Geology Club Seminar

  The Middle East experienced unstable climate during the last interglacial,  varying from wetter intervals to extreme aridity. The ICDP Dead Sea Deep  Drill core reveals thick intervals of halite that precipitated during the  interglacials, representing the driest conditions in the Dead Sea  watershed, which stretches from the Saharan–Arabian desert belt to the  Mediterranean climate zone. The halite layers alternate with mud,  representing cycles of hundreds of years in which the climate varied  between relatively wet (similar to present day precipitation) and arid  climate (below 50% of present precipitation). Based on the chemical  compositions of fluid inclusions in the halite (Na/Cl~0.3-0.6), we  estimate that ~14-16 cm of halite precipitates per 1 m of lake level drop.  Although halite represents extreme aridities, the presence of gypsum and  detritus between the halite layers and crystals shows that even during  arid intervals there was water input into the lake. The halite alternates  between small cumulate crystals that are formed on the water surface and  large bottom-growth crystals that are formed on the lake floor. The large  crystals are associated with mud layers, while the cumulate crystals have  much less detritus and contain 'halite rafts', which are formed under high  evaporation conditions. The frequency of these alternations ranges from  thick layers of only 'bottom-growth halite' to rapid seasonal alternations  between the two crystal types. These different facies of halite represent  the order of aridity and maybe even the seasonality of precipitation.  While proxies and climate models show high precipitation and relatively  wet conditions in the Middle East during the peak of the last  interglacial, the peak margins were clearly extremely dry. The diversion  from the Mediterranean climate (wet winters and dry summers) is also  indicated by climate models showing a continuous decrease in winter  precipitation during the last interglacial, explaining the continuous  negative water budget