Search results for "Speleothem"

Diagenesis of speleothems and its effect on the accuracy of 230 Th/U-ages

2014

Abstract Speleothems can be precisely dated by U-series disequilibrium methods. One basic assumption of the 230Th/U-dating method is that the system remains closed and U and Th isotopes are neither lost nor added after deposition. For stalagmites, this requirement is usually fulfilled due to their protected environment in caves. However, undersaturated drip water may lead to diagenesis of speleothem CaCO3 and altered 230Th/U-ages. Here we present a detailed petrographic investigation using thin sections and 230Th/U-ages of a stalagmite from the Riesenberghohle, northern Germany, which grew during Marine Isotope Stages 5e, c and a. The occurrence of a mosaic fabric in large parts of the stal…

2021

Abstract. Lignin oxidation products (LOPs) are widely used as vegetation proxies in climate archives, such as sediment and peat cores. The total LOP concentration, Σ 8, provides information on the abundance of vegetation, while the ratios C / V and S / V of the different LOP groups also provide information on the type of vegetation. Recently, LOP analysis has been successfully applied to speleothem archives. However, there are many open questions concerning the transport and microbial degradation of LOPs on their way from the soil into the cave system. These processes could potentially alter the original source-dependent LOP signals, in particular the C / V and S / V ratios, and thus compli…

A comparison of different methods for speleothem age modelling

2012

Abstract Speleothems, such as stalagmites and flowstones, can be dated with unprecedented precision in the range of the last 650,000 a by the 230Th/U-method, which is considered as one of their major advantages as climate archives. However, a standard approach for the construction of speleothem age models and the estimation of the corresponding uncertainty has not been established yet. Here we apply five age modelling approaches ( StalAge , OxCal, a finite positive growth rate model and two spline-based models) to a synthetic speleothem growth model and two natural samples. All data sets contain problematic features such as outliers, age inversions, large and abrupt changes in growth rate a…

Millennial-scale climate variability during the last 12.5 ka recorded in a Caribbean speleothem

2013

Abstract We present a speleothem stable oxygen isotope record for the last 12.5 ka based on two stalagmites from western Cuba. The δ18O signal is interpreted to represent past precipitation variability. Both stalagmites show a pronounced transition from higher δ18O values (indicating drier conditions) to more negative δ18O values (suggesting wetter conditions) between 10 and 6 ka. This transition is also visible in a planktonic δ18O record off Haiti. On orbital timescales, the δ18O value of Caribbean precipitation, thus, strongly resembles the oxygen isotope composition of Caribbean surface water. On millenial timescales, the speleothem δ18O record shows a high correlation to a North Atlant…

The magnesium isotope record of cave carbonate archives

2012

Here we explore the potential of magnesium (δ<sup>26</sup>Mg) isotope time-series data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semi-arid to arid (Morocco), the warm-temperate (Germany), the equatorial-humid (Peru) and the cold-humid (Austria) climate zones. Changes in the calcite magnesium isotope signature with time are compared against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a …

Scripts for Quality Control of SISAL workbooks

2020

Files needed for Quality Control checks of the SISALworkbook_v12 (Comas-Bru and Harrison, 2019). This includes a Python script (wb_check_v12_compatible.py) for automatic checks and an R script (plot_agemodels_hiatus_v12) for manual checks. Instructions on how to run these scripts are provided in a README_instructions.txt file. See supplementary material of Comas-Bru et al (2020, https://doi.org/10.5194/essd-2020-39) for further information on the checks.