Seasonal and spatial variations of Southern Ocean diapycnal mixing from Argo profiling floats

Wu, Lixin; Jing, Zhao; Riser, S.; Visbeck, Martin

doi:10.1038/ngeo1156

Cited by 106 publications

(106 citation statements)

References 29 publications

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“…However, diapycnal diffusivity from turbulent mixing in the open ocean thermocline only ranges from 5 × 10 −6 to 3 × 10 −5 m 2 s −1 (Gregg, 1998;Polzin et al, 1995). Therefore, it has been argued that elevated turbulent mixing concentrated over rough topography (Ledwell et al, 2000;Wu et al, 2011) would aid in explaining this discrepancy. In the past decade, elevated diapycnal diffusivities, i.e., O (10 −4 m 2 s −1 ) or higher, have been found in mixing hotspots such as seamounts (Carter et al, 2006;Lueck and Mudge, 1997), ridges (Klymak et al, 2006a;Lee et al, 2006), and canyons (Carter and Gregg, 2002).…”

Section: Introductionmentioning

confidence: 96%

“…Generally, microstructure measurements are fewer and more difficult than the fine-structure measurements (e.g., CTD and ADCP measurements), especially microstructure measurements in the deep sea. Therefore, to study the spatial and temporal distribution of turbulent mixing, researchers often resort to fine-scale parameterizations (Jing and Wu, 2010;Tian et al, 2009;Wu et al, 2011). In addition, fine-scale parameterizations would provide a reference for modelers.…”

Section: -D Shang Et Al: Spatial Distribution Of Turbulent Mixingmentioning

confidence: 99%

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Spatial distribution of turbulent mixing in the upper ocean of the South China Sea

2017

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Abstract. The spatial distribution of the dissipation rate (ε) and diapycnal diffusivity (κ) in the upper ocean of the South China Sea (SCS) is presented from a measurement program conducted from 26 April to 23 May 2010. In the vertical distribution, the dissipation rates below the surface mixed layer were predominantly high in the thermocline where shear and stratification were strong. In the regional distribution, high dissipation rates and diapycnal diffusivities were observed in the region to the west of the Luzon Strait, with an average dissipation rate and diapycnal diffusivity of 8.3 × 10 −9 W kg −1 and 2.7 × 10 −5 m 2 s −1 , respectively, almost 1 order of magnitude higher than those in the central and southern SCS. In the region to the west of the Luzon Strait, the water column was characterized by strong shear and weak stratification. Elevated dissipation rates (ε > 10 −7 W kg −1 ) and diapycnal diffusivities (κ > 10 −4 m 2 s −1 ), induced by shear instability, occurred in the water column. In the central and southern SCS, the water column was characterized by strong stratification and weak shear and the turbulent mixing was weak. Internal waves and internal tides generated near the Luzon Strait are expected to make a dominant contribution to the strong turbulent mixing and shear in the region to the west of the Luzon Strait. The observed dissipation rates were found to scale positively with the shear and stratification, which were consistent with the MacKinnon-Gregg model used for the continental shelf but different from the Gregg-Henyey scaling used for the open ocean.

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Section: Introductionmentioning

confidence: 96%

Section: -D Shang Et Al: Spatial Distribution Of Turbulent Mixingmentioning

confidence: 99%

Spatial distribution of turbulent mixing in the upper ocean of the South China Sea

2017

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“…Models of extreme simplification, while they can illuminate individual mechanisms, also discount the composite and complex essence of ocean observations. General circulation models used within a least-squares framework a priori provide a suitable framework to avoid misinterpreting observations (e.g., aliased small-scale signals) while taking advantage of complementary data sets (e.g., altimetry) and constraints (e.g., atmospheric reanalyses) to infer large-scale ocean balances and diagnose ocean variability (see Wunsch and Heimbach, 2013, for a review). However, the few publications that followed this approach to infer turbulent transport parameters (Stammer, 2005;Ferreira et al, 2005;Liu et al, 2012) provide little, if any, evaluation of the method and its results.…”

