Last Interglacial Sea-level Evolution from U-series Chronology of Ooids, Corals, and Caves Deposits from Crooked Island, Bahamas

Lead PI: Oana-Alexandra Dumitru , Jacqueline Austermann , Dr. Maureen E. Raymo

Unit Affiliation: Biology and Paleo Environment, Lamont-Doherty Earth Observatory (LDEO)

May 2021 - April 2023
Atlantic Ocean ; Central America
Project Type: Research

DESCRIPTION: Sea level rise is one of the greatest climate change challenges. Studies of how sea level has changed in past periods when Earth’s climate was warmer than today help scientists predict how much sea level may rise by the end of this century and beyond. However, the future magnitude and rate of sea level change are still highly uncertain. The proposed study focuses on the Last Interglacial period, 129,000-116,000 years ago, when temperatures were on average ~ 1.5 °C higher than today. This period may provide unique insights into the patterns of near future sea-level rise. This project will combine field and laboratory data from the Bahamas with statistical analysis to estimate Last Interglacial sea level in that region. Those results will in turn improve our understanding of global sea level during the Last Interglacial. The sea level results will help document the response of ice sheets in Greenland and Antarctica to elevated temperature in the past. The ice sheet response is a key unknown in efforts to predict sea-level changes in the coming decades. The study results will thus have strong societal relevance. In addition the results will provide insight into how past changes in sea level influenced the formation and evolution of carbonate islands.
The broader impacts of the project include support for two early-career women scientists, and support for outreach activities hosted by their home institution and by the American Museum of Natural History.

Global mean sea level estimates during the Last Interglacial appear to converge on values of 6 to 9 meters above present levels. Recent observational and modeling studies challenge this canonical range, suggesting values might be significantly lower. Moreover, the timing and source of ice melt that drove the high stand remains debated. This project aims to reduce the uncertainties of Last Interglacial global mean sea level by testing and developing a combined approach that links four sea level indicators (corals, ooids, flank margin caves, and stratigraphic context) from Crooked Island, Bahamas. The study will pair U-series chronology of ooids with detailed stratigraphic analysis to assess their depositional history and the derived sea level position. The study will use both vertical and horizontal context as relative timing, and U-series ages of fossil corals deposited in the same sedimentary succession as absolute timing. The project will document the elevation and timing of abundant flank margin caves to provide additional insight into the local sea level history. The study will translate these local sea level observations into global mean sea level by correcting the records for glacial isostatic adjustment and long-term subsidence. This project addresses three key hypotheses: global mean sea level during the Last Interglacial i) did not exceed 5 meters, a value significantly lower than current IPCC consensus; ii) might have oscillated within the interglacial, which might be indicative of northern and southern hemisphere ice melt that was out of phase; and iii) did not exceed maximum rates of 5 m per kyr, which is indicative of how fast or slow ice sheets might respond to future warming. The methodology that will be tested and developed within this research can be applied to other carbonate islands across the globe improving Last Interglacial sea level reconstructions at other locations, as well as during other time periods.