Subseafloor Microbial Diversity of the Ross Sea, Antarctica (IODP 374), is Linked to Differences in Depositional Regimes

Understanding the influence of environmental and paleoclimatic data over microbial diversity is of vital importance to evaluate community structure and the evolution of biogeochemical cycles. Here we present the microbial diversity in sediments from two sites drilled during the IODP 374 expedition at the Ross Sea. The two investigated sites (U1523 and U1524) are located on the continental shelf and slope of the Ross Sea, respectively, are, and have been, influenced differently by Antarctic currents and bottom water formation. The analysis of 16S rRNA reveals a shift in the dominant community from Proteobacteria and Bacteroidota to Chloroflexota at around 2.5 meters depth. The overall diversity in the sediment cores decreased with depth, possibly influenced by changes in the diversity of electron acceptors available. Beta-diversity analysis reveals that the two sites harbor distinct microbial communities, and that the turnover in beta diversity is controlled mainly by depth. Metagenomes and Metagenome Assembled Genomes (MAGs) were difficult to obtain and were finally successful from only two samples. They reveal a community dominated by enzymes and pathways involved in the degradation of complex organic matter. Overall our data suggest that the microbial communities present in the sediments of the Ross Sea differ taxonomically and functionally among the two stations possibly reflecting differences in the conditions during the depositional regimes.