Tracing Sediment Erosion in the Yangtze River Subaqueous Delta Using Magnetic Methods

Abstract

We assessed the usefulness of magnetic properties for tracing sediment erosion in a deltaic environment. Surface and core sediments from the Yangtze River subaqueous delta were subjected to magnetic, granulometric, geochemical, and radionuclide analyses. Based on magnetic properties and particle size, the surface sediments can be divided into three groups. Groups I and II have a similar particle size distribution and geochemical composition, but the former has higher values of magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM). We interpret Group I as consisting of modern sediments, while Group II represents previously buried sediments that have undergone significant reductive diagenesis and that have been subsequently exposed by erosion. Group III has coarser particle size, which reflects the mixing of delta sediments with Pleistocene relict sands. Two cores from the areas occupied by Groups I and II have significantly different magnetic profiles. Core A3‐4 (Group II) records a partial loss of magnetic mineral concentration due to diagenesis and has much lower χ, SIRM, and S−300 values than core A6‐2 (Group I). Radionuclide dating reveals that core A3‐4 sediments are older. We conclude that core A3‐4 location has undergone erosion, which is consistent with recent bathymetric survey results. We propose that the ratio of SIRM/Fe can be potentially used to trace mobilized old sediment in this environment. Our study demonstrates that magnetic properties provide a robust approach for studying sediment dynamics in this type of environment. In addition, our findings provide insights into the nature of biogeochemical processes associated with deltaic erosion.

The Role of Reactive Iron in the Preservation of Terrestrial Organic Carbon in Estuarine Sediments

“…Consequently, sedimentation rates from the Changjiang Estuary to the Zhe‐Min Coast vary considerably (e.g., from 0.5 to 6.0 cm/year) and generally reflect a decreasing trend southward and seaward (Liu et al, ). Frequent physical reworking, coupled with seasonal erosion and redeposition events, results in the southward transport of terrestrial sediments deposited in the Changjiang Estuary along Zhe‐Min coast, which promote rapid iron redox cycling in ECS inner shelf (DeMaster et al, ; Ge et al, ; Yao et al, ; Zhao et al, ; Zhu et al, ).…”

Magnetic fingerprints of surface sediment in the Bohai Sea, China

“…The post-depositional influence on magnetic minerals in the source regions and Bohai Sea could be rule out, because the iron sulfides were not found in the XRD and SEM results. The greigite can be identified by sensitive magnetic changes such as the increased SIRM/χ lf value (Abrajevitch and Kodama, 2011;Ge et al, 2017;Roberts, 1995). The SIRM/χ lf value lower than 20 kA/m for all samples closes to the iron oxides (Maher, 2007;Roberts, 1995).…”

Characteristics of iron-containing magnetic particles in household dust from an urban area: A case study in the megacity of Shanghai

“…Spherical IMPs, typically produced by coal combustion, are found in fluvial sediments, street dust and urban surface soil (Petrovsky and Ellwood, 1999;Mitchell and Maher, 2009;Wang et al, 2018Wang et al, , 2019. Magnetic measurements that examine the abundance of IMPs, their particle size and mineralogy have been widely used to reflect heavy metal contamination and trace particle sources as a rapid, economic and non-destructive approach (e.g., Maher and Thompson, 1999;Zhang et al, 2011;Chaparro et al, 2017;Ge et al, 2017;Hatfield et al, 2019;Wang et al, 2018Wang et al, , 2019Li et al, 2021). In recent J o u r n a l P r e -p r o o f years, the exposure risk of IMPs themselves, especially for nano-sized particles (<100 nm) has drawn public concerns (Maher et al, 2016;Calderón-Garcidueñas et al 2019;Lu et al, 2020;Liu et al, 2021).…”