Oligocene climate dynamics towards the Oligocene-Miocene transition (IODP Expedition 342, North Atlantic)

渐新世代表了冰窖世界的早期阶段，始于3400万年前南极东部永久冰盖形成后（i-1冰期）。这一区间的特点是深海底栖有孔虫d18O的高变异性和可能与南半球冰盖不稳定有关的高幅度海平面波动。这种变化在最早的中新世~ 2300万年前的第二次主要冰川事件（Mi-1事件）中达到顶峰。然而，由于在这段时间间隔内缺乏高质量的数据集，总体演变，特别是在长时间尺度和短时间尺度（轨道到亚轨道）上所涉及的机制是推测性的和有争议的。在IODP 342考察期间，在纽芬兰附近的J-Anomaly Ridge钻取了覆盖渐新世至早中新世过渡的扩展层序。这些沉积物含有保存非常完好的钙质微化石，其特点是沉积速率高，可以在岁差到亚轨道时间尺度上产生高分辨率的代用记录。本项目旨在提供覆盖渐新世上部至中新世早期（~26.5-21.7 Ma）的1.8分辨率底栖有孔虫稳定同位素记录，对应于南极渐新世冰盖生长的第二阶段。到目前为止，这个时间间隔的高分辨率数据集很少见，而且仅限于太平洋中部和南半球。因此，在纽芬兰附近恢复的沉积物不仅具有很高的潜力，可以提供非常高分辨率的代理数据集，而且还可以提供北大西洋对地球气候演化这一关键时期的看法。由于大量的地球化学分析(大约。3000个样本)是完成这个项目目标所必需的，这项工作将在一个国际联盟中进行，包括来自德国（本提案）、英国和韩国的342远征队参与者。本文研究的时间区间为~4.8 Ma的渐新统上段（~25.7 ~ 24 Ma）。此外，将以20键的分辨率研究原始保存的玻璃状浮游有孔虫试验，以揭示Mi-1冰期事件的长期气候演变。为了实现这一目标，将使用双代理方法（d18O, Mg/Ca）估计绝对海面和温跃层温度。这将有助于重建北大西洋表层海洋对米-1事件的反应，以及它是如何受到全球气候动力学的影响的。

The Oligocene represents an early stage of the icehouse world that commenced after the formation of a permanent east Antarctic ice sheet ~34 Million years ago (Oi-1 glaciation). This interval is characterized by a high variability in the d18O of deep-sea benthic foraminifera and high-amplitude sea-level fluctuations probably related to southern hemisphere ice sheet instability. This variability culminates in a second major glaciation event during the earliest Miocene ~23 Million ago (Mi-1 event). Due to the scarcity of high-quality data sets across this time interval, however, the overall evolution and especially the mechanisms involved on long and short time scales (orbital to suborbital) are speculative and a matter of debate. During IODP Expedition 342 expanded sequences covering the Oligocene to early Miocene transition have been drilled at J-Anomaly Ridge off Newfoundland. These sediments contain exceptionally well-preserved calcareous microfossils and are characterized by high sedimentation rates allowing for the generation of a high-resolution proxy-record on precessional to suborbital time scales. This project aims at providing a 1.8-ky-resolution benthic foraminiferal stable isotope record covering the upper Oligocene to early Miocene (~26.5-21.7 Ma), corresponding to the second phase of Oligocene ice sheet growth on Antarctica. So far, high-resolution data sets from this time interval are rare and limited to the central Pacific and southern hemisphere. Thus, the sediments recovered off Newfoundland have a high-potential not only to provide a very high-resolution proxy data set, but also a North Atlantic view of this crucial interval of Earth s climate evolution. Since an enormous amount of geochemical analyses (approx. 3000 samples) are necessary to accomplish the goal of this project, the effort will be carried out in an international consortium including Expedition 342 participants from Germany (this proposal), the UK and South Korea. The time interval focused on in this proposal is the upper Oligocene part (~25.7 to 24 Ma) of the ~4.8 Ma long record. In addition, pristinely preserved, glassy planktic foraminiferal tests will be studied at a resolution of 20 kys to unravel the long-term climate evolution across the Mi-1 glaciation event. To achieve this goal, absolute sea-surface and thermocline temperatures will be estimated, using a dual-proxy approach (d18O, Mg/Ca). This will allow the reconstruction of North Atlantic surface ocean response to the Mi-1 event and how it was influenced by global climate dynamics.