BAHAMIAN CORAL-REEFS YIELD EVIDENCE OF A BRIEF SEA-LEVEL LOWSTAND DURING THE LAST INTERGLACIAL

The growth of large, bank-barrier coral reefs on the Bahamian islands of Great Inagua and San Salvador during the last interglacial was inte rrupted by at least one major cycle of sea regression and transgressio n. The fall of sea level resulted ire the development of a wave-cut pl atform that abraded early Sangamon corals in pasts of the Devil's Poin t reef on Great Inagua, and produced erosional breaks in the reefal se quences elsewhere in the Devil's Point reef and in the Cockburn Town r eef on San Salvador. Minor red caliche and plant trace fossils formed on earlier interglacial reefal rocks during the low stand. The erosion al surfaces subsequently were bored by sponges and bivalves, encrusted by serpulids, and recolonized by corals of younger interglacial age d uring the ensuing sea-level rise. These later reefal deposits form the base of a shallowing-upward sequence that developed during the rapid fall of sea level that marked the onset of Wisconsinan glacial conditi ons. Petrographic studies reveal a diagenetic sequence that supports t his sea-level history. Preservation of pristine coralline aragonite, c oupled with advances in U/Th age elating, allow these events in the hi story of the reefs to be placed in a precise chronology. We use these data to show that there was a time window of 1,500 years or less durin g which the regression/transgression cycle occurred and that rates of sea-level change must have been very rapid. We compare our results wit h the GRIP ice-core data, and show that the history of the Bahamian co ral reefs indicates an episode of climate variability during the last interglacial greater than any reported in what is widely believed to b e the more stable climate of the Holocene interglacial..