Preprints
https://doi.org/10.5194/npg-2021-21
https://doi.org/10.5194/npg-2021-21

  25 May 2021

25 May 2021

Review status: this preprint is currently under review for the journal NPG.

Enhanced diapycnal mixing by polarity-reversing internal solitary waves in the South China Sea

Yi Gong1, Haibin Song1, Zhongxiang Zhao2, Yongxian Guan3, Kun Zhang1, Yunyan Kuang1, and Wenhao Fan1 Yi Gong et al.
  • 1State Key laboratory of Marine Geology, School of Ocean and Earth Science, Tongji University, Shanghai 200092, China
  • 2Applied Physics Laboratory, University of Washington, Seattle, WA, USA
  • 3MNR Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, China Geological Survey, Guangzhou 510760, China

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.

Yi Gong et al.

Status: open (until 20 Jul 2021)

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Yi Gong et al.

Yi Gong et al.

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When the internal solitary wave propagates to the continental shelf and slope, the polarity reverses due to the shallower water depth. In this process, the internal solitary wave dissipates energy and enhances diapycnal mixing, thus affecting the local oceanic environment. In this study, we used reflection seismic data to evaluate the spatial distribution of the diapycnal mixing around the polarity-reversing internal solitary waves.