PII S0016-7037(02)00954-7 Sr and Nd isotope composition of Late Pleistocene sapropels and nonsapropelic sediments from the Eastern Mediterranean Sea: Implications for detrital influx and climatic conditions in the source areas SYEE WELDEAB, a,b, *KAY-CHRISTIAN EMEIS, b CHRISTOPH HEMLEBEN, a TORSTEN W. VENNEMANN, c and HARTMUT SCHULZ b a Institut und Museum fu ¨r Geologie and Pala ¨ontologie, Universita ¨t Tu ¨bingen, Tu ¨bingen, Germany b Institut fu ¨r Ostseeforschung Warnemu ¨nde, Warnenu ¨nde, Germany c Institut fu ¨r Mineralogie, Petrologie und Geochemie, Universita ¨t Tu ¨bingen, Tu ¨bingen, Germany (Received February 8, 2001; accepted in revised form May 29, 2002) Abstract—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. Copyright © 2002 Elsevier Science Ltd 1. INTRODUCTION Sedimentary sequences from the eastern basin of the Medi- terranean Sea and aerially exposed sections of Neogene age in southern Italy, Sicily, and Crete contain a series of sapropel layers (cm to m thick) sandwiched between hemipelagic, car- bonate-rich sediments deposited under oxic conditions. The sapropels are rich in organic carbon and were deposited during periods when the deep waters of the eastern basins were oxygen depleted (Olausson, 1961; Kidd et al., 1978; Emeis et al., 2000). Low oxygen content in the eastern basins was probably preceded by the establishment of a density stratification of the water column and by enhanced productivity (Rossignol-Strick et al., 1982; Rohling and Gieskes, 1989). This requires an increased input of freshwater (Rossignol-Strick et al., 1982). The geographic origin of the increased freshwater influx has not been identified yet. A review and summary of existing models proposed for sapropel genesis has been presented by Cramp and O’Sullivan (1999). The mineralogical and chemical composition of sapropel- containing sedimentary cycles indicates that changes in the source of detrital matter vary cyclically between eolian and riverine end members (Foucault and Me `lie `res, 2000; Wehausen and Brumsack, 2000). The chemical and mineralogical charac- teristics permit a differentiation between materials originating from different locations in the Eastern Mediterranean catch- ment area. Aluminum-normalized element ratios, according to Wehausen and Brumsack (2000) and Calvert and Fontugne (2001) indicate rhythmic alternations of eolian and fluvial input that are related to precession-induced climatic variations. A similar pattern of rhythmic changes for the origin of detrital material has been observed from clay-mineral analyses (Fou- cault and Me `lie `res, 2000). Characteristic chemical composi- tions (low K and Mg content) and mineral assemblages (high smectite content), indicative of the Nile provenance, are pro- nounced for sapropel members in the central and eastern part of the Levantine Basin, whereas the intervening nonsapropel sed- iments mainly contain material characteristic of modern Sa- haran and Damascus dust—that is, material blown in from the eastern borderland of the Eastern Mediterranean Sea (EMS; high Ti, Zr, palygorskite, and kaolinite content). In the west- ernmost Levantine and Ionian basins, the eolian end member is also dominated by sediments of Saharan origin; the composi- tion of detrital matter of riverine origin is consistent with a source in the northern watershed of the EMS (high K, Mg, smectite, and chlorite contents). The latter is pronounced dur- ing insolation maxima and sapropel formation (Dominik and Stoffers, 1978; Foucault and Me `lie `res, 2000). Strontium and neodymium isotopes have been successfully applied to characterize sediment provenance and reconstruct atmospheric and temporal variation of sediment supply to ba- sins (e.g., Dia et al., 1992; Grousset et al., 1992; Revel et al., 1996; Asahara et al., 1999; Krom et al., 1999a, b). The reason for their extensive use is that their isotope ratios bear a finger- print of their source rocks. Although the Nd isotope composi- tion is little affected by grain-size differences of the sediment fractions and also robust to changes during weathering, trans- port, and winnowing processes (Goldstein et el., 1984; Walter et al., 2000), the Sr isotope composition can be influenced by * Author to whom correspondence should be addressed, at Fachbereich Geowissenschaften, Universita ¨t Bremen, Postfach 330 440 28334 Bremen Germany (sweldeab@uni-bremen.de). Pergamon Geochimica et Cosmochimica Acta, Vol. 66, No. 20, pp. 3585–3598, 2002 Copyright © 2002 Elsevier Science Ltd Printed in the USA. All rights reserved 0016-7037/02 $22.00 + .00 3585