Modification and preservation of environmental signals in speleothems

Speleothems are primarily studied in order to generate archives of climatic change and results have led to significant advances in identifying and dating major shifts in the climate system. However, the climatological meaning of many speleothem records cannot be interpreted unequivocally; this is particularly so for more subtle shifts and shorter time periods, but the use of multiple proxies and improving understanding of formation mechanisms offers a clear way forward. An explicit description of speleothem records as time series draws attention to the nature and importance of the signal filtering processes by which the weather, the seasons and longer-term climatic and other environmental fluctuations become encoded in speleothems. We distinguish five sources of variation that influence speleothem geochemistry: atmospheric, vegetation/soil, karstic aquifer, primary speleothem crystal growth and secondary alteration and give specific examples of their influence. The direct role of climate diminishes progressively through these five factors. \ud \ud We identify and review a number of processes identified in recent and current work that bear significantly on the conventional interpretation of speleothem records, for example: \ud \ud 1) speleothem geochemistry can vary seasonally and hence a research need is to establish the proportion of growth attributable to different seasons and whether this varies over time. \ud \ud 2) whereas there has traditionally been a focus on monthly mean Ã�´18O data of atmospheric moisture, current work emphasizes the importance of understanding the synoptic processes that lead to characteristic isotope signals, since changing relative abundance of different weather types might 1Corresponding author, fax +44(0)1214145528, E-mail: [email protected] control their variation on the longer-term. \ud \ud 3) the ecosystem and soil zone overlying the cave fundamentally imprint the carbon and trace element signals and can show characteristic variations with time. \ud \ud 4) new modelling on aquifer plumbing allows quantification of the effects of aquifer mixing. \ud \ud 5) recent work has emphasized the importance and seasonal variability of CO2-degassing leading to calcite precipitation upflow of a depositional site on carbon isotope and trace element composition of speleothems. \ud \ud 6) Although much is known about the chemical partitioning between water and stalagmites, variability in relation to crystal growth mechanisms and kinetics is a research frontier. \ud \ud 7) Aragonite is susceptible to conversion to calcite with major loss of chemical information, but the controls on the rate of this process are obscure. \ud \ud Analytical factors are critical to generate high-resolution speleothem records. A variety of methods of trace element analysis are available, but standardization is a common problem with the most rapid methods. New stable isotope data on Irish stalagmite CC3 compares rapid laser-ablation techniques with the conventional analysis of micromilled powders and ion microprobe methods. A high degree of comparability between techniques for Ã�´18O is found on the mm-cm scale, but a previously described high-amplitude oxygen isotope excursion around 8.3 ka is identified as an analytical artefact related to fractionation of the laser-analysis associated with sample cracking. High-frequency variability of not less than 0.5o/oo may be an inherent feature of speleothem Ã�´18O records

Late Pleistocene paleoclimate in the Black Hills of South Dakota from isotope records in speleothems

Two coeval speleothems from the Black Hills are used to investigate δ18O and δ13C variations within Reed’s Cave and reconstruct climate during the Wisconsin glacial period from 82 000 to 24 000 years ago. Variation in growth rates between the two speleothems reveals a strong control of hydrology and surface vegetation on isotopic variability and response of δ18O to climate. High-resolution δ18O and δ13C data show that local environmental conditions can produce an offset of δ18O values of up to 4‰ in coeval speleothems but still reveal important climate events. The transition from warmer to cooler periods results in an increase in δ18O of calcite (δ18Oct) in sample RC2 while in sample RC20, another equilibrium deposit coeval to part of the RC2 record, δ18Oct is offset from RC2 by between 0 and −3.5‰, and shows much higher frequency isotopic variation. Speleothem RC2 records interglacial/glacial transitions and interstadial events that are also present in speleothems from North America and Europe. Spectral analysis of the δ18Oct records for both speleothems reveals periodicity at 1000 to 2000 years, similar to millennial scale variability seen in the North Atlantic sediments and the Greenland ice cores

The Twannberg (Switzerland) IIG iron meteorites: Mineralogy, chemistry, and CRE ages

The original mass (15915 g) of the Twannberg IIG (low Ni-, high P) iron was found in 1984. Five additional masses (12 to 2488 g) were recovered between 2000 and 2007 in the area. The different masses show identical mineralogy consisting of kamacite single crystals with inclusions of three types of schreibersite crystals: cm-sized skeletal (10.5% Ni), lamellar (17.2% Ni), and 1-3 x 10 micrometer-sized microprismatic (23.9% Ni). Masses I and II were compared in detail and have virtually identical microstructure, hardness, chemical composition, cosmic-ray exposure (CRE) ages, and 10Be and 26Al activities. Bulk concentrations of 5.2% Ni and 2.0% P were calculated. The preatmospheric mass is estimated to have been at least 11,000 kg. The average CRE age for the different Twannberg samples is 230 +/- 50 Ma. Detrital terrestrial mineral grains in the oxide rinds of the three larger masses indicate that they oxidized while they were incorporated in a glacial till deposited by the Rhne glacier during the last glaciation (Würm). The find location of mass I is located at the limit of glaciation where the meteorite may have deposited after transport by the glacier over considerable distance. All evidence indicates pairing of the six masses, which may be part of a larger shower as is indicated by the large inferred pre-atmospheric mass.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Oxygen and hydrogen isotopic variations between adjacent drips in three caves at increasing elevation in a temperate coastal rainforest, Vancouver Island, Canada

The interpretation of speleothem paleoenvironmental records requires understanding of spatial–temporal variations in vadose drip water chemistry and isotopic composition. This study reports on intra- and inter-cave differences in δD, δ18O and electrical conductivity, using 18 monthly water samples from three adjacent drips (\u3c20 m apart) in each of three caves at increasing elevation (0, 550, and 740 m ASL) on very steep ground at the head of Tahsis Inlet fjord on the Pacific coast of Vancouver Island, British Columbia

Speleothem-derived Asian summer monsoon variations in Central China, 54-46 ka

The oxygen isotope signature (delta O-18) of stalagmite SI3 collected from Shizi Cave in north-east Sichuan Province provides an Asian Summer Monsoon (ASM) record in Central China for the period 54-46 ka. The SI3 delta O-18 record clearly shows a negative delta O-18 excursion centred around 49.4 ka, which was reported in Hulu Cave in East China but not identified in the speleothem records from South-west China. As a whole, this record displays a higher coherence with the two Hulu records from East China than with the speleothem delta O-18 records from South-west China, suggesting that at 54-46 ka, Central China was influenced more by the East Asian Summer Monsoon than by the Indian Summer Monsoon. It also displays a significant negative delta O-18 excursion at 47.5-46.6 ka, which is not clearly documented in two other speleothem delta O-18 records previously reported from South-west China. This suggests that details of the Greenland interstadial 12 warrant further investigations in future in monsoonal China. The SI3 delta O-18 record displays more significant centennial-scale variations than the other four speleothem delta O-18 records from East and South-west China, which may be due to the fact that the study site is closer to the north-west boundary of the ASM and more sensitive to variations of the ASM than East and South-west China. Copyright (C) 2011 John Wiley & Sons, Ltd