Climatic effects on the delta O-18 and delta C-13 of cellulose in the desert tree Tamarix jordanis

The C-13/C-12 and O-18/O-16 ratios of stem cellulose of Tamarix jordanis (a tree common in wadis of arid regions) increased with decreasing relative humidity (RH) in individual trees growing along a climatic gradient in Israel. The response to RH observed in the delta(18)O of the wood cellulose was strongly similar to that observed in leaf water over a diurnal cycle. Most of the data for delta(13)C and all of the data for delta(18)O could be fitted to two independent linear equations that, combined, allowed the reconstruction of RH and the delta(18)O of source water from the isotopic composition of ancient T. jordanis wood previously reported from the ancient fortress of Masada. Since the Roman period, RH at Masada decreased by about 17%, while the delta(18)O value of local groundwater remained similar to present-day values, suggesting that changing atmospheric circulation has played a role in climate change in the Middle East over the past two millennia.