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Highlights

  • Isotopic fractionation is studied in Cueva Ensueño to pre-calibrate stalagmite δ18O
  • Seasonal isotopic fractionation is found between wet and dry months
  • Hendy test on farmed carbonates suggest kinetic fractionation
  • Drip water isotopes are affected by epikarst storage
  • Prior calcite precipitation increases in the dry season

Abstract

Stalagmites are invaluable archivers of past climate conditions, as their oxygen isotopic composition (δ¹⁸Oc) closely mirrors the isotopic signature of the drip water (δ¹⁸Ow) from which they precipitate. This isotopic relationship is governed by the fractionation factor (1000ln¹⁸α), which is temperature dependent. In this research, we studied 1000ln¹⁸α within Cueva Ensueño, a cave situated in Puerto Rico’s northern karst region, as a step toward calibrating δ¹⁸Oc for paleoclimate interpretations using stalagmites. We collected drip waters, measured their temperature in situ, and sampled carbonates from ten selected stations within the cave. Sampling was conducted in December and May, representing months of the dry and wet seasons, respectively. To better understand isotopic variations in stalagmites, we farmed calcite at the same drip sampling locations during both seasons. Our findings reveal a seasonal bias in isotopic fractionation of farmed carbonates at Cueva Ensueño, with higher 1000ln¹⁸α values in May (30.7–32.7) and lower values in December (27.8–29.7), but when these values are averaged, they merge towards the isotopic fractionation of the shaved stalagmites. We also found that stable isotope transfer into the cave is delayed, which could be due to epikarst storage effect and piston flow recharge, with the May drip water likely affected by moisture recycling before reaching the cave (as shown by the high d-excess values). In contrast to stable isotopes, the drip elemental composition suggests an immediate prior calcite precipitation response, which could be evidence of a dual transfer process. This research illuminates our understanding of oxygen isotope fractionation, which is useful for paleoclimate reconstructions and can provide insights into similar settings in the region.

DOI

https://doi.org/10.5038/1827-806X.ijs2555

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Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

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