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| Titel |
Evidence for aggregation and export of cyanobacteria and nano-eukaryotes from the Sargasso Sea euphotic zone |
| VerfasserIn |
M. W. Lomas, S. B. Moran |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 1 ; Nr. 8, no. 1 (2011-01-26), S.203-216 |
| Datensatznummer |
250005355
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| Publikation (Nr.) |
 copernicus.org/bg-8-203-2011.pdf |
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| Zusammenfassung |
| Pico-plankton and nano-plankton are generally thought to represent a
negligible fraction of the total particulate organic carbon (POC) export
flux in oligotrophic gyres due to their small size, slow individual sinking
rates, and tight grazer control that leads to high rates of recycling in the
euphotic zone. Based upon recent inverse modeling and network analysis
however, it has been hypothesized that pico-plankton, including the
cyanobacteria Synechococcus and Prochlorococcus, and nano-plankton contribute significantly to POC export,
via formation and gravitational settling of aggregates and/or consumption of
those aggregates by mesozooplankton, in proportion to their contribution to
net primary production. This study presents total suspended particulate
(>0.7 μm) and particle size-fractionated (10–20 μm, 20–53 μm, >53 μm) pigment concentrations from within and below the euphotic
zone in the oligotrophic subtropical North Atlantic, collected using Niskin
bottles and large volume in-situ pumps, respectively. Results show the indicator
pigments for Synechococcus, Prochlorococcus and nano-eukaryotes are; (1) found at depths down to 500 m,
and; (2) essentially constant, relative to the sum of all indicator pigments,
across particle size fractions ranging from 10 μm to >53 μm.
Based upon the presence of chlorophyll precursor and degradation pigments,
and that in situ pumps do not effectively sample fecal pellets, it is concluded
that these pigments were redistributed to deeper waters on larger, more
rapidly sinking aggregates likely by gravitational settling and/or
convective mixing. Using available pigment and ancillary data from these
cruises, these Synechococcus, Prochlorococcus and nano-plankton derived aggregates are estimated to
contribute 2–13% (5 ± 4%), 1–20% (5 ± 7%), and
6–43% (23 ± 14%) of the total sediment trap POC flux measured on
the same cruises, respectively. Furthermore, nano-eukaryotes contribute
equally to POC export and autotrophic biomass, while cyanobacteria
contributions to POC export are one-tenth of their contribution to
autotrophic biomass. These field observations provide direct evidence that
pico- and nano-plankton represent a significant contribution to the total
POC export via formation of aggregates in this oligotrophic ocean gyre. We
suggest that aggregate formation and fate should be included in ecosystem
models, particularly as oligotrophic regions are hypothesized to expand in
areal extent with warming and increased stratification in the future. |
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