NOAA/WDS Paleoclimatology - Paleo-pCO2 Database: Western Equatorial Pacific Atmospheric CO2 estimates derived from foraminiferal d11B Over the Past 15.69 Ma

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, records vary in their temporal and spatial coverage and 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 16 million years using the boron isotopic composition (d11B) of planktic foraminifera from 89 samples obtained from two sites in the West Pacific Warm Pool, Ocean Drilling Program (ODP) Sites 806 and 807, measured using high-precision multi-collector inductively coupled plasma mass spectrometry. We compare our results to published data from ODP Site 872, also in the Western Equatorial Pacific, that goes back to 22 million years ago. These sites are in a region that today is near equilibrium with the atmosphere and are thought to have been in equilibrium with the atmosphere for the interval studied. We show that d11B data from this region are consistent with other boron-based studies. The data show evidence for elevated pCO2 during the Middle Miocene and Early to Middle Pliocene, and reductions in pCO2 of ~200 ppm during the Middle Miocene Climate Transition, ~250 ppm during Pliocene Glacial Intensification and ~50 ppm during the Mid-Pleistocene Climate Transition. During the Mid-Pleistocene Transition there is a minimum pCO2 at marine isotopic stage (MIS) 30. Our results are consistent with a coupling between pCO2, temperature and ice sheet expansion from the Miocene to the late Quaternary.

对地球整个历史时期大气二氧化碳（CO₂）浓度演化的约束研究，是理解古气候变化的核心基石。尽管已有大量研究投入，但现有记录在时间与空间覆盖范围上存在差异，且古CO₂浓度的估算结果并非总能达成一致，因此新的记录与代用指标具有重要研究价值。本研究采用高精度多接收器电感耦合等离子体质谱法，对取自西太平洋暖池两处大洋钻探计划（Ocean Drilling Program, ODP）站位806与807的89个浮游有孔虫样品的硼同位素组成（d11B）进行测试，重建了过去1600万年以来各主要气候转型期的大气CO₂浓度值，并将所得结果与同样来自西赤道太平洋、可追溯至2200万年前的ODP站位872的已发表数据进行了对比。上述两个站位所在区域现今与大气处于近乎平衡状态，且被认为在本研究覆盖的时间区间内始终维持大气-海水平衡状态。研究表明，该区域的d11B数据与其他基于硼同位素的古气候研究结果一致。本研究数据显示，中新世中期以及上新世早-中期的大气CO₂分压（pCO₂）存在升高现象；而在中新世中期气候转型期、上新世冰盖强化期与更新世中期气候转型期，pCO₂分别下降了约200 ppm、250 ppm与50 ppm。在更新世中期转型期，海洋同位素阶段（MIS）30对应pCO₂的最低值。本研究结果与中新世至晚更新世期间pCO₂、温度与冰盖扩张之间的耦合关系假说相一致。