GLACIAL-INTERGLACIAL PALEO-TEMPERATURES AND PALEO-HYDROLOGY IN THE JORDAN RIVER VALLEY, USING CLUMPED-ISOTOPES IN FRESH WATER SNAILS

Oxygen isotope composition of carbonate minerals is the most popular proxy in paleo-climate research and is especially common in the marine environment; however, since implementation of δ¹⁸O records for reconstruction of environmental temperatures requires an independent estimate of paleo-water composition, it is difficult to interpret this proxy in terrestrial records. Carbonate clumped isotopes thermometry is based on the relationship of ¹³C-¹⁸O bond abundance in the carbonate lattice (measured as Δ₄₇) with the carbonate formation temperature. Most marine biogenic carbonates are consistent with the laboratory precipitation experiments that are used as calibration for the clumped isotopes thermometer.

We examine Δ₄₇ in fresh water snails, focusing on Melanopsis snails that were collected in various water-bodies along the Jordan Valley (Israel). The modern samples cover a range of ~10°C. As in marine biogenic carbonates, the temperatures derived from clumped isotopes in these modern shells are consistent with the water temperatures. Measured oxygen isotopic compositions of sampled water-bodies broadly agrees with δ¹⁸O water values calculated from clumped isotope temperatures and living-shell δ¹⁸O. This suggests that clumped isotopes in Melanopsis shells, as most marine organisms, agree with the clumped isotopes thermometer calibration.

We further analyzed fossil Melanopsis snails collected in the Northern Jordan Valley and at sites near the modern-day northern and the southern banks of the Sea of Galilee. Our samples ages range from MIS 3 to Late-Holocene. We find fairly constant temperatures during the glacial period with low temperatures and δ¹⁸O water. Post-glacial temperatures increase to a peak in Mid-Holocene, followed by a decrease to intermediate modern values. Mid-Holocene Jordan River and northern Sea of Galilee water are δ¹⁸O -enriched by ~2‰ relative to both the LGM and modern values.

This enrichment is opposite to the depletion glacial-interglacial trend observed in other regional records such as Dead Sea sediments, Soreq cave speleothems, and Mediterranean Sea foraminifera. It is likely to reflect a change in the hydrological balance, mainly in the contribution of snow-melt to the Jordan River.