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议集中在中新世晚期赤道太平洋是否存在永久性的类似厄尔尼诺现象。由于人为的全球变暖预测预测到2100年平均气温将上升4摄氏度，因此了解中新世晚期的气候系统是至关重要的，当时的气候系统平均比今天高4.5摄氏度。研究温暖的晚中新世期间是否存在永久性的类厄尔尼诺现象，可以为未来气候的发展提供关键信息。由于赤道太平洋在推动全球大气环流、降水、热量输送和碳循环方面的重要作用，现代厄尔尼诺现象，即温暖的海面海水远远越过赤道太平洋，导致全球降水和温度异常。长期的类厄尔尼诺现象可能已经造成了严重的、广泛的、全球性的后果，并潜在地引发了在中新世晚期观察到的全球干旱的加剧。这项拟议项目的主要科学目标是检验在6.5 Ma至9.7 Ma期间赤道太平洋存在长期的晚中新世类厄尔尼诺现象的假设。为了解决这一问题，我建议利用最近从U1488站点(IODP考察队363)采集的沉积物，以前所未有的冰期-间冰期分辨率重建西太平洋暖池水柱结构和温跃层深度的变化，方法是在6.0-9.7 Ma之间产生高分辨率的底栖生物和浮游生物(混合层和温跃层)稳定同位素记录。将冰川-间冰期分辨率的新的WPWP记录与赤道东太平洋的记录进行比较，可以区分短期和长期的变化。因此，我们可以测试晚中新世类厄尔尼诺条件的真实程度，并表征~6.5 Ma向类拉尼娜条件转变的性质。高分辨率海底地层学将用于建立天文年龄模型，并在新的U1488记录和赤道东太平洋U1337和U1338站点现有天文调谐记录之间提供强有力的关联(IODP Exp。320/321)。该项目可能最终解决中新世晚期永久性厄尔尼诺现象的争论，并极大地促进我们对在比现在更温暖的气候中主导厄尔尼诺现象的全球后果的理解。

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.