Abstract
The biological carbon pump (BCP) is the process by which ocean organisms transfer carbon from surface waters to the ocean interior and seafloor sediments for sequestration. Viruses are thought to increase the efficiency of the BCP by fostering primary production and facilitating the export of carbon-enriched materials in the deep sea (the viral “shunt and pump”). A prior study using an oligotrophic ocean-dominated dataset from the Tara Oceans expedition revealed that bacterial dsDNA viruses are better associated with variation in carbon export than either prokaryotes or eukaryotes, but eukaryotic viruses were not examined. Because eukaryotes contribute significantly to ocean biomass and net production (> 40%), their viruses might also play a role in the BCP. Here, we leveraged deep-sequencing molecular data generated in the framework of Tara Oceans to identify and quantify diverse lineages of large dsDNA and smaller RNA viruses of eukaryotes. We found that the abundance of these viruses explained 49% of the variation in carbon export (compared with 89% by bacterial dsDNA viruses) and also substantially explained the variation in net primary production (76%) and carbon export efficiency (50%). Prasinoviruses infecting Mamiellales as well as Mimivirus relatives putatively infecting haptophytes are among the eukaryotic virus lineages predicted to be the best contributors to BCP efficiency. These findings collectively provide a first-level window into how eukaryotic viruses impact the BCP and suggest that the virus-mediated shunt and pump indeed plays a role.
