The Equatorial Undercurrent and the Oxygen Minimum Zone in the Pacific

Busecke, Julius; Resplandy, Laure; Dunne, John

doi:10.1029/2019gl082692

Cited by 52 publications

(76 citation statements)

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“…The extension of extreme hypoxic zones over great depths drives extremely high organic carbon transfer efficiencies to deep waters ( Figure 19). Recent work has reinforced the hypothesis that higher resolution ocean models may partly address the bias by more fully resolving the equatorial jets ventilating the hypoxic regions (Busecke et al, 2019). Other lines of evidence have pointed to productivity biases linked to exogenous nutrient supplies (Cabré et al, 2015) or vertical zooplankton and fish migrations .…”

Section: Journal Of Advances In Modeling Earth Systemsmentioning

confidence: 95%

Ocean Biogeochemistry in GFDL's Earth System Model 4.1 and Its Response to Increasing Atmospheric CO₂

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Dunne

Fan

et al. 2020

J Adv Model Earth Syst

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This contribution describes the ocean biogeochemical component of the Geophysical Fluid Dynamics Laboratory's Earth System Model 4.1 (GFDL-ESM4.1), assesses GFDL-ESM4.1's capacity to capture observed ocean biogeochemical patterns, and documents its response to increasing atmospheric CO 2. Notable differences relative to the previous generation of GFDL ESM's include enhanced resolution of plankton food web dynamics, refined particle remineralization, and a larger number of exchanges of nutrients across Earth system components. During model spin-up, the carbon drift rapidly fell below the 10 Pg C per century equilibration criterion established by the Coupled Climate-Carbon Cycle Model Intercomparison Project (C4MIP). Simulations robustly captured large-scale observed nutrient distributions, plankton dynamics, and characteristics of the biological pump. The model overexpressed phosphate limitation and open ocean hypoxia in some areas but still yielded realistic surface and deep carbon system properties, including cumulative carbon uptake since preindustrial times and over the last decades that is consistent with observation-based estimates. The model's response to the direct and radiative effects of a 200% atmospheric CO 2 increase from preindustrial conditions (i.e., years 101-120 of a 1% CO 2 yr −1 simulation) included (a) a weakened, shoaling organic carbon pump leading to a 38% reduction in the sinking flux at 2,000 m; (b) a two-thirds reduction in the calcium carbonate pump that nonetheless generated only weak calcite compensation on century timescales ; and, in contrast to previous GFDL ESMs, (c) a moderate reduction in global net primary production that was amplified at higher trophic levels. We conclude with a discussion of model limitations and priority developments. Plain Language Summary This paper describes and evaluates the ocean biogeochemical component of the Geophysical Fluid Dynamics Laboratory's Earth System Model 4.1 (GFDL-ESM4.1). GFDL-ESM4.1 was developed to study the past, present, and future evolution of the Earth system under scenarios for natural and anthropogenic drivers of Earth system change, including greenhouse gases and aerosols. The response of the ocean's vast carbon and heat reservoirs to accumulating greenhouse gases greatly reduces their atmospheric and terrestrial impacts, but also puts ocean environments and the marine resources they support at risk. Relative to previous models, GFDL-ESM4.1 improves the representation of (a) ocean food webs connecting plankton and fish; (b) biological processes influencing the sequestration of carbon in the deep ocean; and (c) land-atmosphere-ocean nutrient exchanges. While simulations have biases, they capture many critical aspects of the global ocean carbon cycle and ocean ecosystem, including the observed uptake of anthropogenic carbon over the last~150 yr. Projections suggest that continued CO 2 increases could significantly decrease ocean productivity and the ocean's capacity to sequester atmospheric carbon.

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Section: Journal Of Advances In Modeling Earth Systemsmentioning

confidence: 95%

Ocean Biogeochemistry in GFDL's Earth System Model 4.1 and Its Response to Increasing Atmospheric CO₂

Stock

Dunne

Fan

et al. 2020

J Adv Model Earth Syst

Self Cite

122

137

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“…The northern low and southern high anomalies spread towards the tropics at intermediate depth. A fraction of the positive oxygen anomaly recirculates at upper thermocline level due to a combination of upwelling and zonal advection by the tropical current system (for instance the EUC at thermocline level is a major supplier of oxygen as shown in observations by Stramma et al, 2010 and in ocean models by Duteil et al, 2014, Busecke et al, 2019.…”

Section: Oxygen Levels In the Lower Thermoclinementioning

confidence: 96%

“…-the GFDL (Geophysical Fluid Dynamics Laboratory) CM2-0 suite (Delworth et al, 2012;Griffies et al, 2015, Dufour et al, 2015: the suite is based on the GFDL global climate model and includes a fully coupled atmosphere with a resolution of approximately 50 km. It consists of three configurations that differ in their ocean horizontal resolutions: GFDL1 with a nominal 1°r esolution, GFDL025 with a nominal 0.25° and GFDL01 with a nominal 0.1° resolution (e.g used in Frenger et al, 2018 andBusecke et al, 2019 for studies on ocean oxygen). The climate models are forced with preindustrial atmospheric pCO2 concentrations.…”

Section: Mean Statementioning

confidence: 99%

“…Consistent with the low oxygen bias of models at subtropical latitudes (Fig 2b), models also feature a bias in the tropical ocean (20°S-20°N) by 20 -50 mmol.m -3 (Fig 2a, Fig 2c) is less pronounced between the volume of the OMZs and the mean oxygen levels in the layer 500 -1500 m at 30°S (Fig 2e). Reasons of this weaker correlation are due to the OMZs being a result of several processes next to oxygen supply by IWM, e.g, vertical mixing with other water masses (Duteil et al, 2011), isopycnal mixing in the upper thermocline (Gnanadesikan et al, 2013;Bahl et al, 2019), supply by the upper thermocline circulation (Shigemitsu et al, 2017;Busecke et al, 2019). A correlation, even weak, suggests a major role of the IWM in regulating the OMZ volume In order to better understand the role of IWM entering the subtropical domain from higher latitudes for the oxygen levels in the eastern tropical Pacific Ocean, we perform sensitivity experiments (see 2.2.1) in the following.…”

