Variations in Ocean Deoxygenation Across Earth System Models: Isolating the Role of Parameterized Lateral Mixing

Bahl, Alexis; Gnanadesikan, Anand; Pradal, Marie-Aude

doi:10.1029/2018gb006121

Cited by 37 publications

(52 citation statements)

References 70 publications

(112 reference statements)

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“…ABER2D uses the distribution found by Abernathey and Marshall (2013), who used velocities derived from altimetric measurements to advect tracers and invert a diffusion coefficient. Maps of this coefficient can be found in previous work (Gnanadesikan et al, 2015a,b;Bahl et al, 2019, Figure 2) and in the Supplemental Material.…”

Section: Experimental Designmentioning

confidence: 89%

“…Because the response of the Earth System is dependent on a multitude of parameterizations a full exploration of the third question is impossible in one manuscript. However, we know from previous work (Palter and Trossman, 2018;Bahl et al, 2019) that the response of oceanic oxygen to global warming is extremely sensitive to the representation of lateral mixing from oceanic mesoscale eddies. While mesoscale eddies dominate both spatial and temporal variability in velocity (Lermusiaux, 2006), they occur at spatial scales that are generally smaller than the grid boxes used in models.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, simulating long-term biogeochemical cycles will require that the effects of eddy velocity variability on the large-scale tracer field be parameterized for the foreseeable future. In this study we take advantage of key insights gained from Bahl et al (2019) to examine how this uncertainty is reflected in the linearity of biogeochemical response. The key variable or parameter used to represent the lateral mixing due to turbulent eddies is the turbulent diffusion coefficient, A REDI (Redi, 1982).…”

Section: Introductionmentioning

confidence: 99%

“…The key variable or parameter used to represent the lateral mixing due to turbulent eddies is the turbulent diffusion coefficient, A REDI (Redi, 1982). In previous work we have shown how the ocean uptake of anthropogenic carbon dioxide (Gnanadesikan et al, 2015a), as well as the patterns and rates of oceanic deoxygenation (Bahl et al, 2019), are impacted by the value and/or spatial distribution of this parameter. However, we have not examined the impact of changing diffusivity on the linearity of response.…”

Section: Introductionmentioning

confidence: 99%

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Scaling Global Warming Impacts on Ocean Ecosystems: Lessons From a Suite of Earth System Models

2020

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An important technique used by climate modelers to isolate the impacts of increasing greenhouse gasses on Earth System processes is to simulate the impact of an abrupt increase in carbon dioxide. The spatial pattern of change provides a "fingerprint" that is generally much larger than natural variability. Insofar as the response to radiative forcing is linear (the impact of quadrupling CO 2 is twice the impact of doubling CO 2) this fingerprint can then be used to estimate the impact of historical greenhouse gas forcing. However, the degree to which biogeochemical cycles respond linearly to radiative forcing has rarely been tested. In this paper, we evaluate which ocean biogeochemical fields are likely to respond linearly to changing radiative forcing, which ones do not, and where linearity breaks down. We also demonstrate that the representation of lateral mixing by mesoscale eddies, which varies significantly across climate models, plays an important role in modulating the breakdown of linearity. Globally integrated surface rates of biogeochemical cycling (primary productivity, particulate export) respond in a relatively linear fashion and are only moderately sensitive to mixing. By contrast, the habitability of the interior ocean (as determined by hypoxia and calcite supersaturation) behaves non-linearly and is very sensitive to mixing. This is because the deep ocean, as well as certain regions in the surface ocean, are very sensitive to the magnitude of deep wintertime convection. The cessation of convection under global warming is strongly modulated by the representation of eddy mixing.

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Section: Experimental Designmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Scaling Global Warming Impacts on Ocean Ecosystems: Lessons From a Suite of Earth System Models

2020

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“…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%

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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Bottom mixed layer oxygen dynamics in the Celtic Sea

et al. 2020

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The seasonally stratified continental shelf seas are highly productive, economically important environments which are under considerable pressure from human activity. Global dissolved oxygen concentrations have shown rapid reductions in response to anthropogenic forcing since at least the middle of the twentieth century. Oxygen consumption is at the same time linked to the cycling of atmospheric carbon, with oxygen being a proxy for carbon remineralisation and the release of CO2. In the seasonally stratified seas the bottom mixed layer (BML) is partially isolated from the atmosphere and is thus controlled by interplay between oxygen consumption processes, vertical and horizontal advection. Oxygen consumption rates can be both spatially and temporally dynamic, but these dynamics are often missed with incubation based techniques. Here we adopt a Bayesian approach to determining total BML oxygen consumption rates from a high resolution oxygen time-series. This incorporates both our knowledge and our uncertainty of the various processes which control the oxygen inventory. Total BML rates integrate both processes in the water column and at the sediment interface. These observations span the stratified period of the Celtic Sea and across both sandy and muddy sediment types. We show how horizontal advection, tidal forcing and vertical mixing together control the bottom mixed layer oxygen concentrations at various times over the stratified period. Our muddy-sand site shows cyclic spring-neap mediated changes in oxygen consumption driven by the frequent resuspension or ventilation of the seabed. We see evidence for prolonged periods of increased vertical mixing which provide the ventilation necessary to support the high rates of consumption observed.

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Variations in Ocean Deoxygenation Across Earth System Models: Isolating the Role of Parameterized Lateral Mixing

Cited by 37 publications

References 70 publications

Scaling Global Warming Impacts on Ocean Ecosystems: Lessons From a Suite of Earth System Models

Scaling Global Warming Impacts on Ocean Ecosystems: Lessons From a Suite of Earth System Models

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

Bottom mixed layer oxygen dynamics in the Celtic Sea

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