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Pliocene CO2 rise due to sea-level fall as a mechanism for the delayed ice age
Global and Planetary Change ( IF 3.9 ) Pub Date : 2024-03-28 , DOI: 10.1016/j.gloplacha.2024.104431 Shiling Yang , Yongda Wang , Xiaofang Huang , Minmin Sun , Jingtai Han , Xu Wang , Zuoling Chen , Shihao Zhang , Wenying Jiang , Zihua Tang , Zhaoyan Gu , Shangfa Xiong , Zhongli Ding
Global and Planetary Change ( IF 3.9 ) Pub Date : 2024-03-28 , DOI: 10.1016/j.gloplacha.2024.104431 Shiling Yang , Yongda Wang , Xiaofang Huang , Minmin Sun , Jingtai Han , Xu Wang , Zuoling Chen , Shihao Zhang , Wenying Jiang , Zihua Tang , Zhaoyan Gu , Shangfa Xiong , Zhongli Ding
Global sea level fell progressively during the Pliocene in response to the growth of ice sheets at high northern latitudes. However, not until ∼2.7 Ma did the climate system actually generate and maintain major ice sheets in the Northern Hemisphere. A decline in atmospheric CO levels (CO) is thought to be responsible for the Pleistocene ice ages. However, the link between CO and Pliocene glaciations, or their delay, is not well understood, mainly because the magnitude of CO remains uncertain beyond the maximum age of ice cores (∼0.8 Ma). Here, we develop a carbonate clumped isotope (∆) geothermometer specifically for pedogenic carbonate in Chinese loess, which we use to reconstruct temperatures in northern China, and CO, for the past 7.24 Ma. The palaeotemperature results show an oscillatory cooling trend over time in the East Asian monsoon region, in good agreement with coeval tropical sea surface temperature records. The CO reconstruction using the pedogenic carbonate palaeobarometer reveals low values (150–325 ppmv) during the intervals of 7.24–4.3 Ma and 2.6–0 Ma. In contrast, there is a three-step rise in CO up to 535 ppmv from 4.3 to 2.6 Ma, coincident with an oscillatory decrease in sea level and in benthic δC. We suggest that the Pliocene CO rise was causally related to the sea-level fall and associated organic carbon oxidation on exposed continental shelves, thereby delaying the onset of the ice age. This implies a negative feedback mechanism induced by long-term cooling since the Late Miocene, which may have delayed the onset of the ice age but did not prevent it.
更新日期：2024-03-28
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