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| Titel |
A geographical and seasonal comparison of nitrogen uptake by phytoplankton in the Southern Ocean |
| VerfasserIn |
R. Philibert, H. Waldron, D. Clark |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 11, no. 2 ; Nr. 11, no. 2 (2015-03-13), S.251-267 |
| Datensatznummer |
250117175
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| Publikation (Nr.) |
 copernicus.org/os-11-251-2015.pdf |
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| Zusammenfassung |
The impact of light and nutrients (such as silicate and iron) availability on
nitrogen uptake and primary production vary seasonally and regionally in the
Southern Ocean. The seasonal cycle of nitrogen uptake by phytoplankton in the
Southern Ocean is not fully resolved over an annual scale due to the lack of
winter in situ measurements. In this study, nitrate and ammonium uptake rates
were measured using 15N tracers during a winter cruise in July 2012 and
a summer cruise in February–March 2013. The winter cruise consisted of two
legs: leg 1 extended from Cape Town to the ice margin along the GoodHope line
and leg 2 stretched from the ice margin to Marion Island. The summer cruise
was mostly focused on the subantarctic zone of the Atlantic sector. In
winter, nitrogen uptake rates were measured at 55 and 1% of the surface
photosynthetically active radiation (sPAR). The summer uptake rates were
measured at four light depths corresponding to 55, 30, 10 and 3% sPAR. The
integrated nitrate uptake rates during the winter cruise ranged from
0.17 to 5.20 mmol N m−2 d−1 (average 1.14 mmol N m−2 d−1) while the
ammonium uptake rates ranged from 0.60 to 32.86 mmol N m−2 d−1 (average
6.73 mmol N m−2 d−1). During the summer cruise, the mean-integrated nitrate uptake rate was 0.20 mmol N m−2 d−1 with
a range between 0.10 and 0.38 mmol N m−2 d−1. The integrated
ammonium uptake rate averaged 4.39 mmol N m−2 d−1 and ranged
from 1.12 to 9.05 mmol N m−2 d−1.
The factors controlling nitrogen uptake in winter and summer were
investigated. During the winter cruise, it was found that the different nitrogen
uptake regimes were not separated by the fronts of the Antarctic Circumpolar
Current (ACC). Light (in terms of day length) and ammonium concentration had the
most influence on the nitrogen uptake. In the summer, increases in the mixed layer depth (MLD) resulted in increased nitrogen uptake rates. This suggests
that the increases in the MLD could be alleviating nutrient limitations
experienced by the phytoplankton at the end of summer. |
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