Formation mechanism of drift-moat contourite systems revealed by in-situ observations in the South China Sea

• Published in: Earth and planetary science letters Vol. 628; p. 118585
• Main Authors: Zhao, Yulong, Liu, Zhifei, Zhang, Yanwei, Zhang, Xiaodong, Ma, Pengfei, Yu, Xun, Ling, Chen, Lin, Baozhi, Zhang, Jingwen
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.02.2024
• Subjects: Contour current; Contourite drift; Contourite moat; Mooring observation; South China Sea; Suspended sediment concentration (SSC); Contourite moat; South China Sea; Suspended sediment concentration (SSC); Contour current; Contourite drift; Mooring observation
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2024.118585

•Contour currents with different physical natures observed over a drift-moat system•High SSC on the drift due to long-range sediment transport by contour currents•High SSC in the moat due to moat wall erosion by tidal-induced secondary flows•Formation of drifts forced by upslope sediment transport of tidal currents Contourite drifts are ubiquitous sedimentary features in the world′s oceans, and their formation are usually ascribed to sedimentation from contour currents. However, in-situ observations of contour currents and their associated sedimentary processes were inadequate. Here, we present mooring observation results from a drift-moat contourite system in the South China Sea to gain insight into its sediment dynamics and formation mechanism. We found that quasi-persistent contour currents develop in the moat, on and below the drift, yet subject to diverse physical oceanographic processes. High suspended sediment concentrations observed on the drift mainly occur in winter, induced by high levels of sediments transported by contour currents from Taiwan. In the moat, however, high suspended sediment concentrations are mostly caused by erosion of the moat wall during periods of strong tidal currents and low shear variance. Such results underscore the complexity of current patterns and sedimentary processes across various topographic units in the drift-moat contourite system. A novel formation mechanism of the contourite drift is thereby proposed, wherein sediment transport by contour currents brings materials for constructing the drift, while its formation is driven by near-critical reflection and upslope transport of sediments by tidal currents.