WHAT’S PAST IS PROLOGUE: EVIDENCE OF CLIMATE INSTABILITY AND INTENSE STORMS DURING THE LAST INTERGLACIAL ON ELEUTHERA ISLAND, BAHAMAS

In order to understand the potential of sea-level rise during the current interglacial, it is critical to examine the climatic shifts of the last interglacial (MIS 5e). The Bahamas are dominated by carbonate sediments which, due to rapid cementation, often preserve sedimentary structures that reveal conditions at the time of deposition. Eleuthera is located on the Atlantic margin of the Bahamian platform near the boundary of the Westerlies and Trade wind belts where depositional environments are particularly sensitive to wind variability and the influence of tropical storms.

Prior studies on Eleuthera have shown sea-level fluctuated rapidly and storms intensified toward the end of the last interglacial. By examining sedimentary structures such as cross-bed geometry, rhizomorphs, fenestrae (keystone vugs), and grain composition, along with stratigraphic relationships within several additional exposures on Eleuthera, the sea-level and climate history of the last interglacial can be better resolved.

Detailed descriptions from a previously undescribed MIS 5e eolianite exposure in the town of Tarpum Bay indicate that dune deposition occurred rapidly with limited lateral migration. This is evidenced by well-preserved backset and topset bedding coupled with trees buried in upright position and a relative lack of rhizomorphs. Furthermore, abundant fenestral beds occur within the dune at multiple horizons, often with scour and rip-ups, signifying an increase in storm wave activity.

Additional evidence of storm intensification and a destabilized climate has been observed at eight other localities on Eleuthera. Overall, MIS 5e eolian bedding has the same signature of rapid deposition at each location. At low elevations, coastal dunes were reworked by high energy waves, forming storm beach ridges rich in fenestrae, while at high elevations, fenestral beds are present in eolianites, in some cases up to 43 meters above sea-level. Along the Atlantic sea cliffs, large boulders were broken off and emplaced on top of MIS 5e eolianites. Collectively, these storm deposits on Eleuthera indicate a rapid destabilization of climate at the end of the last interglacial. Thus when it comes to the current interglacial, what’s past may be prologue.