 |
| Titel |
On the role of circulation and mixing in the ventilation of oxygen minimum zones with a focus on the eastern tropical North Atlantic |
| VerfasserIn |
P. Brandt, H. W. Bange, D. Banyte, M. Dengler, S.-H. Didwischus, T. Fischer, R. J. Greatbatch, J. Hahn, T. Kanzow, J. Karstensen, A. Körtzinger, G. Krahmann, S. Schmidtko, L. Stramma, T. Tanhua, M. Visbeck |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 2 ; Nr. 12, no. 2 (2015-01-27), S.489-512 |
| Datensatznummer |
250117785
|
| Publikation (Nr.) |
 copernicus.org/bg-12-489-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| Ocean observations are analysed in the
framework of Collaborative Research Center 754 (SFB 754)
"Climate-Biogeochemistry Interactions in the Tropical Ocean" to study (1)
the structure of tropical oxygen minimum zones (OMZs), (2) the processes that
contribute to the oxygen budget, and (3) long-term changes in the oxygen
distribution. The OMZ of the eastern tropical North Atlantic (ETNA), located
between the well-ventilated subtropical gyre and the equatorial oxygen
maximum, is composed of a deep OMZ at about 400 m in depth with its core
region centred at about 20° W, 10° N and a shallow OMZ at
about 100 m in depth, with the lowest oxygen concentrations in proximity to
the coastal upwelling region off Mauritania and Senegal. The oxygen budget of
the deep OMZ is given by oxygen consumption mainly balanced by the oxygen
supply due to meridional eddy fluxes (about 60%) and vertical mixing
(about 20%, locally up to 30%). Advection by zonal jets is crucial
for the establishment of the equatorial oxygen maximum. In the latitude range
of the deep OMZ, it dominates the oxygen supply in the upper 300 to 400 m
and generates the intermediate oxygen maximum between deep and shallow OMZs.
Water mass ages from transient tracers indicate substantially older water
masses in the core of the deep OMZ (about 120–180 years) compared to regions
north and south of it. The deoxygenation of the ETNA OMZ during recent
decades suggests a substantial imbalance in the oxygen budget: about 10%
of the oxygen consumption during that period was not balanced by ventilation.
Long-term oxygen observations show variability on interannual, decadal and
multidecadal timescales that can partly be attributed to circulation changes.
In comparison to the ETNA OMZ, the eastern tropical South Pacific OMZ shows a
similar structure, including an equatorial oxygen maximum driven by zonal
advection but overall much lower oxygen concentrations approaching zero in
extended regions. As the shape of the OMZs is set by ocean circulation, the
widespread misrepresentation of the intermediate circulation in ocean
circulation models substantially contributes to their oxygen bias, which
might have significant impacts on predictions of future oxygen levels. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|