Survival of the Qaidam mega-lake system under mid-Pliocene climates and its restoration under future climates

Abstract

The Qaidam Basin in the north of the Tibetan Plateau has undergone drastic environmental changes during the last millions of years. During the Pliocene, the Qaidam Basin contained a freshwater mega-lake system although the surrounding regions showed increasingly arid climates. With the onset of the Pleistocene glaciations, lakes began to shrink and finally disappeared almost completely. Today, hyperarid climate conditions prevail in the low-altitude parts of the Qaidam Basin. The question of how the mega-lake system was able to withstand the regional trend of aridification for millions of years has remained enigmatic so far. This study reveals that the mean annual water balance, i.e. the mean annual change in terrestrial water storage in the Qaidam Basin, is nearly zero under present climate conditions due to positive values of net precipitation in the high mountain ranges and shows positive annual values during warmer, less dry years. This finding provides a physically based explanation for how mid-Pliocene climates could have sustained the mega-lake system and that near-future climates not much different from present conditions could cause water storage in reservoirs, raising lake levels and expanding lake areas, and may even result in restoration of the mega-lake system over geological timescales. The study reveals that a region discussed as being an analogue to Mars due to its hyperarid environments is at a threshold under present climate conditions and may switch from negative values of long-term mean annual water balance that have prevailed during the last 2.6 million years to positive ones in the near future.