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| Titel |
Seasonal to multi-decadal oxygen variability in the eastern tropical North Atlantic |
| VerfasserIn |
Peter Brandt, Johannes Hahn, Gerd Krahmann, Sunke Schmidtko |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106227
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| Publikation (Nr.) |
 EGU/EGU2015-5887.pdf |
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| Zusammenfassung |
| Ocean observations taken in the oxygen minimum zone (OMZ) of the eastern tropical North Atlantic (ETNA) are analysed to study seasonal variability to long-term changes in the oxygen distribution and its causes. The dataset includes repeat shipboard hydrographic and velocity measurements along 23°W and multi-year moored observations at several locations between 4°N and 11.5°N. Below the mixed layer, the water column in the ETNA OMZ can be devided into two regimes. A well-ventilated upper layer (above 300 m depth) is separated by a sharp oxycline from the core of the OMZ below. The observations show that the upper layer is dominantly ventilated by zonal advection, while the ventilation of the OMZ core is due to lateral eddy fluxes, vertical mixing, and advection. Both regimes differ in their oxygen variability on seasonal to decadal time-scales. Amplitudes of the annual oxygen cycle are enhanced at the locations of main eastward current bands at approximately 5°N and 8°–9°N. Seasonal variability is out of phase between the upper and deeper layers as well as between the two current bands. Oxygen changes during the last decade are characterized by a strong deoxygenation of the upper layer, while oxygen levels in the OMZ core increased. These differing decadal trends are superimposed on the multi-decadal oxygen decline observed since the 1960s. Spatial patterns of seasonal to decadal oxygen variability suggest a dominant role of the advective oxygen supply for the observed changes. |
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