Dripwater and Calcite Geochemistry Variations in a Monitored Bahamas Cave

Abstract

A cave-monitoring study in Hatchet Bay Cave on the island of Eleuthera, Bahamas, has examined the origins of variations in oxygen and carbon isotopic and minor element composition in cave calcites. Every 3 to 8 months, between 2012 and 2016, temperature, humidity, cave air (δ13CCO2), dripwaters (δ18O and δ2H values, and Ca, Sr, and Mg concentrations), and the chemical composition of precipitating calcite (δ18O and δ13C values, and Ca, Sr, and Mg concentrations) were analyzed in two rooms in the cave. Results from the elemental analyses show that throughout the cave prior calcite precipitation was a driver of the elemental chemistry of the precipitated calcites. In addition, cave calcites show that δ13C and δ18O values were positively correlated with Mg/Ca ratios. The Mg/Ca ratios were also positively correlated with lower calcite precipitation rates. Therefore, water/rock interactions may also influence δ13C and δ18O values and Mg/Ca ratios of the calcite. Differences were observed between the two rooms, with the Main Room of the cave exhibiting increased prior calcite precipitation, more ventilation, lower calcite precipitation rates, and δ18O values, which were farther from equilibrium when compared to the more isolated portion of the cave. These results also validated previous interpretations from Pleistocene stalagmites collected from a nearby Bahamian cave suggesting that a positive covariation between Mg/Ca and δ13C values reflects water/rock interactions.