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This short article provides detailed descriptions of custom-made and commercially available hand-held drilling gear and options for water-flushing units specifically designed to obtained good-quality core material from speleothems even in remote cave regions. We use small-diameter (6-7 mm) diamond drill-core bits to obtain aliquots of calcite (as little as a few hundred milligrams) from the interior of the basal part of in-situ stalagmites. These small cores are used to date the onset of stalagmite growth and occasionally to obtain other compositional information. Larger diameter drill-core bits produce cores 25-32 mm in diameter and up to 1.3 m in length which reveal internal structures and provide axial transects for chemical and isotope analysis and material for preparation of thin sections. This system has been successfully employed to sample flowstone and thick stalagmites. Given the growing interest in speleothem as archives of past environmental change, careful sample selection is primordial to keep the impact of sampling in these unique environments at a minimum. Low-invasive drilling is an essential technique and maximizes the amount of information gained.

Understanding the temperature evolution during the Holocene is crucial for future climate projections. However, a puzzling discrepancy between climate models simulating a warming trend during the second half of the Holocene parallel to the rise in atmospheric CO2 concentrations and proxy data suggesting cooling during this period – known as the Holocene temperature conundrum – limits our understanding of how climate will evolve in the future. To solve this conundrum, the inclusion of quantitative paleotemperature records from high-latitude sites, which are extremely rare, is essential. Here, we use the hydrogen isotopic composition of fluid inclusions in speleothems from southeastern Alaska to create a quantitative temperature reconstruction of the entire Holocene. We show that the temperature in southeastern Alaska followed CO2, in agreement with modeling results. Because our data show no proxy-model bias, they support a seasonal proxy bias to account for the Holocene temperature conundrum. [ABSTRACT FROM AUTHOR]

Cryogenic cave carbonates (CCCs) are a type of speleothem, typically dated with 230Th/U disequilibrium methods, that provide evidence of palaeo-permafrost conditions. In the field, CCCs occur as distinct patches of millimetre- to centimetre-sized loose crystals and crystal aggregates on the floors of cave chambers, so they lack a framework that would allow ages to be validated by stratigraphic order. Correction factors for the initial 230 Th (230 Th 0) are often based on the bulk-earth-derived initial 230Th/232Th activity ratio ((230Th/232Th)0), which is a well-established approach when 230 Th 0 is moderately low. For samples with elevated levels of 230 Th 0 , however, accuracy can be improved by constraining (230Th/232Th)0 independently. Here, we combine detailed morphological observations from three CCC patches found in Water Icicle Close Cavern in the Peak District (UK) with 230Th/U analyses. We find that individual CCC crystals show a range of morphologies that arise from non-crystallographic branching in response to the chemical evolution of the freezing solution. Results of 230Th/U dating indicate that samples with a large surface area relative to the sample volume are systematically more affected by contamination with 230 Th 0. By fitting isochrons to these results, we test whether the CCCs in a patch formed during the same freezing event, and demonstrate that (230Th/232Th)0 can deviate substantially from the bulk-earth-derived value and can also vary between the different CCC patches. Where CCCs display elevated 230 Th 0 , isochrons are a useful tool to constrain (230Th/232Th)0 and obtain ages with improved accuracy. Detritus absorbed to the crystal surface is shown to be the most likely source of 230 Th 0. Our results suggest that some previously published CCC ages may merit re-assessment, and we provide suggestions on how to approach future dating efforts. [ABSTRACT FROM AUTHOR]