Petrography, strontium, barium and uranium concentrations, and strontium and uranium isotope ratios in speleothems as palaeoclimatic proxies: Soreq Cave, Israel

The reconstruction of the palaeoclimate of the eastern Mediterranean region for the last 60 ka BP is based on the delta(18)O and delta(13)C variations of speleothems from Soreq Cave, Israel. Climatic conditions during most of the rime interval between 60 and 17 ka BP (the period equivalent to the last glacial) were relatively cold and dry, while they were warmer and wetter from 17 ka BP to the present. At similar to 17 ka BP, there was a major climatic change with a sharp increase in annual rainfall and temperature and a very wet period occurring between 8.5 and 7.0 ka BP. During the colder and drier period, large, detritus-free, preferentially oriented calcite crystals were deposited from slow-moving water. As a result of a sharp change in the hydrological regime at similar to 17 ka BP, fast-moving water started entrainment of the soil and carrying detrital material into the cave, and the calcite crystals deposited became small and anhedral. Coinciding with the petrographic and isotopic changes, a sharp drop occurred in the concentrations of strontium, barium and uranium, and in the ratios Sr-87/Sr-86 and (U-234/U-238)(0), which reached mini mum values during the wettest period. This drop reflects enhanced weathering of the soil dolomite host rock. During colder and drier periods, higher trace-element concentrations and higher isotopic ratios reflect an increase in the contribution of salts derived from exogenic sources (sea spray and aeolian dust), and a reduced contribution of weathering from the host dolomites.