Section: Iwm Oxygen Levels In Modelsmentioning

confidence: 99%

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Intermediate water masses, a major supplier of oxygen for the eastern tropical Pacific ocean

Duteil

Frenger

Getzlaff

2020

Preprint

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It is well known that Intermediate Water Masses (IWM) are sinking in high latitudes and ventilate the lower thermocline (500 -1500 m depth). We here highlight how the IWM oxygen content and the IWM pathway along the Equatorial Intermediate Current System (EICS) towards the eastern tropical Pacific ocean are essential for the supply of oxygen to the lower thermocline and the Oxygen Minimum Zones (OMZs). To this end, we assess here a heterogeneous subset of ocean models characterized by a horizontal resolution ranging from 0.1° to 2.8°. Subtropical oxygen levels in the lower thermocline, i.e., IWM are statistically correlated with tropical oxygen levels andOMZs. Sensitivity simulations suggest that the oxygen biases of the subtropical IWM oxygen levels contribute to oxygen biases of the tropical thermocline : an increase of the IWM oxygen by 60 mmol.m -3 results in a 10 mmol.m -3 increase in the tropical ocean in a timescale of 50 years. In the equatorial regions, the IWM recirculates into the Equatorial Intermediate Current System (EICS). By comparing tracer and particle release simulations, we show that a developed EICS increases eastern tropical ventilation by 30 %. Typical climate models lack in representing crucial aspects of this supply: biases in IWM properties are prominent across climate models and the EICS is basically absent in models with typical resolutions of ~1°. We emphasize that these biases need to be reduced in global climate models to allow reliable projections of OMZs in a changing climate.

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“…It seems not very appropriated to model OMZ borders, as these latter are found far north of 20 • N. If the aim of the study is to investigate the importance of DO physical supply, one may not ignore the ventilation processes at play in the OMZ borders (Bettencourt et al, 2015). And even in a case of tropical study (as reflected by the analyses restricted to 15 • S-15 • N), one may not ignore the critical representation of the equatorial undercurrent (EUC) to model the tropical OMZ structure (Busecke et al, 2019). As both processes are highly resolutiondependent (see for example Fig.…”

Section: General Commentsmentioning

confidence: 99%

Review of "Evaluation of asymmetric Oxygen Minimum Zones in the tropical Pacific: a basin-scale OGCM-DMEC V1.0" by Kai Wang, Xiujun Wang, Raghu Murtugudde, Dongxiao Zhang, Rong-Hua Zhang

Anonymous

2020

Preprint

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Wang and co-authors investigate the impacts of physical supply and biological consumption of dissolved oxygen (DO) on the dynamics and asymmetry of the OMZs in the tropical Pacific.They perform 4 numerical experiments to evaluate the sensibility of the mid-depth oxygen concentration to these aspects in their model, OGCM-DMEC v1.0. The physical supply is evaluated through the background diffusion parameterisation (that the authors test by changing a partial mixing parameter) and the effects of biological consumption on oxygen are tested by changing the C:O utilization ratio. The final aim is to advance their model capacity to simulate the oceanic oxygen cycle, and to explore the mechanisms driving the asymmetric OMZs in the tropical Pacific (introduction, l.67-68).

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The Equatorial Undercurrent and the Oxygen Minimum Zone in the Pacific

Cited by 52 publications

References 50 publications

Ocean Biogeochemistry in GFDL's Earth System Model 4.1 and Its Response to Increasing Atmospheric CO₂

Ocean Biogeochemistry in GFDL's Earth System Model 4.1 and Its Response to Increasing Atmospheric CO₂

Intermediate water masses, a major supplier of oxygen for the eastern tropical Pacific ocean

Review of "Evaluation of asymmetric Oxygen Minimum Zones in the tropical Pacific: a basin-scale OGCM-DMEC V1.0" by Kai Wang, Xiujun Wang, Raghu Murtugudde, Dongxiao Zhang, Rong-Hua Zhang

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The Equatorial Undercurrent and the Oxygen Minimum Zone in the Pacific

Cited by 52 publications

References 50 publications

Ocean Biogeochemistry in GFDL's Earth System Model 4.1 and Its Response to Increasing Atmospheric CO2

Ocean Biogeochemistry in GFDL's Earth System Model 4.1 and Its Response to Increasing Atmospheric CO2

Intermediate water masses, a major supplier of oxygen for the eastern tropical Pacific ocean

Review of &quot;Evaluation of asymmetric Oxygen Minimum Zones in the tropical Pacific: a basin-scale OGCM-DMEC V1.0&quot; by Kai Wang, Xiujun Wang, Raghu Murtugudde, Dongxiao Zhang, Rong-Hua Zhang

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Ocean Biogeochemistry in GFDL's Earth System Model 4.1 and Its Response to Increasing Atmospheric CO₂

Ocean Biogeochemistry in GFDL's Earth System Model 4.1 and Its Response to Increasing Atmospheric CO₂

Review of "Evaluation of asymmetric Oxygen Minimum Zones in the tropical Pacific: a basin-scale OGCM-DMEC V1.0" by Kai Wang, Xiujun Wang, Raghu Murtugudde, Dongxiao Zhang, Rong-Hua Zhang