Abstract
A one-year monitoring survey has been carried out in La Paz and La Vina Caves in the Ortigosa de Cameros Cave System (NE Iberian Peninsula), in order to track the oxygen isotope signal from rainfall to speleothem calcite, assessing the ability of this signal to retain environmental information. Oxygen isotope signals of rainfall events, drip water —sampled every three months—, and speleothem calcite, precipitated over three-months, are compared. Water dripping follows precipitation events in winter, spring and summer, more closely in the near-surface drip points than in the deeper ones. In autumn, dripping is delayed with respect to rainfall, suggesting that water stays in the epikarst before dripping resumes after summer. This delay causes a deviation of the total drip water signal (average δ 18 O=−8.39‰ V-SMOW) from the rainfall signal (average δ 18 O=−7.41‰ V-SMOW). On the contrary, in winter the isotopic signal of drip water keeps the rainfall signal. Calcite isotopic signal (total average δ 18 O=−6.83‰ V-PDB) shows a small offset (0.62–0.75%) with respect to the signal predicted by drip water oxygen composition; this points to a limited kinetic effect in calcite precipitation, therefore calcite retains the signal of rainfall, especially in winter.
Highlights
Study area and cave featuresStalagmite oxygen isotope (δ18O) is commonly used as a proxy of external environmental conditions (Lachniet et al, 2009; McDermott, 2004) for palaeoclimate reconstructions, inasmuch as the rainfall isotopic composition is transposed to the speleothem calcite
Calcite isotopic signal shows a small offset (0.62–0.75%) with respect to the signal predicted by drip water oxygen composition; this points to a limited kinetic effect in calcite precipitation, calcite retains the signal of rainfall, especially in winter
Through sampling and analyses of the isotopic composition of rainfall, drip waters and in-situ resulting precipitated calcite, we explore the transference of the isotopic signature, in order to assess the processes prevailing in the intermediate reaches in the Ortigosa Cave System (Northern Iberian Peninsula)
Summary
Study area and cave featuresStalagmite oxygen isotope (δ18O) is commonly used as a proxy of external environmental conditions (Lachniet et al, 2009; McDermott, 2004) for palaeoclimate reconstructions, inasmuch as the rainfall isotopic composition is transposed to the speleothem calcite. The isotopic changes in the pathway from the rainfall to the speleothem are not completely understood, because of the many complex factors involved, which are related to climate, soil and vegetation, epikarst and cave environment (McDermott, 2004; Lachniet et al, 2009; Feng et al, 2014). Through sampling and analyses of the isotopic composition of rainfall, drip waters and in-situ resulting precipitated calcite, we explore the transference of the isotopic signature, in order to assess the processes prevailing in the intermediate reaches (from rainfall to drip water and from drip water to calcite) in the Ortigosa Cave System (Northern Iberian Peninsula)
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