Farmed calcite δ18O, δ13C, and Δ47 at Ascunsă cave, Romania

Abstract

<p>Ascunsă cave (Romania) is the subject of a monitoring program since 2012. While the cave air temperature was very stable around 7°C for most of the time, it experienced in 2019 a 3°C rise, and remained high until the present.</p><p>We present here δ<sup>18</sup>O, δ<sup>13</sup>C, and clumped isotope results from calcite farmed at two drip points inside the cave (POM X and POM 2). POM X has a slower drip rate than POM 2 and deposits calcite more continuously. Calcite deposition has been shown to depend on cave air CO<sub>2</sub> concentration, which controls the drip water pH and, further, the calcite saturation index.</p><p>In 2019, δ<sup>18</sup>O values at both sites quickly shifted to lower values as a response to the increase in temperature. At POM X, values were situated between approximately -7.2‰ and -7.6‰ before this transition, whereas in 2019 they shifted to -7.8‰ - -8.0‰. At POM 2, where values were generally lower, they shifted from -7.5‰ to -7.8‰ to -8.0‰.</p><p>Clumped isotope temperature estimates mostly agree, within measurement error, with measured cave temperature. This agreement is notable given that strong offsets are commonly observed in mid-latitude caves, reflecting kinetic fractionation effects. However, intervals with deviations from cave temperature are also observed, suggesting variations in isotopic disequilibrium conditions with time.</p><p>Here we will discuss these isotope changes in relation to cave air temperature and CO<sub>2</sub> concentration, drip water isotope values and elemental chemistry, as well as in relation to drip rates, in order to improve our understanding of calcite precipitation and isotope effects in caves.</p>