The Potential Influence of Rainfall on Calcite Raft Formation in Great Cistern Sinkhole, Abaco Island, The Bahamas
MetadataShow full item record
The stratigraphic record in Great Cistern sinkhole on Abaco Island, The Bahamas, contains coarse-grained layers composed of calcite rafts. Calcite rafts usually form in quiescent cave waters saturated with CaCO3. The appearance of calcite rafts in the Great Cistern sediment record is the first documented occurrence of raft precipitation in a coastal sinkhole. Due to the scarcity of calcite raft formation outside of caves, an examination of raft kinetics, morphology, and ties to regional paleo-environmental factors is warranted. Calcite precipitation in caves can occur at air-water interfaces when the saturation index of water with respect to CaCO3 is near or past equilibrium (i.e., supersaturated), and when there is a higher CO2 concentration in the water versus the overlying atmosphere. Raft formation at the air-water interface, their external crystal morphology, and longevity are all tied to the kinetic state of the waters from where they derive. Calcite rafts sink below the air-water interface and become part of the local sediment record when the water is agitated, or when the weight of individual calcite rafts (e.g., downward gravitational force) exceeds the force of surface tension buoying them at the surface. It is possible that calcite raft abundance in Great Cistern is a long-term proxy for regional rainfall. Correlation of calcite raft abundance in Great Cistern sinkhole to δ18O values from a Cuban speleothem further evaluates the potential of calcite rafts in Great Cistern as a long-term hydroclimate proxy for Abaco.
Kelley, Kevin Ryan (2017). The Potential Influence of Rainfall on Calcite Raft Formation in Great Cistern Sinkhole, Abaco Island, The Bahamas. Undergraduate Research Scholars Program. Available electronically from