Climate and vegetation history from a 14,000-year peatland record, Kenai Peninsula, Alaska

Analysis of pollen, spores, macrofossils, and lithology of an AMS ¹⁴C-dated core from a subarctic fen on the Kenai Peninsula, Alaska reveals changes in vegetation and climate beginning 14,200 cal yr BP. Betula expansion and contraction of herb tundra vegetation characterize the Younger Dryas on the Kenai, suggesting increased winter snowfall concurrent with cool, sunny summers. Remarkable Polypodiaceae (fern) abundance between 11,500 and 8500 cal yr BP implies a significant change in climate. Enhanced peat preservation and the occurrence of wet meadow species suggest high moisture from 11,500 to 10,700 cal yr BP, in contrast to drier conditions in southeastern Alaska; this pattern may indicate an intensification and repositioning of the Aleutian Low (AL). Drier conditions on the Kenai Peninsula from 10,700 to 8500 cal yr BP may signify a weaker AL, but elevated fern abundance may have been sustained by high seasonality with substantial snowfall and enhanced glacial melt. Decreased insolation-induced seasonality resulted in climatic cooling after 8500 cal yr BP, with increased humidity from 8000 to 5000 cal yr BP. A dry interval punctuated by volcanic activity occurred between 5000 and 3500 cal yr BP, followed by cool, moist climate, coincident with Neoglaciation. Tsuga mertensiana expanded after ~ 1500 cal yr BP in response to the shift to cooler conditions.     

Middle pleistocene variations in palaeoclimate,palaeoenvironment and vegetation of the las tablas de daimiel national park (Spain)

The Middle Pleistocene palaeoclimate and palaeoenvironment evolution of the Las Tablas de Daimiel wetlands is described using a combination of sedimentology, pollen and δ¹³C and δ¹⁸O isotopic records of Unit B of core LT‐199906. This unit mostly contains fluvial and palustrine sediments. U/Th and amino acid racemization (AAR) dating and a comparison of the δ¹⁸O curve of Unit B with oceanic records suggests that Unit B spans the period from the end of Marine Isotope Stage (MIS) 10 (340 ka) to the first stages of MIS 7 (ca. 210 ka). MIS 9 was characterised by a regional vegetation dominated by Cupressaceae, with Pinus as a tree element. The water level was high and temperatures were very probably higher than during the Holocene. MIS 8 and the first substages of MIS 7 (7e, 7d and 7c) were dominated by xerophilous steppe vegetation in lowlands (elevations around 610 m above sea level) near to the wetland. At higher altitudes, far away from the wetland, there were fewer Pinus than in MIS 9, and a greater presence of warm, temperate and cool climate tree elements. The aquatic system in MIS 9 became shallower, with eutrophication and the accumulation of organic matter occurring; temperatures were similar to or lower than those of the Holocene. Copyright © 2011 John Wiley & Sons, Ltd.     

Pursuing Local Group blue massive stars with WSO-ISSIS

The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of massive stars through spectroscopic analyses. However, color-based target selection for spectroscopy (in absence of known spectral types), though relatively successful, usually produces lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies (Garcia et al. in Astron. Astrophys. 502:1015, 2009; Bull. Soc. R. Sci. Liege 80:381, 2011a). The interpretation of the association’s color-magnitude diagrams (CMDs) and the automatic determination of evolutionary masses for the members, allow a more insightful choice of candidates for spectroscopy and to spot out potential advanced evolutionary stages (Garcia et al. in Astron. Astrophys. 523:A23, 2010). We show our results on the dwarf irregular IC 1613 as illustration of the potential of the method.     

Hot spring deposits on the East Pacific Rise at 21°N: preliminary description of mineralogy and genesis

