The mid Miocene represents an important target for paleoclimatic study because the atmospheric CO₂ concentration ranged from near modern values to ∼800 ppm, while a large, dynamic Antarctic ice sheet was likely to have been present throughout much of this interval. In this special issue, Modestou et al. (2020) (doi.org/10.1029/2020PA003927) reconstruct deep ocean warmth based on the clumped isotopic composition of benthic foraminifera, a technique that allows the ice volume and thermal components of the benthic oxygen isotope stack to be separated. These data reveal a very warm deep ocean while simultaneously suggesting that continental ice volume may, at times, have been greater than today. Here, I review these results in the context of recent developments in geochemical proxies and ice sheet modeling, and explore how the presence of a large Miocene ice sheet could be reconciled with CO₂ at least as high as present. More broadly, I argue that many of the 'paradoxes' that pepper the paleoclimate literature result as much from our imperfect understanding of the proxies, as from our understanding of the climate system. Robust proxies with a well‐understood mechanistic basis, as employed by Modestou et al. (2020), as well as advances in model‐data comparability usher in a new era of palaeoclimate research; an exciting future of untangling Earth's myriad past climate states awaits.

中文翻译：

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深热：代理，中新世冰和古气候悖论的终结？

中新世中期是古气候研究的重要目标，因为大气中的CO ₂浓度范围从接近现代值到约800 ppm，而在此间隔的大部分时间里，可能会出现一个大型的动态南极冰盖。在本期特刊中，Modestou等人。（2020）（doi.org/10.1029/2020PA003927）基于底栖有孔虫的成簇同位素组成重建深海温暖，这项技术可以分离底栖氧同位素堆的冰量和热成分。这些数据揭示了一个非常温暖的深海，同时表明大陆的冰量有时可能会比今天更大。在此，我将结合地球化学代理和冰盖模型的最新发展来回顾这些结果，并探讨如何将大型中新世冰盖与CO ₂协调起来。至少和现在一样高 更广泛地说，我认为，使古气候文献泛滥的许多“悖论”，很大程度上是由于我们对代理的不完全理解以及对气候系统的理解所致。如Modestou等人所使用的那样，具有可靠的机械基础的可靠代理。（2020年），以及模型数据可比性的进步，开创了古气候研究的新纪元。解开地球无数过去的气候状态的令人兴奋的未来等待着。