ARIDIFICATION OF CENTRAL ASIA AND UPLIFT OF THE ALTAI AND HANGAY MOUNTAINS, MONGOLIA: STABLE ISOTOPE EVIDENCE
ARIDIFICATION OF CENTRAL ASIA AND UPLIFT OF THE ALTAI AND HANGAY MOUNTAINS, MONGOLIA: STABLE ISOTOPE EVIDENCE
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DOI：
10.2475/08.2014.01
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发表时间：
2014-10-01
影响因子：
2.9
通讯作者：
Chamberlain, C. Page
中科院分区：
文献类型：
--
作者：
Caves, Jeremy K.;Sjostrom, Derek J.;Chamberlain, C. Page
中亚在新生代期间变得越来越干旱，尽管这种干旱背后的机制仍未得到解决。然而，与印度-亚洲辐合有关但位于高原北部的山脉，包括阿尔泰、萨扬和汉盖山脉，在形成中亚干旱气候中的作用却鲜为人知。今天，这些山脉形成了一个突出的雨影，有效地将北方的北方森林与中亚的沙漠分开。为了探讨始新世晚期以来这些山脉对气候的影响，我们在蒙古戈壁沙漠北缘和阿尔泰山脉和汉盖山脉背风处沿650公里长的样带测量了三个盆地的古土壤碳酸盐的碳和氧稳定同位素。我们将这些数据与现代气包反轨迹模型相结合，以了解每个盆地的区域水分输送路径。在所有盆地中，δ C-13均增加，其中蒙古西部增幅最大。渐新世首次δ C-13升高发生在蒙古中部和西南部。从上中新世到第四纪，蒙古西部和西南部的C-13三角洲再次增加。我们使用一维土壤扩散模型来证明，这些δ C-13的增加与干旱急剧增加导致的土壤呼吸下降有关。利用平均年降水量和土壤呼吸之间的现代经验关系，我们估计在新近纪，降水量可能减少了一半以上。考虑到汉盖和阿尔泰在蒙古水汽控制中的重要作用，我们将这些变化归因于汉盖和阿尔泰的不同地表隆升。汉盖的地表隆起始于渐新世早期，阻断了西伯利亚的水汽，使戈壁北部干旱化。相比之下，阿尔泰的地表隆起始于中新世晚期，阻止了水汽到达蒙古西部。因此，晚始新世以来，北戈壁逐渐由东向西发展，这可能是受渐新世汉盖和晚中新世至上新世阿尔泰地形发育的驱动。
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 back-trajectory modeling to understand regional moisture transport pathways at each basin. In all basins, delta C-13 increases, with the largest increase in western Mongolia. The first delta C-13 increase occurs in central and southwestern Mongolia in the Oligocene. delta C-13 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 delta C-13 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 and 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.