Aridification of Central Asia and uplift of the Altai and Hangay Mountains, Mongolia: Stable isotope evidence

Abstract

Central Asia has become increasingly arid during the Cenozoic, though the mechanisms behind this aridification remain unresolved. Much attention has focused on the influence and uplift history of the Tibetan Plateau. However, the role of ranges linked to India-Asia convergence but well north of the Plateau-including the Altai, Sayan, and Hangay-in creating the arid climate of Central Asia is poorly understood. Today, these ranges create a prominent rain shadow, effectively separating the boreal forest to the north from the deserts of Central Asia. To explore the role of these mountains in modifying climate since the late Eocene, we measured carbon and oxygen stable isotopes in paleosol carbonates from three basins along a 650 km long transect at the northern edge of the Gobi Desert in Mongolia and in the lee of the Altai and Hangay mountains. We combine these data with modern air-parcel backtrajectory modeling to understand regional moisture transport pathways at each basin. In all basins, ␦ 13 C increases, with the largest increase in western Mongolia. The first ␦ 13 C increase occurs in central and southwestern Mongolia in the Oligocene. ␦ 13 C again increases from the upper Miocene to the Quaternary in western and southwestern Mongolia. We use a 1-D soil diffusion model to demonstrate that these ␦ 13 C increases are linked to declines in soil respiration driven by dramatic increases in aridity. Using modern-day empirical relations between mean annual precipitation and soil respiration, we estimate that precipitation has likely more than halved over the Neogene. Given the importance of the Hangay and Altai in steering moisture in Mongolia, we attribute these changes to differential surface uplift of the Hangay and Altai. Surface uplift in the Hangay began by the early Oligocene, blocking Siberian moisture and aridifying the northern Gobi. In contrast, surface uplift of the Altai began in the late Miocene, blocking moisture from reaching western Mongolia. Thus, the northern Gobi became increasingly arid east to west since the late Eocene, likely driven by orographic development in the Hangay during the Oligocene and the Altai in the late Miocene through Pliocene.

Role of the westerlies in Central Asia climate over the Cenozoic

“…HYSPLIT has been used to demonstrate the origin of moisture-bearing air parcels to explain both modern and sedimentary δ 18 O data (e.g., Bershaw et al, 2012;Breitenbach et al, 2010;Caves et al, 2014;Feng et al, 2014;Oster et al, 2012;Sjostrom and Welker, 2009). We focus specifically on two sites that span the latitudinal breadth of Central Asia: western Mongolia (western Valley of Lakes; 47.14N 93.06E) in northern Central Asia and the Qaidam Basin (37.3N 96.7E) on the northern edge of the Tibetan Plateau.…”

Stepwise Onset of the Icehouse World and Its Impact on Oligo- Miocene Central Asian Mammals

“…A comparable climate-sensitivity is documented for δ 13 C values in soil carbonates. Carbon isotopes in the Eocene to Upper Miocene section of the Valley of Lakes have been studied by Caves et al 11 , who identified two main mechanisms to explain the observed increase in δ 13 C in paleosol carbonates. These are a decrease in primary productivity due to increasing aridity and an increase in evaporation coupled with lowered precipitation.…”

“…Between 34 and 32 Ma (biozone A) δ 26 . Intensified uplift of the Tibetan plateau and the Hangay Mountains, as well as, and the prevailing westerlies which carry low moisture, amplified aridity 10,11,30 . Based on sedimentological evidence, the depositional environments in the Taatsiin Gol Basin is interpreted as semiarid open steppe with ephemeral rivers and playa lakes 7 .…”

“…In addition, the intensified uplift of the Tibetan plateau and of the Hangay range ( Fig. 1) amplified aridification 10,11 . The subsequent climatic and biotic developments during the Oligocene and early Miocene in Central Asia have received less attraction, although these epochs saw dramatic shifts in global climate, expressed by major ice sheet oscillations in the southern Hemisphere [12][13][14][15][16] .…”

A review of the Pseudocleonus subgenus Phryganocleonus Arnol’di, with the description of a new species from Afghanistan (Coleoptera, Curculionidae: Lixinae)

“…Considering its present day distribution (Fig. 15), the differentiation of the subgenus Phryganocleonus may have been triggered by the uplift of the Asian mountain chains, with subsequent habitat aridification, that occurred in the late Miocene (Caves et al, 2014). These species are nowadays adapted to the montane xerophytic habitat and appear to have a relict, very limited areal, probably determined by isolation and speciation by vicariance.…”