Riverine supply to the eastern Mediterranean during last interglacial sapropel S5 formation: A basin-wide perspective

Jiawang Wu*, Amalia Filippidi, Gareth R. Davies, Gert J. de Lange

*Corresponding author for this work

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Abstract

Organic-rich sapropel sediments were repeatedly deposited in the eastern Mediterranean Sea (EMS), in response to insolation-driven freshwater forcing. However, the exact freshwater sources and causal associated paleoclimate-related processes remain unresolved. Sapropel S5, formed during the insolation maximum of the last interglacial, is one of the most intensely developed sapropels of the Late-Quaternary. Here, detrital sediments of sapropel S5 obtained from 8 cores, together with 13 EMS surface samples, are analyzed for major elements, rare earth elements (REE), and Sr and Nd isotopes. This permits a basin-wide investigation of the source and distribution of river-borne material to the EMS for sapropel S5, and its comparison to the present-day and the Holocene sapropel S1 period. During the sapropel S5, there was minor Saharan dust input. The marked east–west geochemical gradient in S5 detrital sediments across the EMS is therefore attributed to mixing between fluvial contributions, being Nile discharge, Aegean/Adriatic riverine inputs, and Libyan-Tunisian paleodrainage fluxes. The offshore distribution of Nile sediments during sapropel S5 was comparable to those during S1 and the present. The Nile sediment contribution appears to be only dominant for the Levantine Basin, decreasing to negligible values south of Crete. This rather limited sediment delivery, despite inferred increased runoff during S5, is related to denser vegetation cover on the Ethiopian Highlands. By contrast, small rivers around the Aegean (and Adriatic) Sea brought large amounts of detrital material into the EMS. This is particularly noticeable around Crete and the northern Ionian Sea. The enhanced riverine input is probably due to strong precipitation seasonality over the northern EMS borderlands, particularly for the early phase of the last interglacial maximum. Furthermore, there are substantial fluvial contributions from the Libyan-Tunisian margin to the Ionian Sea sediments, in particular during the last part of sapropel S5. The inferred river-borne material was transported via paleodrainage systems reactivated by intensified monsoon precipitation, and derived from central-Saharan mountains. Compared to sapropel S1, these S5-related paleodrainage fluxes were not only stronger, but also had a more predominant provenance from eastern rather than western Libya. In addition, a similar, averaged endmember of Saharan dust sources is revealed by REE signatures.

Original languageEnglish
Pages (from-to)74-89
Number of pages16
JournalChemical Geology
Volume485
Early online date27 Mar 2018
DOIs
Publication statusPublished - 10 May 2018

Funding

We thank the captain & crew, scientists, and technicians on board the cruises of MD69-MARFLUX 1991, MD81-PALEOFLUX 1995 with RV Marion Dufresne , SIN-SAP 1998 with RV Urania , SMILABLE 1999 with RV Logachev , as well as of PASAP 2000, BIOPASS 2001, PALEOPASS & MIMES 2004, and CORTADO 2011 with RV Pelagia , for their contributions to sample collection. Financial support from EU-projects MARFLUX ( MAST1-90022C ), PALEOFLUX ( MAS2-CT93-0051 ) & SAP ( MAS3-CT97-0137 ), and from CNR and NWO for shiptime and logistics are acknowledged. We are grateful to Coen Mulder and Helen de Waard for ICP-OES and -MS analyses at Utrecht University. Many thanks are given to Richard J. Smeets who helped with chromatography, to Alice Knaf, Mathijs van de Ven, and Bas van der Wagt for Sr and Nd isotope measurements at VU Amsterdam. We appreciate the constructive comments from two anonymous reviewers that have improved the final manuscript, and the editorial handling of Michael Böttcher. This study is part of JW's PhD project, funded by the China Scholarship Council – Utrecht University PhD Program (CSC No. 201206260116 ; USES contribution No. 146). Appendix A

FundersFunder number
EU-projects MARFLUXMAST1-90022C
PALEOFLUXMAS2-CT93-0051, MAS3-CT97-0137
Universiteit Utrecht146, 201206260116
Nederlandse Organisatie voor Wetenschappelijk Onderzoek
Consiglio Nazionale delle Ricerche
China Scholarship Council

    Keywords

    • Eastern Mediterranean Sea
    • Major elements
    • Provenance
    • Radiogenic isotopes
    • Rare earth elements
    • Sapropel S5

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