Hydrothermal sulfide-sulfate deposits were sampled from eight active and inactive vent sites along the East Pacific Rise at 21°N during the RISE expedition of April, 1979. The mineralogy of the samples has been determined by X-ray diffractometry, scanning electron microscopy, and X-ray energy dispersive analysis. Mounds of Zn, Fe, and Cu sulfides, dominated by sphalerite, pyrite, and lesser chalcopyrite, are topped by inactive and active chimneys, spouting fluids ≤350°C. The outer zones of active chimneys bear abundant anhydrite precipitated from heated ambient seawater, in addition to hydrothermal pyrite and sphalerite. Mg-hydroxysulfate-hydrate, a phase identified in seawater heating experiments, but previously not observed in nature, is intimately intergrown with anhydrite. Hottest chimneys contain massive chalcopyrite±bornite in their interior zones and belch fluids blackened by a presumably non-equilibrium assemblage of pyrrhotite plus minor sphalerite and pyrite. The early, outer walls of chimneys form from sulfates and the sulfide minerals in black smoke, but metastable pyrrhotite in outer zones is rapidly recrystallized to pyrite or marcasite. Reduction in the permeability of the outer walls permits a high-temperature (>～250°C), low-pH environment within chimneys that enhances precipitation of Cu-Fe sulfides in the central zones. Cooler, worm-covered chimneys emit white fluids bearing particulates of amorphous silica, barite, and pyrite. Amorphous silica and barite are also widely associated with fossilized worm-tubes. Two inactive chimneys are filled with sphalerite, wurtzite, sulfur, pyrite, and marcasite. Anhydrite has been dissolved from these dead chimneys, and the sulfate assemblage is dominated by barite and alteration products such as jarosite and natrojarosite. Silicates other than amorphous silica are not abundant in these deposits, although talc forms in hot chimneys from seawater Mg and hydrothermal silica, and nontronite is found in sediments on the crest of the East Pacific Rise. Other accessory phases identified include copper-rich sulfides such as cubanite, chalcocite, covellite, and digenite; galena; Fe-oxyhydroxides, including goethite; and gypsum. Chimney debris accumulates to form basal mounds, and the mineralogical differences between mounds and chimneys are attributable to weathering of mounds. Mn-oxyhydroxides form crusts within a few meters of the vents, but are not coprecipitating with the sulfide/sulfate minerals.     

The magnetic effects of brecciation and shock in meteorites: II. The ureilites and evidence for strong nebular magnetic fields

We have examined the magnetic characteristics of representative ureilites, with a view to identify the magnetic effects of shock and to isolate a primary component of the natural remanent magnetization (NRM). As a group, the ureilites show remarkably uniform patterns of magnetic behavior, attesting to a common genesis and history. However, a clearly observed gradation in magnetic properties of the ureilites studied with shock level, parallels their classification based on petrologic and chemical fractionation shock-related trends.The ureilite meteorites possess a strong and directionally stable NRM. Laboratory thermal modelling of this presumably primordial NRM preserved in Goalpara and Kenna produced reliable paleointensity estimates of order 1 Oe, thus providing evidence for strong early, nebular magnetic fields. This paleofield strength is compatible with values obtained previously from carbonaceous chondrites and supports isotopic evidence for a contemporary origin of these two groups of meteorites in the same nebular region. The mechanism for recording nebular fields, manifestly different in carbonaceous chondrite vs. ureilite meteorites, is thus relatively unimportant: violent collisional shock in ureilites seems to have only partially altered an original magnetization, by preferential removal of its least stable portion.     

Re-equilibration of natural H2O–CO2–salt-rich fluid inclusions in quartz—Part 1: experiments in pure water at constant pressures and differential pressures at 600 °C

Re-equilibration processes of natural H₂O–CO₂–NaCl-rich fluid inclusions quartz are experimentally studied by exposing the samples to a pure H₂O external fluid at 600 °C. Experimental conditions are selected at nearly constant pressure conditions (309 MPa) between fluid inclusions and pore fluid, with only fugacity gradients in H₂O and CO₂, and at differential pressure conditions (394–398 MPa, corresponding to an internal under-pressure) in addition to similar CO₂ fugacity gradients and larger H₂O fugacity gradients. Modifications of fluid inclusion composition and density are monitored with changes in ice dissolution temperature, clathrate dissolution temperature and volume fraction of the vapour phase at room temperature. Specific modification of these parameters can be assigned to specific processes, such as preferential loss/gain of H₂O and CO₂, or changes in total volume. A combination of these parameters can clearly distinguish between modifications according to bulk diffusion or deformation processes. Bulk diffusion of CO₂ according to fugacity gradients is demonstrated at constant pressure conditions. The estimated preferential loss of H₂O is not in accordance with those gradients in both constant pressure and differential pressure experiments. The development of deformation halos in quartz around fluid inclusions that are either under-pressurized or over-pressurized promotes absorption of H₂O from the inclusions and inhibits bulk diffusion according to the applied fugacity gradients.     

