Provenance of dust in the Pacific Ocean

Abstract

Eolian dust preserved in deep-sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate. In order to identify the provenance of eolian dust, Nd and Sr isotopic compositions and Rb, Sr and rare earth element (REE) concentrations have been determined for the silicate fractions of deep-sea sediments from the north and central Pacific Ocean. Different regions of the Pacific Ocean are characterized by distinct air-borne inputs, producing a large range in ε Nd (−10 to +1), 87Sr/ 86Sr (0.705–0.721), La/Yb (5–15), Eu N/Eu N * (0.6–1.0) and Sr/Nd (4–33). The average Nd isotopic composition of Pacific deep-sea sediments ( ε Nd = −6), is more radiogenic than the average from the Atlantic ( ε Nd = −8). In contrast, the average 147Sm/ 144Nd ratio for Pacific sediments (0.114) is identical to that of Atlantic sediments and to that of global average riverine suspended material. The values of ε Nd and 147Sm/ 144Nd are positively correlated for the Pacific samples but negatively correlated for Atlantic samples, reflecting a fundamental difference between the dominant components in the end members with radiogenic Nd (island-arc components in the Pacific and LREE-enriched intraplate ocean island components in the Atlantic). Samples from the north central Pacific have distinctive unradiogenic ε Nd values of −10, 87Sr/ 86Sr > 0.715, high La/Yb (> 12), and low Eu N/Eu N * (0.6) and Sr/Nd (3–6). These data are virtually identical to the values for loess from Asia and endorse the use of these sediments as indicators of Asian paleoclimate and paleowind directions. Island-arc contributions appear to dominate in the northwest Pacific, resulting in higher ε Nd (−1 to +1) and lower 87Sr/ 86Sr (≈ 0.705) and La/Yb (≈ 5). Sediments from the eastern Pacific tend to have intermediate Sr and Nd isotopic compositions but regionally variable Sr/Nd and REE patterns; they appear to be derived from the west margin of the North and South American continents, rather than from Asia. Our results confirm that dust provenance can be constrained by isotopic and geochemical analyses, which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate.