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| Titel |
Contrasted Saharan dust events in LNLC environments: impact on nutrient dynamics and primary production |
| VerfasserIn |
C. Ridame, J. Dekaezemacker, C. Guieu, S. Bonnet, S. L'Helguen, F. Malien |
| 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 ; 11, no. 17 ; Nr. 11, no. 17 (2014-09-10), S.4783-4800 |
| Datensatznummer |
250117583
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| Publikation (Nr.) |
 copernicus.org/bg-11-4783-2014.pdf |
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| Zusammenfassung |
| The response of the phytoplanktonic community (primary production and algal
biomass) to contrasted Saharan dust events (wet and dry deposition) was
studied in the framework of the DUNE ("a DUst experiment in a low-Nutrient,
low-chlorophyll Ecosystem") project. We simulated realistic dust deposition
events (10 g m−2) into large mesocosms (52 m3). Three distinct
dust addition experiments were conducted in June 2008 (DUNE-1-P: simulation
of a wet deposition; DUNE-1-Q: simulation of a dry deposition) and 2010
(DUNE-2-R1 and DUNE-2-R2: simulation of two successive wet depositions) in
the northwestern oligotrophic Mediterranean Sea. No changes in primary
production (PP) and chlorophyll a concentrations (Chl a) were observed
after a dry deposition event, while a wet deposition event resulted in a
rapid (24 h after dust addition), strong (up to 2.4-fold) and long (at least
a week in duration) increase in PP and Chl a. We show that, in addition to
being a source of dissolved inorganic phosphorus (DIP), simulated wet
deposition events were also a significant source of nitrate (NO3−)
(net increases up to +9.8 μM NO3− at 0.1 m in depth) to
the nutrient-depleted surface waters, due to cloud processes and mixing with
anthropogenic species such as HNO3. The dry deposition event was shown
to be a negligible source of NO3−. By transiently increasing DIP and
NO3- concentrations in N–P starved surface waters, wet deposition of
Saharan dust was able to relieve the potential N or NP co-limitation of the
phytoplanktonic activity. Due to the higher input of NO3− relative to
DIP, and taking into account the stimulation of the biological activity, a
wet deposition event resulted in a strong increase in the
NO3−/DIP ratio, from initially less than 6, to over 150
at the end of the DUNE-2-R1 experiment, suggesting a switch from an initial N
or NP co-limitation towards a severe P limitation. We also show that the
contribution of new production to PP strongly increased after wet dust
deposition events, from initially 15% to 60–70% 24 h after
seeding, indicating a switch from a regenerated-production based system to a
new-production based system. DUNE experiments show that wet and dry dust
deposition events induce contrasting responses of the phytoplanktonic
community due to differences in the atmospheric supply of bioavailable new
nutrients. Our results from original mesocosm experiments demonstrate that
atmospheric dust wet deposition greatly influences primary productivity and
algal biomass in LNLC environments through changes in the nutrient stocks,
and alters the NO3−/DIP ratio, leading to a switch in the
nutrient limitation of the phytoplanktonic activity. |
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