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| Titel |
Open ocean dead zones in the tropical North Atlantic Ocean |
| VerfasserIn |
J. Karstensen, B. Fiedler, F. Schütte, P. Brandt, A. Körtzinger, G. Fischer, R. Zantopp, J. Hahn, M. Visbeck, D. Wallace |
| 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. 8 ; Nr. 12, no. 8 (2015-04-30), S.2597-2605 |
| Datensatznummer |
250117921
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| Publikation (Nr.) |
 copernicus.org/bg-12-2597-2015.pdf |
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| Zusammenfassung |
| Here we present first observations, from instrumentation installed on
moorings and a float, of unexpectedly low (<2 μmol kg−1)
oxygen environments in the open waters of the tropical North Atlantic,
a region where oxygen concentration does normally not fall much below
40 μmol kg−1. The low-oxygen zones are created at shallow
depth, just below the mixed layer, in the euphotic zone of cyclonic eddies
and anticyclonic-modewater eddies. Both types of eddies are prone to high
surface productivity. Net respiration rates for the eddies are found to be 3
to 5 times higher when compared with surrounding waters. Oxygen is lowest in
the centre of the eddies, in a depth range where the swirl velocity, defining
the transition between eddy and surroundings, has its maximum. It is assumed
that the strong velocity at the outer rim of the eddies hampers the transport
of properties across the eddies boundary and as such isolates their cores.
This is supported by a remarkably stable hydrographic structure of the eddies
core over periods of several months. The eddies propagate westward, at about
4 to 5 km day−1, from their generation region off the West
African coast into the open ocean. High productivity and accompanying
respiration, paired with sluggish exchange across the eddy boundary, create
the "dead zone" inside the eddies, so far only reported for coastal areas or
lakes. We observe a direct impact of the open ocean dead zones on the marine
ecosystem as such that the diurnal vertical migration of zooplankton is
suppressed inside the eddies. |
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