Internal Solitary Wave Reflection Near Dongsha Atoll, the South China Sea

Abstract. Shoaling internal solitary waves near the Dongsha Atoll in the South China Sea dissipate their energy and thus enhance diapycnal mixing, which have an important impact on the oceanic environment and primary productivity. The enhanced diapycnal mixing is patchy and instantaneous. Evaluating its spatiotemporal distribution requires comprehensive observation data. Fortunately, seismic oceanography meets the requirements, thanks to its high spatial resolution and large spatial range. In this paper, we studied three internal solitary waves in reversing polarity near the Dongsha Atoll, and calculated the spatial distribution of resultant diapycnal diffusivity. Our results show that the average diffusivities along three survey lines are two orders of magnitude larger than the open-ocean value. The average diffusivity in the internal solitary wave with reversing polarity is three times that of the non-polarity-reversal region. The diapycnal diffusivity is higher at the front of one internal solitary wave, and gradually decreases from shallow to deep water in the vertical direction. Our results also indicates that (1) the enhanced diapycnal diffusivity is related to reflection seismic events; (2) convective instability and shear instability may both contribute to the enhanced diapycnal mixing in the polarity-reversing process; and (3) the difference between our and previous diffusivity profiles is about 2–3 orders of magnitude, but their vertical distribution is almost the same.

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Diversity of Zoantharia (Anthozoa: Hexacorallia) at Dongsha Atoll in the South China Sea

Regional Studies in Marine Science ◽

10.1016/j.rsma.2017.02.006 ◽

2017 ◽

Vol 12 ◽

pp. 49-57 ◽

Cited By ~ 5

Author(s):

James Davis Reimer ◽

Maria Eduarda Alves Santos ◽

Hiroki Kise ◽

Mei Lin Neo ◽

Chaolun Allen Chen ◽

...

Keyword(s):

South China Sea ◽

South China ◽

The South China Sea ◽

The South ◽

China Sea ◽

Dongsha Atoll

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Internal solitary wave refraction at Dongsha Atoll, South China Sea

Geophysical Research Letters ◽

10.1002/grl.50614 ◽

2013 ◽

Vol 40 (12) ◽

pp. 3128-3132 ◽

Cited By ~ 36

Author(s):

Xiaofeng Li ◽

Christopher R. Jackson ◽

William G. Pichel

Keyword(s):

South China Sea ◽

Solitary Wave ◽

South China ◽

Internal Solitary Wave ◽

Wave Refraction ◽

China Sea ◽

Dongsha Atoll

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Submarine Geomorphological Features and Their Origins Analyzed from Multibeam Bathymetry Data in the South China Sea

Journal of Marine Science and Engineering ◽

10.3390/jmse9121419 ◽

2021 ◽

Vol 9 (12) ◽

pp. 1419

Author(s):

Xiaolin Ou ◽

Junjiang Zhu ◽

Sanzhong Li ◽

Yonggang Jia ◽

Zhongjia Jia ◽

...

Keyword(s):

South China Sea ◽

South China ◽

The South China Sea ◽

Internal Solitary Waves ◽

The South ◽

China Sea ◽

The North ◽

Local Areas ◽

Dongsha Atoll ◽

Geomorphological Features

We processed the raw multi-beam bathymetry data acquired in the central and northeastern part of the South China Sea by eliminating noise and abnormal water depth values caused by environmental factors, and a high resolution bathymetric map with a 20-m grid interval was constructed. Various scales of seafloor geomorphological features were identified from the data, including an image of Shenhu canyon, which is located in the northern continental margin of the South China Sea; submarine reticular dunes in the north of the Dongsha atoll; submarine parallel dunes in the northeast of the Dongsha atoll; and several seamounts in the southwest sub-basin and in the east sub-basin. In the processing step, various anomalies in the multi-beam bathymetry data were corrected. The optimal swath filtering and surface filtering methods were chosen for different scales of seafloor topography in order to restore the true geomorphological features. For the large-scale features with abrupt elevation changes, such as seamounts (heights of ~111–778 m) and submarine canyons (incision height of ~90–230 m), we applied swath filtering to remove noise from the full water depth range of the data, and then surface filtering to remove small noises in the local areas. For the reticular dunes and parallel dunes (heights of ~2–32 m), we applied only surface filtering to refine the data. Based on the geometries of the geomorphological features with different scales, the marine hydrodynamic conditions, and the regional structure in the local areas, we propose that the Shenhu submarine canyon was formed by turbidity current erosion during the Sag subsidence and the sediment collapse. The submarine reticular dunes in the north of the Dongsha atoll were built by the multi-direction dominant currents caused by the previously recognised internal solitary waves around the Dongsha atoll. The submarine parallel dunes in the northeast of the Dongsha atoll were built by the repeated washing of sediments with the influence of the tidal currents and internal solitary waves. The conical, linear and irregular seamounts identified from the bathymetry data were formed during the spreading of the southwest sub-basin and the east sub-basin. The identified seamounts in the multi-beam bathymetry data are correlated to deep magmatic activities, the Zhongnan transform fault and the NE-trending faults.

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