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| Titel |
Coastal upwelling off Peru and Mauritania inferred from helium isotope disequilibrium |
| VerfasserIn |
R. Steinfeldt, J. Sültenfuss, M. Dengler, T. Fischer, M. Rhein |
| 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 ; 12, no. 24 ; Nr. 12, no. 24 (2015-12-21), S.7519-7533 |
| Datensatznummer |
250118224
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| Publikation (Nr.) |
 copernicus.org/bg-12-7519-2015.pdf |
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| Zusammenfassung |
| Upwelling is an important process, bringing gases and nutrients into the
ocean mixed layer. The upwelling velocities, however, are too small
to be measured directly. Here we use the surface disequilibrium of
the 3He / 4He ratio measured in two coastal upwelling regions off
Peru in the Pacific ocean and off Mauritania in the Atlantic ocean to
calculate the regional distribution of vertical velocities. To also account
for the fluxes by diapycnal mixing, microstructure-based observations of
the vertical diffusivity have been performed on all four cruises analysed in
this study. The upwelling velocities in the coastal regions vary
between 1.1 ± 0.3 × 10−5
and 2.8 ± 1.5 × 10−5 m s−1
for all cruises.
Vertical velocities are also inferred from the divergence
of the wind-driven Ekman transport. In the coastal regimes, both methods
agree within the error range.
Further offshore, the helium-derived vertical velocity
still reaches 1 × 10−5 m s−1, whereas the wind-driven
upwelling from Ekman suction is smaller by up to 1 order of magnitude.
One reason for this difference is ascribed to eddy-induced upwelling.
Both advective and diffusive nutrient fluxes into the mixed layer are
calculated based on the helium-derived vertical velocities and the
vertical diffusivities. The advective part of these fluxes makes up
at about 50 % of the total. The nutrient flux into the mixed layer
in the coastal upwelling regimes is equivalent to a net community production
(NCP) of 1.3 ± 0.3 g C m2 d−1 off Peru and
1.6–2.1 ± 0.5 g C m2 d−1 off Mauritania. |
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