Abstract
Rationale
Application of clumped isotope palaeothermometry to speleothems (carbonate cave deposits e.g. stalagmites and flowstones) has been restricted largely to subaqueous samples because of kinetic fractionation processes that occur during subaerial speleothem formation, which leads to erroneously high inferred temperatures. Speleothems are spatially near-ubiquitous terrestrial archives that can be dated accurately over million-year timescales. Thus, wider application of the clumped isotope technique in speleothems could dramatically increase understanding of terrestrial thermal history. In this study we assess the potential of speleothem drip cups (concave depressions at a stalagmite apex in which dripwater accumulates to create a subaqueous environment) for reliable palaeotemperature inference.
Methods
We sampled along two isochronous layers that extend across both sides of a pronounced drip cup in stalagmite MAYA 22-7 from Ch’en Mul, Mexico, which was dated to 1650 CE ± 23 years. We measured bulk stable (δ18O and δ13C) and clumped (Δ47) isotope values at increasing distances from the drip cup centre to test for kinetic fractionation effects.
Results
Higher δ18O, δ13C and Δ47 values were obtained from the drip cup’s central subaqueous zone compared with the subaerial flanks, demonstrating reduced (Δ47) isotope fractionation in the subaqueous zone. Average clumped isotope temperatures (TΔ47) inferred from subaqueous samples fall within the range of modern cave temperatures but are on average 5°C warmer than estimated formation paleotemperatures, suggesting a persistent degree of kinetic effects persists.
Conclusions
We propose that drip cup carbonates have the potential to yield reliable palaeotemperatures and describe a widely applicable test for clumped isotope equilibrium precipitation in speleothem drip cups by sampling across isochronous layers.
Application of clumped isotope palaeothermometry to speleothems (carbonate cave deposits e.g. stalagmites and flowstones) has been restricted largely to subaqueous samples because of kinetic fractionation processes that occur during subaerial speleothem formation, which leads to erroneously high inferred temperatures. Speleothems are spatially near-ubiquitous terrestrial archives that can be dated accurately over million-year timescales. Thus, wider application of the clumped isotope technique in speleothems could dramatically increase understanding of terrestrial thermal history. In this study we assess the potential of speleothem drip cups (concave depressions at a stalagmite apex in which dripwater accumulates to create a subaqueous environment) for reliable palaeotemperature inference.
Methods
We sampled along two isochronous layers that extend across both sides of a pronounced drip cup in stalagmite MAYA 22-7 from Ch’en Mul, Mexico, which was dated to 1650 CE ± 23 years. We measured bulk stable (δ18O and δ13C) and clumped (Δ47) isotope values at increasing distances from the drip cup centre to test for kinetic fractionation effects.
Results
Higher δ18O, δ13C and Δ47 values were obtained from the drip cup’s central subaqueous zone compared with the subaerial flanks, demonstrating reduced (Δ47) isotope fractionation in the subaqueous zone. Average clumped isotope temperatures (TΔ47) inferred from subaqueous samples fall within the range of modern cave temperatures but are on average 5°C warmer than estimated formation paleotemperatures, suggesting a persistent degree of kinetic effects persists.
Conclusions
We propose that drip cup carbonates have the potential to yield reliable palaeotemperatures and describe a widely applicable test for clumped isotope equilibrium precipitation in speleothem drip cups by sampling across isochronous layers.
| Original language | English |
|---|---|
| Journal | Rapid Communications in Mass Spectrometry |
| DOIs | |
| Publication status | Accepted/In press - 26 Dec 2025 |
Keywords
- clumped isotypes
- speleothem
- drip cup
- isotopic equilibrium
- temperature reconstruction
- palaeoclimate