scholarly journals Oxygen minimum zone in the North Atlantic south and east of the Cape Verde Islands

2008 ◽  
Vol 113 (C4) ◽  
Author(s):  
Lothar Stramma ◽  
Peter Brandt ◽  
Jens Schafstall ◽  
Friedrich Schott ◽  
Jürgen Fischer ◽  
...  
Keyword(s):  
North Atlantic ◽  
Oxygen Minimum Zone ◽  
Cape Verde ◽  
Cape Verde Islands ◽  
The North ◽  
Minimum Zone ◽  
The North Atlantic ◽  
Oxygen Minimum

scholarly journals Isopycnal Mixing in the North Atlantic Oxygen Minimum Zone Revealed by RAFOS Floats

2019 ◽  
Vol 124 (9) ◽  
pp. 6478-6497 ◽  
Author(s):  
Donald Rudnickas ◽  
Jaime Palter ◽  
David Hebert ◽  
H. Thomas Rossby
Keyword(s):  
North Atlantic ◽  
Oxygen Minimum Zone ◽  
The North ◽  
Minimum Zone ◽  
The North Atlantic ◽  
Oxygen Minimum ◽  
Isopycnal Mixing

scholarly journals The flow field of the upper hypoxic eastern tropical North Atlantic oxygen minimum zone

Ocean Science ◽  
2016 ◽  
Vol 12 (1) ◽  
pp. 153-167 ◽  
Author(s):  
L. Stramma ◽  
R. Czeschel ◽  
T. Tanhua ◽  
P. Brandt ◽  
M. Visbeck ◽  
...  
Keyword(s):  
North Atlantic ◽  
Mesoscale Eddy ◽  
Oxygen Sensors ◽  
Oxygen Minimum Zone ◽  
Cape Verde ◽  
Cape Verde Islands ◽  
Near Surface ◽  
Tropical North Atlantic ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. A subsurface low oxygen zone is located in the eastern tropical North Atlantic Ocean (ETNA) in the upper ocean with the core of the hypoxic (O2 ≦60 µmol kg−1) oxygen minimum zone (OMZ) at 400 to 500 m depth. The subsurface circulation in the OMZ region is derived from observations and data assimilation results. Measurements in the ETNA of velocity, oxygen and of a tracer (CF3SF5) that was released in April 2008 at  ∼  8° N, 23° W (at  ∼  330 m depth) in November–December 2008, in November–December 2009 and October–November 2010 show the circulation in the upper part of the OMZ with spreading to the east in the North Equatorial Countercurrent (NECC) region and northwestward around the Guinea Dome. Three floats equipped with oxygen sensors deployed at  ∼  8° N, 23° W with parking depths at 330, 350 and 400 m depths were used to estimate velocity along the float trajectory at the surface and at the parking depth. At the 350 m park depth north of 9° N a cyclonic northwestward flow across the OMZ was observed. The northward drift of a float into the upper OMZ and a stronger cyclonic flow around the Guinea Dome seem to be connected to a strong Atlantic Meridional Mode (AMM) event in 2009. A near-surface cyclonic circulation cell east of the Cape Verde Islands reaches down into the OMZ layer. The circulation of the upper OMZ mirrors the near-surface circulation. Oxygen measurements from the cruises used here, as well as from other recent cruises up to the year 2014, confirm the continuous deoxygenation trend in the upper OMZ since the 1960s near the Guinea Dome. The three floats deployed with the tracer show spreading paths consistent with the overall observed tracer spreading. Oxygen sensors on the floats remained well calibrated for more than 20 months, and so the oxygen profiles can be used to investigate mesoscale eddy signatures. Mesoscale eddies may modify the oxygen distribution in OMZs. However, in general eddies are less energetic in the ETNA south of the Cape Verde Islands compared to similar latitudes in the eastern tropical South Pacific.

scholarly journals The flow field of the upper hypoxic Eastern Tropical North Atlantic oxygen minimum zone

