The expansion of C4 grasses and global change in the late Miocene: Stable isotope evidence from the Americas
The expansion of C4 grasses and global change in the late Miocene: Stable isotope evidence from the Americas
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DOI：
10.1016/s0012-821x(96)00231-2
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发表时间：
1997
影响因子：
5.3
通讯作者：
C. Latorre;J. Quade;W. Mcintosh
中科院分区：
文献类型：
--
作者：
C. Latorre;J. Quade;W. Mcintosh
古土壤和化石牙齿中的δ~(13)C值已被用来记录南亚、非洲和北美晚中新世C4植物的扩张。然而，由于缺乏高分辨率的记录，C4植被在旧大陆以外的确切时间和扩张速度尚不清楚。我们提供了一个来自阿根廷西北部的高分辨率记录，其中土壤碳酸盐的δ13C值高于−8‰的阈值，表明存在C4植物，开始于7.3M a-6.7M a。南美洲和北美年代较早的化石牙齿的δ13C值显示，大型食草动物的饮食中C4植物的含量伴随着增加。这些结果表明，晚中新世C4植物的扩张是全球性的，但在不同地区发生的速度不同。虽然有人认为，新近纪晚期pCO2水平的下降导致了C4植物的扩张，但气候变化，如全球夏季为主的降雨制度的增加，是另一种解释。南亚、东非和现在的阿根廷西北部的δ18O土壤碳酸盐记录都表明，新近纪晚期至少增加了3-4‰，这要么是气候变化的结果，要么是平均草原土壤蒸发增加的结果。
δ13C values in paleosols and fossil teeth have been used to document the expansion of C4plants in South Asia, Africa, and North America during the late Miocene. However, the exact timing and rate of expansion of C4vegetation is unclear outside the Old World because of a lack of high-resolution records. We present a high-resolution record from northwest Argentina in which the δ13C values of soil carbonate rise above a threshold of −8‰, suggesting the presence of C4plants, starting at 7.3-6.7 Ma. δ13C values of fossil teeth from well dated sections in South and North America display a concomitant increase of C4plants in the diets of large herbivores. These results show that the late Miocene expansion of C4plants was global, but occurred at different rates in each region. While it is has been suggested that declining pCO2levels during the late Neogene caused C4plant expansion, climate change, such as an increase in summer-dominated rainfall regimes globally, is an alternative explanation. The δ18O soil carbonate records from South Asia, East Africa and now also northwest Argentina all show an increase of at least 3–4‰ in the late Neogene, either the result of climate change or of greater evaporation in average grassland soils.