Influence of plankton community structure on the sinking velocity of marine aggregates

Bach, Lennart T., Boxhammer, Tim, Larsen, A., Hildebrandt, N., Schulz, Kai G. and Riebesell, Ulf (2016) Influence of plankton community structure on the sinking velocity of marine aggregates Global Biogeochemical Cycles, 30 (8). pp. 1145-1165. DOI 10.1002/2016GB005372.

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About 50 Gt of carbon is fixed photosynthetically by surface ocean phytoplankton communities every year. Part of this organic matter is reprocessed within the plankton community to form aggregates which eventually sink and export carbon into the deep ocean. The fraction of organic matter leaving the surface ocean is partly dependent on aggregate sinking velocity which accelerates with increasing aggregate size and density, where the latter is controlled by ballast load and aggregate porosity. In May 2011, we moored nine 25 m deep mesocosms in a Norwegian fjord to assess on a daily basis how plankton community structure affects material properties and sinking velocities of aggregates (Ø 80–400 µm) collected in the mesocosms' sediment traps. We noted that sinking velocity was not necessarily accelerated by opal ballast during diatom blooms, which could be due to relatively high porosity of these rather fresh aggregates. Furthermore, estimated aggregate porosity (Pestimated) decreased as the picoautotroph (0.2–2 µm) fraction of the phytoplankton biomass increased. Thus, picoautotroph-dominated communities may be indicative for food webs promoting a high degree of aggregate repackaging with potential for accelerated sinking. Blooms of the coccolithophore Emiliania huxleyi revealed that cell concentrations of ~1500 cells/mL accelerate sinking by about 35–40%, which we estimate (by one-dimensional modeling) to elevate organic matter transfer efficiency through the mesopelagic from 14 to 24%. Our results indicate that sinking velocities are influenced by the complex interplay between the availability of ballast minerals and aggregate packaging; both of which are controlled by plankton community structure.

Document Type: Article
Additional Information: We thank all participants of the 2011 SOPRAN mesocosm study, in particular, Signe Koch-Klavsen and Peter Fritzsche for measuring the chlorophyll a, BSi, and nutrient concentrations; Andrea Ludwig for the support on logistics and organization of the study; and Scarlett Sett, Jan Büdenbender, Jan Czerny, Michael Sswat, Sonja Endres, Luisa Galgani, Hendrik Schultz, Christian Howe, Hubert Kraus, Allanah Paul, Aljosa Zavisic, Allison Webb, Rafael Bermudez, Jorun Egge, Barbara Niehoff, Daniela Freese, and Michael Meyerhöfer for their technical support. We are grateful to the crews of R/V Alkor (AL376), R/V Håkan Mosby (2011609), and R/V Heinke (HE360) for the mooring and transportation of the mesocosms. This paper profited from the constructive comments from two anonymou s reviewers. The project was funded by German Ministry for Science and Education (BMBF) in the framework of the SOPRAN and BIOACID projects with additional support (salary Aud Larsen) from the projects MicroPolar (RCN project 225956/E10) and MINOS (EU-ERC 250254). All data used here will be made available on and can also be requested directly from the corresponding author (lbach@geo- - WOS:000388457500002
Keywords: sinking velocity; plankton community structure; aggregates; ballast; porosity; biological pump
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Kiel University
Refereed: Yes
DOI etc.: 10.1002/2016GB005372
ISSN: 0886-6236
Projects: SOPRAN, BIOACID, MicroPolar, MINOS
Date Deposited: 30 Aug 2016 09:22
Last Modified: 19 Dec 2017 12:45

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