Fossil Coral Records of ENSO during the Last Glacial Period

该项目旨在从热带太平洋西部瓦努阿图的Espiritu Santo岛恢复珊瑚化石，以便利用珊瑚骨骼地球化学重建最后一次冰期期间的厄尔尼诺/南方涛动。很少有古气候记录可以解决末次盛冰期（LGM）期间的年际变化，这段时间可以用来帮助限制ENSO对全球温度变化的反应的巨大不确定性。珊瑚提供了这样的记录之一，但从LGM仍然存在的珊瑚化石通常在现在海平面以下120-140米的水深处发现，因此需要昂贵和后勤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，使末次盛冰期古海岸线上升到这样一个程度，即冰川珊瑚预计将接近地表，可以从岸上浅钻到达。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，用于开发厄尔尼诺/南方涛动的高分辨率时间序列，并调查末次盛冰期期间热带西太平洋的变化。该研究小组将修改现有的钻井系统，使其足够便携，以手携带到难以到达的地点，然后进行一个扩展的现场计划，部署和钻探一系列陆上珊瑚断面沿着瓦努阿图海岸。将使用铀-钍年代测定法来确定回收珊瑚的年龄，并将评估所获样本是否适合用于以后的地球化学研究。该项目将支持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显示，在捕捉厄尔尼诺/南方涛动的水文印记方面有很高的技巧。对现代珊瑚记录的信心表明，珊瑚化石记录可用于估计ENSO变率过去的变化。在瓦努阿图，构造隆起使末次盛冰期古海岸线上升到接近现在的海平面，使古老的珊瑚接近地表，研究小组的初步实地考察证明了这一点。作为该项目的一部分，该团队将建立一个新的钻机系统，该系统是便携式的，具有成本效益和时间效率的浅孔（5-25米），目前还不存在的系统。该战略将是拥有一个人类便携式钻孔系统，可以快速移动到几乎任何地点，钻尽可能多的孔，增加恢复LGM珊瑚材料的可能性。钻探作业将利用一个地区，以前的调查已经确定珊瑚年龄为14.25 kyrs在几米的目前海平面。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。这大大减少了成岩作用改变的机会，而成岩作用改变往往会影响老珊瑚的地球化学。将使用铀-钍法测定回收的珊瑚样品的年代，并对其进行地球化学完整性筛选。从瓦努阿图成功恢复原始冰川时代珊瑚将为随后的研究打开大门，以确定厄尔尼诺/南方涛动和热带气候在平均气候发生巨大变化的LGM期间可能作出的反应。一个更大的社区的额外好处将是改进的Winkie钻系统的开发和制造。这样一个便携式系统预计将发现相当多的其他研究人员使用陆基钻井作业在粗糙terraf.This奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。

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.