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| Titel |
Biotic stoichiometric controls on the deep ocean N:P ratio |
| VerfasserIn |
T. M. Lenton, C. A. Klausmeier |
| 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 ; 4, no. 3 ; Nr. 4, no. 3 (2007-06-20), S.353-367 |
| Datensatznummer |
250001731
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| Publikation (Nr.) |
 copernicus.org/bg-4-353-2007.pdf |
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| Zusammenfassung |
| We re-examine what controls the deep ocean N:P ratio in the light of
recent findings that the C:N:P stoichiometry of phytoplankton varies
with growth rate, nutrient and light limitation, species and phylum,
and that N2-fixation may be limited by Fe, temperature and/or
light in large parts of the world ocean. In particular, we assess
whether a systematic change in phytoplankton stoichiometry can alter
the deep ocean N:P ratio. To do this we adapt recent models to
include non-Redfieldian stoichiometry of phytoplankton and
restriction of N2-fixers to a fraction of the surface ocean. We
show that a systematic change in phytoplankton C:N:P can alter the
concentrations of NO3 and PO4 in the deep ocean but cannot
greatly alter their ratio, unless it also alters the N:P threshold
for N2-fixation. This occurs if competitive dynamics set the
N:P threshold for N2-fixation, in which case it remains close
to the N:P requirement of non-fixers (rather than that of
N2-fixers) and consequently so does the deep ocean N:P ratio.
Then, even if N2-fixers are restricted to a fraction of the
surface ocean, they reach higher densities there, minimising
variations in deep ocean N:P. Theoretical limits on the N:P
requirements of phytoplankton suggest that whilst the deep ocean has
been well oxygenated (i.e. since the Neoproterozoic, with the
possible exception of Oceanic Anoxic Events), its N:P ratio is
unlikely to have varied by more than a factor of two in either
direction. Within these bounds, evolutionary changes in
phytoplankton composition, and increased phosphorus weathering due
to the biological colonisation of the land surface, are predicted to
have driven long-term changes in ocean composition. |
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