scholarly journals Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific oceans

2016 ◽  
Vol 13 (12) ◽  
pp. 3585-3606 ◽  
Author(s):  
Carolin R. Löscher ◽  
Hermann W. Bange ◽  
Ruth A. Schmitz ◽  
Cameron M. Callbeck ◽  
Anja Engel ◽  
...  
Keyword(s):  
Organic Matter ◽  
Nutrient Cycling ◽  
Ocean Circulation ◽  
North Atlantic ◽  
South Pacific ◽  
Gas Production ◽  
Biological Interactions ◽  
Oxygen Minimum Zones ◽  
Tropical North Atlantic ◽  
Oxygen Minimum

Abstract. Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence, the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs), which are connected to the most productive upwelling systems in the ocean. There are numerous feedbacks among oxygen concentrations, nutrient cycling and biological productivity; however, existing knowledge is insufficient to understand physical, chemical and biological interactions in order to adequately assess past and potential future changes. In the following, we summarize one decade of research performed in the framework of the Collaborative Research Center 754 (SFB754) focusing on climate–biogeochemistry interactions in tropical OMZs. We investigated the influence of low environmental oxygen conditions on biogeochemical cycles, organic matter formation and remineralization, greenhouse gas production and the ecology in OMZ regions of the eastern tropical South Pacific compared to the weaker OMZ of the eastern tropical North Atlantic. Based on our findings, a coupling of primary production and organic matter export via the nitrogen cycle is proposed, which may, however, be impacted by several additional factors, e.g., micronutrients, particles acting as microniches, vertical and horizontal transport of organic material and the role of zooplankton and viruses therein.

scholarly journals Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific Oceans

2015 ◽  
Vol 12 (6) ◽  
pp. 4495-4556 ◽  
Author(s):  
C. R. Löscher ◽  
H. W. Bange ◽  
R. A. Schmitz ◽  
C. M. Callbeck ◽  
A. Engel ◽  
...  
Keyword(s):  
Organic Matter ◽  
Nutrient Cycling ◽  
Water Column ◽  
North Atlantic ◽  
South Pacific ◽  
N2o Production ◽  
Oxygen Minimum Zones ◽  
Tropical North Atlantic ◽  
The Impact ◽  
Oxygen Minimum

Abstract. Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs). There are numerous feedbacks between oxygen concentrations, nutrient cycling and biological productivity; however, existing knowledge is insufficient to understand physical, chemical and biological interactions in order to adequately assess past and potential future changes. We investigated the pelagic biogeochemistry of OMZs in the eastern tropical North Atlantic and eastern tropical South Pacific during a series of cruise expeditions and mesocosm studies. The following summarizes the current state of research on the influence of low environmental oxygen conditions on marine biota, viruses, organic matter formation and remineralization with a particular focus on the nitrogen cycle in OMZ regions. The impact of sulfidic events on water column biogeochemistry, originating from a specific microbial community capable of highly efficient carbon fixation, nitrogen turnover and N2O production is further discussed. Based on our findings, an important role of sinking particulate organic matter in controlling the nutrient stochiometry of the water column is suggested. These particles can enhance degradation processes in OMZ waters by acting as microniches, with sharp gradients enabling different processes to happen in close vicinity, thus altering the interpretation of oxic and anoxic environments.

scholarly journals On the role of circulation and mixing in the ventilation of oxygen minimum zones with a focus on the eastern tropical North Atlantic

2014 ◽  
Vol 11 (8) ◽  
pp. 12069-12136 ◽  
Author(s):  
P. Brandt ◽  
D. Banyte ◽  
M. Dengler ◽  
S.-H. Didwischus ◽  
T. Fischer ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Oxygen Supply ◽  
Oxygen Minimum Zones ◽  
Oxygen Budget ◽  
Tropical North Atlantic ◽  
Oxygen Minimum ◽  
Oxygen Concentrations

Abstract. Ocean observations carried out in the framework of the Collaborative Research Center 754 (SFB 754) "Climate-Biogeochemistry Interactions in the Tropical Ocean" are used 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 depth with its core region centred at about 20° W, 10° N and a shallow OMZ at about 100 m depth with 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 time scales 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.

scholarly journals On the role of circulation and mixing in the ventilation of oxygen minimum zones with a focus on the eastern tropical North Atlantic

2015 ◽  
Vol 12 (2) ◽  
pp. 489-512 ◽  
Author(s):  
P. Brandt ◽  
H. W. Bange ◽  
D. Banyte ◽  
M. Dengler ◽  
S.-H. Didwischus ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Oxygen Supply ◽  
Oxygen Minimum Zones ◽  
Oxygen Budget ◽  
Tropical North Atlantic ◽  
Oxygen Minimum ◽  
Oxygen Concentrations

Abstract. 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.

