Palaeoecological Implications of Archaeological Seal Bone Assemblages: Case Studies from Labrador and Baffin Island

In recent years, increasing scientific attention has been paid to sea mammals as biological indicators of Arctic environmental change. The usefulness of animals such as ringed seal (Phoca hispida), harp seal (Phoca groenlandica), bearded seal (Erignathus barbatus), and harbour seal (Phoca vitulina) as indicator species is due to the close relationship of their range, reproductive cycles, and life histories to sea ice. The behaviour and distribution of these species correlate with ice conditions in the areas where the animals are encountered. The proportions of seal species represented in archaeological deposits may therefore reflect, at least in part, environmental conditions characterizing past seascapes. This paper examines zooarchaeological data from several Thule and historic Inuit archaeological sites in Baffin Island and Labrador, sites occupied during the last 700 years, to determine whether regional relationships can be demonstrated between subsistence economies, seal populations, and sea ice conditions. Ratios of ringed seal, harbour seal, bearded seal, and walrus (Odobenus rosmarus) bone frequencies from several archaeological sites are analyzed and discussed in light of new high-resolution proxy sea ice and regional palaeoenvironmental data. This exploratory study suggests that characteristics in seal species composition reflected in these assemblages can, in some circumstances, be correlated with recent sea ice reconstructions. However, a regional comparison of a larger number of more precisely dated archaeological sites is required for a full examination of these relationships. Au cours des dernières années, on a porté de plus en plus d'attention scientifique aux mammifères marins en tant qu'indicateurs biologiques du changement global dans l'Arctique. L'utilité d'animaux tels que le phoque annelé (Phoca hispida), le phoque du Groenland (Phoca groenlandica), le phoque barbu (Erignathus barbatus) et le phoque commun (Phoca vitulina) comme espèces indicatrices est due au rapport étroit que leurs aires de distribution, leurs cycles de reproduction et leurs cycles de vie ont avec la glace marine. Le comportement et la distribution de ces espèces sont corrélés avec les conditions de la glace dans les zones où l'on rencontre ces animaux. Les proportions des espèces de phoques qui se trouvent dans les dépôts archéologiques pourraient donc refléter, du moins partiellement, les conditions environnementales qui caractérisaient les paysages marins du passé. Cet article se penche sur les données zooarchéologiques provenant de plusieurs sites archéologiques Thulé et inuits dans l'île Baffin et le Labrador, sites occupés au cours des 700 dernières années, pour déterminer si l'on peut démontrer l'existence de rapports régionaux entre les économies de subsistance, les populations de phoques et les conditions de glace marine. Des taux de fréquence d'os de phoque annelé, de phoque commun, de phoque barbu et de morse provenant de plusieurs sites archéologiques font l'objet d'une analyse et d'une discussion à la lumière de nouvelles données indirectes à haute résolution sur la glace marine et sur le paléoenvironnement régional. Cette étude préliminaire suggère que les caractéristiques présentes dans la composition des espèces de phoques reflétée dans ces assemblages peuvent, dans certaines conditions, être corrélées aux reconstructions récentes de la glace marine. Une comparaison régionale d'un plus grand nombre de sites archéologiques datés de façon plus précise est toutefois nécessaire pour un examen exhaustif de ces rapports.

Palaeoecological Implications of Archaeological Seal Bone Assemblages: Case Studies from Labrador and Baffin Island

