Submesoscale dynamics directly shape bacterioplankton community structure in space and time

Abstract

Submesoscale eddies and fronts are recognized as important components of oceanic mixing and energy fluxes. These submesoscale phenomena occur in the surface ocean for a period of a few days on scales between several hundred meters and a few tens of kilometers. Remote sensing and modeling suggest that they may influence marine ecosystem dynamics, but their limited temporal and spatial scales make them challenging for observation and in situ sampling. Here, the study of a submesoscale filament in summerly Arctic waters (depth 0 - 400 m) revealed enhanced vertical mixing of Polar and Atlantic water masses, resulting in a ca. 4 km wide and ca. 50 km long filament with distinct physical and biogeochemical conditions. Compared to the surrounding waters the filament was characterized by a distinct phytoplankton bloom dominated by diatoms and two-fold higher bacterioplankton cell densities. High-throughput 16S rRNA gene sequencing of both bacterioplankton communities revealed 3-4 orders of magnitude higher sequence abundance of Synechococcus inside the filament, as well as tenfold higher sequence abundance of taxonomic groups typically found during summertime in aging phytoplankton blooms (e.g., Flavobacteriales). In contrast, the surrounding waters contained severalfold higher sequence abundance of winterly taxonomic groups that are also associated with polar water masses (e.g., SAR202 clade). Altogether, our results show that physical submesoscale processes in the ocean can shape distinct biogeochemical conditions and microbial communities within a few kilometers. Furthermore, our results underline the importance of such submesoscale features for our understanding of surface ocean diversity and biogeochemical processes.