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| Titel |
Diapycnal diffusivity in the core and oxycline of the tropical North Atlantic oxygen minimum zone |
| VerfasserIn |
Manuela Köllner, Martin Visbeck, Toste Tanhua, Tim Fischer |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128009
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| Publikation (Nr.) |
 EGU/EGU2016-7949.pdf |
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| Zusammenfassung |
| Diapycnal diffusivity plays an important role in the ventilation of the
Eastern Tropical North Atlantic (ETNA) Oxygen Minimum Zone (OMZ). Studies by
Fischer et al. (2013), Banyte et al. (2012) and the synthesis by Brandt et
al. (2015) found that diapycnal mixing contributes up to 20{\%}, locally up
to 30{\%}, to the oxygen supply in the OMZ. This comparatively high
contribution to the oxygen supply for the ETNA OMZ is the consequence of the
weak horizontal circulation within the so-called shadow zone of the
subtropical gyre (Luyten et al., 1983) and possibly enhanced mixing over
rough topography in the seamount area south of the Guinea Dome (Brandt et
al., 2015).
Diapycnal diffusivity estimates from two Tracer Release Experiments (TREs)
and microstructure measurements in the oxycline and core of the oxygen
minimum zone (OMZ) in the eastern tropical North Atlantic are compared. For
the first time, two TREs within the same area at different depths were
realized: the Guinea Upwelling Tracer Release Experiment (GUTRE) initiated
in 2008 in the oxycline at approximately 320 m depth, and the Oxygen Supply
Tracer Release Experiment (OSTRE) initiated in 2012 in the core of the OMZ
at approximately 410 m depth. The mean diapycnal diffusivity D$^{z}$ was
found to be insignificantly smaller in the OMZ core with (1.06 $\pm $ 0.24)
\times 10$^{-5}$ m$^{2}$ s$^{-1}$ compared to (1.11 $\pm $ 0.22) ) \times 10$^{-5}$
m$^{2}$ s$^{-1}$ 90 m shallower in the oxycline. Unexpectedly, GUTRE tracer
was detected during two of the OSTRE surveys which allowed to estimate
diapycnal diffusivity from GUTRE over a time period of seven years. The
results are consistent with the D$^{z}$ estimates from microstructure
measurements and demonstrate that D$^{z}$ does not vary significantly in the
OMZ within the depth range of 200-600 m. For both experiments no significant
vertical displacements of the tracer larger than 5 m per year were observed
over the entire time period of both experiments.
REFERENCES
Banyte, D., Tanhua, T., Visbeck, M., Wallace, D., Karstensen, J., Krahmann, G., Schneider, A., Stramma, L. and Dengler, M., 2012. Diapycnal diffusivity at the upper boundary of the tropical North Atlantic oxygen minimum zone. J. Geophys. Res., 117, C09016.
Brandt, P., Banyte, D., Dengler, M., Didwischus, S.-H., Fischer, T.,
Greatbatch, R., Hahn, J., Kanzow, T., Karstensen, J., K\"{o}rtzinger, A., Krahmann, G., Schmidtko, S., Stramma, L., Tanhua, T., Visbeck, M., 2015 On the role of circulation and mixing in the ventilation of oxygen minimum zones with a focus on the tropical North Atlantic. Biogeosciences 12, 489-512, doi: 10.5194/bg-12-489-2015.
Fischer, T., Banyte, D., Brandt, P., Dengler, M., Krahmann, G., Tanhua, T. and Visbeck, M. 2013. Diapycnal oxygen supply to the tropical North Atlantic oxygen minimum zone. Biogeosciences, 10, 5079-5093. |
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