From the Pleistocene to the Present: Climate induced water poverty in the Altai Mountains

The Altai Mountains of Mongolia form the western boundary between China and Mongolia and trend from the northwest to the southeast before terminating in the Gobi Desert. Although these mountains are not the most formidable with the highest peak reaching a modest 4374 m [Khüiten Peak], these mountains do facilitate a rare and important glaciated landscape, which as of 2010 cover a total area of 372 km² (Kamp and Pan 2015). The Altai’s glaciated landscape may seem negligible and even meager when compared to other mountain complexes within the High Mountains of Asia [HMA]; but the importance of these glaciers must not be understated in understanding past, present, and future climates and as an invaluable water resource for herders and their livestock in an already water restricted [semi-arid] country.

Traveling back in time to the Pleistocene [27,000 – 20,000 BP] the global climate was far different from what we observe today and as a result, the glaciations of this era covered an astounding ~20,700 km² (Lehmkuhl et al. 2004). As time moved forward the earth’s axial tilt began to change [these changes are known as Milankovitch cycles] and the Pleistocene Epoch began to naturally give way to the incoming Holocene Epoch [~11,000 BP]. The new influx of solar forcing caused global climates to warm and during this period the glaciers in the Altai began to dramatically decrease over the next few thousand years. It was recently discovered that in certain mountain ranges within the greater Altai complex, the glaciers disappeared. But in the mid-Holocene [~6,000 BP] the glaciers began to reappear. This neoglaciation is largely believed to be caused by a strong presence of the Indian Summer Monsoon which brings seasonal precipitation to the region by way of the Indian Ocean. This implies that the Altai’s modern glaciers are not remnants of the Last Glacial Maximum [LGM] but rather a neoglaciation during the mid-Holocene (Herren et al. 2013).

The Westerlies have again taken precedence in Mongolia’s climate in lieu of the Indian Summer Monsoon. This transition of climate influence engenders limited precipitation and increased evaporation, creating a semi-arid to arid environment inspiring glaciers to retreat. Throughout these shifts in climate, Milankovitch cycles, and glaciations, Mongolia has profited from vast wealth in water. In some areas, lake levels were up to 12 m higher than modern lake levels. However, these same lakes have been observed to completely disappear, leaving Mongolia water-destitute (Klinge and Lehmkuhl 2013). Fortunately, the glacier fed lakes in the Altai Mountains have seen only slight variations in lake levels over the past 20 years, remaining a consistent and reliable water resource for local herders. However as one moves east and to lower elevations, close to 68 lakes [larger than 1 km²] have disappeared from between 1990 to 2010 (Tao et al. 2015). Soon, the buffer provided by the glacier melt and altitude will no longer be able to defend the Altai’s lakes from impending aridity and the lakes may once again dry-up.