Down-core variation of Nd, Sr and Pb isotopic composition in northeast Pacific silicate sediments

Eolian components of a sediment core from the northeast Pacific (16°12'N and 125°59'W were investigated for Nd, Sr and Pb isotopic compositions to infer temporal variations in the provenance of eolian input during late Cenozoic. The lower part of the core from 250 cm to 328 cm, corresponding age of 8 to 15Ma, showed isotopic values (ɛNd = -5.1~-6.8, 87Sr/86Sr = 0.7069~0.7078, ^{208}Pb/204Pb = 38.68~38.71) similar to those of Equatorial and Southeast Pacific surface sediments. In contrast, the upper part from surface to 250 cm, up to 8 Ma, showed isotopic values close to those of Central Pacific surface sediments and China loess (ɛNd = -8.4~-10.3, 87Sr/86Sr = 0.7134~0.7214, ^{208}Pb/204Pb = 38.69~38.93). This indicates that eolian particles of the study core were supplied from Central and South America for the lower sediments and China and North America for the upper sediments. The observed temporal source change occurs spatially across the hemispheric dust barrier of the Intertropical Convergence Zone (ITCZ). This suggests a possibility that the study site was under the influence of southeast trade winds prior to 8 Ma due to the northerly position of the ITCZ, and subsequently of the northeast trade winds from 8 Ma. This interpretation is consistent with a mineralogical and geochemical study published elsewhere that assigned the provenance of the study core dust to Central/South America for the lower part and to Asia for the upper part.