Neglected role of continental circulation in cross-shelf sediment transport: Implications for paleoclimate reconstructions

Abstract

Coastal currents play a key role in regulating alongshore sediment transport, and their relationships with winter storms (burst of the East Asian winter monsoon) and formation of the coastal mud deposits on the eastern China shelf have been established, based on which the evolution of the East Asian winter monsoon has been widely explored. Unlike that of coastal deposits, the formation of offshore deposits on the eastern China shelf is very complex and highly debated, leading to enormous challenges on paleoclimate reconstructions based on these deposits. In this study, cross-front sediment transport under a variable Yellow Sea Warm Current (YSWC) was explored using remote sensing imagery and sedimentary records (seismic profile and sediment grain size) from the North Yellow Sea (NYS). The results indicate that, although the offshore mud deposit in the western NYS is formed by winter storms through triggering cross-front transport of coastal sediment around the Shandong Peninsula, the winter storm signal was completely obscured by that of the YSWC, which might determine the flux of cross-front sediment transport on a millennial scale. The 1500 y sub-orbital climate variability cycle could also be observed in distal muds after 2.8 ka. By comparing the sediment composition within the same mud deposit or between adjacent mud deposits in the NYS, we found that the response of cross-front sediment transport to the YSWC varied spatially, which may be a reason for discrepancies observed in previous winter monsoon reconstructions on the eastern China shelf. Therefore, as indicated by this study, offshore deposits on the eastern China shelf are not suitable for inversions of the winter monsoon. In addition, mud deposits on the eastern China shelf are also dramatically affected by other dynamic factors, including typhoons and river flooding; thus, deeply exploring the dynamic characteristics and formation mechanism of these deposits are prerequisites for paleoclimate reconstruction.