scholarly journals Sources of dissolved iron to oxygen minimum zone waters on the Senegalese continental margin in the tropical North Atlantic Ocean: Insights from iron isotopes

2018 ◽  
Vol 236 ◽  
pp. 60-78 ◽  
Author(s):  
J.K. Klar ◽  
C. Schlosser ◽  
J.A. Milton ◽  
E.M.S. Woodward ◽  
F. Lacan ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Continental Margin ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Oxygen Minimum Zone ◽  
Iron Isotopes ◽  
Dissolved Iron ◽  
Tropical North Atlantic ◽  
Minimum Zone ◽  
Oxygen Minimum

scholarly journals Diapycnal oxygen supply to the tropical North Atlantic oxygen minimum zone

2012 ◽  
Vol 9 (10) ◽  
pp. 14291-14325 ◽  
Author(s):  
T. Fischer ◽  
D. Banyte ◽  
P. Brandt ◽  
M. Dengler ◽  
G. Krahmann ◽  
...  
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Oxygen Supply ◽  
Water Layer ◽  
Oxygen Minimum Zone ◽  
Depth Interval ◽  
Diapycnal Mixing ◽  
Tropical North Atlantic ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. The replenishment of consumed oxygen in the open ocean oxygen minimum zone (OMZ) off West Africa in the tropical North Atlantic Ocean is studied, with a focus on oxygen transport across density surfaces (diapycnal flux). The latter is obtained from a large observational set of oxygen profiles and diapycnal mixing data from years 2008 to 2010. Diapycnal mixing is inferred from different sources: a large scale tracer release experiment, microstructure profiles, and shipboard acoustic current measurements plus density profiles. The average diapycnal diffusivity in the study area is 1 × 10−5 m2 s−1. No significant vertical gradient of average diapycnal diffusivities exists in the depth interval from 150 to 500 m. The diapycnal flux is found to contribute substantially to the oxygen supply of the OMZ. Within the OMZ core, 1.5 µmol kg−1 a−1 of oxygen is supplied via diapycnal mixing, contributing about a third of the total demand. The oxygen that is contributed via diapycnal mixing originates from oxygen that has been laterally supplied within the overlying Central Water layer by advective and eddy fluxes. Due to the existence of a separate shallow oxygen minimum at about 100 m depth throughout most of the study area, there is no direct net vertical oxygen flux from the surface layer of the study area into the Central Water layer. Thus all oxygen supply of the OMZ is associated with remote pathways.

scholarly journals Changes in the Ventilation of the Oxygen Minimum Zone of the Tropical North Atlantic

2010 ◽  
Vol 40 (8) ◽  
pp. 1784-1801 ◽  
Author(s):  
Peter Brandt ◽  
Verena Hormann ◽  
Arne Körtzinger ◽  
Martin Visbeck ◽  
Gerd Krahmann ◽  
...  
Keyword(s):  
North Atlantic ◽  
Oxygen Minimum Zone ◽  
Time Interval ◽  
Depth Range ◽  
Oxygen Levels ◽  
The Core ◽  
Zonal Jets ◽  
Tropical North Atlantic ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract Changes in the ventilation of the oxygen minimum zone (OMZ) of the tropical North Atlantic are studied using oceanographic data from 18 research cruises carried out between 28.5° and 23°W during 1999–2008 as well as historical data referring to the period 1972–85. In the core of the OMZ at about 400-m depth, a highly significant oxygen decrease of about 15 μmol kg−1 is found between the two periods. During the same time interval, the salinity at the oxygen minimum increased by about 0.1. Above the core of the OMZ, within the central water layer, oxygen decreased too, but salinity changed only slightly or even decreased. The scatter in the local oxygen–salinity relations decreased from the earlier to the later period suggesting a reduced filamentation due to mesoscale eddies and/or zonal jets acting on the background gradients. Here it is suggested that latitudinally alternating zonal jets with observed amplitudes of a few centimeters per second in the depth range of the OMZ contribute to the ventilation of the OMZ. A conceptual model of the ventilation of the OMZ is used to corroborate the hypothesis that changes in the strength of zonal jets affect mean oxygen levels in the OMZ. According to the model, a weakening of zonal jets, which is in general agreement with observed hydrographic evidences, is associated with a reduction of the mean oxygen levels that could significantly contribute to the observed deoxygenation of the North Atlantic OMZ.

scholarly journals Fluxes and distribution of dissolved iron in the eastern (sub‐) tropical North Atlantic Ocean

2012 ◽  
Vol 26 (3) ◽  
Author(s):  
Micha J. A. Rijkenberg ◽  
Sebastian Steigenberger ◽  
Claire F. Powell ◽  
Hans Haren ◽  
Matthew D. Patey ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Dissolved Iron ◽  
Tropical North Atlantic

Dissolved iron in the tropical North Atlantic Ocean

2013 ◽  
Vol 154 ◽  
pp. 87-99 ◽  
Author(s):  
Jessica N. Fitzsimmons ◽  
Ruifeng Zhang ◽  
Edward A. Boyle
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Dissolved Iron ◽  
Tropical North Atlantic

scholarly journals Decadal oxygen change in the eastern tropical North Atlantic

Ocean Science ◽  
2017 ◽  
Vol 13 (4) ◽  
pp. 551-576 ◽  
Author(s):  
Johannes Hahn ◽  
Peter Brandt ◽  
Sunke Schmidtko ◽  
Gerd Krahmann
Keyword(s):  
North Atlantic ◽  
Oxygen Supply ◽  
Oxygen Minimum Zone ◽  
Decadal Change ◽  
Oxygen Budget ◽  
Tropical North Atlantic ◽  
Minimum Zone ◽  
Oxygen Minimum ◽  
Density Space

Abstract. Repeat shipboard and multi-year moored observations obtained in the oxygen minimum zone (OMZ) of the eastern tropical North Atlantic (ETNA) were used to study the decadal change in oxygen for the period 2006–2015. Along 23° W between 6 and 14° N, oxygen decreased with a rate of −5.9 ± 3.5 µmol kg−1 decade−1 within the depth covering the deep oxycline (200–400 m), while below the OMZ core (400–1000 m) oxygen increased by 4.0 ± 1.6 µmol kg−1 decade−1 on average. The inclusion of these decadal oxygen trends in the recently estimated oxygen budget for the ETNA OMZ suggests a weakened ventilation of the upper 400 m, whereas the ventilation strengthened homogeneously below 400 m. The changed ventilation resulted in a shoaling of the ETNA OMZ of −0.03 ± 0.02 kg m−3 decade−1 in density space, which was only partly compensated by a deepening of isopycnal surfaces, thus pointing to a shoaling of the OMZ in depth space as well (−22 ± 17 m decade−1). Based on the improved oxygen budget, possible causes for the changed ventilation are analyzed and discussed. Largely ruling out other ventilation processes, the zonal advective oxygen supply stands out as the most probable budget term responsible for the decadal oxygen changes.

scholarly journals Diapycnal diffusivity at the upper boundary of the tropical North Atlantic oxygen minimum zone

2012 ◽  
Vol 117 (C9) ◽  
pp. n/a-n/a ◽  
Author(s):  
Donata Banyte ◽  
Toste Tanhua ◽  
Martin Visbeck ◽  
Douglas W. R. Wallace ◽  
Johannes Karstensen ◽  
...  
Keyword(s):  
North Atlantic ◽  
Oxygen Minimum Zone ◽  
Tropical North Atlantic ◽  
Minimum Zone ◽  
Diapycnal Diffusivity ◽  
Oxygen Minimum ◽  
Upper Boundary
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