Mediterranean Paleoclimate During the Last 60 Ky as Derived From Speleothems, Soreq Cave, Israel

M Bar-Matthews; A Ayalon (Both at: Geological Survey of Israel, Jerusalem, 95501; ph. 972-2-5314201; fax: 972-2-5380688; e-mail: Matthews@mail.gsi.gov.il); A. Kaufman (Weizman Institute of Science, Rehovot,76100, Israel); G.J Wasserburg (Division of Geological and Planetary Sciences, CALTECH, Pasadena, CA, 91125; e-mail: isotopes@gps.caltech.edu)

Oxygen and carbon isotopic records of speleothems from the Soreq cave (Israel) covering the last 60 Ky, reflect the regional climatic variations of the Eastern Mediterranean region. The high precision of the TIMS ages also permits correlation of the isotopic time-series from the Soreq cave with other global records.

Speleothems that were deposited during the period ~60 to 18 Ky, have oxygen (~-2 to -4 permil) and carbon (~8- to -10 permil) isotopic values which are ~3.5 to 4 permil higher than those forming under present-day conditions. Their isotopic compositions follow a periodic cyclicity similar in age and duration to those of the Dansgaard-Oeschger cooling cycles, reflecting oscillations in temperature (~12 - 160C) and in annual rainfall (~250 - 400 mm/yr). Maximum oxygen isotopic values occur at times equivalent to those of Heinrich events and the last glacial maximum. The correlation between the oxygen isotopic events of the Soreq cave speleothems to events recorded in ice cores and in deep sea sediments from the North Atlantic indicates that the Atlantic Ocean's great conveyer belt circulation was probably the cause of rapid climatic change in the Eastern Mediterranean region. The period from 18 Ky to 8.5 Ky (equivalent to the period of deglaciation) includes a sharp drop of ~4 permil in oxygen and~5 permil in the carbon isotopic values, followed by isotopic peaks that can be correlated with H1 and with the Younger Dryas events. The 4 permil drop in d18O during deglaciation was caused by a sharp change in the oxygen isotopic compositions of precipitation, warming and increase in the annual rainfall from a ~300 to 800 mm/yr due to a change in the moisture source.

A unique isotopic record of minimum oxygen isotopic values (~-6.5 permil) associated with maximum carbon isotopic values (~-5 to -4 permil) occurs during a deluge period between 8.5 to 8.2 and between 8 to 7 Ky. This is probably due to rapidly moving waters through large fracture systems during heavy rainstorms, although another possible scenario is that during these time periods a major change occurred in the isotopic composition of atmospheric CO2. The isotopic record of speleothems formed during the last 7000 years is more similar to present-day values, but characterized by many short-lived isotopic variations.

U and Sr concentrations and their isotopic ratios are shown to be climate-related due to changes in the chemistry of the seepage water, the origin of storm tracks, and to water-soil-rock interactions.