Organic geochemical evidence of late Glacial-Holocene climate instability in the north Aegean sea

Sedimentary molecular biomarker compositions, organic carbon and CaCO3 concentrations, and bulk organic delta C-13 and total delta N-15 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, 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. (c) 2007 Elsevier B.V. All rights reserved.