Reconstructing Last Interglacial Sea Level Based on Models and Observation from the Bahamas

Lead PI: Jacqueline Austermann , Dr. Maureen E. Raymo , , Blake Chandler Dyer

Unit Affiliation: Seismology, Geology and Tectonophysics, Lamont-Doherty Earth Observatory (LDEO)

April 2019 - March 2022
; Bahamas
Project Type: Research

DESCRIPTION: Today's major ice sheets are shrinking and therefore contribute to global sea level rise. Understanding how much and how fast they will melt in the future is a pressing question for public health, coastal infrastructure, and economic stability. This research project will investigate how susceptible major ice sheets are to modest amounts of warming. This project will address this question by reconstructing sea level during the most recent time in Earth's history when global mean temperatures were slightly warmer (+1-2 degrees C) than pre-industrial values due to natural and periodic variations in the Earth's orbit. This time period, the last interglacial, occurred approximately 125,000 years ago. Controversy exists around how much higher global sea level was and whether abrupt sea level rise (ice sheet collapse) occurred at the end of this prolonged warm period. Both the magnitude and rate of sea level change during this time are important for improving predictions of sea level rise over the next century. Sea level will be reconstructed over the last interglacial from the geologic record of the Bahamas. Measurements of the current elevations of last interglacial marine sediments and fossil corals will be combined with models of ancient ice sheets and sea level change to infer the response and evolution of sea level during this critical past warm period. The work will improve the fidelity of predictions for future sea-level change and will support a new investigator in the field of sea-level studies

To improve our understanding of future sea level rise we can turn to periods in the geologic past that recorded the response of polar ice sheets to prolonged warming. The Last Interglacial (LIG, ~ 128 - 116 ka) is a prime target for this approach as temperatures were slightly elevated relative to today. Reconstructions of global mean sea level and ice loss during this period indicate that global mean sea level was higher during this time period, however, the exact magnitude and timing of ice melt is still debated. A major obstacle in improving these reconstructions is currently a limited understanding of how much the solid Earth has moved up or down since the LIG, hence how much local reconstructed sea level deviates from the past global mean. This component is generally corrected for using model predictions, however, models are uncertain due to an incomplete knowledge of Earth's internal structure and past ice sheet evolution. This project aims to advance the debate about the magnitude and timing of ice melt during the LIG by combining sea level observations from the Bahamas with models of solid Earth deformation. The sediments deposited across the Bahamian archipelago are excellent archives of past sea level and are ideal to improve models of solid Earth deformation due to their spatial extent and unique location close to the former ice sheet, which allows them to experience and capture gradients in solid Earth deformation. The project will produce high-precision 3D reconstructions of outcrops over three field seasons in the Bahamas to obtain unprecedented elevation constraints and ages on LIG stratigraphic data. We will generate model predictions of solid Earth deformation - glacial isostatic adjustment and dynamic topography, and constrain them with existing observations from the Holocene and Neogene, respectively. Combining the field observations with predictive models will allow us to produce uncertainty ranges for excess polar ice melt and ice evolution over the LIG as well as constrain Earth properties.

(Pictured above: the surface of a dead Elkhorn coral, photo credit Blake Dyer)