Last Interglacial Sea Level: Stratigraphic analysis and chronological constraints from the Crooked-Acklins platform, Bahamas

Abstract:

To better understand future sea level, we can turn to periods in the geologic past that record how sea level varied the last time Earth’s ice sheets endured prolonged warming. The Last Interglacial (LIG, ~128 - 116 thousand years ago), an interval marked by atmospheric CO₂ levels similar to pre-industrial values and temperatures consistent with ~1 to 2^oC global warming, is a prime target for this approach. Canonical estimates suggest that LIG global mean sea level was as high as ~6 to 9 meters above present levels. More recent analyses, however, argue that sea level may have peaked lower than this range. The timing and source of the ice melt that drove global mean sea level change remains debated. Reconstructing sea level and ice volume during the LIG is hindered by glacial isostatic adjustment (GIA), which causes local sea level to deviate from global mean sea level. GIA is the response of Earth’s solid surface, gravity field, and rotation axis to changes in ice and ocean load.

In this work we present a new record of LIG sea level and stratigraphic evolution from the Crooked-Acklins platform, Bahamas, with primary focus on Crooked Island and Long Cay. We present a series of new U-Th dated ages from in-situ corals obtained from several Crooked-Acklins landforms including platform-margin paleo reefs and nearshore isolated coral colonies that grew on flooded lithified dunes. We pair these results with a stratigraphic analysis to recreate the relative timing of major geomorphological features on the platform including the formation and erosion of dunes, lagoon flooding, strand plain migration, spit growth, tombolo evolution, and reef burial. This analysis results in a reconstruction of local sea level over the LIG. We correct local sea level for GIA using a set of models that are most consistent with Holocene and LIG sea level data across the Bahamian archipelago. This results in an estimate of global mean sea level during the LIG that allows us to test hypotheses about the timing and amount of ice melt during this past pronounced warming.