Vegetation history and environmental development since ca 6000 cal yr BP in and around Ispani 2 (Kolkheti lowlands,Georgia)

The Kolkheti lowlands of western Georgia have a unique vegetation and a rich cultural history. Palynological and macrofossil analysis accompanied by AMS ¹⁴C-dates of the deposits of the Ispani 2 mire near Kobuleti allow the reconstruction of regional vegetation, environmental history and local peatland development within the context of Black Sea level and cultural changes. Comparison of two adjacent peatland cores confirms spatial differences in wetland development. Prior to 5400 cal yr BP, the Ispani basin was a floodplain of an active river system where overbank deposits with fluvially transported Castanea pollen were deposited. Subsequently, a lake or lagoon developed in which reeds expanded. These were succeeded by herb-rich open alder carrs. After 1900 cal yr BP, Carpinus and Fagus expanded on the dry grounds, where formerly Quercus was more abundant. Also Castanea declined. Local reedbeds, that burned regularly, succeeded the alder carr. After 1000 cal yr BP, a percolation bog developed resulting in the formation of 4 m of loose, porous, and largely undecomposed Sphagnum austinii peat with Molinia roots. The upper 50 cm of the analysed section show extensive human impact on the landscape during the 20th century.     

Searching for hidden Wolf–Rayet stars in the Galactic plane – 15 new Wolf–Rayet stars

We report the discovery of 15 previously unknown Wolf–Rayet (WR) stars found as part of an infrared (IR) broad-band study of candidate WR stars in the Galaxy. We have derived an empirically based selection algorithm which has selected ∼5000 WR candidate stars located within the Galactic plane drawn from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (mid-IR) and Two-Micron All-Sky Survey (near-IR) catalogues. Spectroscopic follow-up of 184 of these reveals 11 nitrogen-rich (WN) and four carbon-rich (WC) WR stars. Early WC subtypes are absent from our sample and none shows evidence for circumstellar dust emission. Of the candidates which are not WR stars, ∼120 displayed hydrogen emission-line features in their spectra. Spectral features suggest that the majority of these are in fact B supergiants/hypergiants, ∼40 of these are identified Be/B[e] candidates.
Here, we present the optical spectra for six of the newly detected WR stars, and the near-IR spectra for the remaining nine of our sample. With a WR yield rate of ∼7 per cent and a massive star detection rate of ∼65 per cent, initial results suggest that this method is one of the most successful means for locating evolved, massive stars in the Galaxy.     

Subglacial drainage system structure and morphology of Brewster Glacier,New Zealand

A global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of Brewster Glacier. These are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure (P_w): (i) P_w = ice overburden; (ii) P_w = half ice overburden; (iii) P_w = atmospheric. Additionally, 16 dye‐tracing experiments at 12 locations were performed through a summer melt season. Dye return curve shape, together with calculations of transit velocity, dispersivity and storage, are used to infer the likely morphology of the subglacial drainage system. Taken together, the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden. By mid‐summer, water pressures are closer to half‐ice overburden and the channelised drainage system is more hydraulically efficient. Surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout. Streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system. Copyright © 2008 John Wiley & Sons, Ltd.     

A real-time software backend for the GMRT

The new era of software signal processing has a large impact on radio astronomy instrumentation. Our design and implementation of a 32 antennae, 33 MHz, dual polarization, fully real-time software backend for the GMRT, using only off-the-shelf components, is an example of this. We have built a correlator and a beamformer, using PCI-based ADC cards and a Linux cluster of 48 nodes with dual gigabit inter-node connectivity for real-time data transfer requirements. The highly optimized compute pipeline uses cache efficient, multi-threaded parallel code, with the aid of vectorized processing. This backend allows flexibility in final time and frequency resolutions, and the ability to implement algorithms for radio frequency interference rejection. Our approach has allowed relatively rapid development of a fairly sophisticated and flexible backend receiver system for the GMRT, which will greatly enhance the productivity of the telescope. In this paper we describe some of the first lights using this software processing pipeline. We believe this is the first instance of such a real-time observatory backend for an intermediate sized array like the GMRT.     

In situ U–Pb SIMS (IN-SIMS) micro-baddeleyite dating of mafic rocks: Method with examples

An in situ U–Pb SIMS (IN-SIMS) method to date micro-baddeleyite crystals as small as 3 μm is presented with results from three samples that span a variety of ages and geologic settings. The method complements ID-TIMS geochronology by extending the range of dateable crystals to sizes smaller than can be recovered by physical separation. X-ray mapping and BSE imaging are used to locate target grains in thin section, followed by SIMS analysis on a CAMECA ims 1270, using the field aperture in the transfer column to screen out ions from host phases. Internal age precisions for the method are anticipated to range from 0.1% for Precambrian rocks to 3–7% for Phanerozoic rocks. Results establish a 2689 ± 5 Ma age for mafic dikes in the Wyoming craton, USA, a 1540 ± 30 Ma age for a subaerial lava flow from the Thelon Basin of northern Canada, and a 457 ± 34 Ma age for mafic dikes in the platform sequence of southeastern Siberia. The method is ideal for relatively non-destructive dating of small samples such as extraterrestrial rocks and precious terrestrial samples.     

Comparison of Canadian daily ice charts with surface observations off Newfoundland,winter 1992

Abstract

Forecast ice drift rates and thicknesses displayed on daily ice charts and forecast winds for the Canadian east coast are compared to on‐ice observations made during the second Canadian Atlantic Storm Program (CASP II) of March 1992. Observed and 24‐hour forecasts of daily ice drift rates were weakly correlated even though long‐term means closely matched observations. Daily drift rates have an RMS error of 13 cm s^‐1 relative to a 15 cm s^‐1 mean in addition to an RMS direction error of 50 degrees. Contributions towards daily drift uncertainties were: the estimation of winds, unmodelled physics of ocean and ice cover processes; and the inconsistency in the methods used by the ice forecaster. Correlation coefficients between forecast winds and on‐ice observed winds decreased from 0.8 at 0‐hour to 0.7 for the 30‐hour forecast. Similar results were found between ice drift rates from forecast winds. Histograms of ice thicknesses observed along narrow swaths using a helicopter‐towed electromagnetic sensor compared well with undeformed ice thicknesses representing large areas on ice charts, with differences mainly caused by difference in ice type representation and by co‐registering the two data sets.     

A snapshot of the Labrador current inferred from ice‐floe movement in NOAA satellite imagery

Abstract

Ice floes along the Labrador Coast were tracked using visible NOAA satellite images on two consecutive days (26 and 27 April, 1984) when the ice‐pack extended beyond the Labrador Current, and winds were weak. The resulting “snapshot” of the velocity field reveals strong topographic steering of the Labrador Current, such that the current speed and width in different areas are dependent on the steepness of the continental slope, and the current deflects into and out of Hopedale Saddle. Between 55 and 58°N, the main core of the current is 60–90 km wide, with speeds of 30–55 cm s^?1. The overall circulation pattern is in good agreement with historical water mass analyses over the shelf and slope, and with estimates of the speed of the Labrador Current obtained by other methods.