Controlling factors on a paleo-lake oxygen isotope record (Yammouneh, Lebanon) since the Last Glacial Maximum

Late Quaternary paleochmatic changes in the Levant are difficult to extract from carbonate oxygen isotope records partly because the factors controlling the terrestrial delta O-18 signals are not fully understood in this region characterized by sharp climatic gradients Here, we address this purpose by presenting the first C-14-dated isotope record from the northern Levant. The record is based on oxygen isotopes from ostracod shells from lacustnne-palustrine deposits accumulated in a small karstic, hydrologically open basin (Yammouneh), located on the eastern flank of Mount Lebanon We have first constructed a composite isotopic record obtained from three different ostracod taxa This yields an oxygen isotope record of ostracods (delta(ost)) related to the most widespread species (Ilyocypns inermis), and converted to delta O-18 values coeval with calcite precipitated in equilibrium (delta(C)) with the lake water (delta(L)) As with other records from the Mediterranean region, the Yammouneh profile shows maximum and minimum delta(C) values during the LGM and the early Holocene, respectively, and a slight late Holocene increase. In order to discuss the potential causes of the observed delta O-18 values fluctuations (e.g., changes in the isotopic composition of the moisture source, temperature, precipitation minus evaporation (P-E) balance, or atmospheric circulation), we tentatively reconstruct the lake water Isotope composition by correcting the delta(C) values for lake water temperature using regional paleotemperature estimates. Inferred L values were then corrected for the isotopic composition of the Eastern Mediterranean sea surface water (the moisture source) derived from planktonic forminifera delta O-18 values corrected for alkenone-based sea surface temperature. Our study suggests that Holocene delta(L) fluctuations are primarily linked to changes in the sea surface water composition (source effect) amplified by enhanced inland rainfall during the early Holocene. During the LGM, low delta(L) values at Yammouneh are likely due to the ground-temperature effect on the rainfall isotope composition, possibly associated with a steeper altitudinal thermal gradient inland, and with changes in air mass trajectories over the Mediterranean Sea (C) 2009 Elsevier Ltd All rights reserved