Anoxic metabolism after the 21st century in oxygen minimum zones

2020 ◽  
Author(s):  
Wolfgang Koeve ◽  
Angela Landolfi
Keyword(s):  
Organic Matter ◽  
Ocean Circulation ◽  
Large Scale ◽  
Deep Ocean ◽  
Sulphate Reduction ◽  
Oxygen Minimum Zones ◽  
The Future ◽  
Ocean Models ◽  
The Impact ◽  
Oxygen Minimum

<p>Global models project a decrease of marine oxygen over the course of the 21th century. The future of marine oxygen becomes increasingly uncertain further into the future after yr 2100 , partly because ocean models differ in the way organic matter remineralisation continues under oxygen- and nitrate-free conditions. Using an Earth system model of intermediate complexity we found that under a business-as-usual CO2-emission scenario ocean deoxygenation further intensifies for several centuries until eventually ocean circulation re-establishes and marine oxygen increases again. (Oschlies et al. 2019, DOI 10.1038/s41467-019-10813-w).</p><p>In the Pacific Ocean the deoxygenation after yr 2100 goes along with the large scale loss of nitrate from oxygen minimum zones. Here we explore the impact on simulated ocean biogeochemistry of three different process formulation of anoxic metabolism, which have been used in other ocean models: (1) implicit sulphate reduction (organic matter degradation continues without oxidant), (2) no sulphidic metabolism (organic matter is not degraded under anoxic conditions), and (3) explicit sulphate reduction (with H2S as explicit model tracer). The model with explicit sulfphate reduction supports larger regional organic matter fluxed into the deep ocean and an increase in respired carbon storage, compared with the model applying implicit sulphate. We discuss the impact of anoxic metabolism on the coupling between export production and respired carbon stored in the ocean interior.</p>

scholarly journals Particle export fluxes to the oxygen minimum zone of the Eastern Tropical North Atlantic

2016 ◽  
Author(s):  
Anja Engel ◽  
Hannes Wagner ◽  
Frédéric A. C. Le Moigne ◽  
Samuel T. Wilson
Keyword(s):  
North Atlantic ◽  
Euphotic Zone ◽  
Carbon Export ◽  
Heterotrophic Activity ◽  
Oxygen Minimum Zones ◽  
Tropical North Atlantic ◽  
Water Layers ◽  
Minimum Zone ◽  
Particle Export ◽  
Oxygen Minimum

Abstract. In the ocean, sinking of particulate organic matter (POM) drives carbon export from the euphotic zone and supplies nutrition to mesopelagic communities, the feeding and degradation activities of which in turn lead to export flux attenuation. Oxygen minimum zones (OMZs) with suboxic water layers ( 100 μmol O2 kg−1), supposedly due to reduced heterotrophic activity. This study focuses on sinking particle fluxes through hypoxic mesopelagic waters (

scholarly journals Particle export fluxes to the oxygen minimum zone of the eastern tropical North Atlantic

2017 ◽  
Vol 14 (7) ◽  
pp. 1825-1838 ◽  
Author(s):  
Anja Engel ◽  
Hannes Wagner ◽  
Frédéric A. C. Le Moigne ◽  
Samuel T. Wilson
Keyword(s):  
Organic Matter ◽  
North Atlantic ◽  
Organic Phosphorus ◽  
Euphotic Zone ◽  
Carbon Export ◽  
Organic Matter Quality ◽  
B Values ◽  
Chl A ◽  
Tropical North Atlantic ◽  
Particle Export

