Last glacial pollen record from Lanzhou (Northwestern China) and possible forcing mechanisms for the MIS 3 climate change in Middle to East Asia
Last glacial pollen record from Lanzhou (Northwestern China) and possible forcing mechanisms for the MIS 3 climate change in Middle to East Asia
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DOI：
10.1016/j.quascirev.2010.12.024
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发表时间：
2011-03
影响因子：
4
通讯作者：
Hanchao Jiang;Xuegang Mao;Hongyan Xu;Jessica A. Thompson;Ping Wang;Xiaolin Ma
中科院分区：
文献类型：
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作者：
Hanchao Jiang;Xuegang Mao;Hongyan Xu;Jessica A. Thompson;Ping Wang;Xiaolin Ma
青藏高原东北缘的植被对气候变化高度敏感，因此是一个潜在的有趣的环境档案。对兰州范家坪黄土剖面的花粉样品进行了光释光测年分析。结果表明，B带（60.6-46.0 ka，对应于MIS 3早期）的柏科、铁杉科、禾本科和莎草科花粉丰度最高，表明末次冰期处于暖期。这些花粉类群的丰度在C区（46.0-39.0 ka）和D区（39.0-27.0 ka）显著减少，反映了从MIS 3中期到MIS 2的气候变冷。这些结果与南海、CLP、贝加尔湖、北美、北大西洋等地区的气候记录相关联，可能与北方高纬度太阳辐射的下降和全球冰量的增加相对应。特别是乔木花粉、蕨类孢子和藻类的丰度在1040 ka以来急剧下降，而灌木和草本花粉的丰度达到最高。针叶树花粉云杉和冷杉的丰富度也显着上升，并增加了部分。这意味着显著的气候恶化，并可能对应于自2040 ka以来极地冰盖的大幅增长。末次冰期日照下降导致的温度下降可能加强了“雪/冰/冰”反馈中的冷却效应，这将导致气候对辐射强迫的敏感性降低。与此同时，末次冰期北方半球植被的减少和高纬度冻原的发展可能导致了额外的冷却，促进了40 ka以来极地冰盖的生长。40-30 ka期间，极地冰盖的发展增大了极赤道温度和气压梯度，加强了西风带，为西北地区提供了充足的水汽。40-30 ka期间青藏高原湖泊沉积广泛发育，这可能与中低纬日照季节性增加导致高原冰川融化增强有关。
The vegetation on the northeastern margin of the Tibetan Plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive. Pollen samples from the Fanjiaping Loess section in Lanzhou on the western Chinese Loess Plateau (CLP) were analyzed in conjunction with OSL dating. The results indicate that pollen zone B (60.6–46.0 ka, correlative to the early MIS 3) had the greatest abundances of Cupressaceae, Tsuga, Gramineae and Cyperaceae of the entire section, suggesting a warm phase during the last glacial period. These pollen taxa decreased significantly in abundance in the zones C (46.0–39.0 ka) and D (39.0–27.0 ka), reflecting a substantial climate cooling from the middle MIS 3 to MIS 2. These results correlate with climate records from the South China Sea, the CLP, Baikal Lake, North America, North Atlantic Ocean and other regions, and probably correspond with the decline of northern high-latitude insolation and the increase of global ice volume from 50 to 20 ka. In particular, arboreal pollen, fern spore and algae abundances declined sharply since ∼40 ka, while shrub and herb pollen reached the highest abundances. Conifer pollen Picea and Abies abundance also rose markedly and increased up the section. This implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since ∼40 ka. The decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a ‘snow/ice/albedo’ feedback, which would result in less climate sensitivity to radiative forcing. Meanwhile, vegetation decline in the Northern Hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling, enhancing the growth of polar ice sheets since 40 ka. The development of polar ice sheets increased the polar-to-equator temperature and pressure gradients, strengthening the westerlies and supplying plenty of moisture to Northwest China during 40–30 ka. Lake sediments developed widely on the Tibetan Plateau during 40–30 ka, probably related to an increase in the seasonality of middle-to-low latitude insolation which caused an enhancement of glacier melting on the Plateau.