Editorial: Sedimentation on the continental margins: From modern processes to deep-time records

The continental margin, which connects the land and the sea (Fig. 1), is a key area of land-sea interaction (Walsh and Nittrouer, 2009), where its sedimentation process is closely related to tectonic activities, climatic conditions, oceanic dynamics, and human activities (Fan and Li, 2002; Syvitski et al., 2022; Xu et al., 2017). Therefore, sediments on the continental margin can effectively record the environmental evolution both in the terrestrial source area and in the marine depositional area (Dong et al., 2021; Pei et al., 2020; Shang et al., 2018). The continental margin is also the main location for the mineralization of organic matter (Liu et al., 2022; McKee et al., 2004), which affects the global carbon cycle (Bianchi and Allison, 2009; Ren et al., 2019). Sedimentation on different types of continental margins exhibits unique characteristics, such as the broad shelf dominated by the large East Asian rivers and the narrow shelf fed by the mountainous rivers of East Africa (Liu et al., 2004; Liu et al., 2009; Liu et al., 2016; Liu et al., 2018; Xu et al., 2021), which needs comparative studies on specific types of continental margins. However, the complexity of signal interpretation from sedimentation processes to depositional records has limited our understanding of different types of continental marginal sedimentation (Fig. 1). To fill this gap, this topic integrates the research results of different geological backgrounds and different time scales to form a new understanding on the knowledge system of sedimentation on global continental margins. Figure 1. Schematic diagram of sedimentation process and depositional record on the continental margin.This topic collected 27 articles from 162 authors over the world, including modern sedimentary dynamics and biogeochemical processes, history depositional records, and impacts of human activity on sedimentation on continental margins. 1) Modern sedimentation dynamics on the continental marginDongfeng Xie et al. analyzed water levels, daily river discharge, as well as bathymetric data from the Qiantang Estuary, China in 2015 and delineated the seasonal tidal evolution along the estuary. Based on the CTD profiles and mooring measurements of the Line W program in the North Atlantic at about 35°N/70°W, Liming Fan et al. found that the internal wave strain variance over the slope could be up to five times larger than that in the interior. According to analyses of the vertical variation of Rossby number, kinetic energy in the submesoscale range, and kinetic energy spectra, Jianing Li et al. suggested that submesoscale motions between New Jersey Shelf and Bermuda are mainly confined within the surface mixed layer with seasonality that is strong in winter and weak in summer. Shuang Sun et al. reconstructed the migration of coastline and river channels in the Northern Bohai Sea during the last hundred years based on the clay minerals. Junjin Chen et al. firstly applied grain size trend analysis (GSTA) and end-member analysis (EMA) on 232 surface sediment samples in the deep-sea environment to reveal sedimentary dynamics around isolated carbonate platforms in the northern South China Sea. By summarizing and analyzing the research in the shelf-slope region offshore northeast of Taiwan, Cheng-Shing Chiang et al. refined the morphology of the Huapinghsu Channel/Mienhua Canyon System and proposed a new idea to illustrate this channel/canyon system as a sediment conduit transporting sediments from western Taiwan rivers to the southern Okinawa Trough.2) Biogeochemical cycles in sediments on the continental marginElena T. Bruni et al. used a combination of literature and new data to study the drivers and biogeochemical consequences of wave- and current-induced resuspension on organic carbon cycling in modern, oxygen-depleted, “Semi-Liquid Ocean Bottom” regions, such as the Benguela upwelling region. Xiaowei Zhu et al. discovered bottom water DO conditions of the coastal northern South China Sea in the 20th century by sedimentary C28Δ22/Δ5,22 ratios of steroids and proposed that net photosynthetic oxygen production outweighs source water– and warming-induced increasing deoxygenation in the study area. In order to retrieve the historical redox state in the hypoxic zone near the Changjiang River Estuary and its adjacent waters, Xiaotong Zhang et al. investigated the distribution and enrichment degree of Mo, U, and V in core 3050-2 and found a general oxic–suboxic environment since 2005. Yipeng Wang et al. reported spatial distribution of brGDGT related indicators in surface sediments from the East China Sea and suggested that mixed sources of soil-derived brGDGTs were dominant, and marine in situ brGDGTs were overprinted. Yuanyuan Li et al. found that there was a significant contribution from lateral allochthonous organic matter from the mountainous river in hydrate-bearing sediments from three long sedimentary sites in the Shenhu area, northern South China