A multi-array competitive immunoassay for the detection of broad-range molecular size organic compounds relevant for astrobiology

We have developed antibodies and a multi-array competitive immunoassay (MACIA) for the detection of a wide range of molecular size compounds, from single aromatic ring derivatives or polycyclic aromatic hydrocarbons (PAHs), through small peptides, proteins or whole cells (spores). Multiple microarrays containing target molecules are used simultaneously to run several competitive immunoassays. The sensitivity of the MACIA for small organic compounds like naphthalene, 4-phenilphenol or 4-tertbutilphenol is in the range of 100–500 ppb (ng ml⁻¹), for others like the insecticide terbutryn it is at the ppt (ng l⁻¹) level, while for small peptides, as well as for more complex molecules like the protein thioredoxin, the sensitivity is approximately 1–2 ppb, or 10⁴–10⁵ spores of Bacillus subtilis per milliliter. For organic compounds, a water–methanol solution was used in order to achieve a better dissolution of the organics without compromising the antibody–antigen interaction. The above-mentioned compounds were detected by MACIA in water–(10%) methanol extracts from spiked pyrite and hematite-containing rock powder samples, as well as from a spiked-sand sample subjected to organic extraction with dichloromethane–methanol (1/1).     

Provenance and distribution of tethyan pelagic and hemipelagic siliceous sediments,pindos mountains,Greece

The broad range of time over which ribbon bedded cherts were deposited does not extend into the present marine environment, and no ribbon cherts have been recovered from the sea floor by the Deep Sea Drilling Project. The depositional environment of bedded cherts is difficult to determine, but extra-silicic impurities in the rock may offer clues about the provenance of the non-biogenic component. To test the usefulness of relative abundances of the extra silicic components in extracting information on the depositional environment of the chert, I analyzed the major element chemistry of chert samples from a broad range of environments including ophiolite-associated chert from the Franciscan Formation of California, deep-sea chert and porcellanite from the northwest Pacific (DSDP Leg 32), shallow pelagic shelf chert nodules from the Chalk of Britain, continental marginal basin chert from the Monterey Formation of California, and continental marginal basin chert from the Pindos Zone of Greece. The ratios FeO/A1₂O₃, TiO₂/A1₂O₃ and A1/A1+Fe+Mn were considered in detail. The interpretative logic is simple but empirically supported by observations of these ratio values at different depositional environments in the Pacific: A1 is concentrated most highly in continental material while Fe and Mn are more concentrated in pelagic sediments. FeO/A1₂O₃ can be used to differentiate between ophiolite associated chert and chert associated only with other sediments. TiO₂/A1₂O₃ is not a useful indicator, possibly because of the equalizing effect of widespread eolian transport. The A1/A1+Fe+Mn ratio was measured in detail in one stratigraphic section in central continental Greece. This ratio varied with the type of sediment admixture, decreasing in value after the influx of ophiolite debris-bearing sediments, even when their presence was undetectable in hand sample or under petrographic microscope.To help clarify the paleogeography of the main study area, the Pindos Zone, and to identify sources and dispersal patterns of extra-basinal materials, isopach maps of sedimentary facies of the Pindos were constructed. Superimposed directly upon the series of imbricated thrust slices that comprise the Pindos Zone, the maps are at best compressed pictures of the Pindos Sea Floor. Persistent regional variation of facies thicknesses over time suggests the existence of several smaller depressions surrounded by submarine highs in the Pindos Basin.     

Evidence for extensive diagenesis,Madagascar Basin,Deep Sea Drilling Site 245

Deep Sea Drilling Hole 245 (31°32′S, 52° 18′E) in the southwest Indian Ocean shows pronounced linear concentration-depth gradients in interstitial dissolved Ca, Mg and Sr. Electrical conductivity tests enable us to make the estimate of a constant diffusion coefficient with depth of about 2 × 10^?6 cm²/sec. The shapes of the concentration-depth gradients suggest that the major reaction sites in this hole are situated in the basal sediments and/or underlying basalts. It is proposed that observed interstitial water concentration changes in Ca and Mg are related to alteration of basaltic material, whereas those in Sr are due to calcium carbonate recrystallization processes. Support for the basaltic material alteration hypothesis comes from petrochemical and mineralogical data. Geochemical data also indicate that the high contents in Fe and Mn of the basal sediments can be related to low temperature alteration of basaltic glass and not necessarily to ‘hydrothermal’ activity.