Low resolution paleoclimate reconstruction, from stable isotope analysis of two speleothems from the El-Kassarat and Rahwe caves, in Lebanon -

Abstract

Two stalagmites were investigated from the coastal El-Kassarat cave, EKC-01 (located in central Lebanon), and a high elevation Rahwe cave, RC-01 (located in North Lebanon), respectively. The paleo-climatic records observed are based on oxygen and carbon stable isotope ratios, absolute dating of U-Th series, petrographic analysis, and growth patterns. Groundwater, dripwater, rainwater, and snow samples were acquired for isotope analyses and physico-chemical parameter determination. Continuous temperature measurements were conducted for a whole year. Glass plates were placed inside each cave, and modern calcite precipitates were collected for calibration. All these measurements allowed for a detailed calibration of the stable isotopic and age data collected from the two stalagmites. Four samples were drilled in the RC-01 stalagmite for U-Th dating. This stalagmite showed age reversals and alteration, thus requiring further assessment in the future. The candlestick section of EKC-01 was drilled for U-series dating (3 samples). This stalagmite segment was also analyzed for carbonate δ¹⁸O and δ¹³C isotopes (64 samples), and for trace elements. Dating results show that this stalagmite started to grow at about 62 ka BP. Isotopic results from the EKC-01 stalagmite indicates that major changes in local and global climatic records have been recorded in the stalagmites’ laminae. These can be subdivided into five major climatic phases; Phase 1 (27.5 to 15.0 ka) was characterized by lower temperatures and lesser rainfall, with a mixture of C₃ (e.g. shrubs, wheat, trees) and C₄ (e.g. maize, sugar cane) vegetation types present in the region. As glaciers in much of the northern hemisphere melted, there was a sharp increase in temperature and rainfall, and a possible increase in C₃ vegetation between 15.0 and 13.0 ka. The climatic phase spanning from 13.0 to 9.0 showed comparatively more humid conditions, with an increase in rainfall during the early Holocene epo