Roles of changes in land weathering intensity in the Nd cycle of the South China Sea during the past 30 kyr as inferred from neodymium isotopic composition in foraminifera

• Published in: Chemical Geology
• Main Authors: Huang, Yi, Colin, Christophe, Liu, Zhifei, Joffrey, Bertaz, Dapoigny, Arnaud, Douville, Eric, Yu, Zhaojie, Lin, Andrew Tien -Shun
• Format: Report
• Language: English
• Published: ELSEVIER 2024
• Subjects: Foraminiferal eNd; Weathering; River discharge; Paleohydrology; East Asian Summer Monsoon; South China Sea; Geochemistry & Geophysics; EAST-ASIAN MONSOON; DEEP-WATER CIRCULATION; PACIFIC-OCEAN; INDIAN-OCEAN; AUTHIGENIC PHASES; NORTH PACIFIC; GEOCHEMICAL INVESTIGATIONS; FLUVIAL SEDIMENTS; SURFACE SEDIMENTS; TIBETAN PLATEAU; Indian; Pacific; Planktonic foraminifera
• Online Access: http://ir.qdio.ac.cn/handle/337002/184700; https://doi.org/10.1016/j.chemgeo.2024.121954

Neodymium isotopic compositions (eNd) in the marginal sea is influenced by the ocean circulations as well as the lithogenic input from continents, but their relative contributions and the impact of detrital sediments are not well constrained. In this study, Nd isotopic compositions of mixed planktonic foraminifera species and carbonate-free fraction of sediment from two cores collected at 1250-1350 m water depth in the southwestern (core MD01-2393) and northeastern (core MD18-3569) South China Sea (SCS) have been investigated in order to constrain the relative contributions of lithogenic Nd inputs from large Asian rivers and hydrological variations at intermediate depth in the SCS. The foraminiferal eNd values of both cores (-7.3 +/- 0.2 to -5.8 +/- 0.2 for core MD18-3569 and - 8.1 +/- 0.2 to -7.2 +/- 0.2 for core MD01-2393) indicate strong modifications of the initial eNd of the North Pacific Intermediate Water (NPIW) (eNd of -4) flowing into the SCS by unradiogenic sediments (-13 to -11) from large Asian rivers. The foraminiferal eNd record of core MD01-2393 displays significantly unradiogenic values from 18 to 8 cal kyr BP which are associated with intensification of monsoon rainfall and river input of detrital material characterized by strongly altered minerals (high illite chemical index and kaolinite/illite ratio) deriving from tropical plain soils of the Mekong River basin. We suggest here that pedogenetic minerals from tropical plain soils are more efficient in terms of Nd exchange with the seawater than primary minerals produced by intense physical erosion during the glacial period. In contrast, the foraminiferal eNd record for the northern core MD18-3569 is characterized by radiogenic eNd values from 18 to 12 cal kyr BP; these values have been linked to an increased intrusion of radiogenic glacial NPIW to the northern SCS and greater ventilation of water masses (deduced from Delta 14C) in the northern deep basin of the SCS compared to the southern one. This time interval is associated with newly formed ...