Deep Sea Currents Driven by Breaking Internal Tides on the Continental Slope

Xie, Xiang; Liu, Qian; Zhao, Zhenwei; Shang, Xiaodong; Cai, Shuqun; Wang, Dongxiao; Chen, Dake

doi:10.1029/2018gl078372

Cited by 35 publications

(32 citation statements)

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“…The South China Sea (SCS) is a semienclosed basin with energetic internal tides originating from the Luzon Strait (LS) and propagating westward across the center basin (Alford et al, ; Cai et al, ). Over the recent decade, a large number of observations and simulations have been carried out to investigate problems such as characteristics, generation, evolution, dissipation, and variability of internal tides in the northeastern SCS, including the LS (Buijsman et al, ; Buijsman et al, ; Huang et al, ; Jan et al, ; Pickering et al, ; Xie et al, ). However, because of the lack of in situ data, baroclinic tides in the northwestern SCS (NWSCS) are still poorly understood.…”

Section: Introductionmentioning

confidence: 99%

Seasonal and Spatial Features of Barotropic and Baroclinic Tides in the Northwestern South China Sea

Tong

Jing

et al. 2020

JGR Oceans

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Seven seasonal moorings distributed over the shelf and slope east of Hainan Island and south of western Guangdong Province are used to investigate the seasonal characteristics of barotropic and baroclinic tides in the northwestern South China Sea (NWSCS). The barotropic K 1 current intensified during summer over the shelf sites. The diurnal baroclinic tides are much more prominent than the semidiurnal tides at each mooring site. Over the continental shelf, accompanied by large phase speeds and wavelengths, baroclinic tides are significantly enhanced in summer whereas they decrease to minimum values in winter when the water column is vertically well mixed, suggesting the key role of seasonal stratification in modulating the seasonal variation of baroclinic tide. To aid in elucidating these observations, a circulation-tide coupled model covering the whole South China Sea (SCS) is set up for baroclinic tidal energetics in the NWSCS. Comparisons with moorings, tidal gauges, altimeters, and so on show that the model reasonably predicts the barotropic and baroclinic tides and seasonal upper circulations in the SCS and NWSCS. The model results present significant summer intensification of barotropic K 1 energy in the NWSCS, which is in accordance with the observed summer-enhanced barotropic K 1 current. Strong baroclinic tides are reproduced over the summer shelf, which is related to intense stratification. The slope south of Hainan Island is a major local generation source for diurnal baroclinic tides that radiate southeastward approximately 500 km away. Both the Xisha Islands and Shenhu-Yitong shoals act as baroclinic tidal energy sink subregions. Plain Language Summary The South China Sea (SCS) is a semienclosed marginal basin wherethe diurnal barotropic tide is amplified because of the resonance, and the baroclinic tide is extremely active. Previous studies on baroclinic tides in the SCS mainly focused on the northeastern SCS and Luzon Strait. Due to limited in situ observations, the basic characteristics of baroclinic tides and their seasonality in the northwestern SCS (NWSCS) are rarely reported. Past sporadic research has demonstrated the existence of baroclinic tides in the Xisha Islands and northeastern shelf of Hainan Island by short-term observations. In the present paper, a large amount of in situ data, including seven seasonal ADCPs and CTDs, is used to identify the seasonal characteristics of barotropic and baroclinic tides over the shelf and slope east of Hainan Island and the shelf southeast of western Guangdong Province. Subsequently, a high-resolution circulation-tide coupled ocean model for SCS is used to analyze the seasonal distribution of baroclinic tide energetics in the NWSCS. Multiple sources, integrated baroclinic tidal energy fluxes and energy budgets for three important subregions, are identified by the model results, which have been validated with diverse data sets.

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Section: Introductionmentioning

confidence: 99%

Seasonal and Spatial Features of Barotropic and Baroclinic Tides in the Northwestern South China Sea

Tong

Jing

et al. 2020

JGR Oceans

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“…However, due to the sparsity of in-situ observations, little is known about the spatial structure of the currents and the variability of the deep circulation, especially in the sub-inertial range. The direct impacts of the (sub-)mesoscale eddies and internal waves on the mean flow in such realistic configuration remain largely unknown as well, while several possible mechanisms have been identified (Holloway and Wang, 2009;Venaille et al, 2011;Grisouard and Bühler, 2012;Xie et al, 2018). For instance, Clément and Thurnherr (2018) recently reported evidence of non-linear interactions between internal waves and the mean flow in a submarine valley, thus showing that these mechanisms could play a significant role in the deep-ocean dynamics.…”

Section: Introductionmentioning

confidence: 99%

Deep Currents in the Rift Valley of the North Mid-Atlantic Ridge

et al. 2019

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Over mid-ocean ridges, the interaction between the currents and the topography gives rise to complex flows, which drive the transport properties of biogeochemical constituents, and especially those associated with hydrothermal vents, thus impacting associated ecosystems. This paper describes the circulation in the rift valley along the Azores sector of the North Mid-Atlantic Ridge, using a combination of in-situ data from several surveys and realistic high-resolution modeling. It confirms the presence of a mean deep current with an up-valley branch intensified along the right inner flank of the valley (looking downstream), and a weaker down-valley branch flowing at shallower depth along the opposite flank. The hydrographic properties of the rift-valley water, and in particular the along-valley density gradient that results from a combination of the topographic isolation, the deep flow and the related mixing, are quantified. We also show that the deep currents exhibit significant variability and can be locally intense, with typical values greater than 10 cm/s. Finally, insights on the dynamical forcings of the deep currents and their variability are provided using numerical simulations, showing that tidal forcing of the mean circulation is important and that the overlying mesoscale turbulence triggers most of the variability.

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“…1A; Guan, 1978;Guan and Fang, 2006). In addition, the northern SCS margin is frequently attacked by typhoons (storms) and develops world-known strong internal waves, which facilitate cross-shelf transport and diapyncal mixing, respectively (Tian et al, 2009;Alford et al, 2015;Zhou et al, 2017;Xie et al, 2018). and DR1).…”

Section: Oceanographical Backgroundmentioning

confidence: 99%