Elemental and Sr‐Nd Isotope Geochemistry of Sinking Particles in the Northern South China Sea: Implications for Provenance and Transportation

Abstract

Major and trace elements, Sr and Nd isotopes of bulk particles from the SCS‐NW and SCS‐N‐03 traps were studied to trace the provenance of sinking particles in the northern South China Sea (SCS). About 63% of biogenic materials and most of lithogenic materials from the SCS‐NW trap may be contributed from resuspended sediments, and more biogenic materials are collected in winter than in summer. The immobile‐element discrimination diagrams also indicate that the lithogenic materials of particles are, to a large degree, from local seafloor sediments, and that the lithogenic materials of particles from SCS‐N and SCS‐W traps have seasonal variations. Sr isotopes (87Sr/86Sr and δ88Sr) of bulk particles are significantly influenced by biogenic materials and cannot be used in provenance tracing. In contrast, Nd isotopes are ideal tools to trace particle provenance. However, the traditional Nd isotope (143Nd/144Nd) shows no statistical difference on the particles of the SCS‐NW and SCS‐N‐03 traps, making it unable to identify their provenance. Fortunately, the stable Nd isotope, ε146Nd, shows different correlation trends to ε143Nd in these two traps, suggesting that stable Nd isotope can potentially identify the sources of lithogenic materials in the northern SCS. Our results indicate that distribution and transportation of sinking particles are controlled by currents of the SCS mainly driven by the East Asian Monsoon.

Enhancement of Mesopelagic Sinking Particle Fluxes Due to Upwelling, Aerosol Deposition, and Monsoonal Influences in the Northwestern South China Sea

“…The two mechanisms of nutrient supplementation by aerosol deposition are presumed to be direct nutrient inputs from the deposited aerosols (Guo et al, ) and upper ocean N 2 fixation stimulated by eolian Fe input (Gaye et al, ; Kao et al, ). In our sampled sinking particles (Table ), the relatively high particulate nitrogen (PN) flux, the high percentage of PN in the biogenic matter, and the moderate Fe 2 O 3 and Al 2 O 3 proportions (Liu et al, ) indicate that the primary factor serving to enhance surface Chl a concentrations seems to have been direct nutrient inputs rather than Fe stimulation of diazotrophic activity.…”

“…However, even these gentle along‐slope flows were likely capable of keeping sediments suspended above the steep continental slope (Zhao et al, ), which was only a few tens of kilometers from the SCS‐NW site. The strontium (Sr) and neodymium (Nd) isotopes of the sinking particles in our trap indicate that high quantities of these slowly sinking resuspended sediments could have been advected to our sampling station (Liu et al, ). This scenario may be similar to that seen in the southwestern deep basin, where observed high vertical fluxes of clay minerals may result from lateral advection of resuspended sediments from neighboring shelves (Schroeder et al, ).…”

“…The lithogenic (inorganic) flux was set equal to TMF minus the fluxes of organic matter and biogenic minerals (i.e., organic matter, CaCO 3 , and opal). Lithogenic matter content (%, estimated by mass balance) and Al (%, Liu et al, ) were significantly positively correlated ( R 2 = 0.9088, p < 0.001). This correlation suggests that the mass balance estimates of lithogenic matter flux are reasonable.…”

Ce and Nd stable isotope purification and determination of geological samples by MC-ICP-MS

“…Recently, this fractionation (about 0.25&) has also been observed in natural samples, and has been applied with success in magmatic differentiation, [32][33][34][35] early evolution of the Earth 36 and sediment provenances. 37 From this point of view, stable Nd isotopes can provide new insights in many scientic elds and is uncovering a new set of tools in geochemical studies.…”

Carbon Isotopic Constraints on Basin‐Scale Vertical and Lateral Particulate Organic Carbon Dynamics in the Northern South China Sea

“…Multiple lines of evidence for geochemical parameters (i.e., clay mineral composition, 210 Po-210 Pb isotopes, Sr/ Nd isotopes, and 234 Th inventories) indicate that resuspended surface sediments from the continental margin are an important source of sinking particles in the SCS basin (X. Liu et al, 2018;H. Ma et al, 2017;Schroeder et al, 2015;Yang et al, 2022).…”