Uranium-series ages of speleothems from South Andros, Bahamas: Implications for quaternary sea-level history and palaeoclimate

Speleothem samples were collected from fracture-guided blue holes on South Andros Island using mixed gas diving techniques. Uranium-series ages were determined using alpha-spectrometric and, for selected samples, thermal ionisation mass-spectrometric analysis. In situ speleothem was absent below 57m depth suggesting that sea levels have fallen below this depth for only a limited period (although dissolution associated with present-day groundwater chemistry may also be a contributing factor). The oldest samples collected dated from Marine Isotope Stage (MIS) 6, and form false floors associated with oolitic sediments previously emplaced within the cave void. This implies latest ages of MIS 7 for the cave, and MIS 9 for the host rock. The general pattern of sea-level for MIS 4/3 defined by speleothem ages parallel the progressive lowering demonstrated by global ice volume records. Estimates of high-stands derived from Barbados and from earlier work in the Huon Peninsula agree well with the constraints provided by Bahamas speleothem, but the global ice volume and more recent estimates are somewhat lower. Speleothem growth on South Andros ceased before flooding of the caves by rising sea-levels, probably related to a regional decrease in precipitation associated with the discharge of melt-water into the Gulf of Mexico. Cessation of growth in MIS 6 may also be controlled by palaeoclimate, and suggests an early commencement of deglaciation.