Preprints
https://doi.org/10.5194/egusphere-2022-439
https://doi.org/10.5194/egusphere-2022-439
 
20 Jun 2022
20 Jun 2022

Spatial-temporal characteristics of the oceanic bottom mixed layer in the South China Sea

Wenhu Liu1,2, Guihua Wang1,3, Changlin Chen1,2, and Muping Zhou4 Wenhu Liu et al.
  • 1Department of Atmospheric and Oceanic Sciences & Institute of Atmospheric Sciences, Fudan University, Shanghai, 200433, China
  • 2Southern Laboratory of Ocean Science and Engineering (Guangdong, Zhuhai), Zhuhai, 519000, China
  • 3CMA- FDU Joint Laboratory of Marine Meteorology, Shanghai, 200433, China
  • 4State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, 310012, China

Abstract. The oceanic bottom mixed layer (BML) has an important role in transporting mass, heat, and momentum between the ocean interior and the bottom boundary. However, the spatial-temporal variability of the BML in the South China Sea (SCS) is not well understood. Using historical hydrological data from 2004 to 2018 and observations from two hydrographic moorings in the SCS, it has been found that the BML in the SCS has significant inhomogeneity. In particular, while the BML is relatively thin and stable over the continental shelf and in deep-sea regions, it is thick and unstable over the northern continental slope. The typical thicknesses of the BML on the continental shelf, continental slope, and deep-sea regions are around 30–60 m, 80–120 m, and 10–50 m, respectively. Statistically, the mean, median, and one standard deviation values of BML thickness over the entire SCS are 73 m, 56 m, and 55 m, respectively. Further analysis reveals that energetic high-frequency dynamic processes, together with steep bottom topography (large slope and roughness), cause strong tidal dissipation and vertical mixing near the bottom over the continental slope, resulting in thicker BMLs there. In contrast, the dynamic processes in the deep ocean are less energetic and low-frequency and the topography is relatively smooth (smaller slope and roughness). Therefore, the tidal dissipation and bottom vertical mixing in the deep-sea regions are weaker, and the BML is relatively thin. These findings may enhance our understanding of the BML dynamics in the SCS and other marginal seas and provide insights that help to improve parameterizations of physical processes in ocean models.

Wenhu Liu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-439', Anonymous Referee #1, 14 Jul 2022
    • AC1: 'Reply on RC1', Wenhu Liu, 29 Sep 2022
  • RC2: 'Comment on egusphere-2022-439', Anonymous Referee #2, 15 Aug 2022
    • AC2: 'Reply on RC2', Wenhu Liu, 29 Sep 2022

Wenhu Liu et al.

Wenhu Liu et al.

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Short summary
We explore the spatial-temporal characteristics of oceanic bottom mixed layer (BML) in the South China Sea (SCS) and investigated its potential formation mechanisms. We found that the BML in the SCS has significant inhomogeneity. In particular, the BML is thick and unstable over the northern continental slope and is relatively thin and stable over the continental shelf and in deep-sea regions. These findings may enhance our understanding of the BML dynamics in the SCS and other marginal seas.