EVIDENCE AND AMPLITUDE OF SEA-LEVEL OSCILLATIONS DURING THE LAST INTERGLACIAL HIGHSTAND (MIS 5E) FROM THE BAHAMAS

Sea level was 6-7 m higher than present during the last interglacial highstand 125,000-115,000 years before present (MIS 5e). Evidence from New Providence Platform, Bahamas, indicates that it was not a single rise and fall but instead oscillated a minimum of 12 m over a few thousand years. Exposure horizons and lithologic changes in cores and outcrops combined with age dating in the Exuma Cays and New Providence, Bahamas, provide sedimentologic and stratigraphic evidence of sea-level oscillations during MIS 5e.

Cores drilled in the Exuma Cays reveal older MIS 5e subtidal deposits, followed by an exposure horizon, then a shallow-water reef on top, indicating two highstands with an exposure in between. Beach deposits that are +7.6 m above present sea level on New Providence Island represent the older peak of MIS 5e sea level. A down-stepping beach ridge indicates a subsequent sea-level position at +7.0 m. A calcrete in the subtidal deposits adjacent to the beach documents the mid-MIS 5e sea level drop. In the Exumas, a calcrete associated with this fall separates subtidal facies at -5.2 m. Sea level rises again to form the younger MIS 5e highstand; this rise is represented by a beach ridge at +5.1 m on New Providence Island and Exumas reefs up to +1.5 m above modern sea level. Parallel down-stepping beach to eolian dune transitions provide evidence for a pulsed down-stepping of sea level at the end of MIS 5e. The lowest occurrence of this transition is approximately -12 m below present sea level.

Taking the lowest occurrence of calcretes that mark the mid-MIS 5e sea level fall and the highest beach elevation into account, the MIS 5e sea level oscillated a minimum of 12 m. This sedimentologic evidence corroborates the 15 m estimate from Caribbean corals. In addition, the down-stepping pattern within and at the end of MIS 5e documents pulsed changes of sea level during MIS 5e. These highstand oscillations recorded in the Bahamas and elsewhere require another, yet unexplained, forcing mechanism of much shorter duration than Milankovitch frequencies but also document rapid climate changes during warm interglacial periods.