Abstract. Constraints on the evolution of atmospheric CO₂ levels throughout Earth's history are foundational to our understanding of past variations in climate. Despite considerable effort, estimates of past CO₂ levels do not always converge and therefore new records and proxies are valuable. Here we reconstruct atmospheric CO₂ values across major climate transitions over the past 17 million years using the boron isotopic composition (δ¹¹B) of planktic foraminifera from 89 samples obtained from two sites in the West Pacific Warm Pool, Ocean Drilling Program (ODP) Sites 806 and 807. These sites are in a region that today is in equilibrium with the atmosphere and are thought to have been in equilibrium with the atmosphere for the interval studied. We use high-precision multi-collector inductively-coupled plasma mass spectrometry and show that data from these sites can reproduce the ice core record. Estimates of early Miocene pCO₂ are generally higher than published reconstructions from other sites, while values for the Pliocene and Pleistocene are more similar to other datasets. We find evidence for reductions in pCO₂ of ~280 µatm during the Middle Miocene Climate Transition, ~270 µatm during Pliocene Glacial Intensification, and ~50 µatm during the Mid-Pleistocene Climate Transition. There is possible evidence for a larger reduction in glacial pCO₂ during the Mid-Pleistocene Transition compared to interglacial pCO₂, and a minimum in pCO₂ during glacial MIS 30. Our results are consistent with a coupling between pCO₂, temperature and ice sheet expansion throughout the past 17 million years.

中文翻译：

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大气CO ₂的中新世更新世估计基于有孔虫δ ¹¹在赤道西太平洋的大洋钻探计划站点806和807乙

摘要。限制地球历史上大气CO ₂含量演变的基础是我们对过去气候变化的理解的基础。尽管付出了巨大的努力，对过去的CO ₂含量的估算并不总是收敛，因此新的记录和代理很有价值。在这里，我们重建大气CO ₂使用硼同位素组成（δ各主要气候转变值在过去的1700万年¹¹B）从89个样品中获得的有板有孔虫，这些样品是从西太平洋暖池的两个站点（海洋钻探计划（ODP）站点806和807）获得的。这些站点位于如今与大气平衡的区域，并且据认为已经在研究的时间间隔内与大气保持平衡。我们使用高精度的多收集器电感耦合等离子体质谱法，并显示来自这些站点的数据可以复制冰芯记录。中新世早期pCO _2的估算值通常高于其他站点公布的重建数据，而上新世和更新世的值与其他数据集更为相似。我们发现降低pCO _2的证据在中新世中期气候变迁中约280 µatm，在上新世冰川强化期间约270 µatm，在中更新世气候过渡中约50 µatm。存在用于在冰的pCO较大减少可能的证据₂的中更新世过渡期间相比的间的pCO ₂，和在的pCO最小₂期间冰MIS 30.我们的结果与的pCO之间的耦合一致₂，温度和冰片在过去的1700万年中不断扩展。