Processes in ice caves : and their significance for paleoenvironmental reconstructions

Unterirdisches Eis wird in den meisten alpinen Karstregionen dokumentiert und dies, obwohl die durchschnittliche Aussenlufttemperatur die Nullgradgrenze manchmal weit überschreitet. Trotz des historischen Interesses für diese "Eishöhlen", sind nur wenige Daten vorhanden um deren Entwicklung in einem ändernden Klimakontext vorauszusagen. Diese Doktorarbeit behandelt die Frage unter dem Aspekt der Thermodynamik. Eine Fallstudie aus der Eishöhle Monlési (Schweiz) unterstreicht die Hauptrolle der unterirdischen Luftzirkulationen für die Bildung und die Erhaltung des Höhleneises. Daraus folgt, dass die Massenbilanz einer Eishöhle hauptsächlich die winterlichen Aussenbedingungen widerspiegelt. Die Datierung tausend jährigen Eisablagerungen kündigt interessante paläoklimatische Beiträge an. The presence of subsurface ice is documented in numerous alpine karst regions even though the mean annual air temperature sometimes greatly exceeds 0°C. Despite the historical interest raised by these "ice caves", little data is available to predict their evolution in a changing climate context. This doctoral research project approaches the issue from a thermodynamics perspective. Data from a case study of Monlési ice cave in Switzerland emphasizes the major role of subsurface air circulations in the formation and the conservation of cave ice. Results lead to the conclusion that the cave ice mass balance reflects mainly the external winter atmospheric conditions. The dating of thousand-yearold ice deposits predicts interesting paleoclimatological contributions

Timing and causes of North African wet phases during the last glacial period and implications for modern human migration

We present the first speleothem-derived central North Africa rainfall record for the last glacial period. The record reveals three main wet periods at 65-61 ka, 52.5-50.5 ka and 37.5-33 ka that lead obliquity maxima and precession minima. We find additional minor wet episodes that are synchronous with Greenland interstadials. Our results demonstrate that sub-tropical hydrology is forced by both orbital cyclicity and North Atlantic moisture sources. The record shows that after the end of a Saharan wet phase around 70 ka ago, North Africa continued to intermittently receive substantially more rainfall than today, resulting in favourable environmental conditions for modern human expansion. The encounter and subsequent mixture of Neanderthals and modern humans – which, on genetic evidence, is considered to have occurred between 60 and 50 ka – occurred synchronously with the wet phase between 52.5 and 50.5 ka. Based on genetic evidence the dispersal of modern humans into Eurasia started less than 55 ka ago. This may have been initiated by dry conditions that prevailed in North Africa after 50.5 ka. The timing of a migration reversal of modern humans from Eurasia into North Africa is suggested to be coincident with the wet period between 37.5 and 33 ka

Ancient DNA from speleothems: opportunity or challenge?

Ancient environmental DNA retrieved from sedimentary records (sedaDNA) can complement fossil-morphological approaches for characterizing Quaternary biodiversity changes. PCR-based DNA metabarcoding is so far the most widely used method in environmental DNA studies, including sedaDNA. However, degradation of ancient DNA and potential contamination, together with the PCR amplification drawbacks, have to be carefully considered. Here we tested this approach on speleothems from an Alpine cave that, according to a previous palynomorphological study, have shown to contain abundant pollen grains. This offers a unique opportunity for comparing the two methods and, indirectly, trying to validate DNA-based results. The plant taxa identified by sedaDNA are fewer than those by pollen analysis, and success rate of PCR replicates is low. Despite extensive work performed following best practice for sedaDNA, our results are suboptimal and accompanied by a non-negligible uncertainty. Our preliminary data seem to indicate that paleoenvironmental DNA may be isolated from speleothems, but the intrinsic weakness of PCR-based metabarcoding poses a challenge to its exploitation. We suggest that newly developed methods such as hybridization capture, being free from PCR drawbacks and offering the opportunity to directly assess aDNA authenticity, may overcome these limitations, allowing a proper exploitation of speleothems as biological archive

Enhanced Mediterranean water cycle explains increased humidity during MIS 3 in North Africa

