Tracing ventilation source of tropical pacific oxygen minimum zones with an adjoint global ocean transport model

2018 ◽  
Vol 139 ◽  
pp. 95-103
Author(s):  
Weiwei Fu ◽  
Ann Bardin ◽  
François Primeau
Keyword(s):  
Transport Model ◽  
Tropical Pacific ◽  
Global Ocean ◽  
Oxygen Minimum Zones ◽  
Oxygen Minimum

scholarly journals Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends

2015 ◽  
Vol 12 (8) ◽  
pp. 6525-6587 ◽  
Author(s):  
A. Cabré ◽  
I. Marinov ◽  
R. Bernardello ◽  
D. Bianchi
Keyword(s):  
Climate Change ◽  
Tropical Pacific ◽  
Cmip5 Models ◽  
Upper Ocean ◽  
Intermediate Water ◽  
Climate Change Projections ◽  
Oxygen Minimum Zones ◽  
Mean State ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. We analyze simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth System model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean combined with a too large biologically-driven downward flux of particulate organic carbon at depth, caused by too high particle export from the euphotic layer and too weak remineralization in the upper ocean. At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific. Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface, deep and high latitudes ocean due to an overall slow-down of ventilation and increased temperature.

scholarly journals Following the N<sub>2</sub>O consumption in the oxygen minimum zone of the eastern South Pacific

2012 ◽  
Vol 9 (8) ◽  
pp. 3205-3212 ◽  
Author(s):  
M. Cornejo ◽  
L. Farías
Keyword(s):  
Primary Productivity ◽  
High Reliability ◽  
South Pacific ◽  
Global Ocean ◽  
Field Observations ◽  
N2o Production ◽  
Oxygen Minimum Zones ◽  
Minimum Zone ◽  
Existing Data ◽  
Oxygen Minimum

Abstract. Oxygen minimum zones (OMZs), such as those found in the eastern South Pacific (ESP), are the most important N2O sources in the global ocean relative to their volume. N2O production is related to low O2 concentrations and high primary productivity. However, when O2 is sufficiently low, canonical denitrification takes place and N2O consumption can be expected. N2O distribution in the ESP was analyzed over a wide latitudinal and longitudinal range (from 5° to 30° S and from 71–76° to ~ 84° W) based on ~ 890 N2O measurements. Intense N2O consumption, driving undersaturations as low as 40%, was always associated with secondary NO2– accumulation (SNM), a good indicator of suboxic/anoxic O2 levels. First, we explore relationships between ΔN2O and O2 based on existing data of denitrifying bacteria cultures and field observations. Given the uncertainties in the O2 measurements, a second relationship between ΔN2O and NO2– (> 0.75 μM) was established for suboxic waters (O2 < 8 μM). We reproduced the apparent N2O production (ΔN2O) along the OMZ in ESP with high reliability (r2 = 0.73 p = 0.01). Our results will contribute to the quantification of the N2O that is recycled in O2 deficient waters, and improve the prediction of N2O behavior under future scenarios of OMZ expansion and intensification.

scholarly journals Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends

2015 ◽  
Vol 12 (18) ◽  
pp. 5429-5454 ◽  
Author(s):  
A. Cabré ◽  
I. Marinov ◽  
R. Bernardello ◽  
D. Bianchi
Keyword(s):  
Climate Change ◽  
Tropical Pacific ◽  
Cmip5 Models ◽  
Upper Ocean ◽  
Intermediate Water ◽  
Climate Change Projections ◽  
Oxygen Minimum Zones ◽  
Mean State ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. We analyse simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean, combined with too large a biologically driven downward flux of particulate organic carbon at depth, caused by particle export from the euphotic layer that is too high and remineralization in the upper ocean that is too weak. At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific. Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface and deep ocean at low latitudes and over all depths at high latitudes due to an overall slow-down of ventilation and increased temperature.

scholarly journals Evaluation of asymmetric Oxygen Minimum Zones in the tropical Pacific: a basin-scale OGCM-DMEC V1.0

2020 ◽  
Author(s):  
Kai Wang ◽  
Xiujun Wang ◽  
Raghu Murtugudde ◽  
Dongxiao Zhang ◽  
Rong-Hua Zhang
Keyword(s):  
Model Simulation ◽  
Tropical Pacific ◽  
Scale Model ◽  
Oxygen Minimum Zones ◽  
The North ◽  
Basin Scale ◽  
Dominant Process ◽  
Fully Coupled ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. The tropical Pacific Ocean holds the world’s two largest Oxygen Minimum Zones (OMZs), showing a prominent hemispheric asymmetry, with a much stronger and broader OMZ north of the equator. However, there is a lack of quantitative assessments of physical and biological regulations on the asymmetry of tropical Pacific OMZs. Here, we apply a fully coupled basin-scale model (OGCM-DMEC V1.0) to investigate the impacts of physical supply and biological consumption on the dynamics of OMZs in the tropical Pacific. We first utilize observational data to evaluate and improve our model simulation, and find that mid-depth DO is more sensitive to the parameterization of background diffusion. Enhanced background diffusion results in higher DO concentrations at mid-depth, leading to significant improvement of our model capability to reproduce the asymmetric OMZs. Our study shows that while physical supply of DO is increased in majority of the tropical Pacific due to enhanced background diffusion, there is little increase in the largest OMZ to the north. Interestingly, enhanced background diffusion results in lower rates of biological consumption over ~ 300–1000 m in the entire basin, which is associated with redistribution of dissolved organic matter (DOM). Our analyses demonstrate that weaker physical supply in the ETNP is the dominant process responsible for the asymmetric DO in the core OMZs (~ 200–600 m) while higher biological consumption to the north plays a larger role in regulating DO concentration beneath the OMZs (~ 600–800 m), with implication for the asymmetric OMZs. This study highlights the roles of physical supply and biological consumption in shaping the asymmetric OMZs in the tropical Pacific, underscoring the need to understand both physical and biological processes for accurate projections of DO variability.

