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| Titel |
Implications of elevated CO2 on pelagic carbon fluxes in an Arctic mesocosm study – an elemental mass balance approach |
| VerfasserIn |
J. Czerny, K. G. Schulz, T. Boxhammer, R. G. J. Bellerby, J. Büdenbender, A. Engel, S. A. Krug, A. Ludwig, K. Nachtigall, G. Nondal, B. Niehoff, A. Silyakova, U. Riebesell |
| 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 ; 10, no. 5 ; Nr. 10, no. 5 (2013-05-08), S.3109-3125 |
| Datensatznummer |
250018241
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| Publikation (Nr.) |
 copernicus.org/bg-10-3109-2013.pdf |
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| Zusammenfassung |
Recent studies on the impacts of ocean acidification on pelagic communities
have identified changes in carbon to nutrient dynamics with related shifts
in elemental stoichiometry. In principle, mesocosm experiments provide the
opportunity of determining temporal dynamics of all relevant carbon and
nutrient pools and, thus, calculating elemental budgets. In practice,
attempts to budget mesocosm enclosures are often hampered by uncertainties
in some of the measured pools and fluxes, in particular due to uncertainties
in constraining air–sea gas exchange, particle sinking, and wall growth. In
an Arctic mesocosm study on ocean acidification applying KOSMOS
(Kiel Off-Shore Mesocosms for future Ocean Simulation), all relevant element pools and fluxes
of carbon, nitrogen and phosphorus were measured, using an improved
experimental design intended to narrow down the mentioned uncertainties.
Water-column concentrations of particulate and dissolved organic and
inorganic matter were determined daily. New approaches for quantitative
estimates of material sinking to the bottom of the mesocosms and gas
exchange in 48 h temporal resolution as well as estimates of wall growth
were developed to close the gaps in element budgets. However, losses elements from
the budgets into a sum of insufficiently determined pools were detected, and are principally
unavoidable in mesocosm investigation. The comparison of variability patterns of
all single measured datasets revealed analytic precision to be the main
issue in determination of budgets. Uncertainties in dissolved organic carbon
(DOC), nitrogen (DON) and particulate organic phosphorus (POP) were much
higher than the summed error in determination of the same elements in all
other pools. With estimates provided for all other major elemental pools,
mass balance calculations could be used to infer the temporal development of
DOC, DON and POP pools.
Future elevated pCO2 was found to enhance net autotrophic community
carbon uptake in two of the three experimental phases but did not
significantly affect particle elemental composition. Enhanced carbon
consumption appears to result in accumulation of dissolved organic carbon
under nutrient-recycling summer conditions. This carbon over-consumption
effect becomes evident from mass balance calculations, but was too small to
be resolved by direct measurements of dissolved organic matter. Faster
nutrient uptake by comparatively small algae at high CO2 after nutrient
addition resulted in reduced production rates under future ocean CO2
conditions at the end of the experiment. This CO2 mediated shift
towards smaller phytoplankton and enhanced cycling of dissolved matter
restricted the development of larger phytoplankton, thus pushing the system
towards a retention type food chain with overall negative effects on export
potential. |
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