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A calibrated, coupled model of the Bohai and Yellow Seas is developed to investigate sediment transport and deposition processes around a distinct clinoform east of the Shandong Peninsula. On the clinoform, deposition patterns vary seasonally with the regional hydrography and the East Asian Monsoon. A local maximum in sediment deposition is located offshore from spring to autumn, whereas sediment deposition is greater near the coast and decreases seaward in winter. From spring to autumn, a thermal front develops around the Yellow Sea Cold Water Mass and limits sediment transport seaward, enhancing sediment deposition and leading to high deposition rate in a focused region offshore. Sediment is transported to the region by the southward basin-scale cyclonic circulation, and the cross-shelf gradient in stratification, sediment resuspension, and vertical mixing at the front lead to a convergence in sediment transport and deposition. Sediment deposition over the clinoform is the greatest during the transition from summer to autumn when the thermal front persists but sediment supply increases. This results from weakened stratification and greater resuspension near the coast due to stronger winds, waves, and sea-surface cooling. A seasonal seaward shift of the frontal position toward deeper water is consistent with the decreasing heat flux, and the corresponding shift in location of maximum sediment deposition shifts seaward. In winter, the thermocline disappears and vertical mixing increases throughout the region. SSC over the clinoform increases due to active resuspension and net deposition decreases, and instead sediment is transported seaward and deposits in the South Yellow Sea. Current velocity, SSC and sediment deposition rates decrease seaward, in contrast to the focused trapping at the thermal front from spring to autumn. The deposition rates around the thermal front from spring to autumn are greater than in the winter, so the high net sediment accumulation over an annual cycle occurs in the same region as the longer-term accumulation preserved in the omega-shaped clinoform. • Sediment deposition rates are increased at a thermal front from spring to autumn at east of the Shandong Peninsula. • Seasonal shifts of the position of thermal front and sediment depo-center broaden the sediment accumulation region. • The monsoonal climate plays a dominant role in the seasonally varying circulation and sediment transport in the Yellow Sea. [ABSTRACT FROM AUTHOR]

A calibrated, coupled model (COAWST) of the Bohai and Yellow Seas was employed to examine the contributions of waves and tides to the sediment transport, and to understand the dynamic factors controlling bottom sediment resuspension around the Shandong Peninsula. The numerical results, which were consistent with the in-situ observations, illustrated two events with large values of suspended sediment concentration (SSC). The two events had similar wave heights, but SSC during the second event was more than twice that of the first one. Numerical experiments indicated that the large values of SSC east of the Shandong Peninsula were mainly ascribed to local resuspension, and that waves played a primary role in sediment resuspension for both high SSC events. The differences in SSC and bottom shear stress between the two events were mainly due to differences in wave period, representing about 65% of the total difference, and the non-linear interactions of wave and currents played a secondary role. Therefore, wave period is an important factor along with wave amplitude in the contribution of waves to sediment resuspension in this region. The combined actions of waves and currents dynamics dominate the sediment resuspension rather than either factor in isolation. Due to sheltering effect by the Shandong Peninsula, the wave effect on sediment resuspension was less to the south of the Peninsula than that to the north and east. In addition, the Shandong Coastal Current was enhanced by the northerly wind leading to more sediment transport southward along the coast of Shandong Peninsula, but this has small effect on the difference of suspended sediment concentration between two storm events. • Large values of suspended sediment concentration east of the Shandong Peninsula is mainly due to local resuspension. • The combined actions of waves and tidal dynamics dominate the sediment resuspension. • Wave period is an important factor along with wave amplitude in the contribution of waves to sediment resuspension. [ABSTRACT FROM AUTHOR]

Mud depocenters play an important role in the sediment source–sink system of marginal seas; however, the factors controlling the formation of mud deposits are not well understood. This study focused on Core LHSD-1, which is located on the southern margin of the Shandong Peninsula mud wedge in the northwestern part of the South Yellow Sea. Elemental ratios, such as the C/S ratio (the mass ratio of total organic carbon and total sulfur) and Sr/Ba ratio, were used to track the changes in paleosalinity during the late Quaternary and to investigate the mechanisms that influenced the formation of the mud wedge off the Shandong Peninsula. Our results indicate that Core LHSD-1 likely recorded two transgression events, corresponding to MIS3 and MIS1. Following sea-level rise after the Last Glacial Maximum (LGM), transgressive deposition began in the study area at approximately 11.5 kyr BP. During the early Holocene, fluctuating water salinity was recorded by Sr/Ba ratios, which became stable at approximately 6.8 kyr BP when the sea level reached its highstand. At the same time, the modern current system was established, and a significant amount of terrestrial material, such as refractory organic carbon and iron, has been transported to the study area by enhanced coastal currents, which was documented by elevated C/S ratios (C/S > 2.8) in mud sediments. Our findings indicate that marine transgressions controlled the initial development of the mud depocenter and that the establishment of the modern ocean current system promoted the rapid deposition of mud sediments, which corresponded to the growth of global mud depocenters. • C/S and Sr/Ba ratios indicate two transgressions corresponding to MIS1 & MIS3. • Mud sediments were initially deposited at 11.5 ka due to the deglacial sea-level rise. • Paleosalinity records indicate the mud depocenter was mainly formed after 6.8 ka. • High C/S ratios since 6.8 ka indicate the establishment of the modern current system. [ABSTRACT FROM AUTHOR]

Huanghe (Yellow River) is one of the largest contributors of global terrestrial materials to the sea. A large amount of the Huanghe-derived sediment are responsible for forming not only the nearshore delta depositional system, but also a distal mud patch off the Shandong Peninsula, some 350 km east of the present-day river mouth. To better understand the spatial and temporal variations of sediment dynamics in the distal mud area, two field surveys employing the phase-averaging method (PAM) were conducted in September 2017 and January 2018, respectively along a 108-km East-West transect across the mud patch. The residual currents derived from the PAM surveys were featured by the southward current in the nearshore area and the northward current in the offshore region in summer, while a unidirectional current transported from south to north across the entire transit line in winter. These patterns, which deviate from the traditional understandings of circulations in magnitude and even in direction, are believed to result from episodic wind reversals and associated strengthening and weakening sea level pressure gradients. The northerly wind episodes in summer, works hand-in-hand with sea-level tilt by preceding southerly wind, to enhance the water exchange between the Bohai Sea and the Yellow Sea by intensifying both the southward flow along the coast and the northward flow of the South Yellow Sea water further offshore. In winter, episodic southerly wind causes relaxation or even reversal of the prevailing winter northerly wind that created the northward sea-level tilt in the Bohai Sea and the Yellow Sea, effectively enhances the South Yellow Sea water transport to the North Yellow Sea and the Bohai Sea. Consequently, a considerable amount of sediment previously exported out of the Bohai Sea to the mud patch actually return with these backflows. Since the synoptic time scale oscillations in the Bohai and Yellow seas are considerably frequent throughout summer and winter, the cumulative effects on the long-term sediment transport need to be further investigated. The observations in this study provide a base for new understanding of how episodic weather events impact the regional circulation and sediment dynamics on the Huanghe-derived distal mud patch. • Residual currents across the Shandong muddy area were examined for the first time. • Nearshore southward current and offshore northward current were evident in summer. • Northerly wind reversals in winter forced northward flowing via the entire section. • Synoptic events could largely change the sediment dynamics in the muddy area. [ABSTRACT FROM AUTHOR]