Resolving contradictory hypotheses concerning prolonged late Miocene El Niño-like conditions using the first high-resolution equatorial Pacific climate records

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A key dispute concerning Neogene climate centres on whether or not permanent El Niño-like conditions existed in the equatorial Pacific during the Late Miocene. Because anthropogenic global warming projections predict an up to 4°C mean temperature increase by 2100, it is of utmost importance to understand the late Miocene climate system, which was on average 4.5 °C warmer than today. Investigating the existence of permanent El Niño-like conditions during the warm late Miocene can provide critical information for the development of future climate. A modern El Niño, when warm sea surface waters extend far across the equatorial Pacific, causes global precipitation and temperature anomalies, due to the important role of the equatorial Pacific Ocean in driving global atmospheric circulation, precipitation, heat transport and carbon cycling. Prolonged El Niño-like conditions may have had serious, widespread, global consequences and potentially triggered the increase in global aridity observed during the late Miocene.The main scientific goal of this proposed project is to test the hypothesis that permanent late Miocene El Nino-like conditions existed in the equatorial Pacific between 6.5 and 9.7 Ma. To resolve this, I propose reconstructing changes in the water column structure and thermocline depth of the Western Pacific Warm Pool (WPWP), at unprecedented glacial-interglacial resolution, by generating high-resolution benthic and planktonic (mixed layer and thermocline) stable isotope records between 6.0-9.7 Ma, using recently recovered sediments from Site U1488 (IODP Expedition 363). Comparing the new WPWP records at glacial-interglacial resolution with eastern equatorial Pacific records will allow short- and long-term changes to be distinguished from each other. We can thereby test the true extent of late Miocene El Niño-like conditions to be tested and characterise the nature of the ~6.5 Ma transition to La Niña-like conditions. The high-resolution benthic stratigraphy will be used to develop an astronomical age model and to provide a robust correlation between the new U1488 records and existing astronomically tuned records from eastern equatorial Pacific Sites U1337 and U1338 (IODP Exp. 320/321). This project may ultimately resolve the late Miocene permanent El Niño debate and significantly advance our understanding of the global consequences of dominant El Niño conditions during climates warmer than the present.