Interannual Bacterial Diversity Variability in Antarctic Snow/Ice Samples in the Vicinity of Concordia Station

In this study, we compared the bacterial diversity of two independent snow and ice sampling campaigns conducted in 2015-2016 and 2018-2019 at Dome C, Concordia Station, Antarctica. Using 16S rRNA gene amplicon sequencing, we analysed 81 samples and, after quality filtering and rarefaction, obtained approximately 3.8 million high-quality reads. Alpha diversity analyses revealed comparable richness between the two sampling periods, while community evenness was higher in 2018-2019. In contrast, all beta diversity metrics consistently showed significant differences in community composition between years, while beta dispersion analyses indicated distinct levels of heterogeneity within the year. The results of the Raup-Crick null model (R0) analyses showed that the observed differences did not deviate from random expectations under the applied null hypothesis. Overall, these results indicate pronounced interannual variability in bacterial assemblages at Concordia Station and suggest that temporal changes in community composition are consistent with assembly processes dominated by episodic inputs and limited persistence under extreme environmental conditions. This study implements previous investigations by providing a comparative temporal perspective and contributes to a better understanding of microbial dynamics in one of the most isolated and low-biomass environments on Earth.