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| Titel |
Phytoplankton dynamics in contrasting early stage North Atlantic spring blooms: composition, succession, and potential drivers |
| VerfasserIn |
C. J. Daniels, A. J. Poulton, M. Esposito, M. L. Paulsen, R. Bellerby, M. St. John, A. P. Martin |
| 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 ; 12, no. 8 ; Nr. 12, no. 8 (2015-04-24), S.2395-2409 |
| Datensatznummer |
250117909
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| Publikation (Nr.) |
 copernicus.org/bg-12-2395-2015.pdf |
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| Zusammenfassung |
The spring bloom is a key annual event in the phenology of pelagic
ecosystems, making a major contribution to the oceanic biological carbon
pump through the production and export of organic carbon. However, there is
little consensus as to the main drivers of spring bloom formation,
exacerbated by a lack of in situ observations of the phytoplankton community
composition and its evolution during this critical period.
We investigated the dynamics of the phytoplankton community structure at two
contrasting sites in the Iceland and Norwegian basins during the early stage
(25 March–25 April) of the 2012 North Atlantic spring bloom. The plankton
composition and characteristics of the initial stages of the bloom were
markedly different between the two basins. The Iceland Basin (ICB) appeared
well mixed down to >400 m, yet surface chlorophyll a
(0.27–2.2 mg m−3) and primary production
(0.06–0.66 mmol C m−3 d−1) were elevated in the upper 100 m.
Although the Norwegian Basin (NWB) had a persistently shallower mixed layer
(<100 m), chlorophyll a (0.58–0.93 mg m−3) and primary
production (0.08–0.15 mmol C m−3 d−1) remained lower than in
the ICB, with picoplankton (<2 μm) dominating chlorophyll a
biomass. The ICB phytoplankton composition appeared primarily driven by the
physicochemical environment, with periodic events of increased mixing
restricting further increases in biomass. In contrast, the NWB phytoplankton
community was potentially limited by physicochemical and/or biological
factors such as grazing.
Diatoms dominated the ICB, with the genus Chaetoceros
(1–166 cells mL−1) being succeeded by Pseudo-nitzschia
(0.2–210 cells mL−1). However, large diatoms (>10 μm)
were virtually absent (<0.5 cells mL−1) from the NWB, with only
small nano-sized (<5 μm) diatoms (i.e. Minidiscus
spp.) present (101–600 cells mL−1). We suggest microzooplankton
grazing, potentially coupled with the lack of a seed population of bloom-forming diatoms, was restricting diatom growth in the NWB, and that large
diatoms may be absent in NWB spring blooms. Despite both phytoplankton
communities being in the early stages of bloom formation, different
physicochemical and biological factors controlled bloom formation at the two
sites. If these differences in phytoplankton composition persist, the
subsequent spring blooms are likely to be significantly different in terms of
biogeochemistry and trophic interactions throughout the growth season, with
important implications for carbon cycling and organic matter export. |
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