Temporal variability of diapycnal mixing in the northern South China Sea

Sun, Hui; Yang, Qingxuan; Zhao, Wei; Liang, Xinfeng; Tian, Jiwei

doi:10.1002/2016jc012044

Cited by 15 publications

(10 citation statements)

References 39 publications

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“…It is reasonable to expect that the dissipation of mesoscale eddy energy is a possible mechanism to maintain turbulent mixing in the SCS. Although a few studies tried to explore the influence of mesoscale eddies on the turbulent mixing in the SCS 21,22 , the relationship between eddy dissipation and mixing are needed to be improved. The goal of this study is to inspect possible contribution of mesoscale eddies to small scale mixing using numerical simulation with a high horizontal resolution of 1/30° (see Methods).…”

Section: Introductionmentioning

confidence: 99%

Dissipation of mesoscale eddies and its contribution to mixing in the northern South China Sea

Yang

Nikurashin

Sasaki

et al. 2019

Sci Rep

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It is reported that turbulent mixing is enhanced in the South China Sea (SCS), and it is highly variable in both space and time. Generation and breaking of internal tides has been identified as the main process to drive turbulent mixing in the SCS, while the contributions from other processes are not clear enough. Here we investigate the potential contribution from mesoscale eddies to turbulent mixing in the SCS using a high resolution numerical simulation. Our results show that mesoscale eddies in the SCS effectively dissipate over complex rough topography and indicate that the generation of submesoscale motions and lee waves are two pathways for the transfer of mesoscale eddy energy down to small dissipation scales. The energy loss from mesoscale eddies near the Xisha Islands is estimated to be sufficient to sustain turbulent kinetic energy dissipation rate of O (10−8) W/kg. This study suggests an alternative and potentially efficient mechanism to internal tides for the local maintenance of turbulent mixing in the SCS.

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Section: Introductionmentioning

confidence: 99%

Dissipation of mesoscale eddies and its contribution to mixing in the northern South China Sea

Yang

Nikurashin

Sasaki

et al. 2019

Sci Rep

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“…Those 410 studies are difficult to arrange with conventional research vessel surveys only. Autonomous measurement platforms, such are profiling moorings (Lips et al, 2016;Sun et al, 2016), moored sensor chains (Bailey et al, 2019;Venkatesan et al, 2016), which allow capturing the variability in necessary vertical-temporal resolution can be used. Underwater gliders (Liblik et al, 2016;Rudnick, 2016) might be complicated to use due to strong tidal velocities and heavy ship traffic, but are worthy to consider as well.…”

Section: Discussionmentioning

confidence: 99%

Wind-driven stratification patterns and dissolved oxygen depletion in the area off the Changjiang (Yangtze) Estuary

Liblik

Fan

2019

Preprint

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Abstract. The area off the Changjiang Estuary is under strong impact of fresh water and anthropogenic nutrient load from the Changjiang River. The seasonal hypoxia in the area has variable location and range, but the decadal trend reveals expansion and intensification of the dissolved oxygen (DO) depletion. Two oceanographic cruises, conducted in summer 2015 and 2017, revealed very different stratification and DO conditions in the area. Strongly inclined oxycline well correlated with the thermocline in both years. Southerly wind caused reversal of the Chinese Coastal Current and as a result, spreading of the CDW (Changjiang Diluted Water) caused pronounced hypoxic zone in the area east and northeast of the river mouth in 2017. Hypoxic layer started right below the CDW layer at 5&#8211;8&#8201;m depth and extended down to bottom. Strong DO depletion was also observed in the shallow coastal slope in the southern part of the study area. High DO utilization there closely coincided with the interaction zone of the upwelling and fresher surface water. The stratification and hypoxia pattern observed in the area in 2017 is prevailing phenomena during summers if considering the long-term wind statistics. Northeasterly winds supported southward transport of the CDW before the survey in 2015. Consequently, low DO was found in the southern part of the study area while subsurface layer in the northern part was ventilated. Weaker than long-term average summer monsoon is required for the existence of such pattern. Importance of the wind forcing was confirmed by remotely sensed sea surface salinity fields and by circulation simulation. We suggest wind forcing, together with river run-off are likely main contributors of determining the synoptic, seasonal and inter-annual time scale variations of the extent and location of low DO areas off the Changjiang Estuary.

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“…As pointed out by Hui and Xu (), the total surface currents in the open ocean are mainly determined by the Ekman currents and geostrophic currents. H. Sun, Yang, et al () and S. Sun, Fang, et al () showed that the geostrophic currents generated by mesoscale eddies can significantly change the SST when there was a SST front. As shown in Figure , the GCA is much smaller than the local AGC but is significant along Transects A and B (28 ± 10 cm/s).…”

Section: Scaling Of Tke Dissipation Ratementioning

confidence: 99%

“…The enhanced surface TKE dissipation rates observed in the Kuroshio Extension region can be well scaled by an empirical scaling that considers the EBF and the wind (D'Asaro et al, ; Nagai et al, ). The mesoscale eddies also have important effect on turbulence mixing (H. Sun, Yang, et al, ; S. Sun, Fang, et al, ; Yang et al, , ). Recent observations have shown that active submesoscale motions exist in the periphery of mesoscale eddies and can significantly elevate the TKE dissipation rates in the mixed layer (Yang et al, ).…”

Section: Introductionmentioning

confidence: 99%

Effect of a Mesoscale Eddy on Surface Turbulence at the Kuroshio Front in the East China Sea

et al. 2019

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Field observations were conducted along three west‐east transects in the East China Sea Kuroshio Front in July 2017. The microstructure observations results show that the surface turbulence kinetic energy (TKE) dissipation rates in the northern and southern transects are about 2 orders larger than those in the middle transect. The sea surface temperature, mixed layer depth, and the submesoscale motions (with horizontal scales smaller than 30 km) also suggest the surface turbulences are more active in the northern and southern transects. The current velocity data and sea level anomaly show that the middle transect was located at the northern edge of a cyclonic eddy. The eddy‐generated cross‐front geostrophic current was observed to flow toward the opposite direction of the cross‐front Ekman transport and believed to counteract the Ekman buoyancy flux (EBF)‐induced turbulence enhancement. The TKE dissipation rates can be well scaled by a scaling considering the EBF and the wind in the northern and southern transects but wind scaling only in the middle transect, suggesting the EBF does not contribute to the surface turbulence in the middle transect. An improved empirical scaling considering the cross‐front geostrophic current is defined and can scale the TKE dissipation rates better, indicating an eddy plays a key role in surface turbulent mixing in the East China Sea Kuroshio front.

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Temporal variability of diapycnal mixing in the northern South China Sea

Cited by 15 publications

References 39 publications

Dissipation of mesoscale eddies and its contribution to mixing in the northern South China Sea

Dissipation of mesoscale eddies and its contribution to mixing in the northern South China Sea

Wind-driven stratification patterns and dissolved oxygen depletion in the area off the Changjiang (Yangtze) Estuary

Effect of a Mesoscale Eddy on Surface Turbulence at the Kuroshio Front in the East China Sea

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