scholarly journals Parallel Evolution of Key Genomic Features and Cellular Bioenergetics Across the Marine Radiation of a Bacterial Phylum

2018 ◽  
Author(s):  
Eric W. Getz ◽  
Saima Sultana Tithi ◽  
Liqing Zhang ◽  
Frank O. Aylward
Keyword(s):  
Nutrient Dynamics ◽  
Genomic Organization ◽  
Parallel Evolution ◽  
Global Ocean ◽  
Oxygen Minimum Zones ◽  
Respiratory Complex ◽  
Respiratory Complex I ◽  
Cellular Bioenergetics ◽  
Key Features ◽  
Oxygen Minimum

AbstractDiverse bacterial and archaeal lineages drive biogeochemical cycles in the global ocean, but the evolutionary processes that have shaped their genomic properties and physiological capabilities remain obscure. Here we track the genome evolution of the globally-abundant marine bacterial phylum Marinimicrobia across its diversification into modern marine environments and demonstrate that extant lineages have repeatedly switched between epipelagic and mesopelagic habitats. Moreover, we show that these habitat transitions have been accompanied by repeated and fundamental shifts in genomic organization, cellular bioenergetics, and metabolic modalities. Lineages present in epipelagic niches independently acquired genes necessary for phototrophy and environmental stress mitigation, and their genomes convergently evolved key features associated with genome streamlining. Conversely, lineages residing in mesopelagic waters independently acquired nitrate respiratory machinery and a variety of cytochromes, consistent with the use of alternative terminal electron acceptors in oxygen minimum zones (OMZs). Further, while surface water clades have retained an ancestral Na+-pumping respiratory complex, deep water lineages have largely replaced this complex with a canonical H+-pumping respiratory complex I, potentially due to the increased efficiency of the latter together with more energy-limiting environments deep in the ocean’s interior. These parallel evolutionary trends across disparate clades suggest that the evolution of key features of genomic organization and cellular bioenergetics in abundant marine lineages may in some ways be predictable and driven largely by environmental conditions and nutrient dynamics.

scholarly journals Sensitivity of asymmetric Oxygen Minimum Zones to remineralization rate and mixing intensity in the tropical Pacific using a basin-scale model (OGCM-DMEC V1.2)

2021 ◽  
Author(s):  
Kai Wang ◽  
Xiujun Wang ◽  
Raghu Murtugudde ◽  
Dongxiao Zhang ◽  
Rong-Hua Zhang
Keyword(s):  
Vertical Mixing ◽  
Tropical Pacific ◽  
Scale Model ◽  
Oxygen Minimum Zones ◽  
The North ◽  
Basin Scale ◽  
Dominant Process ◽  
Fully Coupled ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. The tropical Pacific Ocean holds the world’s two largest Oxygen Minimum Zones (OMZs), showing a prominent hemispheric asymmetry, with a much stronger and broader OMZ north of the equator. However, many models have difficulties in reproducing the observed asymmetric OMZs in the tropical Pacific. Here, we apply a fully coupled basin-scale model (OGCM-DMEC V1.2) to evaluate the impacts of remineralization rate and the intensity of vertical mixing on the dynamics of OMZs in the tropical Pacific. We first utilize observational data of dissolved oxygen (DO), dissolved organic nitrogen (DON) and oxygen consumption to calibrate and validate the basin-scale model. Our model experiments demonstrate that enhanced vertical mixing combined with reduced remineralization rate can significantly improve our model capability of reproducing the asymmetric OMZs. Our study shows that DO is more sensitive to biological processes over 200–400 m but to physical processes over 400–1000 m. Enhanced vertical mixing not only causes an increase in DO supply at mid-depth, but also results in lower rates of biological consumption in the OMZs, which is associated with redistribution of DON. Our analyses demonstrate that weaker physical supply in the ETNP is the dominant process responsible for the asymmetry of the lower OMZs whereas greater biological consumption to the north plays a larger role in regulating the upper OMZs. This study highlights the complex roles of physical supply and biological consumption in shaping the asymmetric OMZs in the tropical Pacific.

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