2015 ◽  
Vol 12 (5) ◽  
pp. 2147-2187
Author(s):  
L. Stramma ◽  
R. Czeschel ◽  
T. Tanhua ◽  
P. Brandt ◽  
M. Visbeck ◽  
...  
Keyword(s):  
North Atlantic ◽  
Oxygen Sensors ◽  
Oxygen Minimum Zone ◽  
Cape Verde ◽  
Surface Velocity ◽  
Cape Verde Islands ◽  
Near Surface ◽  
Tropical North Atlantic ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. A subsurface low oxygen zone is located in the eastern tropical North Atlantic Ocean (ETNA) in the upper ocean with the core of the hypoxic (O2 ≤ 60 μmol kg−1) oxygen minimum zone (OMZ) at 400 to 500 m depth. The poorly known subsurface circulation in the OMZ region is derived from observations and data assimilation results. Measurements in the eastern tropical North Atlantic in November/December 2008, in November/December 2009 and October/November 2010 of velocity, oxygen and of a tracer (CF3SF5) that was released in April 2008 at ∼ 8° N, 23° W (at ∼ 330 m depth) show circulation in the upper part of the OMZ with spreading to the east in the North Equatorial Countercurrent (NECC) region and northwestward around the Guinea Dome. Three floats equipped with oxygen sensors deployed at ∼ 8° N, 23° W with parking depths at 330, 350 and 400 m depths were used to estimate velocity along the float trajectory at the surface and at the park depth. South of 9° N, the zonal surface velocity estimate from float data alternate seasonally. At the 350 m park depth north of 9° N a cyclonic northwestward flow across the OMZ was observed. The northward shift into the upper OMZ and the cyclonic flow around the Guinea Dome seem to be connected to a strong Atlantic Meridional Mode (AMM) event in 2009. A near-surface cyclonic circulation cell east of the Cape Verde Islands expands into the OMZ layer. The circulation of the upper OMZ mirrors the near surface circulation. Oxygen measurements from the cruises used here, as well as other recent cruises up to the year 2014 confirm the continuous deoxygenation trend in the upper OMZ since the 1960's near the Guinea Dome. The three floats deployed with the tracer show spreading paths consistent with the overall observed tracer spreading. Mesoscale eddies may modify the oxygen distribution in the OMZs. Oxygen sensors on the floats remained well calibrated for more than 20 months and so the oxygen profiles can be used to investigate mesoscale eddy signatures. However, in general eddies are less energetic in the ETNA south of the Cape Verde Islands compared to similar latitudes in the Eastern Tropical South Pacific.

scholarly journals Water mass pathways to the North Atlantic oxygen minimum zone

2015 ◽  
Vol 120 (5) ◽  
pp. 3350-3372 ◽  
Author(s):  
Jesús Peña-Izquierdo ◽  
Erik van Sebille ◽  
Josep L. Pelegrí ◽  
Janet Sprintall ◽  
Evan Mason ◽  
...  
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Oxygen Minimum Zone ◽  
The North ◽  
Minimum Zone ◽  
The North Atlantic ◽  
Oxygen Minimum

scholarly journals Ventilation time scales of the North Atlantic subtropical cell revealed by coral radiocarbon from the Cape Verde Islands

2015 ◽  
Vol 30 (7) ◽  
pp. 938-948 ◽  
Author(s):  
Alvaro Fernandez ◽  
Thomas J. Lapen ◽  
Rasmus Andreasen ◽  
Peter K. Swart ◽  
Christopher D. White ◽  
...  
Keyword(s):  
Time Scales ◽  
North Atlantic ◽  
Cape Verde ◽  
Cape Verde Islands ◽  
Ventilation Time ◽  
The North ◽  
The North Atlantic ◽  
Subtropical Cell

scholarly journals Madrepora oculata forms large frameworks in hypoxic waters off Angola (SE Atlantic)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Covadonga Orejas ◽  
Claudia Wienberg ◽  
Jürgen Titschack ◽  
Leonardo Tamborrino ◽  
André Freiwald ◽  
...  
Keyword(s):  
North Atlantic ◽  
Environmental Conditions ◽  
Coral Community ◽  
Hypoxic Conditions ◽  
The North ◽  
Minimum Zone ◽  
The North Atlantic ◽  
Age Range ◽  
Local Oxygen ◽  
Oxygen Minimum

AbstractThis study aims to map the occurrence and distribution of Madrepora oculata and to quantify density and colony sizes across recently discovered coral mounds off Angola. Despite the fact that the Angolan populations of M. oculata thrive under extreme hypoxic conditions within the local oxygen minimum zone, they reveal colonies with remarkable heights of up to 1250 mm—which are the tallest colonies ever recorded for this species—and average densities of 0.53 ± 0.37 (SD) colonies m−2. This is particularly noteworthy as these values are comparable to those documented in areas without any oxygen constraints. The results of this study show that the distribution pattern documented for M. oculata appear to be linked to the specific regional environmental conditions off Angola, which have been recorded in the direct vicinity of the thriving coral community. Additionally, an estimated average colony age of 95 ± 76 (SD) years (total estimated age range: 16–369 years) indicates relatively old M. oculata populations colonizing the Angolan coral mounds. Finally, the characteristics of the Angolan populations are benchmarked and discussed in the light of the existing knowledge on M. oculata gained from the North Atlantic and Mediterranean Sea.

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.

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