Fossil Coral Records of ENSO during the Last Glacial Period

该项目旨在从热带太平洋西部的瓦努阿图埃斯皮里图岛恢复珊瑚化石，利用珊瑚骨架地球化学恢复上一次冰期期间的厄尔尼诺/南方涛动(ENSO)。很少有古气候记录可以解决最后一次冰川盛期(LGM)期间的年际变化，这一时间可以帮助限制ENSO对全球气温变化反应的巨大不确定性。珊瑚提供了一项这样的记录，但LGM中仍然存在的化石珊瑚通常是在低于当前海平面120-140米的水深处发现的，因此需要昂贵和复杂的近海方法才能获得。相比之下，瓦努阿图经历了快速的构造抬升速度，使冰盖运动古海岸线上升到冰川珊瑚预计接近地表，从陆上地点进行浅层钻探即可到达的地步。因此，该项目为古海洋学界提供了一个难得的重要机会，以获取珊瑚样本，用于编制高分辨率的ENSO时间序列，并在末次盛冰期调查西热带太平洋的变率。研究小组将修改现有的钻探系统，使其足够便携，可以手持到难以到达的地点，然后实施一个扩展的现场计划，在瓦努阿图海岸部署和钻探一系列陆上珊瑚断面。将使用U-Th测年来确认回收的珊瑚的年龄，并将评估所获得的样本是否适合于以后的地球化学研究。该项目将支持一名早期职业研究人员以及研究生和本科生。瓦努阿图的现代珊瑚地球化学记录表明，在捕捉ENSO的水文印记方面具有相当高的技能。对现代珊瑚记录的信心表明，化石珊瑚记录可以用来估计过去ENSO变异性的变化。在瓦努阿图，构造抬升使LGM古海岸线上升到接近现在的海平面，使老珊瑚接近海面，研究小组的初步野外工作证明了这一点。作为该项目的一部分，该团队将建造一种新的钻探系统，该系统便于携带，具有成本效益，并能节省时间，用于钻探浅孔(5-25米)，而目前尚不存在这种系统。其战略将是拥有一个可携带的钻探系统，可以快速移动到几乎任何地点，钻出尽可能多的洞，增加回收LGM珊瑚材料的可能性。钻探行动将利用一个地区，此前的调查发现，在距离当前海平面几米的范围内，珊瑚的年龄最大可达14.25年。将这一战略应用于瓦努阿图的另一个好处是，LGM珊瑚很可能仍然淹没在海水中，而不是完全上升到陆地上。这大大减少了成岩改变的机会，而成岩改变往往会影响较老珊瑚的地球化学。回收的珊瑚样本将使用U-Th方法测定年龄，并对其地球化学完整性进行筛选。在瓦努阿图成功恢复冰川时期的原始珊瑚，将为随后的研究打开大门，以确定ENSO和热带气候可能在末次盛冰期做出了怎样的反应，这一时期的平均气候发生了很大变化。对更大的社区来说，另一个好处是改进的Winkie钻探系统的开发和制造。这种便携式系统预计将被其他研究人员大量用于崎岖地形的陆基钻井作业。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project seeks to recover fossil corals from the island of Espiritu Santo, Vanuatu in the western tropical Pacific that will enable reconstruction of the El Nino/Southern Oscillation (ENSO) during the last glacial period using coral skeleton geochemistry. Few paleoclimate records exist that can resolve interannual changes during the Last Glacial Maximum (LGM), a time that can be used to help constrain the large uncertainty in ENSO's response to changes in global temperature. Corals provide one such record but fossil corals still in place from the LGM are normally found at water depths of 120-140 m below present sea level, and hence require expensive and logistically complex offshore approaches to obtain. In contrast, Vanuatu has experienced rapid rates of tectonic uplift which has raised the LGM paleo-shoreline to the point where glacial corals are expected to be near the surface and reachable by shallow drilling from onshore sites. The project thus offers a rare and important opportunity for the paleoceanographic community to acquire coral samples that can be used to develop high resolution time-series of ENSO and investigate western tropical Pacific variability during the LGM. The research team will modify an existing drill system to make it portable enough to hand-carry into hard to reach locations, and then conduct an extended field program to deploy and drill a series of onshore coral transects along the Vanuatu coast. U-Th dating will be used to confirm the ages of recovered corals and the samples obtained will be assessed for their suitability for later geochemical studies. The project will support an early career researcher as well as graduate and undergraduate students. Modern coral geochemical records from Vanuatu show a significant degree of skill in capturing the hydrological imprint of ENSO. Confidence in modern coral records suggest that fossil coral records can be used to estimate past changes in ENSO variability. On Vanuatu, tectonic uplift has raised the LGM paleo-shoreline to near present sea level, bringing old corals close to the surface as demonstrated by the research team's preliminary fieldwork. As part of this project, the team will build a new drill system that is portable, cost-efficient, and time-efficient for drilling shallow holes (5-25 m), a system that currently does not exist. The strategy will be to have a human-portable drill system that can be quickly moved to virtually any site to drill as many holes as possible, increasing the likelihood of recovering LGM coral material. The drilling operation will capitalize on an area where previous surveys have identified corals as old as 14.25 kyrs within a few meters of present sea level. A further advantage of applying this strategy to Vanuatu is that LGM corals are most likely still submerged in seawater rather than being uplifted completely onto dry land. This greatly reduces the chance for diagenetic alteration that all too often affects the geochemistry of older corals. The recovered coral samples will be dated using U-Th methods and screened for their geochemical integrity. The successful recovery of pristine glacial-age corals from Vanuatu will open the door for subsequent studies to determine how ENSO and tropical climate may have responded during the LGM, a time of greatly altered mean climate. An additional benefit for the larger community will be development and fabrication of the modified Winkie drill system. Such a portable system is expected to find considerable use by other researchers for land-based drilling operations in rough terrain.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.