Modification and preservation of environmental signals in speleothems

Abstract

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.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: 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.2) whereas there has traditionally been a focus on monthly mean δ 18 O 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 1 Corresponding author, fax +44(0)1214145528, E-mail: i.j.fairchild@bham.ac.uk control their variation on the longer-term. 3) the ecosystem and soil zone overlying the cave fundamentally imprint the carbon and trace element signals and can show characteristic variations with time. 4) new modelling on aquifer plumbing allows quantification of the effects of aquifer mixing. 5) recent work has emphasized the importance and seasonal variability of CO 2 -degassing leading to calcite precipitation upflow of a depositional site on carbon isotope and trace element composition of speleothems. 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. 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.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 ...

Radiocarbon evidence for decomposition of aged organic matter in the vadose zone as the main source of speleothem carbon

“…While much work has been done to understand the physical and chemical controls on speleothem carbon isotope ratios (e.g. Hendy, 1971;Genty et al, 2001;Mickler et al, 2004;Sp€ otl et al, 2005;Fairchild et al, 2006;Dreybrodt, 2008;Frisia et al, 2011), the basic conceptual model of the sources of speleothem carbon which suggests that it is derived from two main sources e soil CO 2 and carbonate bedrock e has remained largely unchanged.…”

Technical note: GUARD – an automated fluid sampler preventing sample alteration by contamination, evaporation and gas exchange, suitable for remote areas and harsh conditions

“…Other examples of a promising application are dripwater monitoring schemes in karst caves that are necessary especially, if not exclusively, in speleothem science (Ford and Williams, 2007;Fairchild and Baker, 2012). The case study presented here illustrates well the GUARD's potential for offering new research opportunities.…”

“…The goal was (1) to prove the existence of high-frequency (daily) variability in the carbon isotope values (δ 13 C) of dissolved inorganic carbon (DIC) in cave dripwaters and (2) to quantify its amplitude. This variability has important implications for the reconstruction of past environmental changes from speleothem δ 13 C values as these are not only a function of the dripwater δ 13 C signal originating from the surface environment, but also of the intensity of degassing of excess CO 2 from the dripwater (Fairchild et al, 2006). However, to date δ 13 C DIC variability has only been documented on the seasonal and annual scale (e.g.…”

Bronze Age volcanic event recorded in stalagmites by combined isotope and trace element studies

“…19,20 The sulphur concentration within a stalagmite, however, is not only controlled by the sulphate content and variability of the atmosphere since it can be modified by several factors, e.g. enhanced weathering of surrounding rocks, storage in the soil zone and biogenic activity.…”