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| Titel |
Seasonal variation in marine C:N:P stoichiometry: can the composition of seston explain stable Redfield ratios? |
| VerfasserIn |
H. Frigstad, T. Andersen, D. O. Hessen, L.-J. Naustvoll, T. M. Johnsen, R. G. J. Bellerby |
| 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. 10 ; Nr. 8, no. 10 (2011-10-18), S.2917-2933 |
| Datensatznummer |
250006163
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| Publikation (Nr.) |
 copernicus.org/bg-8-2917-2011.pdf |
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| Zusammenfassung |
| Seston is suspended particulate organic matter, comprising a mixture of
autotrophic, heterotrophic and detrital material. Despite variable
proportions of these components, marine seston often exhibits relatively
small deviations from the Redfield ratio (C:N:P = 106:16:1). Two time-series
from the Norwegian shelf in Skagerrak are used to identify drivers of the
seasonal variation in seston elemental ratios. An ordination identified
water mass characteristics and bloom dynamics as the most important drivers
for determining C:N, while changes in nutrient concentrations and biomass
were most important for the C:P and N:P relationships. There is no
standardized method for determining the functional composition of seston and
the fractions of POC, PON and PP associated with phytoplankton, therefore
any such information has to be obtained by indirect means. In this study, a
generalized linear model was used to differentiate between the live
autotrophic and non-autotrophic sestonic fractions, and for both stations
the non-autotrophic fractions dominated with respective annual means of 76
and 55%. This regression model approach builds on assumptions (e.g.
constant POC:Chl-a ratio) and the robustness of the estimates were explored
with a bootstrap analysis. In addition the autotrophic percentage calculated
from the statistical model was compared with estimated phytoplankton carbon,
and the two independent estimates of autotrophic percentage were comparable
with similar seasonal cycles. The estimated C:nutrient ratios of live
autotrophs were, in general, lower than Redfield, while the non-autotrophic
C:nutrient ratios were higher than the live autotrophic ratios and above, or
close to, the Redfield ratio. This is due to preferential remineralization
of nutrients, and the P content mainly governed the difference between the
sestonic fractions. Despite the seasonal variability in seston composition
and the generally low contribution of autotrophic biomass, the variation
observed in the total seston ratios was low compared to the variation found
in dissolved and particulate pools. Sestonic C:N:P ratios close to the
Redfield ratios should not be used as an indicator of phytoplankton
physiological state, but could instead reflect varying contributions of
sestonic fractions that sum up to an elemental ratio close to Redfield. |
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