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

关于新近纪气候的一个关键争论集中在晚中新世赤道太平洋是否存在永久性El Niño-like条件。由于人为的全球变暖预测预测到2100年平均气温将上升4°C，因此了解中新世晚期的气候系统至关重要，该系统比现在平均温度高4.5°C。在温暖的晚中新世，研究永久El Niño-like条件的存在可以为未来气候的发展提供关键信息。由于赤道太平洋在驱动全球大气环流、降水、热输送和碳循环方面的重要作用，当温暖的海表水延伸到赤道太平洋很远的地方时，一个现代El Niño会导致全球降水和温度异常。持续的厄尔尼诺Niño-like现象可能会产生严重的、广泛的、全球性的后果，并可能引发中新世晚期观测到的全球干旱加剧。该项目的主要科学目标是验证赤道太平洋在6.5至9.7 Ma之间存在永久的晚中新世厄尔尼诺现象的假设。为了解决这一问题，作者建议利用最近从U1488站点（IODP Expedition 363）回收的沉积物，通过生成6.0-9.7 Ma之间的高分辨率底栖生物和浮游生物（混合层和温跃层）稳定同位素记录，以前所未有的冰期-间冰期分辨率重建西太平洋暖池（WPWP）水柱结构和温跃层深度的变化。将新WPWP记录在冰期-间冰期分辨率下与赤道东太平洋记录进行比较，将有助于区分短期和长期变化。因此，我们可以测试晚中新世El Niño-like条件的真实程度，并表征~6.5 Ma向La Niña-like条件过渡的性质。高分辨率底栖生物地层学将用于开发天文年龄模型，并提供新的U1488记录与赤道东太平洋站点U1337和U1338 （IODP Exp. 320/321）的现有天文校正记录之间的强大相关性。这个项目可能最终解决中新世晚期永久厄尔尼诺Niño的争论，并大大提高我们对厄尔尼诺Niño在比现在更温暖的气候条件下的全球影响的理解。

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.