Microbial fingerprinting of marine water masses in an Antarctic and hydrographically complex area

Microorganisms are ubiquitous in marine ecosystems, yet the influence of water masses on their distribution remains underexplored, particularly in extreme environments such as Antarctica. This study examines microbial communities in the Gerlache-Bismarck Strait, a region with complex hydrography. We analyzed both prokaryotic and eukaryotic diversity alongside multiple oceanographic and biogeochemical variables. Water samples were collected from 1 to 400 m depth across three size fractions: pico- (0.2-3 µm), nano- (3-20 µm), and microparticles (20-200 µm).

Our results indicate that water mass composition is a primary driver of microbial community assembly. Surface water masses included Antarctic Surface Waters (AASW), Glacially Modified Waters (GMW), and Transitional Zonal Waters influenced by the Bellingshausen Sea (TBW), whereas intermediate and deep layers comprised Transitional Zonal Waters influenced by the Weddell Sea (TWW) and Circumpolar Deep Waters (CDW). This study provides direct evidence of close links between microorganisms and water masses, showing that marine microbial communities are shaped not only by local conditions but also by water masses circulation. We use the concept of "microbial fingerprinting of water masses" establishing microbial communities as ecological indicators and providing framework applicable to other marine systems.

Microbial fingerprints provided insight into the role of the water masses in biogeochemistry and food webs of this area (e.g., the ammonia-oxidizing archaea Nitrosopumilaceae in the CDW, and the phototroph Chrysochromulina simplex in the GMW). This information is useful to predict how future changes in ocean circulation and microbial distribution may alter ecosystem services in this critical region.