Microbial community structure in the firn associated with a ∼1000 km transect of the Eastern Antarctic Ice Sheet

The surface snow and shallow ice of the Antarctic have traditionally been considered biologically inactive environments with low biomass. However, recent studies have begun to describe the complexity of microbial populations present, their biogeographic distribution and local spatial variation. This study characterized the microbial communities of Eastern Antarctic high altitude plateau firn cores (up to 27 m in depth), collected along a 989 km inland transect culminating near the Southern Pole of Inaccessibility. These cores were collected in the 4th International Polar Year (IPY), during a Norwegian-U.S. scientific traverse of East Antarctica. Microbial community composition varied both between different cores and within individual cores, indicating spatial and vertical heterogeneity. Patterns of variation were not consistent across cores or depths, and regional differences were also apparent at the phylum level. Differences in measured ion concentrations, particularly phosphate, also correlated with microbial diversity. Overall, firn across the high-altitude inland plateau of the Eastern Antarctic hosts a spatially structured and depth-dependent microbiome likely influenced by depositional variability and local geochemical conditions. This study highlights the complexity of microbial distribution within firn profiles, and emphasizes the importance of understanding the local microbial diversity of surface snow and shallow ice when investigating subsurface cryosphere environments.