Relative sea-level change during the Last Interglacial as recorded in Bahamian fossil reefs

Despite an abundance of UTh age data for Last Interglacial fossil corals in the Bahamas, the accuracy and precision of corresponding elevation data are poor, casting uncertainty on existing estimates of peak relative sea level and rates of sea-level change inferred from these deposits. We revisited two key sites at Great Inagua (GI) and San Salvador (SS) Island to test existing hypotheses about (1) the rate of sea level changes during the Last Interglacial period and (2) a possible gradient in peak sea level between these sites. Here, we provide precise elevation survey results for discrete stratigraphic horizons preserved at both locations, where two stages of reef growth are separated by a discontinuity that truncates corals in the lower reef. The discontinuity at Great Inagua manifests as a sharp wave-cut bench, with a maximum elevation of +1.14 m above mean sea level (MSL), that is sub-horizontal on the promontories and gradually slopes seaward in the embayments. At San Salvador, we observed a discontinuity that undulates between +0.85 and + 1.52 m. The uppermost surface of corals in growth position was measured at +1.94 m (GI) and +2.76 m (SS), although in situ collapse and truncation of large Acropora palmata colonies at the latter site implies that primary coral elevations were somewhat higher. Ultimately, assumptions regarding the amount of material truncated and paleowater depth of the observed reef facies at both sites dominate the uncertainty in calculating past sea level position and hence rates of sea-level change. Full consideration of errors associated with age and elevation data implies an ephemeral sea level drop of at least 1 m over a time frame of approximately one thousand years between two peaks in sea level.