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| Titel |
Stable isotopes and turnover of nitrate in the German Bight |
| VerfasserIn |
K. Dähnke, A. Johannsen, K. Emeis |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022489
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| Zusammenfassung |
| The German Bight is a hot-spot of river-induced eutrophication of the North Sea due to
nitrate loads discharged into this semi-isolated embayment by several large rivers. We
analysed stable isotope signatures of water column nitrate in the area on a grid of
stations in winter and early spring 2007. Overall spatial patterns of δ15N-NO3-
and δ18O-NO3- image the predominant influence of the rivers Rhine and Elbe on
the German Bight. On a smaller scale, however, and in offshore stations, nitrate
assimilation of an incipient phytoplankton bloom is indicated by parallel enrichment of
δ15N-NO3- and δ18O-NO3-. Intriguingly, the enrichment ratio in ɛ18: ɛ15 is 1.5:1,
differing from the ratio of 1:1 associated with uptake by marine phytoplankton.
These data suggest that the shift in nitrate isotopes is not solely due to beginning
phytoplankton assimilation, but that, despite low temperatures, nitrate in the outer
regions of the German Bight derives to a considerable extent from nitrification. These
novel data mark remineralization in sediments as an important source of DIN and
underscore the role of sediments in recharging water column nutrient inventories. |
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