Section: G Forget Et Al: On the Observability Of Turbulent Transpormentioning

confidence: 99%

“…However, the vast collection of in situ profiles provided by Argo (Roemmich et al, 1999(Roemmich et al, , 2009) may offer new opportunities to infer turbulent transport rates from the sea surface to 2000 m depth. Inferences of diffusivities is possible through the analysis of Argo variance fields combined with conceptual turbulence models (Wu et al, 2011;Whalen et al, 2012;Cole et al, 2015). The extensive observation of the broad-scale hydrography characteristics by Argo may also provide a basis for the inversion of turbulent transport rates.…”

Section: Introductionmentioning

confidence: 99%

On the observability of turbulent transport rates by Argo: supporting evidence from an inversion experiment

2015

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Abstract. Although estimation of turbulent transport parameters using inverse methods is not new, there is little evaluation of the method in the literature. Here, it is shown that extended observation of the broad-scale hydrography by Argo provides a path to improved estimates of regional turbulent transport rates. Results from a 20-year ocean state estimate produced with the ECCO v4 (Estimating the Circulation and Climate of the Ocean, version 4) non-linear inverse modeling framework provide supporting evidence. Turbulent transport parameter maps are estimated under the constraints of fitting the extensive collection of Argo profiles collected through 2011. The adjusted parameters dramatically reduce misfits to in situ profiles as compared with earlier ECCO solutions. They also yield a clear reduction in the model drift away from observations over multi-century-long simulations, both for assimilated variables (temperature and salinity) and independent variables (biogeochemical tracers). Despite the minimal constraints imposed specifically on the estimated parameters, their geography is physically plausible and exhibits close connections with the upper-ocean stratification as observed by Argo. The estimated parameter adjustments furthermore have first-order impacts on upper-ocean stratification and mixed layer depths over 20 years. These results identify the constraint of fitting Argo profiles as an effective observational basis for regional turbulent transport rate inversions. Uncertainties and further improvements of the method are discussed.

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“…In a model study, Watanabe and Hibiya [2008] showed that most of the wind-induced near-inertial energy flux (hereafter denoted by WNEF) fed into the ocean interior is dissipated within the top 1000 m depth. Using high-resolution hydrographic profiles from Argo floats, Wu et al [2011] found that the seasonal variation of diapycnal mixing at a depth of 1500 m in the Southern Ocean can be largely attributed to the seasonal cycle of the WNEF over smooth topography. Their results are similar to Jing and Wu [2010] from a northwestern Pacific section at 137 E. However, in the subtropical northwestern Pacific and at Station ALOHA near Hawaii Ridge, turbulent mixing forced by wind work on near inertial motions was found to be confined within the upper 600 m [Jing and Wu, 2013;Jing et al, 2011].…”

mentioning

confidence: 99%

Penetration depth of diapycnal mixing generated by wind stress and flow over topography in the northwestern Pacific

Liu

2014

JGR Oceans

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The role of turbulent diapycnal mixing in the northwestern Pacific was estimated by employing a fine-scale parameterization method based on 6756 high-resolution CTD profiles spanning a period of 8 years from the Japan Oceanography Data Center (JODC) and the Kuroshio Extension System Study (KESS). The rate of turbulent mixing in the upper ocean within 300-1800 m depth displayed a distinct seasonal cycle, bearing a statistically significant correlation to wind-induced near-inertial energy flux (hereafter denoted by WNEF). Enhanced turbulent mixing was also found near the rough seafloor relative to that over smooth topography. Enhanced dissipation at surface and bottom was found to be able to penetrate the ocean interior up to 1800 m and 3300 m, respectively, with penetration depths varying with the WNEF and topographic roughness. Our study here provides evidence for the important role of near-inertial energy input from wind stress and the influence of bottom topography in maintaining mixing in the ocean interior.

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Seasonal and spatial variations of Southern Ocean diapycnal mixing from Argo profiling floats

Cited by 106 publications

References 29 publications

Spatial distribution of turbulent mixing in the upper ocean of the South China Sea

Spatial distribution of turbulent mixing in the upper ocean of the South China Sea

On the observability of turbulent transport rates by Argo: supporting evidence from an inversion experiment

Penetration depth of diapycnal mixing generated by wind stress and flow over topography in the northwestern Pacific

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