We report a new fluid inclusion dataset from northeastern Libyan speleothem SC-06-01, which is the largest speleothem fluid inclusion dataset for North Africa to date. The stalagmite was sampled in Susah Cave, a low-altitude coastal site, in Cyrenaica, on the northern slope of the Jebel Al-Akhdar. Speleothem fluid inclusions from the latest Marine Isotope Stage (MIS) 4 and throughout MIS 3 (∼67 to ∼30 kyr BP) confirm the hypothesis that past humid periods in this region reflect westerly rainfall advected through the Atlantic storm track. However, most of this moisture was sourced from the western Mediterranean, with little direct admixture of water evaporated from the Atlantic. Moreover, we identify a second moisture source likely associated with enhanced convective rainfall within the eastern Mediterranean. The relative importance of the western and eastern moisture sources seems to differ between the humid phases recorded in SC-06-01. During humid phases forced by precession, fluid inclusions record compositions consistent with both sources, but the 52.5–50.5 kyr interval forced by obliquity reveals only a western source. This is a key result, showing that although the amount of atmospheric moisture advections changes, the structure of the atmospheric circulation over the Mediterranean does not fundamentally change during orbital cycles. Consequently, an arid belt must have been retained between the Intertropical Convergence Zone and the midlatitude winter storm corridor during MIS 3 pluvials

Caracterización de carbonatos criogénicos en una cueva helada del Pirineo

Se aportan datos micromorfológicos, isotópicos y cronológicos de carbonatos criogénicos CCC) de la cueva helada Sarrios-6, situada a 2780 m s.n.m. en el macizo de Monte Perdido (Pirineo central). Es el primer estudio de este tipo de espeleotemas en la Peninsula Ibérica. En una masa de hielo aparecen cristales romboédricos de calcita de tamaño milimétrico constituidos por un núcleo interno de cristales esqueléticos rodeados por un crecimiento externo de color pardo-rojizo. Indican una fase rápida inicial de precipitación de calcita y otra posterior más lenta. Los dos tipos de calcita presentan composición isotópica diferente (núcleo: valor medio de δ13C = 4,8‰VPDB, valor medio de δ18O = -20,8‰VPDB; crecimiento externo: valor medio de δ13C = 5,3‰ VPDB, valor medio de δ18O = -21,3‰ VPDB). La datación de una semilla incluida en la masa de hielo indica que la formación de la CCC tuvo lugar durante la Anomalía Climática MedievalWe provide micromorphological, isotopic and chronological data on cryogenic cave carbonates (CCC) from Sarrios-6 ice cave (2780 m a.s.l.) in the Monte Perdido Massif (central Pyrenees). It is the first report of such speleothems on the Iberian Peninsula.Millimeter-sized white skeletal calcite rhombohedrons overgrown by brown rhombohedral crystals are present within a perennial ice body. The morphology of two carbonate generations suggests an early stage of fast carbonate precipitation followed by a second phase formed at a slower precipitation rate. The two generations show distinct isotopic compositions (skeletal cores:mean δ13C = 4.8‰,mean δ18O = -20.8‰; overgrowths: mean δ13C = 5.3‰, mean δ18O = -21.3‰). A preliminary radiocarbon date of a seed found in the same ice layer suggests that the precipitation of CCC likely occurred during the Medieval Climate Anomal

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

Adrenal Venous Sampling: Where Is the Aldosterone Disappearing to?

Adrenal venous sampling (AVS) is generally considered to be the gold standard in distinguishing unilateral and bilateral aldosterone hypersecretion in primary hyperaldosteronism. However, during AVS, we noticed a considerable variability in aldosterone concentrations among samples thought to have come from the right adrenal glands. Some aldosterone concentrations in these samples were even lower than in samples from the inferior vena cava. We hypothesized that the samples with low aldosterone levels were unintentionally taken not from the right adrenal gland, but from hepatic veins. Therefore, we sought to analyze the impact of unintentional cannulation of hepatic veins on AVS. Thirty consecutive patients referred for AVS were enrolled. Hepatic vein sampling was implemented in our standardized AVS protocol. The data were collected and analyzed prospectively. AVS was successful in 27 patients (90%), and hepatic vein cannulation was successful in all procedures performed. Cortisol concentrations were not significantly different between the hepatic vein and inferior vena cava samples, but aldosterone concentrations from hepatic venous blood (median, 17 pmol/l; range, 40–860 pmol/l) were markedly lower than in samples from the inferior vena cava (median, 860 pmol/l; range, 460–4510 pmol/l). The observed difference was statistically significant (P < 0.001). Aldosterone concentrations in the hepatic veins are significantly lower than in venous blood taken from the inferior vena cava. This finding is important for AVS because hepatic veins can easily be mistaken for adrenal veins as a result of their close anatomic proximity