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| Titel |
Impact of dust deposition on carbon budget: a tentative assessment from a mesocosm approach |
| VerfasserIn |
C. Guieu, C. Ridame, E. Pulido-Villena, M. Bressac, K. Desboeufs, F. Dulac |
| 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. 19 ; Nr. 11, no. 19 (2014-10-14), S.5621-5635 |
| Datensatznummer |
250117639
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| Publikation (Nr.) |
 copernicus.org/bg-11-5621-2014.pdf |
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| Zusammenfassung |
| By bringing new nutrients and particles to the surface ocean, atmospheric
deposition impacts biogeochemical cycles. The extent to which those changes
are modifying the carbon balance in oligotrophic environments such as the
Mediterranean Sea that receives important Saharan dust fluxes is unknown. The
DUNE (DUst experiment in a low Nutrient, low chlorophyll Ecosystem) project provides the first attempt to evaluate the changes induced in
the carbon budget of a large body of oligotrophic waters after simulated
Saharan dust wet or dry deposition events, allowing us to measure (1) the
metabolic fluxes while the particles are sinking and (2) the particulate
organic carbon export. Here we report the results for the three distinct
artificial dust seeding experiments simulating wet or dry atmospheric
deposition onto large mesocosms (52 m3) that were conducted in the
oligotrophic waters of the Mediterranean Sea in the summers of 2008 and 2010.
Although heterotrophic bacteria were found to be the key players in the
response to dust deposition, net primary production increased about twice in
case of simulated wet deposition (that includes anthropogenic nitrogen). The
dust deposition did not produce a shift in the metabolic balance as the
tested waters remained net heterotrophic (i.e., net primary production to
bacteria respiration ratio <1) and in some cases the net heterotrophy was
even enhanced by the dust deposition. The change induced by the dust addition
on the total organic carbon pool inside the mesocosm over the 7 days of the
experiments, was a carbon loss dominated by bacteria respiration that was at
least 5–10 times higher than any other term involved in the budget. This
loss of organic carbon from the system in all the experiments was
particularly marked after the simulation of wet deposition. Changes in
biomass were mostly due to an increase in phytoplankton biomass but when
considering the whole particulate organic carbon pool it was dominated by the
organic carbon aggregated to the lithogenic particles still in suspension in
the mesocosm at the end of the experiment. Assuming that the budget is
balanced, the dissolved organic carbon (DOC) pool was estimated by the
difference between the total organic carbon and the particulate organic
carbon (POC) pool. The partitioning between dissolved and particulate organic
carbon was dominated by the dissolved pool with a DOC consumption over 7 days
of ∼1 μmol C L−1 d−1 (dry deposition) to
∼2–5 μmol C L−1 d−1 (wet deposition). This
consumption in the absence of any allochthonous inputs in the closed mesocosms
meant a small <10% decrease of the initial DOC stock after a dry
deposition but a ∼30–40% decrease of the initial DOC stock after
wet deposition. After wet deposition, the tested waters, although dominated
by heterotrophy, were still maintaining a net export (corrected from
controls) of particulate organic carbon (0.5 g in 7 days) even in the
absence of allochthonous carbon inputs. This tentative assessment of the
changes in carbon budget induced by a strong dust deposition indicates that
wet deposition by bringing new nutrients has higher impact than dry
deposition in oligotrophic environments. In the western Mediterranean Sea, the
mineral dust deposition is dominated by wet deposition and one perspective of
this work is to extrapolate our numbers to time series of deposition during
similar oligotrophic conditions to evaluate the overall impact on the carbon
budget at the event and seasonal scale in the surface waters of the
northwestern Mediterranean Sea. These estimated carbon budgets are also
highlighting the key processes (i.e., bacterial respiration) that need to be
considered for an integration of atmospheric deposition in marine
biogeochemical modeling. |
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