The Oligocene-Miocene Transition: New insights from the Newfoundland Margin

As a major site of deep water formation, the North Atlantic plays a critical role in global climate. To understand better how Earth’s climate system works it should therefore be a priority for geologists to study the record of past climate change encoded in the sedimentary archives that accumulate in the deep Atlantic. Here, sediment drilled in several cores on the Newfoundland Margin by International Ocean Discovery Program (IODP) Expedition 342 is utilized to provide fresh insights into palaeoclimate history, focusing on one of the more enigmatic events of the Cenozoic: the Oligocene-Miocene Transition (OMT), 23 million years ago. This is a time interval that Expedition 342 sediments have recorded in an continuous and expanded fashion unparalleled in previous records. This thesis aims to shed new light on North Atlantic OMT climate variability on both orbital and millennial-centennial timescales, and to increase the fidelity of foraminiferal proxies in this time interval. In Chapter 3, late Oligocene climate is shown to change cyclically on sub-orbital timescales. Centennial-millennial timescale variability is a key feature of Plio- Pleistocene climate; the record presented here is the first such record from earlier in the Cenozoic. These results show that Atlantic meridional overturning circulation is variable on sub-orbital timescales over a wider range of climate states than previously recognized. In Chapter 4, orbital- resolution planktic stable isotope records spanning the OMT are presented. These results – the first orbital-timescale record of sea surface conditions over the OMT – reveal that temperature changes in North Atlantic surface waters precede Antarctic glaciation/deglaciation and bottom water cooling/warming by tens of kyrs. In Chapter 5, the excellent preservation quality of foraminifera recovered by IODP Expedition 342 is exploited in a rigorous assessment of the taxonomy of several planktic foraminiferal species often used to generate palaeoclimate records over the OMT, with a focus on Globigerina bulloides. This quantitative, statistical approach enables non- subjective delineation of morphological variability into morphospecies, and highlights subtle morphological features that are critical to distinguish when picking foraminifera for stable isotope analyses. Together, the results of this thesis reveal that Earth’s climate system in the late Oligocene to early Miocene was much more dynamic and complex than previously recognized