Fossil Coral Records of ENSO during the Last Glacial Period

University Of Texas At Austin, Austin TX

Investigators

Abstract

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.