17Oexcess in Soreq Cave Speleothems

¹⁷O_excess is the deviation of d¹⁷O from the generally accepted ¹⁷O-¹⁸O mass dependent reference line. In carbonates, it records mostly the ¹⁷O_excess of the parent water. In rainfall, ¹⁷O_excess allows to reconstruct the relative humidity moisture source region, with lower relative humidity corresponding to higher ¹⁷O_excess. In some cases, however, partial re-evaporation of the raindrops may result in lower ¹⁷O_excess.

We measure ¹⁷O_excess in rain and cave water, as well as in speleothems from Soreq cave. ¹⁷O_excess of 50 per meg obtained in the weighted mean modern rainfall is consistent with the relative humidity at the moisture source region of the Eastern Mediterranean Sea. In small rain events ¹⁷O_excess is affected by raindrop partial evaporation.

¹⁷O_excess values of paleo water was reconstructed from ¹⁷O_excess in Soreq cave speleothems, at an age range of 0 - 160 ka, and compared to fluid inclusions d-excess. Water ¹⁷O_excess reconstruction was based on the ¹⁷O carbonate-water fractionation in modern Soreq stalagmites and cave water, which we found to be consistent with that in biogenic and synthetic carbonates, using previously measured clumped isotopes temperatures. The results show that ¹⁷O_excess and d-excess in paleo cave water vary together in some time periods but behave differently in other times, with variations in ¹⁷O_excess that likely reflect a combination of increase in normalized relative humidity in the moisture source region and local evaporation.