Sea. Handan Zhang et al. illustrated the depth profiles of sedimentary wtCaCO3% from the West Pacific based on a newly compiled CaCO3 data set and a carbonate model. Yuying Zhang et al. carried out a comprehensive study of a long-term organic carbon record over the past 380kyr from a sediment core St10-PC in the Northwest Pacific, which highlighted the important contribution of environmental redox conditions on organic carbon burial in the deep Northwest Pacific. Miao Chen et al. analyzed the archaeal ammonia oxidation rate indicator GDGT-[2]/[3] ratio (Glycerol Dialkyl Glycerol Tetraether) from the collected data profiles since the last glacial period in the northern South China Sea and found that the GDGT-[2]/[3] values were higher during the Holocene compared to the last glacial period.3) Sedimentation in response to paleoclimatic and palaeoceanographic evolutionXue Ding et al. presented the first high-resolution grain-size record from Core CF1 in the Okinawa Trough and found the Kuroshio Current slow-down during 4.6–2.0 ka, followed by quick enhancement after 2.0 ka, with centennial-scale variabilities (500–700 years). Yao Zhang et al studied the sedimentological characteristics of the mud periphery area and reconstruct the sedimentary evolution at the east edge of the Central Yellow Sea Mud since MIS3a (45 ka). Xin Zhang et al. used optically stimulated luminescence (OSL) dating and lithology of core YRD-1401 from the Yellow River delta to establish the late Quaternary sedimentary evolution of the southwestern coast of the Bohai Sea. Pham Nhu Sang et al used the clay mineralogy, major-element geochemistry, and Sr-Nd isotopic compositions from Core MD05-2896 collected in the southern South China Sea to investigate the discrimination of sediment provenance and reconstruct a history of chemical weathering in the Mekong River basin over the last 45 ka. Yi Wu et al conducted a high-resolution rock magnetic investigation of the Holocene sediments of core DS01, drilled in the vicinity of the West River channel in the head area of the Pearl River deltaic plain, to study how the sea-level change, monsoon-driven discharge, and especially human activity since the late Holocene regulate the regional environmental and sedimentary evolution. Harunur Rashid et al studied the Late Pleistocene Labrador Sea depositional systems developed in front of ice streams and glacier outlets from the Laurentide Ice Sheet (LIS) using Huntec and 3.5 kHz seismic profiles and piston cores which cover >1800 km of the eastern Canadian continental margin and the Labrador Basin. Guogang Li et al. studied a sediment core (ANT32-RA05C) collected from the continental slope of the Ross Sea, Antarctica by paleomagnetic and 230Th dating and geochemical properties and revealed the relationship between paleoenvironmental processes and the Antarctic temperature since the Late Pleistocene. Xuan Lyu et al. investigated iron oxide mineral contents along with major element compositions of the oceanic red beds at Site U1433 to reveal the Miocene deep-sea oxidation environment of the South China Sea and its interaction with the West Pacific. Meinan Shi et al. refined the chronostratigraphy of the upper 160 m sedimentary succession from Hole U1501C using paleomagnetic measurements and cyclostratigraphic analysis on the Natural Gamma Radiation (NGR) data, producing a high-resolution 15.54 Myr age model. Yibing Li et al. retrieved a record of the East Asian Summer Monsoon by studying the colour reflectance of coastal sediments in the south Bohai Sea, East Asia, demonstrating an integrated forcing of ice–sheet evolution and solar insolation in the East Asian Summer Monsoon in the late Quaternary. Ao Liu et al. identified three facies from the Liangshan Formation successions in western South China, which belong to the coastal alluvial plain, estuary and deltaic environments that followed dry-to-wet climatic shifts.4) The impact of human activity on marginal sedimentationJay Lee et al. analyzed foraminiferal records collected from the continental slope off southwestern Taiwan and find that the anthropogenic carbon signal in the West Pacific was not weaker than that recorded in the Atlantic over the last century. Ke Dong et al. provided a 55-year sedimentary record from Songkhla Lake, Thailand and revealed a three-stage sedimentary and input history of trace metals under anthropogenic effects since 1964.In summary, the articles collected on this topic cover comprehensive studies on the sedimentation process and related biogeochemical processes on the continental margin at different times and spaces—from the tropical marginal seas to the high latitude glacial-dominated margins. The research methods included sedimentologic, biogeologic, geochemical, and geophysical data analysis. Therefore, these studies of different types of continental marginal sediments will be of great scientific significance for a better understanding of the earth's surface process and the evolution of the earth's environment.

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