Abstract. In the ocean, sinking of particulate organic matter (POM) drives carbon export from the euphotic zone and supplies nutrition to mesopelagic communities, the feeding and degradation activities of which in turn lead to export flux attenuation. Oxygen (O2) minimum zones (OMZs) with suboxic water layers (< 5 µmol O2 kg−1) show a lower carbon flux attenuation compared to well-oxygenated waters (> 100 µmol O2 kg−1), supposedly due to reduced heterotrophic activity. This study focuses on sinking particle fluxes through hypoxic mesopelagic waters (< 60 µmol O2 kg−1); these represent  ∼  100 times more ocean volume globally compared to suboxic waters, but they have less been studied. Particle export fluxes and attenuation coefficients were determined in the eastern tropical North Atlantic (ETNA) using two surface-tethered drifting sediment trap arrays with seven trapping depths located between 100 and 600 m. Data on particulate matter fluxes were fitted to the normalized power function Fz =  F100 (z∕100)−b, with F100 being the flux at a depth (z) of 100 m and b being the attenuation coefficient. Higher b values suggest stronger flux attenuation and are influenced by factors such as faster degradation at higher temperatures. In this study, b values of organic carbon fluxes varied between 0.74 and 0.80 and were in the intermediate range of previous reports, but lower than expected from seawater temperatures within the upper 500 m. During this study, highest b values were determined for fluxes of particulate hydrolyzable amino acids (PHAA), followed by particulate organic phosphorus (POP), nitrogen (PN), carbon (POC), chlorophyll a (Chl a) and transparent exopolymer particles (TEP), pointing to a sequential degradation of organic matter components during sinking. Our study suggests that in addition to O2 concentration, organic matter composition co-determines transfer efficiency through the mesopelagic. The magnitude of future carbon export fluxes may therefore also depend on how organic matter quality in the surface ocean changes under influence of warming, acidification and enhanced stratification.

scholarly journals Modulation of the vertical particles transfer efficiency in the Oxygen Minimum Zone off Peru

2018 ◽  
Author(s):  
Marine Bretagnon ◽  
Aurélien Paulmier ◽  
Véronique Garçon ◽  
Boris Dewitte ◽  
Sérena Illig ◽  
...  
Keyword(s):  
Organic Matter ◽  
Water Column ◽  
Sediment Traps ◽  
Biogeochemical Cycles ◽  
High Temporal Resolution ◽  
Oxygen Minimum Zones ◽  
Marine Life ◽  
Minimum Zone ◽  
Earth’S System ◽  
Oxygen Minimum

Abstract. The fate of the Organic Matter (OM) produced by marine life controls the major biogeochemical cycles of the Earth’s system. The OM produced through photosynthesis is either preserved, exported towards sediments or degraded through remineralisation in the water column. The productive Eastern Boundary Upwelling Systems (EBUSs) associated with Oxygen Minimum Zones (OMZs) should foster OM preservation due to low O2 conditions, but their intense and diverse microbial activity should enhance OM degradation. To investigate this contradiction, sediment traps were deployed near the oxycline and in the OMZ core on an instrumented moored line off Peru, providing high temporal resolution O2 series characterizing two seasonal steady states at the upper trap: suboxic ([O2] 

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 Anthropogenic carbon in the eastern South Pacific Ocean

2007 ◽  
Vol 4 (3) ◽  
pp. 1815-1837 ◽  
Author(s):  
L. Azouzi ◽  
R. Gonçalves Ito ◽  
F. Touratier ◽  
C. Goyet
Keyword(s):  
Pacific Ocean ◽  
General Trend ◽  
South Pacific ◽  
Hydrodynamic Characteristics ◽  
Eastern Pacific Ocean ◽  
Previous Knowledge ◽  
Oxygen Minimum Zones ◽  
South Pacific Ocean ◽  
Anthropogenic Carbon ◽  
Oxygen Minimum

Abstract. We present results from the BIOSOPE cruise in the eastern South Pacific Ocean. In particular, we present estimates of the anthropogenic carbon CantTrOCA distribution in this area using the TrOCA method recently developed by Touratier and Goyet (2004a, b) and Touratier et al. (2007). We study the distribution of this anthropogenic carbon taking into account of the hydrodynamic characteristics of this region. We then compare these results with earlier estimates in nearby areas of the anthropogenic carbon as well as other anthropogenic tracer (CFC-11). The highest concentrations of CantTrOCA are located around 13° S 132° W and 32° S 91° W, and their concentrations are larger than 80 μmol kg−1 and 70 μmol kg−1, respectively. The lowest concentrations were observed below 800 m depths (≤2 μ mol kg−1) and at the Oxygen Minimum Zones (OMZ), mainly around 140° W (<11 μmol kg−1). The comparison with earlier work in nearby areas provides a general trend and indicates that the results presented here are in general agreement with previous knowledge. This work further improves our understanding on the penetration of anthropogenic carbon in the eastern Pacific Ocean.

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