Organic geochemical evidence of Late Glacial–Holocene climate instability in the North Aegean Sea Alexandra Gogou a, ⁎ , Ioanna Bouloubassi b , Vasilios Lykousis a , Michela Arnaboldi c , Praxia Gaitani a,d , Philip A. Meyers c a Hellenic Centre for Marine Research (HCMR), Institute of Oceanography, P.O. Box 712, 19013 Anavyssos, Greece b Laboratoire d’Océanographie et du Climat: Expérimentation et Approches Numériques (LOCEAN), CNRS UMR 7159, IPSL, Université Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris cedex 05, France c Marine Geology and Geochemistry Program, Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan, 48109-1005, USA d Environmental Chemical Processes Laboratory (ECPL), Department of Chemistry, University of Crete, GR-71409 Heraklion, Greece Received 6 January 2007; received in revised form 4 August 2007; accepted 13 August 2007 Abstract Sedimentary molecular biomarker compositions, organic carbon and CaCO 3 concentrations, and bulk organic δ 13 C and total δ 15 N values document a series of paleoclimatic changes that have affected organic matter production and sedimentation in the North Aegean Sea from the termination of the latest glacial maximum through the middle Holocene. Continental environmental conditions have been inferred from land–plant biomarkers. Paleoproductivity patterns of diatoms, prymnesiophytes, dinoflagellates, and nannoplankton were discerned from marine-derived biomarkers. Although organic matter is predominantly marine, variations in the proportion of marine and land contributions and in its general preservation are evident. Rapid changes in the Eastern Mediterranean thermohaline circulation evidently occurred in parallel to sea surface temperature oscillations. Enhanced deep-water ventilation accompanied cold intervals in the late Last Glacial, the Younger Dryas, and during an interruption of deposition of the S 1 sapropel, probably in response to strengthening of north winds over the region. In contrast, decreased thermohaline circulation occurred during the warm interval associated with the S 1 sapropel. During this period, increased freshwater inputs diminished ventilation of deep- water masses and enhanced organic matter production and preservation. Intriguing fluctuations in sea-surface temperatures and the concentrations of marine and terrestrial biomarkers within the sapropelic layer, most prominently in the interruption from 8.2 to 7.8 calibrated radiocarbon conventional kyr BP, support the hypothesis that several distinct events of deep water reoxygenation occurred in the North Aegean Sea during deposition of the S 1 sapropel. These events reflect centennial excursions to the more common low- productivity and well ventilated conditions of the Mediterranean that may possibly be related to North Atlantic Oscillation cycles. © 2007 Elsevier B.V. All rights reserved. Keywords: Organic matter; S1 sapropel; Biomarker molecules; Alkenone sea-surface temperatures; δ 13 C org ; δ 15 N total 1. Introduction Oceanic sub-basins and marginal seas are often more responsive to paleoceanographic and paleoclimatic changes than global oceans because of their smaller size Available online at www.sciencedirect.com Palaeogeography, Palaeoclimatology, Palaeoecology 256 (2007) 1 – 20 www.elsevier.com/locate/palaeo ⁎ Corresponding author. Present address: Department of Marine Sciences, University of the Aegean, Greece. Tel.: +30 22510 36838; fax: +30 22510 36809. E-mail address: agogou@aegean.gr (A. Gogou). 0031-0182/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2007.08.002