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| Titel |
Nitrogen uptake by phytoplankton in the Atlantic sector of the Southern Ocean during late austral summer |
| VerfasserIn |
W. R. Joubert, S. J. Thomalla, H. N. Waldron, M. I. Lucas, M. Boye, F. A. C. Moigne, F. Planchon, S. Speich |
| 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 (2011-10-21), S.2947-2959 |
| Datensatznummer |
250006165
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| Publikation (Nr.) |
 copernicus.org/bg-8-2947-2011.pdf |
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| Zusammenfassung |
| As part of the Bonus-GoodHope (BGH) campaign, 15N-labelled nitrate,
ammonium and urea uptake measurements were made along the BGH transect from
Cape Town to ~60° S in late austral summer, 2008. Our results are
categorised according to distinct hydrographic regions defined by oceanic
fronts and open ocean zones. High regenerated nitrate uptake rate in the
oligotrophic Subtropical Zone (STZ) resulted in low f-ratios (f = 0.2) with
nitrogen uptake being dominated by ρurea, which contributed up to
70 % of total nitrogen uptake. Size fractionated chlorophyll data showed
that the greatest contribution (>50 %) of picophytoplankton (<2 μm) were found in the STZ, consistent with a community based on regenerated
production. The Subantarctic Zone (SAZ) showed the greatest total integrated
nitrogen uptake (10.3 mmol m−2 d−1), mainly due to enhanced
nutrient supply within an anticyclonic eddy observed in this region. A
decrease in the contribution of smaller size classes to the phytoplankton
community was observed with increasing latitude, concurrent with a decrease
in the contribution of regenerated production. Higher f-ratios observed in
the SAZ (f = 0.49), Polar Frontal Zone (f= 0.41) and Antarctic Zone (f = 0.45)
relative to the STZ (f = 0.24), indicate a higher contribution of NO3−-uptake relative to total nitrogen and potentially
higher export production. High ambient regenerated nutrient concentrations
are indicative of active regeneration processes throughout the transect and
ascribed to late summer season sampling. Higher depth integrated uptake
rates also correspond with higher surface iron concentrations. No clear
correlation was observed between carbon export estimates derived from new
production and 234Th flux. In addition, export derived from 15N
estimates were 2–20 times greater than those based on 234Th flux.
Variability in the magnitude of export is likely due to intrinsically
different methods, compounded by differences in integration time scales for
the two proxies of carbon export. |
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