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The respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the Eocene-Oligocene transition

机译：始新世-渐新世过渡期大气二氧化碳和轨道参数对冰盖演化的作用

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The continental scale initiation of the Antarctic ice sheet at the Eocene-Oligocene boundary (Eocene-Oligocene transition (EOT), 34 Ma) is associated with a global reorganization of the climate. If data studies have assessed the precise timing and magnitudes of the ice steps, modeling studies have been unable to reproduce a transient ice evolution during the Eocene-Oligocene transition in agreement with the data. Here we simulate this transition using general circulation models coupled to an ice sheet model. Our simulations reveal a threshold for continental scale glaciation of 900 ppm, 100 to 150 ppm higher than previous studies. This result supports the existence of ephemeral ice sheets during the middle Eocene, as similar CO_2 levels (900–1000 ppm) have been reached episodically during this period. Transient runs show that the ice growth is accurately timed with EOT-1 and Oi-1, the two δ~(18)O excursions occurring during the transition. We show that CO_2 and orbital variations are crucial in initiating these steps, with EOT-1 corresponding to the occurrence of low summer insolation, whereas Oi-1 is controlled by a major CO_2 drop. The two δ~(18)O steps record both ice growth and temperature, representing some 10–30m eustatic sea level fall and 2–4°C cooling at EOT-1 and 70 ± 20m and 0–2°C for Oi-1. The simulated magnitude of the ice steps (10m for EOT-1 and 63m for Oi-1) and the overall cooling at various locations show a good agreement with the data, which supports our results concerning this critical transition.
机译：在始新世-渐新世边界（始新世-渐新世过渡带（EOT），34 Ma）南极冰盖的大陆尺度启动与全球气候重组有关。如果数据研究已经评估了冰阶的精确时间和大小，那么建模研究将无法与数据相吻合地再现始新世-渐新世过渡期间的短暂冰演化。在这里，我们使用耦合到冰盖模型的一般循环模型来模拟这种过渡。我们的模拟显示，大陆规模冰河的阈值为900 ppm，比以前的研究高100至150 ppm。该结果支持在始新世中期存在短暂的冰盖，因为在此期间已经达到了类似的CO_2水平（900-1000 ppm）。瞬态运行表明，冰的生长是由EOT-1和Oi-1精确计时的，这两个δ〜（18）O偏移发生在过渡期间。我们表明，CO_2和轨道变化对于启动这些步骤至关重要，其中EOT-1对应于夏季低日照的发生，而Oi-1受主要CO_2下降的控制。 δ〜（18）O的两个步骤记录了冰的生长和温度，代表了约10–30m的海平面下降和EOT-1的2-4°C冷却以及Oi-1的70±20m和0–2°C 。冰阶的模拟大小（EOT-1为10m，Oi-1为63m）以及各个位置的整体冷却与数据显示出很好的一致性，这支持了我们关于这一关键转变的结果。

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