Changes in ocean circulation and the global carbon cycle during the last interglacial-glacial transition: Marine Isotope Stage 5a to 4

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The last glacial period was punctuated by repeated, high-amplitude millennial-scale shifts in northern hemisphere climate known as Dansgaard-Oeschger (D-O) oscillations. These events were characterised by the extremely rapid alternation between cold and warmer conditions with temperature increases over Greenland and NW Europe sometimes exceeding 10 degrees Celsius within a few decades. The discovery of D-O oscillations has provided a major stimulus for climate research and fuelled debate over the possible nature of climate change in the future, yet very little is known about the origin of these events. Ocean circulation is a fundamental component of Earth's climate system. Changes in circulation are known to be associated with major shifts in global climate, including glacial-interglacial transitions as well as more rapid events such as D-O oscillations. The transition from the last interglacial period (similar to today) to full glacial conditions, around 75,000 years ago, saw a large build-up of continental ice sheets and a decrease in atmospheric CO2. This period also saw the first appearance of D-O climate variability, suggesting that a critical threshold, between the relative stability of the last interglacial and the instability of glacial times, had been crossed. However, fundamental uncertainties currently exist concerning the role of ocean circulation within the evolving climate system and its apparent threshold behaviour at this time. This project will investigate changes in Atlantic Ocean circulation and their role in global climate change during the MIS 5a/4 transition. The project will improve our understanding of the links between ocean circulation and climate change and will therefore inform scientists working in related fields and potentially policy makers. Palaeoclimate reconstructions will be made on each of five sediment cores taken from the North Atlantic, covering both east and west basins in intermediate and deep waters. Proxies for nutrient distribution and carbon chemistry will be used to reconstruct the evolving deep ocean chemical structure during MIS 5a/4 while dynamical palaeocirculation proxies will enable assessment of physical changes in bottom current speed and mass volume transport. Direct temporal correlation of the reconstructions with records from ice cores and absolutely dated cave deposits will enable the development of extremely robust age models, vital for investigation of potential leads and lags between the reconstructed changes and other climate relevant parameters such as ice volume and atmospheric CO2. A further circulation proxy record will be produced from a core from the Atlantic/Indian sector of the Southern Ocean. This will provide unambiguous evidence for the relative timing between changes in ocean circulation and the global carbon cycle. The data produced as part of this project will provide critical constraints for differentiating between key physical and chemical changes in Earth's climate system during the transition to full glacial conditions and the onset of glacial climate instability.