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

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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.