Fingerprinting Sediment Transport in River‐Dominated Margins Using Combined Mineral Magnetic and Radionuclide Methods

Abstract

Both magnetic properties and radionuclides are widely used to trace sediment transport in aquatic environments; however, these methods have not been used in combination. In this study, the East China Sea (ECS), a typical river‐dominated margin, was chosen to demonstrate the advantages of combining these two methods to track sediment movements on a seasonal to annual timescale. The ratios between saturation isothermal remnant magnetization and anhysteretic remnant magnetization (χARM/SIRM) and 7Be/210Pbex activity ratios as well as mass balance of 7Be provide information on the seasonal transport of sediment from the Changjiang Estuary to the neighboring shelf. Both 210Pb budget and SIRM distribution in the inner shelf of the ECS show that a small fraction (at most 14% of annual Changjiang sediment discharge) of particles could be transported offshore. Most of 7Be activities in inner shelf sediments of the ECS were below detection limit due to relatively lower residence times and dilution by the older sediment. The observation that radionuclide activities exhibit a better correlation with χARM/SIRM ratios than with grain size suggests that iron oxides are the primary carriers of 7Be, 210Pb, and 234Th. The absorption of radionuclides onto magnetic minerals further reinforces the reliability of this combined approach in tracing sediment transport. Our study indicates that radionuclides, with different half‐lives, can be utilized for quantifying sediment dynamics, whereas magnetic properties can yield more detailed information on sediment transport directions. The combined analysis of magnetic parameters and radionuclides offers a better understanding of sediment transport in river‐dominated areas.

Particle Dynamics in a Managed Navigation Channel Under Different Tidal Conditions as Determined Using Multiple Radionuclide Tracers

“…Moreover, the 7 Be/ 210 Pb ex AR in the surface waters of the North Passage increased from S1 to S4 during neap tide, but this activity ratio generally decreases with increasing particle transport distance from the source (Wang et al., 2018). This means that particles could be transported from the river's mouth toward the interior (to S1), in agreement with a previous report that a portion of sedimentary particles in channels of the Changjiang Estuary is derived from beyond the river's mouth (Zhu et al., 2016).…”

“…Mean 7 Be/ 210 Pb ex and 137 Cs/ 210 Pb ex ARs in XLJ could reflect the Changjiang input signal (1.0 and 0.046, respectively). Mean 7 Be/ 210 Pb ex and 137 Cs/ 210 Pb ex ARs beyond the estuary were reported to be 0.14 and 0.12, respectively (Wang et al., 2016, 2018). Observed mean 7 Be/ 210 Pb ex and 137 Cs/ 210 Pb ex ARs in the North Passage were 0.16 and 0.11, respectively.…”

Contrasting Behaviors of 210Pb and 210Po in the Productive Shelf Water Versus the Oligotrophic Water

“…The activities of 226 Ra in the NWPO and the East Sea are from previously published results (Nozaki and Tsunogai, 1976;Chung and Craig, 1980;Harada and Tsunogai, 1986;Nozaki et al, 1990b). The riverine inputs are neglected because 210 Pb is almost completely trapped in the Changjiang estuary (Wang et al, 2018b). The atmospheric input of 210 Po is also neglected since the 210 Po/ 210 Pb ratios in precipitation in this study region are lower than 0.2 (Kim et al, 2005a;Yan et al, 2012).…”

Evaluation of Abandoned Huanghe Delta as an Important Carbon Source for the Chinese Marginal Seas in Recent Decades

“…When the contributions of terrestrial OC to the CMS are considered, the roles of Huanghe and Changjiang have always been the points of the discussion (Deng et al., 2006; Li et al., 2016; Tao et al., 2016; Wang et al., 2018; Wu et al., 2013; Yang et al., 2003); however, the AHD has never been considered as a comparable independent OC source. Because of climate change and intensified anthropogenic activities (such as reservoir construction, agricultural irrigation, water‐sediment regulation schemes, South‐North Water Transfer Project, etc.)…”

“…The sediment yield by coastal erosion from the AHD was estimated to be approximately 700–1,000 Mt/yr (Zhou et al., 2014), comparable to the sediment discharge of the Huanghe and larger than that of the Changjiang before its damming (1,080 and 480 Mt/yr, respectively; Milliman & Meade, 1983). In recent years, using sedimentological, mineralogical, and geochemical approaches (mainly elemental concentration), increasing studies have suggested that the eroded sediment from the AHD plays an important role in the marine sedimentation processes in the Yellow Sea (YS) and East China Sea (ECS) (Bian et al., 2013; Liu et al., 2010; Wang et al., 2011, 2018; Yang et al., 2003; Yang & Youn, 2007; Zhou et al., 2014). Only a few geochemical studies with biomarker tools have been carried out in the AHD (Tao et al., 2016; Xing et al., 2014; Zhao et al., 2011), but most of the samples from these studies largely covered the SYS (water depth > 30 m), some distance away from the major erosion zone of the AHD (water depth < 20 m) (Zhou et al., 2014).…”