Glacial temperatures and moisture transport regimes reconstructed from noble gases and δ18O, Stampriet aquifer, Namibia

A noble gas temperature and δ18O record covering the past 30,000 years has been obtained from the Stampriet artesian aquifer in southeastern Namibia (24 deg. S, 19.5 deg. E). Radiocarbon ages, corrected for water-rock interactions along the flow path, increase uniformly with distance from the recharge area. Dissolved atmospheric noble gases indicate that the mean annual temperature in Namibia was about 5.3 deg. C lower during the last glacial maximum (LGM) than today. Together with the glacial/interglacial temperature changes of the same magnitude (5.5 deg. C to 6 deg. C) recorded at the Uitenhage aquifer and at the Cango caves in South Africa, these data indicate a uniform cooling of southern Africa. A peak in excess air concentration suggests a transition from a dry to a wetter climate at approximately 6000 years BP. The 18O record at Stampriet is characterized by an enrichment of 1.3 per mille during the LGM, in contrast to the Uitenhage aquifer, which shows a depletion of 1 per mille. This pattern may be explained by an increased importance of Atlantic moisture sources during the LGM. (author)