current in the Southern Ocean, isolating the warm stratified subtropical waters from the more homogeneous cold polar waters. The ACC flows from west to east around Antarctica and generates an overturning circulation by fostering deep-cold water upwelling and the formation of new water masses, affecting the Earth's heat balance and the global distribution of carbon. The ACC is characterized by several water mass boundaries or fronts, known as Subtropical Front (STF), Subantarctic Front (SAF), Polar front (PF), and South Antarctic Circumpolar Current Front (SACCF), identified by typical physical and chemical properties. While the physical characteristics of these fronts have been characterized, there is still poor information regarding the microbial diversity of this area. Here we present surface water bacterioplankton community structure based on 16S rRNA sequencing from 13 stations sampled between New Zealand to the Ross Sea crossing the Antarctic Circumpolar Current Fronts.. Our results show a distinct succession in the dominant bacterial phylotypes present in the different water masses and suggest a strong role of sea surface temperatures and the availability of Carbon and Nitrogen in controlling community composition. This work represents an important baseline for future studies on the response of Southern Ocean epipelagic microbial communities to climate change.