Neodymium isotope records of pelagic sediment core from the Northeast Pacific: implications for latitudinal position of the Intertropical Convergence Zone in the early Miocene

Abstract

Delineation of changes in eolian sources recorded in deep-sea sediment cores provides valuable insight into past atmospheric circulation and global climate change. Inorganic silicate fractions of samples from ODP Leg 199, Hole 1215A, located in the central Pacific Ocean (26°N, 147.5°W), were investigated for 143Nd/144Nd compositions, in order to constrain the sources of eolian dust and determine the latitudinal position of the Intertropical Convergence Zone (ITCZ) recorded in the core. 143Nd/144Nd values of eolian dust show a close agreement with those of Asian dust for the last 20 million years, but are much higher than those of Asian dust for the most of 20 - 30 Ma period. Drastic shift in 143Nd/144Nd values at ~20 Ma is associated with changes in compositions of other geochemical attributes (Eu anomaly and La/Sc, Ziegler et al., 2007, EPSL, v. 254, 416-432), indicating changes in sources of eolian dust at ~ 20 Ma. Geochemical compositions of eolian dust in the 20-30 Ma section resemble those of southeast equatorial Pacific surface and down-core dust records. The observed changes, thus, are attributed to the shift of its eolian dust sources from South/Central American to Asian dust due to the southward movement of the ITCZ over the study site. Our results indicate paleolocation of the ITCZ at ~ 20°N at 20 Ma. An exceptional 143Nd/144Nd value at ~28 Ma revealing Asian dust signal might indicate that the ITCZ had d in the central Pacific Ocean (26°N, 147.5°W), were investigated for 143Nd/144Nd compositions, in order to constrain the sources of eolian dust and determine the latitudinal position of the Intertropical Convergence Zone (ITCZ) recorded in the core. 143Nd/144Nd values of eolian dust show a close agreement with those of Asian dust for the last 20 million years, but are much higher than those of Asian dust for the most of 20 - 30 Ma period. Drastic shift in 143Nd/144Nd values at ~20 Ma is associated with changes in compositions of other geochemical attributes (Eu anomaly and La/Sc, Ziegler et al., 2007, EPSL, v. 254, 416-432), indicating changes in sources of eolian dust at ~ 20 Ma. Geochemical compositions of eolian dust in the 20-30 Ma section resemble those of southeast equatorial Pacific surface and down-core dust records. The observed changes, thus, are attributed to the shift of its eolian dust sources from South/Central American to Asian dust due to the southward movement of the ITCZ over the study site. Our results indicate paleolocation of the ITCZ at ~ 20°N at 20 Ma. An exceptional 143Nd/144Nd value at ~28 Ma revealing Asian dust signal might indicate that the ITCZ had