Developing a 3.5-million-year benchmark record of Indian Ocean Dipole variability

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The Indian Ocean Dipole (IOD) is the leading mode of interannual variability of sea surface temperature (SST) in the tropical Indian Ocean. The IOD describes warm (positive) and cold (negative) sea surface temperatures oscillations in the western and eastern part of the Indian ocean. The societal most relevant consequences of IOD variability range from extreme floods in eastern Africa to severe droughts in Australia. These extreme climate events caused by the IOD are predicted to become more common in the future as greenhouse gas emissions increase. Yet despite these alarming predictions and its profound impact on the bordering regions which sustain more than 2 billion people, surprisingly little is known about IOD variability in the past. In particular, the proposed sensitivity of the IOD to CO2 could be further tested if IOD variability during geological time intervals of higher CO2 contents were known. However, the insights into past IOD variability have been severely hampered by the lack of appropriate sedimentary and geochemical data sets from Indian Ocean.The here proposed research aims to elucidate IOD changes during the last 3.5 million years which coincides with distinct changes in the global CO2 level; including the mid-Pliocene warm period considered an analogue for future climate change. At the heart of this project stands the hypothesis that IOD-related SST and the associated surface wind anomalies influenced the Ekman transport of the deep meridional overturning circulation in the Indian Ocean, and thus the ventilation of the deep-water regime. Based on observational data, the weakening (strengthening) of the Ekman transport during positive (negative) IOD phases facilitates less (more) ventilation of the deep-water regime, and consequently a shoaling (deepening) of the lysocline. These new modern hydrographic findings have not yet been applied to the geological past, and thus open up an entire new avenue to research past IOP changes. Hence, this project aims to ground truth the possibility of utilizing deep-water ventilation changes in the western Indian Ocean throughout the geological past as an index of IOD variability. Two hypotheses will be specifically tackled in this project:1) Carbonate dissolution cycles as an indicator of deep-water ventilation changes in the western Indian Ocean can be used as IOD intensity index,2) The amplitude of the IOD is linear correlated to changes in global CO2 levels.To decipher its past deep-water ventilation variability in unprecedented temporal resolution, a sediment core from Site ODP 709 situated in the western equatorial Indian Ocean - a key region of IOD forcing – will be investigated utilizing a novel IOD proxy based on XRF core scanning, stable-isotope and Mg/Ca-paleothermometry based on benthic and planktic foraminifera. The synthesis of the collected data will then be used to develop a new benchmark record of IOD variability during the last 3.5 million years.