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Cave air pCO2 (carbon dioxide partial pressure) is, along with drip rate, one of the most important factors controlling speleothem carbonate precipitation. As a consequence, pCO2 has an indirect but important control on speleothem proxy data (e.g., elemental concentrations, isotopic values). The CO2 concentration of cave air depends on CO2 source(s) and productivity, CO2 transport through the epikarst and karst zone, and cave air ventilation. To assess ventilation patterns in the Bunker-Emst Cave (BEC) System, we monitored the pCO2 value approximately 100 m from the lower entrance (Bunker Cave) at bi-hourly resolution between April 2012 and February 2014. The two entrances of the BEC system were artificially opened between 1860‒1863 (Emst Cave) and 1926 (Bunker Cave). Near-atmospheric minimum pCO2 dynamics of 408 ppmv are measured in winter, and up to 811 ppmv are recorded in summer. Outside air contributes the highest proportion to cave air CO2, while soil, and possibly also ground air, provide a far smaller proportion throughout the whole year. Cave air pCO2 correlates positively with the temperature difference between surface and cave air during summer and negatively in winter, with no clear pattern for spring and autumn. Dynamic ventilation is driven by temperature and resulting density differences between cave and surface air. In summer, warm atmospheric air is entrained through the upper cave entrance where it cools. With increasing density, the cooled air flows toward the lower entrance. In winter, this pattern is reversed, due to cold, atmospheric air entering the cave via the lower entrance, while relatively warm cave air rises and exits the cave via the upper entrance. The situation is further modulated by preferential south-southwestern winds that point directly on both cave entrances. Thus, cave ventilation is frequently disturbed, especially during periods with higher wind speed. Modern ventilation of the BEC system--induced by artificially openings--is not a direct analogue for pre-1860 ventilation conditions. The artificial change of ventilation resulted in a strong increase of δ13Cspeleothem values. Prior to the cave opening in 1860, Holocene δ13Cspeleothem values were significantly lower, probably related to limited ventilation due to the lack of significant connections between the surface and cave. Reduced ventilation led to significantly higher pCO2 values, minimal CO2 degassing from drip water and low kinetic isotope fractionation. Both modern and fossil speleothem precipitation rates are driven by water supply and carbonate saturation, and not by cave air pCO2. Today, pCO2 variability is too small to affect carbonate precipitation rates and the same is likely true for pCO2 variability prior to artificial opening of the cave. Thus, fossil speleothems from BEC System are likely more sensitive to temperature and infiltration dynamics. The Bunker-Emst Cave System, therefore, represents different ventilation patterns and their influence on speleothem proxy data in an exemplary manner, and it may serve as a template for other cave systems. [ABSTRACT FROM AUTHOR]

The nature of cave ventilation is of interest to cavers, speleologists, and paleoclimatologists working with stalagmites. Because cave ventilation systematics may change over the growth span of a stalagmite, understanding what factors affect them is critical for determining events that may have affected climate proxies within the stalagmite. Similarly, understanding how the hydrology of the drips feeding a stalagmite evolves through time is key to building robust records of paleoclimate, particularly because stalagmite records have become critical archives of climate change information of the last 500,000 years. Here we present data from an extensive, on-going monitoring effort at Yok Balum Cave, Belize, initiated in 2011, that characterizes high-resolution ventilation dynamics at this site. Clear seasonal ventilation regimes exist, driven by thermally induced inside-outside air density differences. The winter regime is dominated by air inflow into the cave, decreased drawdown from the epikarst into the cave, and a limited diurnal signal. Conversely, summer ventilation is dominated by air outflow from the cave, greater CO2 drawdown and drip water degassing, and a strong diurnal signal. Active monitoring during a large (M7.4) earthquake in November 2012 provides a unique opportunity to assess the response of the cave atmosphere and hydrology to substantial seismic activity. Cave atmosphere dynamics and hydrology are found to be highly resilient to seismic activity, with no observable disturbance occurring around the earthquake, despite there being considerable evidence of physical disruption in the cave. Monitoring included different kinds of drips, and the earthquake affected none of the monitored drip types. This suggests that stalagmite-derived paleoclimate records are not affected by seismic activity, except in extreme cases where the stalagmite or conjugate stalactite is damaged or reoriented. [ABSTRACT FROM AUTHOR]