Cenozoic global ice volume and temperature simulations over the past 40 million years

Variations in global ice volume and temperature over the Cenozoic era have been investigated with a set of one-dimensional (1-D) ice-sheet models. Simulations include three ice sheets representing glaciation in the Northern Hemisphere, i.e. in Eurasia, North America and Greenland, and two separate ice sheets for Antarctic glaciation. The continental mean Northern Hemisphere surface-air temperature has been derived through an inverse procedure from observed benthic d18O records. These data have yielded a mutually consistent and continuous record of temperature, global ice volume and benthic d18O over the past 35 Ma. The simple 1-D model shows good agreement with a comprehensive 3-D ice-sheet model for the past 3 Ma. On average, differences are only 1.0°C for temperature and 6.2 m for sea level. Most notably, over the 35 Ma period, the reconstructed ice volume–temperature sensitivity shows a transition from a climate controlled by Southern Hemisphere ice sheets to one controlled by Northern Hemisphere ice sheets. Although the transient behaviour is important, equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric, providing limited evidence for hysteresis. Furthermore, the results show a good comparison with other simulations of Antarctic ice volume and observed sea level.本研究采用一维（1-D）冰盖模型集合，对新生代（Cenozoic era）以来全球冰量与地表气温的演变特征展开了系统性探究。模拟设置涵盖代表北半球冰川作用的3个冰盖，即分布于欧亚大陆、北美与格陵兰的冰盖，以及独立发育于南极的2个冰盖。研究通过反演方法，基于观测得到的底栖δ¹⁸O（benthic d18O）记录重建了北半球大陆平均地表气温序列，由此构建了过去35 Ma以来气温、全球冰量与底栖δ¹⁸O的连续且相互自洽的完整记录。该简化一维模型与针对过去3 Ma的综合三维（3-D）冰盖模型模拟结果吻合良好，两者在气温上的平均偏差仅为1.0°C，海平面高度的平均偏差仅为6.2 m。尤为显著的是，在35 Ma的时间跨度内，重建得到的冰量-气温敏感性呈现出从受南半球冰盖主导的气候状态，向受北半球冰盖主导的气候状态的转变过程。尽管瞬态模拟行为具备重要研究价值，但平衡态实验结果表明，气温与海平面高度之间呈线性对称的对应关系，仅能为滞后效应提供有限的佐证。此外，本研究结果与其他南极冰量模拟结果以及观测得到的海平面记录均表现出较好的一致性。