In recent years, increasing scientific attention has been paid to sea mammals as biological indicators of Arctic environmental change. The usefulness of animals such as ringed seal (Phoca hispida), harp seal (Phoca groenlandica), bearded seal (Erignathus barbatus), and harbour seal (Phoca vitulina) as indicator species is due to the close relationship of their range, reproductive cycles, and life histories to sea ice. The behaviour and distribution of these species correlate with ice conditions in the areas where the animals are encountered. The proportions of seal species represented in archaeological deposits may therefore reflect, at least in part, environmental conditions characterizing past seascapes. This paper examines zooarchaeological data from several Thule and historic Inuit archaeological sites in Baffin Island and Labrador, sites occupied during the last 700 years, to determine whether regional relationships can be demonstrated between subsistence economies, seal populations, and sea ice conditions. Ratios of ringed seal, harbour seal, bearded seal, and walrus (Odobenus rosmarus) bone frequencies from several archaeological sites are analyzed and discussed in light of new high-resolution proxy sea ice and regional palaeoenvironmental data. This exploratory study suggests that characteristics in seal species composition reflected in these assemblages can, in some circumstances, be correlated with recent sea ice reconstructions. However, a regional comparison of a larger number of more precisely dated archaeological sites is required for a full examination of these relationships. Au cours des dernières années, on a porté de plus en plus d'attention scientifique aux mammifères marins en tant qu'indicateurs biologiques du changement global dans l'Arctique. L'utilité d'animaux tels que le phoque annelé (Phoca hispida), le phoque du Groenland (Phoca groenlandica), le phoque barbu (Erignathus barbatus) et le phoque commun (Phoca vitulina) comme espèces indicatrices est due au rapport étroit que leurs aires de distribution, leurs cycles de reproduction et leurs cycles de vie ont avec la glace marine. Le comportement et la distribution de ces espèces sont corrélés avec les conditions de la glace dans les zones où l'on rencontre ces animaux. Les proportions des espèces de phoques qui se trouvent dans les dépôts archéologiques pourraient donc refléter, du moins partiellement, les conditions environnementales qui caractérisaient les paysages marins du passé. Cet article se penche sur les données zooarchéologiques provenant de plusieurs sites archéologiques Thulé et inuits dans l'île Baffin et le Labrador, sites occupés au cours des 700 dernières années, pour déterminer si l'on peut démontrer l'existence de rapports régionaux entre les économies de subsistance, les populations de phoques et les conditions de glace marine. Des taux de fréquence d'os de phoque annelé, de phoque commun, de phoque barbu et de morse provenant de plusieurs sites archéologiques font l'objet d'une analyse et d'une discussion à la lumière de nouvelles données indirectes à haute résolution sur la glace marine et sur le paléoenvironnement régional. Cette étude préliminaire suggère que les caractéristiques présentes dans la composition des espèces de phoques reflétée dans ces assemblages peuvent, dans certaines conditions, être corrélées aux reconstructions récentes de la glace marine. Une comparaison régionale d'un plus grand nombre de sites archéologiques datés de façon plus précise est toutefois nécessaire pour un examen exhaustif de ces rapports.

An Optical Readout TPC (O-TPC) for Studies in Nuclear Astrophysics With Gamma-Ray Beams at HIgS

We report on the construction, tests, calibrations and commissioning of an Optical Readout Time Projection Chamber (O-TPC) detector operating with a CO2(80%) + N2(20%) gas mixture at 100 and 150 Torr. It was designed to measure the cross sections of several key nuclear reactions involved in stellar evolution. In particular, a study of the rate of formation of oxygen and carbon during the process of helium burning will be performed by exposing the chamber gas to intense nearly mono-energetic gamma-ray beams at the High Intensity Gamma Source (HIgS) facility. The O-TPC has a sensitive target-drift volume of 30x30x21 cm^3. Ionization electrons drift towards a double parallel grid avalanche multiplier, yielding charge multiplication and light emission. Avalanche induced photons from N2 emission are collected, intensified and recorded with a Charge Coupled Device (CCD) camera, providing two-dimensional track images. The event's time projection (third coordinate) and the deposited energy are recorded by photomultipliers and by the TPC charge-signal, respectively. A dedicated VME-based data acquisition system and associated data analysis tools were developed to record and analyze these data. The O-TPC has been tested and calibrated with 3.183 MeV alpha-particles emitted by a 148Gd source placed within its volume with a measured energy resolution of 3.0%. Tracks of alpha and 12C particles from the dissociation of 16O and of three alpha-particles from the dissociation of 12C have been measured during initial in-beam test experiments performed at the HIgS facility at Duke University. The full detection system and its performance are described and the results of the preliminary in-beam test experiments are reported.Comment: Supported by the Richard F. Goodman Yale-Weizmann Exchange Program, ACWIS, NY, and USDOE grant Numbers: DE-FG02-94ER40870 and DE-FG02-97ER4103

Interstellar Plunging Waves: ALMA Resolves the Physical Structure of Nonstationary MHD Shocks

Magnetohydrodynamic (MHD) shocks are violent events that inject large amounts of energy in the interstellar medium dramatically modifying its physical properties and chemical composition. Indirect evidence for the presence of such shocks has been reported from the especial chemistry detected toward a variety of astrophysical shocked environments. However, the internal physical structure of these shocks remains unresolved since their expected spatial scales are too small to be measured with current instrumentation. Here we report the first detection of a fully spatially resolved, MHD shock toward the infrared dark cloud (IRDC) G034.77-00.55. The shock, probed by silicon monoxide (SiO) and observed with the Atacama Large Millimeter/submillimeter Array (ALMA), is associated with the collision between the dense molecular gas of the cloud and a molecular gas flow pushed toward the IRDC by the nearby supernova remnant (SNR) W44. The interaction is occurring on subparsec spatial scales thanks to the enhanced magnetic field of the SNR, making the dissipation region of the MHD shock large enough to be resolved with ALMA. Our observations suggest that molecular flow–flow collisions can be triggered by stellar feedback, inducing shocked molecular gas densities compatible with those required for massive star formation

