The bottom current is an important component of the three-dimensional ocean circulation, which is of significance for the safeties of ocean bottom engineering and facilities, the research on sediment and pollutant transports, and the ecological environment. Due to the lack of observation data, research on the bottom current in the South China Sea (SCS) has been limited. This study systematically analyzes bottom currents from 0.5 to 5 m above the seafloor based on 20-month-long mooring observations on the shelf slope west of the Dongsha Atoll. The spectral analysis results indicate that currents induced by the internal tides and the internal solitary waves (ISWs) comprise dominant constituents of bottom currents with velocity amplitudes up to O(50–90) cm/s. Dominant internal tide-induced bottom currents of the velocity amplitude of O(50) cm/s occupy 53% of the total horizontal kinetic energy. The pulsating ISW-induced bottom currents reach a maximum amplitude of 93 cm/s, which has intrinsic relation to the amplitude of the ISWs, according to the soliton propagation speed solutions of the Korteweg–De Vries (KdV) equation. The background bottom current is strongest in winter, followed by spring, and weak in summer and autumn, which is closely correlated with the behavior of mesoscale eddies. These results are of significance for understanding the dynamics of the bottom boundary layer.

中文翻译：

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南海北部大陆架系泊观测底流分析

底流是三维海洋环流的重要组成部分，对海底工程和设施的安全、沉积物和污染物运移研究以及生态环境具有重要意义。由于缺乏观测资料，对南海底流的研究一直很有限。本研究基于东沙环礁以西陆架斜坡长达 20 个月的系泊观测，系统地分析了海床以上 0.5 至 5 m 的底流。频谱分析结果表明，由内部潮汐和内部孤立波（ISW）引起的洋流构成了底流的主要成分，速度幅度高达欧(50–90) 厘米/秒。速度振幅的主导内部潮汐底流欧(50) cm/s 占据总水平动能的53%。根据 Korteweg–De Vries (KdV) 方程的孤子传播速度解，脉动 ISW 感应底部电流的最大幅度达到 93 cm/s，这与 ISW 的振幅有内在关系。背景底流冬季最强，春季次之，夏秋季弱，这与中尺度涡的行为密切相关。这些结果对于理解底部边界层的动力学具有重要意义。