Sea-Rain-Lake relation in the Last Glacial East Mediterranean revealed by a δ18O-δ13C in Lake Lisan aragonites

We investigated the Sea-Rain-Lake relation during the Last Glacial-Holocene in the East Mediterranean region by comparing the delta(18)O and delta(13)C records of authigenic aragonite deposited in Lake Lisan, the Dead Sea, Mediterranean foraminifera, and speleothems. The Lisan Formation data display long- and short-term variations of 00, representing steady-state conditions of the lake (e.g., 5.6 parts per thousand +/- 0.5 parts per thousand and 4.5 parts per thousand +/- 1 parts per thousand in the Upper and Lower Members of the Lisan Formation, respectively), and short-term excursions reflecting large floods and droughts. The long-term (steady-state) delta(18)O values of the Lisan aragonites show similarity to the corresponding time-equivalent records of the Eastern Mediterranean foraminifera and Judea Mountain speleothems: The Last Glacial deposits are in all of them 2 parts per thousand-3 parts per thousand heavier than the Holocene ones. We interpret this similarity as reflecting the significance of the source effect on the long-term behavior of isotopic reservoirs: Speleothem delta(18)O is strongly influenced by the marine reservoir that contributes its vapor to rain formation; the lake delta(18)O is dominated by the composition of the inflowing water. Short-term variations in the isotopic composition of rainfall are dominated by the amount effect and the temperature and those of the Lake's upper water mass by the lake's water balance. delta(13)C values are more variable than delta(18)O in the same Lisan sequences (e.g., delta(13)C in the Lower Member is 1.0 parts per thousand +/- 1.7 parts per thousand, whereas delta(18)O is 4.6 parts per thousand +/- 0.7 parts per thousand) and are 1 parts per thousand to 1.5 parts per thousand higher in the Upper Member than in the Lower and Middle Members of the Lisan Formation. These variations reflect significant increase in primary productivity of the lake and algal bloom activity. It appears that the hypersaline-saline lakes were not as dead as the Dead Sea is and that algal activity had an important impact upon the geochemistry of Lake Lisan. The delta(18)O data combined with independent geochemical and limnologic information (e.g., level fluctuations) indicate that Lisan time was characterized by high precipitation-high lake stands-high atmospheric humidity, whereas the Holocene Dead Sea shows the opposite behavior. This paleoclimatic reconstruction is consistent with independent evidence for significantly wetter conditions in the East Mediterranean region during the Last Glacial period. Copyright (c) 2005 Elsevier Ltd.