Ronny Boch

North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems

The European Alps are an effective barrier for meridional moisture transport and are thus uniquely placed to record shifts in the North Atlantic storm track pattern associated with the waxing and waning of Late-Pleistocene Northern Hemisphere ice sheets. The lack of well-dated terrestrial proxy records spanning this time period, however, renders the reconstruction of past atmospheric patterns difficult. Here we present a precisely dated, continuous terrestrial record of meteoric precipitation in Europe between 30 and 14.7 ka. In contrast to present-day conditions, our speleothem data provide strong evidence for preferential advection of moisture from the South across the Alps supporting a southward shift of the storm track during the local Last Glacial Maximum (that is, 26.5–23.5 ka). Moreover, our age control indicates that this circulation pattern preceded the Northern Hemisphere precession maximum by ~3 ka, suggesting that obliquity may have played a considerable role in the Alpine ice aggradation.

Neotectonic extrusion of the Eastern Alps: Constraints from U/Th dating of tectonically damaged speleothems

We suggest that the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault, a major strike-slip system in the European Alps, is active. It has accommodated lateral extrusion of the central part of the Eastern Alps toward the Pannonian Basin. The main tectonic activity of this fault dates back to Oligocene and Miocene time, but until now it was largely unknown whether the fault was still active. We present here the first field evidence of neotectonic activity from a cave in the Hochschwab karst massif (Styria, Austria) that intersects a segment of the SEMP fault zone. Damaged speleothems in this cave include scratched flowstone (a hitherto undescribed feature), massive flowstone disrupted by a fault, and ruptured flowstone. The superposition of younger flowstone layers allows constraining the time frame of the tectonic events using U/Th dating. The youngest flowstone of the pre-damage generation is ca. 118 ka (end of the Last Interglacial) and the oldest post-event layer is ca. 9 ka (early Holocene). The tectonic event bracketed by these layers coincided with a growth hiatus during the last glacial period, consistent with the high alpine setting of the cave. Geologic evidence precludes deformation mechanisms other than tectonic. These new data are consistent with vectors of continuous global positioning system measurements as well as instrumental seismicity data, and collectively suggest that the SEMP is an active fault and that lateral extrusion of the Eastern Alps is ongoing.

Reconciliation of the Devils Hole climate record with orbital forcing.

The difference is all in the water Glacial cycles are in part controlled by the pattern of incident solar energy determined by the geometry of Earths orbit around the Sun. The classic record of the penultimate deglaciation from Devils Hole, Nevada, did not reconcile the presumption of so-called orbital forcing, however, suggesting that deglaciation began ~10,000 years too early. Moseley et al. present analyses of a new set of data from Devils Hole that show that the deglaciation indeed occurred at the time expected on the basis of orbital forcing. The age offset displayed by the older samples apparently was caused by interaction with groundwater, which preferentially affected the deeper original samples but not the new shallower samples. Science, this issue p. 165 Groundwater effects misled us about the Devils Hole climate record for nearly three decades. The driving force behind Quaternary glacial-interglacial cycles and much associated climate change is widely considered to be orbital forcing. However, previous versions of the iconic Devils Hole (Nevada) subaqueous calcite record exhibit shifts to interglacial values ~10,000 years before orbitally forced ice age terminations, and interglacial durations ~10,000 years longer than other estimates. Our measurements from Devils Hole 2 replicate virtually all aspects of the past 204,000 years of earlier records, except for the timing during terminations, and they lower the age of the record near Termination II by ~8000 years, removing both ~10,000-year anomalies. The shift to interglacial values now broadly coincides with the rise in boreal summer insolation, the marine termination, and the rise in atmospheric CO2, which is consistent with mechanisms ultimately tied to orbital forcing.

Uranium Series Dating of Speleothems

Radioactive decay of uranium and thorium isotopes at constant rates provides a tool to determine the age of speleothems with high precision and accuracy. As with any dating method, a fundamental prerequisite is the lack of post-depositional alteration, that is, no gain or loss of isotopes within the decay chain of interest. Using state-of-the-art instrumentation, this method allows dating speleothems between essentially zero and ca. 600,000 years before present. Multiple age determinations are typically performed along the extension axis of a stalagmite to decipher its detailed growth history. Uranium series chronology of speleothems not only provides useful constraints on speleogenetic processes, but forms the backbone of the increasingly important scientific field using stalagmites (and less commonly flowstone) as paleoenvironmental archives.

Scale-fragment formation impairing geothermal energy production: interacting H2S corrosion and CaCO3 crystal growth

BackgroundMineral precipitates (scaling) from deep saline thermal waters often constitute a major problem during geothermal energy production. The occurrence of scale-fragments accumulating and clogging pipes, filters, and heat exchangers is of particular concern regarding an efficient energy extraction.MethodsCarbonate scale-fragments from different sections of two geothermal power plants were collected and studied in a high-resolution scaling forensic approach comprising of microstructural characterization, elemental mapping, and stable carbon and oxygen isotope transects. The solid-phase analyses were evaluated in the context of natural environmental and technical (man-made) production conditions.Results and discussionOur results indicate an interaction of metal sulfide mineral layers mainly from H2S corrosion of the steel pipes and CaCO3 nucleation and crystal growth. A conceptual model of scale-fragment development addresses the relevance of two key interfaces: 1) the corrosion layer between the steel substrate and calcite scale and 2) the scale surface versus thermal fluid flow. The corrosion products constitute an attractive crystallization substrate of brittle and mechanically weak consistency. A rough carbonate scale surface tends to induce (micro) turbulences and increased flow resistance (frictional forces). These factors promote partial exfoliation, scale-fragment mobilization, and rapid clogging. This investigation highlights the potential of detailed petrographic and geochemical analyses of mineral precipitates for evaluating favorable versus unfavorable processes in geotechnical environmental settings.