PROVENANCE OF THE NORTH PACIFIC SEDIMENTS AND PROCESS OF SOURCE MATERIAL TRANSPORT AS DERIVED FROM RB-SR ISOTOPIC SYSTEMATICS

Abstract

Rb–Sr isotopic systematics of 111 samples of sediments in nine cores from the north Pacific of Quaternary and Pliocene ages have been investigated. They provide information on the provenance, the process of particle transport and temporal variation in the flux of source material. The Rb–Sr isotopic systematics of the core sediments show well-correlated pseudo isochrons. The pseudo isochrons reflect the mixing of two types of material, i.e., the Asian continental material with high 87Rb/86Sr ratios (4.5–6.5) and high 87Sr/86Sr ratios (0.723–0.727) and the volcanic material with low 87Rb/86Sr ratios and low 87Sr/86Sr ratios, from island–arc volcanics such as the Izu–Ogasawara–Mariana and the Japanese Islands and oceanic islands such as the Hawaiian Islands (0.0–2.0; 0.703–0.708). The clearness of the pseudo isochrons implies that the Rb–Sr isotopic composition of the weathering products derived from the Asian continental crust is extremely homogenized. The fine fraction (a few μm) with a high 87Rb/86Sr ratio (5.0–6.5) is widely transported into the north Pacific by the middle-latitude westerlies and contributes largely to pelagic sediments. The coarser fraction with a lower 87Rb/86Sr ratio (<5.0) is mainly transported around the Asian continent by rivers and oceanic currents and contributes significantly to marginal sea sediments. These two continental fractions together with some volcanic materials provide distinctive pseudo isochrons. The Rb–Sr signature of the marine sediments constrains the provenance and the process of particle transport and helps the understanding of the climate on continents, atmospheric circulation and water circulation.