In Wind Cave, organic molecules from the surface dissolved in water will slowly filter down into the cave through the porous limestone. While the water slowly proceeds down through the limestone, the water dissolves the limestone along the way. This dissolving of the limestone causes a quasi-equilibrium that deposits the organic molecules into the calcite structures found in Wind Cave. These large trapped organic molecules, mainly humic and fulvic acid, can be tracked by using UV light. The UV light causes these molecules to fluoresce blue, while the calcite structures generally do not have a strong blue fluorescence. The water from the cave shows a similar but stronger signal to that of the organic laced calcite. This water was used to replicate the fluorescence of the crystals in the cave by using the cave water to dissolve calcium chloride and reacted with ammonium carbonate. The fluorescence of the water after being reacted showed that the organic molecules were precipitated out with the calcite. This reaction resulted in the synthesized crystals having a shifted λ<sub>max</sub> and a different crystal morphology when compared to the cave crystals.

Analog studies of organic pathways in Wind Cave through cave water and crystals

ACS Spring 2022

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