Soru

Speleothems—mineral deposits formed inside karst caves—have long served as high-resolution archives of terrestrial paleoclimate. While oxygen isotope ratios (${\delta}^{18}\text{O}$) in speleothem calcite are standard proxies for past precipitation, their interpretation is frequently confounded by temperature fluctuations and varying atmospheric moisture trajectories. To circumvent these ambiguities, paleoclimatologists have increasingly analyzed polymorphic transitions between calcite and aragonite, two crystalline forms of calcium carbonate ($\text{CaCO}_3$). In karst environments where dripping waters experience prolonged cave residence times during protracted droughts, enhanced prior calcite precipitation (PCP) along the cave roof preferentially depletes dissolved calcium while elevating the magnesium-to-calcium ($\text{Mg/Ca}$) ratio of the remaining seepage solution. Because elevated magnesium concentrations kinetically inhibit calcite nucleation without impeding aragonite formation, sustained aragonite deposition in stalagmites reliably signals severe hydrologic deficits. However, this mineralogical proxy becomes uncoupled from regional rainfall when cave ventilation rates shift dramatically, as heightened air circulation accelerates carbon dioxide degassing and induces aragonite crystallization independently of seepage water chemistry.

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