Exploring past environments based on temperature reconstructions from Pliocene Arabian speleothems

The Arabian Desert experienced multiple periods of wetter and greener conditions that sustained human populations and allowed the dispersal of mammal fauna across the Arabian Peninsula. A recently published speleothem-based paleoclimate reconstruction of central Arabia extends the record of such recurrent short-lasting humid periods over at least the past 8 million years. Here, we applied multiple recently developed paleothermometers to this late Miocene to late Pleistocene speleothem record: Fluid inclusion stable isotopes, microthermometry and dual-clumped isotopes. The data indicate that in the late Miocene and Pliocene, wetter episodes in central Arabia were up to ~4 °C warmer than current Mean Annual Air Temperature (MAAT). These temperature estimates imply that potential evapotranspiration was significantly higher during the late Miocene and Pliocene than during the late Pleistocene. From these temperature estimates, we calculated Pliocene potential evapotranspiration and estimated precipitation amounts for the humid periods in central Arabia. All the evidence from the speleothems combined (temperature, precipitation, δ¹³C values) suggests that over the past 8 million years, the wetter phases in central Arabia typically led to savanna-like environments.

Modern climate data show that our study area has already reached Pliocene MAATs in recent years due to anthropogenic warming. The concomitant drying trend in modern settings indicates that higher temperatures are not the key factor in creating wetter conditions on the Arabian Peninsula. Previously proposed orbital control on the incursion of monsoonal moisture from the south into the Arabian Peninsula remains the most important driver of humidity during these past humid periods. In the modern orbital configuration, monsoonal moisture advection is displaced to the south, and increasing temperatures will likely lead to increased potential evaporation and aridity in central Arabia.