Impact of Episodic Warming Events

Lakes in the Taylor Valley, Antarctica were investigated to determine the impact of a significant air temperature warming event that occurred during the austral summer of 2001–2002. The warming in the valleys caused an increase in glacial run-off, record stream discharge, an increase in lake levels, and thinning of the permanent ice covers. These changes in the physical environment drove subsequent changes in the biogeochemistry of the lakes. Primary production in West Lake Bonney during the flood was reduced 23% as a consequence of stream induced water column turbidity. Increased nutrient levels within the lakes occurred in the year following the temperature induced high flow year. For example, soluble reactive phosphorus loading to Lake Fryxell was four-fold greater than the long-term average loading rates. These high nutrient levels corresponded to an increase in primary production in the upper water columns of Lakes Bonney and Fryxell. Depth integrated chlorophyll-a values increased 149% in East Lake Bonney, 48% in West Lake Bonney, and showed little change in Lake Fryxell; chlorophyll-a in Lake Hoare decreased 18% compared to long-term averages recorded as part of our ten year monitoring program, presumably from a reduction in under-ice PAR caused by increased sediment loads on the ice cover. Overall the warming event served to recharge the ecosystem with liquid water and associated nutrients. Such floods may play an important role in the long-term maintenance of liquid water in these dry valley lakes.     

A microtome for sectioning lake sediment cores at a very high resolution

A microtome device for sectioning sediment cores at a very high resolution down to 100 m is described. It is suitable for a variety of applications, but it is described in this paper specifically for diatom analysis. The aim is to facilitate the study of annual or even seasonal variations. The instrument is of simple design and is easy to manipulate.     

Evidence for two burial/exhumation stages during the evolution of the Variscan belt,as exemplified by P–T–t–d paths of metabasites in distinct allochthonous units of the Maures massif (SE France)

This paper examines the metamorphic evolution of three juxtaposed units of the Maures massif (France) with respect to the tectonic processes related to the Variscan orogeny. All sampled rocks are metabasalts or metagabbros metamorphosed during Palaeozoic tectonic events. The inferred metamorphic evolution takes into account the relative chronology of mineral parageneses with respect to microstructures, the mineral chemistry of zoned amphiboles, and calculated P–T–t–d paths derived from each unit. Three successive and contrasting tectono-metamorphic events are clearly identified. The D₁ event is associated with coarse-grained amphiboles of an early S₁–L₁ fabric that recorded prograde/retrograde anticlockwise paths at high-grade amphibolite facies conditions (7–8 kbar/700–750 °C). The D₂ event is related to fine-grained amphiboles of the main S₂ foliation that recorded prograde/retrograde clockwise paths at MP–MT conditions (4–6 kbar/550–650 °C). The D₃ event corresponds to late post-S₂ amphiboles crosscutting the main foliation and recording retrograde clockwise paths at lower grade conditions (4–2 kbar/500–350 °C). The D₁ event results from Silurian–Devonian continental subduction and subsequent thrust tectonics during an early stage of the Variscan evolution, before the Carboniferous. The D₂ event is connected to the Visean continental collision, marked by nappe stacking (burial) then crustal folding and sinistral strike-slip shearing (exhumation). The D₃ event is an effect of the Namurian late-orogenic extension (late exhumation) that mostly affected the previously thickened whole central block. This paper demonstrates that the whole metamorphic history of the Maures massif consists of two successive stages of burial/exhumation at different metamorphic conditions during the Variscan mountain building. Similar stages of subduction-uplift then collision-uplift processes have also been recognised in others parts of the Variscan belt and in the Alpine orogen.     

Identification of isotopically primitive interplanetary dust particles: A NanoSIMS isotopic imaging study

We have carried out a comprehensive survey of the isotopic compositions (H, B, C, N, O, and S) of a suite of interplanetary dust particles (IDPs), including both cluster and individual particles. Isotopic imaging with the NanoSIMS shows the presence of numerous discrete hotspots that are strongly enriched in ¹⁵N, up to ∼1300‰. A number of the IDPs also contain larger regions with more modest enrichments in ¹⁵N, leading to average bulk N isotopic compositions that are ¹⁵N-enriched in these IDPs. Although C isotopic compositions are normal in most of the IDPs, two ¹⁵N-rich hotspots have correlated ¹³C anomalies. CN⁻/C⁻ ratios suggest that most of the ¹⁵N-rich hotspots are associated with relatively N-poor carbonaceous matter, although specific carriers have not been determined. H isotopic distributions are similar to those of N: D anomalies are present both as distinct D-rich hotspots and as larger regions with more modest enrichments. Nevertheless, H and N isotopic anomalies are not directly correlated, consistent with results from previous studies. Oxygen isotopic imaging shows the presence of abundant presolar silicate grains in some of the IDPs. The O isotopic compositions of the grains are similar to those of presolar oxide and silicate grains from primitive meteorites. Most of the silicate grains in the IDPs have isotopic ratios consistent with meteoritic Group 1 oxide grains, indicating origins in oxygen-rich red giant and asymptotic giant branch stars, but several presolar silicates exhibit the ¹⁷O and ¹⁸O enrichments of Group 4 oxide grains, whose origin is less well understood. Based on their N isotopic compositions, the IDPs studied here can be divided into two groups. One group is characterized as being “isotopically primitive” and consists of those IDPs that have anomalous bulk N isotopic compositions. These particles typically also contain numerous ¹⁵N-rich hotspots, occasional C isotopic anomalies, and abundant presolar silicate grains. In contrast, the other “isotopically normal” IDPs have normal bulk N isotopic compositions and, although some contain ¹⁵N-rich hotspots, none exhibit C isotopic anomalies and none contain presolar silicate or oxide grains. Thus, isotopically interesting IDPs can be identified and selected on the basis of their bulk N isotopic compositions for further study. However, this distinction does not appear to extend to H isotopic compositions. Although both H and N anomalies are frequently attributed to the survival of molecular cloud material in IDPs and, thus, should be more common in IDPs with anomalous bulk N compositions, D anomalies are as common in normal IDPs as they are in those characterized as isotopically primitive, based on their N isotopes.     

