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Bar-Matthews, M.; Ayalon, A.; Gilmour, M.; Matthews, A. and Hawkesworth, C. J.
(2002).
Abstract
Speleothems from several caves located in the semi-arid Eastern Mediterranean (EM) type climate (Israel) were studied through high resolution U-230Th TIMS dating and stable isotope composition. Their oxygen isotope (δ18O) records, covering the last 250 kyr, show striking similarities, indicating that they are a robust proxy for the climatic conditions on land. These speleothem δ18O records show a strong match with the marine δ18O records of the planktonic foraminifera G.ruber, which reflect sea surface conditions. The almost constant value of Δ G.ruber speleothems suggests a direct connection between the isotopic composition of EM Sea surface (the rainfall source) and on-land rain, and that calibrated sea surface temperatures (SST) serve as a good proxy for land temperatures.
Presently, minimum rainfall δ18O values occur during periods of enhanced rainfall. The δ18O minima of the speleothems formed during sapropel periods and correspondingly high water level stands in the caves, point to high rainfall on land in the EM region during these periods. This agrees with evidence for increasing rainfall in the entire Mediterranean during sapropel events (Kallel et al., 2000). The EM sea-surface water δ18O value during the post-Holocene sapropel S1 period was similar to present, because there is no evidence for addition of large water amounts from external sources. Thus, it is reasonable to assume that changes in sea surface δ18O mainly reflect temperature variations. Assuming that the calculated SST (Emeis et al., 2000) represent land temperatures, we have calculated the δ18O of the rain and cave water from which the speleothems were deposited. The corresponding amount of rainfall was then estimated using the last decade relationship between mean annual rainfall amount and its δ18O. These calculations show that post-sapropel conditions were associated with a decrease in rainfall, followed by an aridity trend on land. This pattern probably characterizes the conditions that developed after earlier interglacial sapropel periods.