Deuterium fractionation across the infrared-dark cloud G034.77−00.55 interacting with the supernova remnant W44

Context. Supernova remnants (SNRs) may regulate star formation in galaxies. For example, SNR-driven shocks may form new molecular gas or compress pre-existing clouds and trigger the formation of new stars. / Aims. To test this scenario, we measured the deuteration of N2H+, DfracN2H+ – a well-studied tracer of pre-stellar cores – across the infrared-dark cloud (IRDC) G034.77-00.55, which is known to be experiencing a shock interaction with the SNR W44. / Methods. We use N2H+ and N2D+J = 1−0 single pointing observations obtained with the 30m antenna at the Instituto de Radioas-tronomia Millimetrica to infer DfracN2H+ towards five positions across the cloud, namely a massive core, different regions across the shock front, a dense clump, an+d ambient gas. / Results. We find DfracN2H+ in the range 0.03−0.1, which is several orders of magnitude larger than the cosmic D/H ratio (~10−5). The DfracN2H+ across the shock front is enhanced by more than a factor of 2 (DfracN2H+ ~ 0.05 - 0.07) with respect to the ambient gas (≤0.03) and simila+r to that measured generally in pre-stellar cores. Indeed, in the massive core and dense clump regions of this IRDC we measure DfracN2H+ ~ 0.01. / Conclusions. We find enhanced deuteration of N2H+ across the region of the shock, that is, at a level that is enhanced with respect to regions of unperturbed gas. It is possible that this has been induced by shock compression, which would then be indirect evidence that the shock is triggering conditions for future star formation. However, since unperturbed dense regions also show elevated levels of deuteration, further, higher-resolution studies are needed to better understand the structure and kinematics of the deuterated material in the shock region; for example, to decipher whether it is still in a relatively diffuse form or is already organised in a population of low-mass pre-stellar cores

Looking back at superfluid helium

A few years after the discovery of Bose Einstein condensation in several gases, it is interesting to look back at some properties of superfluid helium. After a short historical review, I comment shortly on boiling and evaporation, then on the role of rotons and vortices in the existence of a critical velocity in superfluid helium. I finally discuss the existence of a condensate in a liquid with strong interactions, and the pressure variation of its superfluid transition temperature.Comment: Conference "Bose Einstein Condensation", Institut henri Poincare, Paris, 29 march 200

Deuterium Fractionation across the Infrared Dark Cloud G034.77-00.55 interacting with the Supernova Remnant W44

Supernova remnants (SNRs) may regulate star formation in galaxies. For example, SNR-driven shocks may form new molecular gas or compress pre-existing clouds and trigger the formation of new stars. To test this scenario, we measure the deuteration of $N_2H^+$, $D_{frac}^{N_2H^+}$, a well-studied tracer of pre-stellar cores, across the Infrared Dark Cloud (IRDC) G034.77-00.55, known to be experiencing a shock interaction with the SNR W44. We use N$_2$H$^+$ and N$_2$D$^+$ J=1-0 single pointing observations obtained with the 30m antenna at the Instituto de Radioastronomia Millimetrica to infer $D_{frac}^{N_2H^+}$ toward five positions across the cloud, namely a massive core, different regions across the shock front, a dense clump and ambient gas. We find $D_{frac}^{N_2H^+}$ in the range 0.03-0.1, several orders of magnitude larger than the cosmic D/H ratio ($\sim$10$^{-5}$). Across the shock front, $D_{frac}^{N_2H^+}$ is enhanced by more than a factor of 2 ($D_{frac}^{N_2H^+}\sim$0.05-0.07) with respect to the ambient gas ($\leq$0.03) and similar to that measured generally in pre-stellar cores. Indeed, in the massive core and dense clump regions of this IRDC we measure $D_{frac}^{N_2H^+}$}$\sim$0.1. We find enhanced deuteration of $N_2H^+$ across the region of the shock, at a level that is enhanced with respect to regions of unperturbed gas. It is possible that this has been induced by shock compression, which would then be indirect evidence that the shock is triggering conditions for future star formation. However, since unperturbed dense regions also show elevated levels of deuteration, further, higher-resolution studies are needed to better understand the structure and kinematics of the deuterated material in the shock region, e.g., if it still in relatively diffuse form or already organised in a population of low-mass pre-stellar cores.Comment: Accepted for publication on A&A; 8 pages, 5 figure