Deep-rooted piercement structures in deep sedimentary basins — Manifestations of supercritical water generation at depth?

Deep-rooted enigmatic piercement structures in sedimentary basins, including ‘mud volcanoes’, ‘shale diapirs’, ‘salt diapirs’, and ‘asphalt volcanoes’, range in size from less than 1 km², surface area, up to 64 km², and have often an unknown depth of penetration due to incomplete imaging. We propose that they form a family associated with fluid flow. Our argument is based partly on their inferred location (above deep faults) and on the chemical analysis of emitted products, which includes liquid clays, brines and other substances from salt diapirs, and asphalt and light oils from the asphalt volcanoes. We explain these compositions by chemical alteration caused partly by supercritical water, a phase of water existent at high pressure and temperature, locally and temporarily achieved at depths generally beyond 10 km below surface, i.e., at the sediment–crust boundary. Our hypothesis overcomes some of the problems with interpreting fluid flow products, which are otherwise very difficult to explain. In case this hypothesis can be further verified, the family could perhaps be called ‘hydrothermally associated piercement structures’.     

Classification of Collapsed Buildings for Fast Damage and Loss Assessment

Fast and reliable identification of collapsed buildings is essential in case of earthquake disasters in urban areas. Airborne laserscanning offers the possibility to fulfil this task. Based on height measurements, geometrical surface models of buildings can be generated with this technology. Comparing the undamaged pre-event models with those recorded after an earthquake, the location of collapsed buildings and the dimension and characteristic of their damage can be obtained. The knowledge about typical damage types of collapsed buildings is necessary to interpret the changes found between the pre- and post-event building models. As existing building damage classifications don’t meet the requirements of this novel technique, observations and reports of building collapses were analysed. This leads to a new classification system of collapsed buildings and the definition of the so-called “damage catalogue”.The damage catalogue is a composition of different damage types of entire buildings typically occurring after earthquakes and it contains the observed dimensions of the geometrical features such as volume reduction or inclination change for each damage type. Besides the detectability of these geometrical features in airborne laserscanning data, the differentiation of the damage types takes effects on casualty numbers and on different search and rescue needs into account. The damage catalogue was developed by evaluating the associated database, which contains the characterisation of real damaged buildings by the defined geometrical features.The paper includes the conception of the damage catalogue and of the associated database, their use for the described reconnaissance technique and their further application possibilities.     

The effect of mineralogical and cationic heterogeneities on rheological properties of suspensions with Li-smectites, extracted from Volclay MX-80

The rheological study of colloidal suspensions contributes to the understanding of the aggregation phenomena of colloidal particles within a suspended fluid. The infra-2-μm (equivalent diameter) fraction of a bulk material, Volclay MX-80 bentonite was intensively analysed in order to understand the relative rheological data scattering observed with Li-smectite suspensions, prepared with the usual saturation procedure. A good mineralogical characterisation, especially for secondary minerals, coupled to a verification of cation exchanges on clayey fraction allowed us to propose a new way for investigating the observed differences of the bentonites rheological behaviour. Indeed, for a well Li-saturated smectite obtained from the purified infra-2-μm fraction, rheological data proved to be very accurate and perfectly reproducible. This emphasises the role of other minerals as well as the commonly observed discrepancy between the rheological behaviours of natural and industrial bentonites.     

On the reproducibility of run-away stars formed in collapsing clusters

To test the stability of the trajectories of run-away stars we present the results of a comparative study of 26 star clusters involving very strong encounters. Each one of these clusters was computed with different time steps, different techniques of integration and on different machines. We confirmed that, in general, the values of the energies, velocities and positions for the individual stars are not reproducible from run to run. We found, however, that in all the cases that have been tested, the run-away star preserved its energy, velocity and position from one run to another. It was also found that escapers are more reproducible than stars with negative energy.Part of this work was done at the Department of Aerospace Engineering and Engineering Mechanics of the University of Texas at Austin during a summer stay of C.A.