Variation in the Current Shear Front and Its Potential Effect on Sediment Transport Over the Inner Shelf of the East China Sea in Winter

Abstract

The current shear fronts (CSFs) in the East China Sea have been observed during winter in previous studies. In this research, we systematically study characteristics and variation mechanism of the CSFs and its potential effects on the transport of water and suspended sediment and on the inner shelf mud area (ISMA), using the methods of observation data analysis and numerical simulation. The spatial structures, shear intensities, and sea‐land locations of the CSFs are obviously affected by wind, temperature and salinity. The CSFs curve seaward due to the nonuniformity of topography, and the tide causes its periodic and sea‐land shift. The landward U component near the CSFs indicate little cross‐CSF transport (i.e., the barrier effect). The CSFs are important hydrodynamic factors that affect the formation of the ISMA. The periodic shift of the CSFs in the longitudinal direction and its variations in spatial structure are the main mechanisms affecting the spatial distribution and thickness of the ISMA. However, the barrier effect of the CSFs can be interrupted, and both the strong wind in the northeast direction and baroclinic conditions are beneficial for cross‐CSF transport. Furthermore, cross‐CSF transports occur in the upper layers under northwest wind condition, in areas with nonuniformity of topography and during the spring tide period. Three cross‐shelf channels are identified in areas where the CSFs curve seaward resulting from nonuniformity of topography.

Holocene Climate Modulates Mud Supply, Transport, and Sedimentation on the East China Sea Shelf

“…In addition to the above factors, ocean current shear fronts are a kind of hydrodynamic interface between two different currents with distinctly different velocities or flow directions, which play considerable roles in mud deposition in this mud area (Cromwell & Reid, 1956; Liu, Qiao, et al, 2018; Wang et al, 2007). Multiple‐year seasonal observations reveal that the ocean‐current shear fronts are well developed on the continental shelf in the western and northwestern Pacific, especially during winter (Hickox et al, 2000).…”

“…The above viewpoint can be further tested by sediment‐source analyses because relatively little Changjiang River‐suspended material can be transported across the current shear front based on field observations (Liu, Qiao, et al, 2018). Nonetheless, the material supply from the northwestern Taiwan River northward to the ECS shelf is much lower than that from the Changjiang River (Liu et al, 2008; Milliman & Farnsworth, 2013).…”

“…Because of the interactions among these currents, observations show that well‐developed ocean current shear fronts are widely distributed on the western Pacific continental shelf, especially during wintertime (Hickox et al, 2000; Liu, Qiao, et al, 2018) (Figure 1b). This current shear front is a hydrodynamic interface between two different bodies of water where the flow velocity is very small (~0 m/s), the flow directions are opposite on the different sides, and the velocity gradients on both sides are significant (Cromwell & Reid, 1956; Liu, Qiao, et al, 2018; Wang et al, 2007).…”

“…(a) Schematic diagram of the Asian monsoon and the locations of sediment cores (circles) and a stalagmite cave (star). (b) Spatial distributions of ocean currents (arrows) (Yang et al, 2012), main locations of current shear fronts (colored dots) at different water depths (Liu, Qiao, et al, 2018), and Changjiang River‐dominated Holocene mud wedge (in meters, gray areas) (Liu et al, 2007) on the low‐gradient ECS continental shelf. The triangles represent the river sediment samples.…”

“…Moreover, climate change can affect the intensity and location of oceanic circulation patterns (Hu et al, 2015; Wang & Oey, 2016), which are closely linked with shelf mud transport and sedimentation (Hanebuth et al, 2015; Walsh & Nittrouer, 2009). This phenomenon is particularly obvious in the western Pacific because multiple large rivers in Asia (e.g., the Changjiang [Yangtze] River) discharge abundant suspended materials (Milliman & Farnsworth, 2013), which can be transported or trapped by well‐developed ocean currents (Hu et al, 2015; Li et al, 2016; Liu, Qiao, et al, 2018). Because of the remarkable influence of the Asian summer and winter monsoons, precipitation in the river basin and the current circulations display distinct seasonal changes (Chen & Sheu, 2006; Liu, Gu, et al, 2019; Wu et al, 2003).…”