Widespread deuteration across the IRDC G035.39-00.33

© 2016 The Authors. Infrared Dark Clouds (IRDCs) are cold, dense regions that are usually found within Giant Molecular Clouds. Ongoing star formation within IRDCs is typically still deeply embedded within the surrounding molecular gas. Characterizing the properties of relatively quiescent IRDCs may therefore help us to understand the earliest phases of the star formation process. Studies of local molecular clouds have revealed that deuterated species are enhanced in the earliest phases of star formation. In this paper, we test this towards IRDC G035.39-00.33. We present an 80 arcsec by 140 arcsec map of the J = 2 → 1 transition of N2D+, obtained with the Institut de Radioastronomie Millimétrique 30 m telescope telescope. We find that N2D+ is widespread throughout G035.39-00.33. Complementary observations of N2H+ (1 - 0) are used to estimate the deuterium fraction, DN2H+ frac ≡ N(N2D+)/N(N2H+). We report a mean DN2H+ frac = 0.04 ± 0.01, with a maximum of DN2H+ frac = 0.09 ± 0.02. The mean deuterium fraction is ~3 orders of magnitude greater than the interstellar [D]/[H] ratio. High angular resolution observations are required to exclude beam dilution effects of compact deuterated cores. Using chemical modelling, we find that the average observed values of DN2H+ frac are in agreement with an equilibrium deuterium fraction, given the general properties of the cloud. This implies that the IRDC is at least ~3 Myr old, which is ~8 times longer than the mean free-fall time of the observed deuterated region

The C-Terminal Domain of the Arabinosyltransferase Mycobacterium tuberculosis EmbC Is a Lectin-Like Carbohydrate Binding Module

The D-arabinan-containing polymers arabinogalactan (AG) and lipoarabinomannan (LAM) are essential components of the unique cell envelope of the pathogen Mycobacterium tuberculosis. Biosynthesis of AG and LAM involves a series of membrane-embedded arabinofuranosyl (Araf) transferases whose structures are largely uncharacterised, despite the fact that several of them are pharmacological targets of ethambutol, a frontline drug in tuberculosis therapy. Herein, we present the crystal structure of the C-terminal hydrophilic domain of the ethambutol-sensitive Araf transferase M. tuberculosis EmbC, which is essential for LAM synthesis. The structure of the C-terminal domain of EmbC (EmbCCT) encompasses two sub-domains of different folds, of which subdomain II shows distinct similarity to lectin-like carbohydrate-binding modules (CBM). Co-crystallisation with a cell wall-derived di-arabinoside acceptor analogue and structural comparison with ligand-bound CBMs suggest that EmbCCT contains two separate carbohydrate binding sites, associated with subdomains I and II, respectively. Single-residue substitution of conserved tryptophan residues (Trp868, Trp985) at these respective sites inhibited EmbC-catalysed extension of LAM. The same substitutions differentially abrogated binding of di- and penta-arabinofuranoside acceptor analogues to EmbCCT, linking the loss of activity to compromised acceptor substrate binding, indicating the presence of two separate carbohydrate binding sites, and demonstrating that subdomain II indeed functions as a carbohydrate-binding module. This work provides the first step towards unravelling the structure and function of a GT-C-type glycosyltransferase that is essential in M. tuberculosis. Author Summary Top Tuberculosis (TB), an infectious disease caused by the bacillus Mycobacterium tuberculosis, burdens large swaths of the world population. Treatment of active TB typically requires administration of an antibiotic cocktail over several months that includes the drug ethambutol. This front line compound inhibits a set of arabinosyltransferase enzymes, called EmbA, EmbB and EmbC, which are critical for the synthesis of arabinan, a vital polysaccharide in the pathogen's unique cell envelope. How precisely ethambutol inhibits arabinosyltransferase activity is not clear, in part because structural information of its pharmacological targets has been elusive. Here, we report the high-resolution structure of the C-terminal domain of the ethambutol-target EmbC, a 390-amino acid fragment responsible for acceptor substrate recognition. Combining the X-ray crystallographic analysis with structural comparisons, site-directed mutagenesis, activity and ligand binding assays, we identified two regions in the C-terminal domain of EmbC that are capable of binding acceptor substrate mimics and are critical for activity of the full-length enzyme. Our results begin to define structure-function relationships in a family of structurally uncharacterised membrane-embedded glycosyltransferases, which are an important target for tuberculosis therapy