Vertically structured prokaryotic community can control the efficiency of the biological pump in the oceans

Despite recent advances in molecular and metagenomic approaches, it is still unclear how spatiotemporal variations in microbial communities influence the biological pump, exporting organic carbon from the surface to the deep oceans. We address this important problem by constructing a simple model of a prokaryotic metacommunity in which two generalist ecotypes compete for two resources. The first and the second ecotypes have, respectively, a higher preference for particulate organic carbon (POC) and dissolved organic carbon. Sinking of POC would lead to a higher abundance of the first ecotype in the deep layer compared to the surface layer, but vertical mixing in turn generates a net upward flux of this ecotype to the surface layer. This upward movement accelerates the shifts in the community composition during the phytoplankton bloom, contributing to a higher efficiency in POC remineralization at the surface layer and reducing the carbon flux to the deep layer.