Impacts of nepheloid layers and mineralogical compositions of oceanic margin sediments on REE concentrations and Nd isotopic compositions of seawater

Yi Huang, Christophe Colin, Zhifei Liu, Eric Douville, Arnaud Dapoigny, Frederic Haurine, Qiong Wu, Andrew Tien-Shun Lin

研究成果: 雜誌貢獻期刊論文同行評審

1 引文 斯高帕斯(Scopus)

摘要

Nepheloid layers and turbidity currents transport large quantities of detrital sediments to deep-sea basins. Locally they may control seawater – detrital particle interactions and modify dissolved REE concentrations and εNd distributions of the oceanic margin. However, to date, such processes have been poorly documented, especially in oceanic margins characterized by contrasted mineralogical compositions. Dissolved REEs and εNd from three water stations collected in the northern South China Sea (SCS) close to the Taiwanese deep-sea canyons have been analyzed, with the aim of determining the influence of nepheloid layers and mineralogical composition of lithogenic inputs on dissolved REE and εNd distributions in the ocean. Results indicate that the most radiogenic εNd value (−2.5 ± 0.2), observed at about 400 m, corresponds to the inflow of North Pacific Intermediate Water (NPIW) into the SCS. When compared with previously published Nd isotope, our current study suggests that the εNd value of NPIW which enters the SCS (from 300 to 800 m water depth) is not modified by unradiogenic sediments off the southern margin of Taiwan Island, whereas they become less radiogenic along the margin of eastern China due to Nd exchange with unradiogenic sediments (between −10.2 and −12.6) from the tropical soils of Chinese rivers basins. We have proposed that pedogenetic minerals from Chinese tropical soils modify the Nd isotopic compositions of seawater more efficiently than fresh detrital minerals resulting from very high rates of physical erosion on Taiwan Island. The MREE/MREE*, La/Sm and La/Yb ratios in nepheloid layers indicate that lateral transportation of lithogenic material within the water column can preferentially adsorb LREE compared to MREE and HREE through the scavenging process. However, this process has a negligible impact on seawater εNd of the northern SCS. At the bottom of several water stations, a negative excursion of εNd values, associated with an increase in MREE/MREE* ratios and a decrease in La/Sm ratios, suggests a remineralization flux resulting from the dissolution of Mn oxides during early diagenesis of deep-sea sediments.

原文???core.languages.en_GB???
頁(從 - 到)57-70
頁數14
期刊Geochimica et Cosmochimica Acta
359
DOIs
出版狀態已出版 - 15 10月 2023

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