CA Durkin, CM Preston, KM Yamahara (2019). DNA metabarcoding reveals organisms contributing to particulate matter flux to abyssal depths in the North East Pacific ocean. Deep Sea Research Pt. II: Topical Research in Oceanography.

The sequestration of carbon in the deep ocean relies on the export of sinking particulate organic matter (POM) originating in the surface waters and its attenuation by organisms that reprocess and repackage it. Despite decades of research, predicting the variability of POM to the deep ocean remains difficult as there is still a gap in the knowledge as to which and how organisms control or influence POM export. Here, we used DNA metabarcoding of the 16S and 18S rRNA genes to investigate the community in sinking particulates collected over 9-months (November 2016–July 2017) at Station M, located within the California Current ecosystem. Particle-associated communities were collected in sediment traps (3900 m and 3950 m), in aggregates that settled on the sea floor (4000 m), and in seawater from the overlying water column. For a majority of the deployment, particulate organic carbon (POC) fluxes were within the Station M long-term time series mean ± σ (8.3 ± 7.9 mg C m−2 d−1). In late June, a high flux event (>long-term POC mean+2σ) was captured, accounting for 44% of the POC collected during the study. The rRNA genes within the sinking particles indicated highly variable eukaryal communities over time, including the export of oligotrophic autotrophs likely by various metazoan taxa during winter, the sporadic and dominant presence of diverse radiolarian orders, and the important role of coastal diatoms during seasonal increases in POC flux. Specifically, the onset of the high POC flux event in June was attributed to the export of a single coastal diatom species. A coincident increase in the relative abundance of metazoan sequences suggests that zooplankton grazing on the diatom community played a role in rapid transport of large quantities of POC to the deep sea. Analysis of the 16S rRNA gene community supported the presence of highly processed POM during winter due to the high relative abundance of deep sea Gammaproteobacteria, that transitioned to fresher, more labile POM with the arrival of a diatom bloom community. These observations support long standing paradigms of particulate export to the deep sea, including its origin and mechanisms of export mediated by a diverse community of organisms, and implicate rapidly exported diatom blooms as at least one source of the increasingly frequent episodic flux events that account for most POC sequestered in the deep ocean at Station M.

prepGEM was used to lyse aggregate samples from the sea floor.

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