Trace element abundance, and Sr and Nd isotope ratios of dust samples in the Pacific Ocean (Table 2)

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 epsolin-Nd (-10 to +1), 87Sr/86Sr (0.705-0.721), La/Yb (5-15), EuN/EuN* (0.6-1.0) and Sr/Nd (4-33). The average Nd isotopic composition of Pacific deep-sea sediments (epsilon-Nd = -6), is more radiogenic than the average from the Atlantic (epsilon-Nd = -8). In contrast, the average147Sm/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 epsilon-Nd and147Sm/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 epsilon-Nd values of -10, 87Sr/86Sr > 0.715, high La/Yb (> 12), and low EuN/EuN* (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 epsilon 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.

Sr and Nd composition, stable oxygen isotope record and lithogenic flux in eastern Mediterranean sediments

Isotopic ratios of Sr and Nd from lithogenic components of three isochronous core sections recovered from an east-west transect in the Eastern Mediterranean Sea (EMS) have been analyzed. The data are used for a quantitative estimate of the temporal and spatial variation of detrital flux to the EMS, assuming Saharan dust and Aegean/Nile particulate matter as dominant end members. It was established that the carbonate-free Saharan dust flux during deposition of the nonsapropel layers of marine oxygen isotope stage 5.4 (MIS 5.4) was similar to the present flux. During the deposition of sapropels S5 and S6, however, the Saharan dust input was drastically reduced and was not balanced by a change in the riverine influx at this time. Denser vegetation cover during more humid conditions may have reduced physical erosion and sediment removal in the source area. During marine oxygen isotope stage 6.2 (MIS 6.2) a pronounced increase of Saharan dust and detrital influx from the Aegean region is evident and implies more arid conditions in the southern and northern catchment areas. During this period, intersite variations are interpreted in terms of their geographic location relative to the seaways connecting the Aegean Sea and EMS. The width of the straits and hence the amount of sediment entering the eastern basins may have been affected by a low sea level that impeded interbasin sediment dispersal.