Biological composition and microbial dynamics of sinking particulate organic matter at abyssal depths in the oligotrophic open ocean

Sinking particles are a critical conduit for the export of organic material from surface waters to the deep ocean. Despite their importance in oceanic carbon cycling and export, little is known about the biotic composition, origins, and variability of sinking particles reaching abyssal depths. Here,...

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Published in:	Proceedings of the National Academy of Sciences - PNAS Vol. 116; no. 24; pp. 11824 - 11832
Main Authors:	Boeuf, Dominique, Edwards, Bethanie R., Eppley, John M., Hub, Sarah K., Poff, Kirsten E., Romano, Anna E., Caron, David A., Karl, David M., DeLong, Edward F.
Format:	Journal Article
Language:	English
Published:	United States National Academy of Sciences 11-06-2019
Series:	PNAS Plus
Subjects:	Abyssal zone Animals Aquatic Organisms - metabolism Aquatic Organisms - microbiology Archaea Bacteria Bacteria - growth & development Bacteria - metabolism Biodegradation Biogeochemistry Biological Sciences Carbon - metabolism Carbon cycle Carbon Cycle - physiology Ciliates Composition Deep sea environments Deep water Epsilonproteobacteria Eukaryota - metabolism Eukaryotes Exports Gammaproteobacteria Microorganisms Mineralization Mollusks Nitrogen cycle Nucleic acids Oceans and Seas Organic matter Origins Particulate Matter - metabolism Particulate organic matter PNAS Plus rRNA Seawater - microbiology Shellfish Stochasticity Surface water Water circulation Water column marine microbes particulate organic matter deep sea marine carbon cycle piezophile
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Summary:	Sinking particles are a critical conduit for the export of organic material from surface waters to the deep ocean. Despite their importance in oceanic carbon cycling and export, little is known about the biotic composition, origins, and variability of sinking particles reaching abyssal depths. Here, we analyzed particle-associated nucleic acids captured and preserved in sediment traps at 4,000-m depth in the North Pacific Subtropical Gyre. Over the 9-month time-series, Bacteria dominated both the rRNA-gene and rRNA pools, followed by eukaryotes (protists and animals) and trace amounts of Archaea. Deep-sea piezophile-like Gammaproteobacteria, along with Epsilonproteobacteria, comprised >80% of the bacterial inventory. Protists (mostly Rhizaria, Syndinales, and ciliates) and metazoa (predominantly pelagic mollusks and cnidarians) were the most common sinking particle-associated eukaryotes. Some near-surface water-derived eukaryotes, especially Foraminifera, Radiolaria, and pteropods, varied greatly in their abundance patterns, presumably due to sporadic export events. The dominance of piezophile-like Gammaproteobacteria and Epsilonproteobacteria, along with the prevalence of their nitrogen cycling-associated gene transcripts, suggested a central role for these bacteria in the mineralization and biogeochemical transformation of sinking particulate organic matter in the deep ocean. Our data also reflected several different modes of particle export dynamics, including summer export, more stochastic inputs from the upper water column by protists and pteropods, and contributions from sinking mid- and deep-water organisms. In total, our observations revealed the variable and heterogeneous biological origins and microbial activities of sinking particles that connect their downward transport, transformation, and degradation to deep-sea biogeochemical processes.
Bibliography:	Contributed by Edward F. DeLong, April 22, 2019 (sent for review February 21, 2019; reviewed by Eric E. Allen and Peter R. Girguis) 3Present address: Marine Chemistry & Geochemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543-1050. 1D.B., B.R.E., and J.M.E. contributed equally to this work. Reviewers: E.E.A., University of California, San Diego; and P.R.G., Harvard University. 2Present address: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720. Author contributions: D.M.K. and E.F.D. designed research; D.B., B.R.E., J.M.E., S.K.H., K.E.P., A.E.R., D.A.C., and E.F.D. performed research; J.M.E. contributed new reagents/analytic tools; D.B., B.R.E., J.M.E., S.K.H., K.E.P., A.E.R., D.A.C., D.M.K., and E.F.D. analyzed data; and E.F.D. wrote the paper with D.B., B.R.E., S.K.H., D.A.C., and D.M.K.
ISSN:	0027-8424 1091-6490
DOI:	10.1073/pnas.1903080116