Pollen assemblages and their environmental implications in the Qaidam Basin,NW China     

Shengrui Zhang  Qinghai Xu  Anne Birgitte Nielsen  Hui Chen  Yuecong Li  Manyue Li  Lingyun Hun  Jianyong Li 《Boreas: An International Journal of Quaternary Research》2012,41(4):602-613

The Qaidam Basin is one of the most sensitive areas to climate change in China, owing to its unique geographical position and ecological condition. In this study, 32 surface‐soil pollen samples were collected to reveal the relationship between modern pollen assemblages, vegetation and precipitation in the eastern region of the Qaidam Basin. The results show that Chenopodiaceae (3.8–87%, average 48%), Artemisia (1.7–64.2%, average 17.5%) and Ephedra (0–90%, average 16.3%) are the dominant pollen types in all samples, and that different pollen assemblages correspond to different vegetation types. DCA and CCA of major pollen types demonstrate that precipitation is an important factor in the control of the distribution of vegetation in the study area. The content and concentration of the three major pollen types (Artemisia, Chenopodiaceae and Ephedra) change with the mean annual precipitation, and the optimum mean annual precipitation for Ephedra, Chenopodiaceae and Artemisia is <80, 80–200 and >160 mm, respectively. Correlation analysis between the variation in grain size of the three major pollen types and the main environmental variables shows that the grain size of the three pollen types is positively correlated with precipitation in the Qaidam Basin. The results confirm that precipitation is the most important environmental factor in the Qaidam Basin, and that it has an important effect on pollen grain size in the study area.  相似文献   

Eclipsing Binaries in Open Clusters     

John Southworth  Jens Viggo Clausen 《Astrophysics and Space Science》2006,304(1-4):199-202

The study of detached eclipsing binaries in open clusters can provide stringent tests of theoretical stellar evolutionary models, which must simultaneously fit the masses, radii, and luminosities of the eclipsing stars and the radiative properties of every other star in the cluster. We review recent progress in such studies and discuss two unusually interesting objects currently under analysis. GV Carinae is an A0 m + A8 m binary in the Southern open cluster NGC 3532; its eclipse depths have changed by 0.1 mag between 1990 and 2001, suggesting that its orbit is being perturbed by a relatively close third body. DW Carinae is a high-mass unevolved B1 V + B1 V binary in the very young open cluster Collinder 228, and displays double-peaked emission in the centre of the Hα line which is characteristic of Be stars. We conclude by pointing out that the great promise of eclipsing binaries in open clusters can only be satisfied when both the binaries and their parent clusters are well-observed, a situation which is less common than we would like.  相似文献   

Effects of local meteorology and aerosols on ozone and nitrogen dioxide retrievals from OMI and pandora spectrometers in Maryland,USA during DISCOVER-AQ 2011     

Andra J. Reed  Anne M. Thompson  Debra E. Kollonige  Douglas K. Martins  Maria A. Tzortziou  Jay R. Herman  Timothy A. Berkoff  Nader K. Abuhassan  Alexander Cede 《Journal of Atmospheric Chemistry》2015,72(3-4):455-482

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Parasitic barnacles (Cirripedia: Rhizocephala) from New Zealand off‐shore waters     

J⊘rgen Lützen  Henrik Glenner  Anne‐Nina Lörz 《新西兰海洋与淡水研究杂志》2013,47(2):613-621

Nine genera and species of rhizocephalans were recorded from the off‐shore waters around New Zealand. Mitochondrial and nuclear gene sequences were used to examine base differences between the European and New Zealand species of Parthenopea. Serial sections to study the internal structures of the reproductive organs were made for the genera Thylacoplethus and Thompsonia. Two species, Parthenopea australis n. sp. and Thylacoplethus novaezealandiae n. sp. are new to science and described in detail. Parthenopea australis n. sp. is the first rhizocephalan species recorded from the vicinity of active cold seeps. Three rhizocephalans could not be identified as they were parasitised by hyperparasitic cryptoniscine isopods. The decapodhost species comprised the taxa Paguridae, Lithodidae, Galatheidae, Chirostylidae, and Callianassidae.  相似文献   

Experimental determination of magnesium isotope fractionation during higher plant growth   总被引：1，自引：0，他引：1  

Emile B. Bolou-Bi  Anne Poszwa  Nathalie Vigier 《Geochimica et cosmochimica acta》2010,74(9):2523-6026

Two higher plant species (rye grass and clover) were cultivated under laboratory conditions on two substrates (solution, phlogopite) in order to constrain the corresponding Mg isotope fractionations during plant growth and Mg uptake. We show that bulk plants are systematically enriched in heavy isotopes relative to their nutrient source. The Δ²⁶Mg_plant-source range from 0.72‰ to 0.26‰ for rye grass and from 1.05‰ to 0.41‰ for clover. Plants grown on phlogopite display Mg isotope signatures (relative to the Mg source) ∼0.3‰ lower than hydroponic plants. For a given substrate, rye grass display lower δ²⁶Mg (by ∼0.3‰) relative to clover. Magnesium desorbed from rye grass roots display a δ²⁶Mg greater than the nutrient solution. Adsorption experiments on dead and living rye grass roots also indicate a significant enrichment in heavy isotopes of the Mg adsorbed on the root surface. Our results indicate that the key processes responsible for heavy isotope enrichment in plants are located at the root level. Both species also exhibit an enrichment in light isotopes from roots to shoots (Δ²⁶Mg_leaf-root = −0.65‰ and −0.34‰ for rye grass and clover grown on phlogopite respectively, and Δ²⁶Mg_leaf-root of −0.06‰ and −0.22‰ for the same species grown hydroponically). This heavy isotope depletion in leaves can be explained by biological processes that affect leaves and roots differently: (1) organo-Mg complex (including chlorophyll) formation, and (2) Mg transport within plant. For both species, a positive correlation between δ²⁶Mg and K/Mg was observed among the various organs. This correlation is consistent with the link between K and Mg internal cycles, as well as with formation of organo-magnesium compounds associated with enrichment in heavy isotopes. Considering our results together with the published range for δ²⁶Mg of natural plants and rivers, we estimate that a significant change in continental vegetation would induce a change of the mean river δ²⁶Mg that is comparable to analytical uncertainties.  相似文献   

Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska     

Thomas A. Ager  Paul E. Carrara  Victoria Anne  Joni Johnson 《Quaternary Research》2010,73(2):259-462

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.  相似文献   

Heat capacity, entropy, and magnetic properties of jarosite-group compounds     

Juraj Majzlan  Peter Glasnák  Robert A. Fisher  Mary Anne White  Michel B. Johnson  Brian Woodfield  Juliana Boerio-Goates 《Physics and Chemistry of Minerals》2010,37(9):635-651

Jarosite phases are common minerals in acidic, sulfate-rich environments. Here, we report heat capacities (C _p) and standard entropies (S°) for a number of jarosite samples. Most samples are close to the nominal composition AFe₃(SO₄)₂(OH)₆, where A = K, Na, Rb, and NH₄. One of the samples has a significant number of defects on the Fe sites and is called the defect jarosite; others are referred to as A-jarosite. The samples, their compositions, and the entropies at T = 298.15 K are:

Sample	Chemical composition	S o/(J mol−1 K−1)
K-jarosite	K0.92(H3O)0.08Fe2.97(SO4)2(OH)5.90(H2O)0.10	427.4 ± 0.7
Na-jarosite	Na0.95(H3O)0.05Fe3.00(SO4)2(OH)6.00	436.4 ± 4.4
Rb-jarosite	RbFe2.98(SO4)2(OH)5.95(H2O)0.05	411.9 ± 4.1
NH4-jarosite	(NH4)0.87(H3O)0.13Fe3.00(SO4)2(OH)6.00	447.2 ± 4.5
Defect jarosite	K0.94(H3O)0.06Fe2.34(SO4)2(OH)4.01(H2O)1.99	412.7 ± 4.1

There are additional configurational entropies of 13.14 and 8.23 J mol⁻¹ K⁻¹ in defect and NH₄-jarosite, respectively. A detailed analysis of the synchrotron X-ray diffraction patterns showed a large anisotropic peak broadening for defect and NH₄-jarosite. The fits to the low-temperature (approx. <12 K) C _p data showed that our samples can be divided into two groups. The first group is populated by the K-, Na-, Rb-, and NH₄-jarosite samples, antiferromagnetic at low temperatures. The second group contains the H₃O-jarosite (studied previously) and the defect jarosite. H₃O- and defect jarosite are spin glasses and their low-T C _p was fit with the expression C _p = γT + ΣB _j T _j , where j = (3, 5, 7, 9). The linear term is typical for spin glasses and the sum represents the lattice contribution to C _p. Surprisingly, the C _p of the K-, Na-, Rb-, and NH₄-jarosite samples, which are usually considered to be antiferromagnetic at low temperatures, also contains a large linear term. This finding suggests that even these phases do not order completely, but have a partial spin-glass character below their Néel transition temperature.  相似文献   

Mobility of potentially harmful metals in latosols impacted by the municipal solid waste deposit of Londrina,Brazil     

Raquel Souza Teixeira  Philippe Cambier  Regina Davison Dias  José Paulo Peccinini Pinese  Anne Jaulin-Soubelet 《Applied Geochemistry》2010

The contamination of soils by metals issuing from municipal solid waste (MSW) disposal in tropical environments has hardly been studied with regard to the particular problems associated with them, i.e., generally a high permeability of soils despite the abundance of clay, and the role of reactive Fe compounds. From a previous geotechnical and chemical survey, three latosol profiles differently affected by MSW leachates in the region of Londrina (Paraná, Brazil) were selected. The aims were to evaluate the extent of their contamination, to better understand the fate of potentially harmful metals in tropical soils and rank the determining factors. Samples between 0.5 and 7 m depth were analyzed for their physical, mineralogical and chemical properties, and their micro-morphology was described by optical and transmission electron microscopy. Two steps of a sequential extraction procedure helped to assess the mobility of elements and to better discriminate between metals originating from pedogenesis and issued from MSW. These combined approaches showed that exposed soil profiles have been impacted at various depths, down to 7 m, through increased metal content, especially enhanced mobility of Zn, Co, Mn, Cu and Fe, and through increased salinity and organic matter. The mobility of potentially harmful metals should decrease with pH, which significantly increased in some impacted horizons, but other factors can reverse this trend.  相似文献   

Observation of the thermal structure and dynamics of the stratosphere and the mesosphere from space     

Alain Hauchecorne  Philippe Keckhut  Chantal Claud  Francis Dalaudier  Anne Garnier 《Comptes Rendus Geoscience》2010,342(4-5):323-330

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International viewpoint and news     

Anne Marie de Grosbois 《Environmental Earth Sciences》2010,61(4):883-884

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