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| Titel |
Atmospheric deposition of nutrients and excess N formation in the North Atlantic |
| VerfasserIn |
L. M. Zamora, A. Landolfi, A. Oschlies, D. A. Hansell, H. Dietze, F. Dentener |
| 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 ; 7, no. 2 ; Nr. 7, no. 2 (2010-02-26), S.777-793 |
| Datensatznummer |
250004502
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| Publikation (Nr.) |
 copernicus.org/bg-7-777-2010.pdf |
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| Zusammenfassung |
| Anthropogenic emissions of nitrogen (N) to the atmosphere have been strongly increasing
during the last century, leading to greater atmospheric N deposition to the oceans. The
North Atlantic subtropical gyre (NASTG) is particularly impacted. Here, upwind sources of
anthropogenic N from North American and European sources have raised atmospheric N
deposition to rates comparable with N2 fixation in the gyre. However, the
biogeochemical fate of the deposited N is unclear because there is no detectable
accumulation in the surface waters. Most likely, deposited N accumulates in the main
thermocline instead, where there is a globally unique pool of N in excess of the canonical
Redfield ratio of 16N:1 phosphorus (P). To investigate this depth zone as a sink for
atmospheric N, we used a biogeochemical ocean transport model and year 2000 nutrient
deposition data. We examined the maximum effects of three mechanisms that may transport
excess N from the ocean surface to the main thermocline: physical transport, preferential P
remineralization of sinking particles, and nutrient uptake and export by phytoplankton at
higher than Redfield N:P ratios. Our results indicate that atmospheric deposition may
contribute 13–19% of the annual excess N input to the main thermocline. Modeled nutrient
distributions in the NASTG were comparable to observations only when non-Redfield dynamics
were invoked. Preferential P remineralization could not produce realistic results on its
own; if it is an important contributor to ocean biogeochemistry, it must co-occur with
N2 fixation. The results suggest that: 1) the main thermocline is an important sink
for anthropogenic N deposition, 2) non-Redfield surface dynamics determine the
biogeochemical fate of atmospherically deposited nutrients, and 3) atmospheric N
accumulation in the main thermocline has long term impacts on surface ocean biology. |
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