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  • 1
    ISSN: 1573-0662
    Keywords: DNPH ; silica cartridge ; formaldehyde ; acetaldehyde ; biogenic source
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The 2.4-dinitrophenylhydrazine coated silica cartridge technique (DSC) was used for the measurements of HCHO and CH3CHO during the POPCORN campaign in August 1994. A total number of 505 measurements was carried out using an automatic sampling system. The sampling time for each measurement was 30 minutes. During the first two weeks of the campaign samples were taken every 3 hours and during the last two weeks every 30 minutes. No significant diurnal variation of HCHO and CH3CHO was observed. The average mixing ratios of HCHO and CH3CHO were 1.8 ±1.0 ppb and 1.4 ±1.3 ppb. The results for HCHO are in a good agreement with simultaneous measurements by differential optical absorption spectroscopy (DOAS). The absence of a strong diurnal variation of the HCHO mixing ratio can be explained by production and destruction processes during day and night. The measured mixing ratios of HCHO and CH3CHO, especially the mixing ratios during night, are a strong indication that during the POPCORN campaign the maize was a local source of HCHO and CH3CHO.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2019-07-13
    Description: The Sverrefjell and Sigurdfjell eruptive centers in the Bockfjord Volcanic Complex (BVC) on Svalbard (Norway) formed by subglacial eruptions ca. 1 Ma ago. These eruptive centers carry ubiquitous magnesian carbonate deposits including dolomitemagnesite globules similar to those in the Martian meteorite ALH84001. Carbonates in mantle xenoliths are dominated by ALH84001 type carbonate globules that formed during quenching of CO2-rich mantle fluids. Lava hosted carbonates include ALH84001 type carbonate globules occurring throughout lava vesicles and microfractures and massive carbonate deposits associated with vertical volcanic vents. Massive carbonates include 〈 or equal 5 cm thick magnesite deposits protruding downwards into clear blue ice within volcanic vents and carbonate cemented lava breccias associated with volcanic vents. Carbonate cements comprise layered deposits of calcite, dolomite, huntite, magnesite and aragonite associated with ALH84001 type carbonate globules lining lava vesicles. Combined Mossbauer, XRD and VNIR data show that breccia carbonate cements at Sverrefjell are analog to Comanche carbonates at Gusev crater.
    Keywords: Geosciences (General)
    Type: JSC-CN-22844 , 42nd Lunar and Planetary Science Conference; 7-11 Mar. 2011; Woodlands, TX; United States
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  • 3
    Publication Date: 2019-07-13
    Description: Seeking the signs of life on Mars is often considered the "first among equal" objectives for any potential Mars Sample Return (MSR) campaign. Among the geological settings considered to have the greatest potential for recording evidence of ancient life or its pre-biotic chemistry on Mars are lacustrine (and marine, if ever present) sedimentary depositional environments. This potential, and the possibility of returning samples that could meaningfully address this objective, have been greatly enhanced by investigations of an ancient redox stratified lake system in Gale crater by the Curiosity rover.
    Keywords: Space Sciences (General)
    Type: JSC-E-DAA-TN52615 , International Mars Sample Return Conference; 25-27 Apr. 2018; Berlin; Germany
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  • 4
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 5
    Publication Date: 2019-07-13
    Description: Highly promising locales for biosignature prospecting on Mars are ancient hydrothermal deposits, formed by the interaction of surface water with heat from volcanism or impacts. On Earth, they occur throughout the geological record (to at least approx. 3.5 Ga), preserving robust mineralogical, textural and compositional evidence of thermophilic microbial activity. Hydrothermal systems were likely present early in Mars' history, including at two of the three finalist candidate landing sites for M2020, Columbia Hills and NE Syrtis Major. Hydrothermal environments on Earth's surface are varied, constituting subaerial hot spring aprons, mounds and fumaroles; shallow to deep-sea hydrothermal vents (black and white smokers); and vent mounds and hot-spring discharges in lacustrine and fluvial settings. Biological information can be preserved by rapid, spring-sourced mineral precipitation, but also could be altered or destroyed by postdepositional events. Thus, field observations need to be followed by detailed laboratory analysis to verify potential biosignatures. See Attachment
    Keywords: Space Sciences (General)
    Type: JSC-E-DAA-TN52589 , International Mars Sample Return Conference; 25-27 Apr. 2018; Berlin; Germany
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  • 6
    Publication Date: 2020-02-12
    Description: An ascorbic acid extraction at pH 7.5 has been examined to assess the influence of reaction conditions (pH, ascorbic acid concentration) on the dissolution of Fe from synthetic 2-line ferrihydrite and from other Fe-bearing minerals. The method was highly selective for Fe in ferrihydrite with only small amounts of Fe extracted from other (oxyhydr)oxides or clays. The labile Fe extracted from the synthetic 2-line ferrihydrite stored as a slurry decreased with time, and high resolution microscopy showed that the older materials formed networked aggregates that slow down the dissolution. The apparent rate constant for the dissolution of fresh 2-line ferrihydrite (similar to 10(-3) s(-1)) was an order of magnitude larger than that for aged suspensions (similar to 10(-4) s(-1)). Fresh 2-line ferrihydrite that was filtered, freeze-dried, frozen and freeze-dried, and stored in the dry was even less readily dissolved (apparent rate constants similar to 10(-6) s(-1)). These ferrihydrites also contained networked aggregates and, additionally, appear to occur as granular aggregates (visible to the naked eye) during the early stages of dissolution. Storage of filtered, freeze-dried, and frozen and freeze-dried ferrihydrites, whether in water or air, produced similar dissolution behaviour because aggregation caused by de-watering decreases the labile Fe content and is not reversed by re-hydration. The determination of labile Fe in ferrihydrite requires that natural samples should be collected, stored and extracted wet. The most aged samples dissolved by parabolic dissolution kinetics indicate that the rates of dissolution were controlled by the diffusion of reactant into the internal porosity of aggregates. (C) 2010 Elsevier B.V. All rights reserved.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 7
    Publication Date: 2020-02-12
    Description: We have assessed the microbial ecology on the surface of Mittivakkat glacier in SE-Greenland during the exceptional high melting season in July 2012 when the so far most extreme melting rate for the Greenland Ice Sheet has been recorded. By employing a complementary and multi-disciplinary field sampling and analytical approach, we quantified the dramatic changes in the different microbial surface habitats (green snow, red snow, biofilms, grey ice, cryoconite holes). The observed clear change in dominant algal community and their rapidly changing cryo-organic adaptation inventory was linked to the high melting rate. The changes in carbon and nutrient fluxes between different microbial pools (from snow to ice, cryoconite holes and glacial forefronts) revealed that snow and ice algae dominate the net primary production at the onset of melting, and that they have the potential to support the cryoconite hole communities as carbon and nutrient sources. A large proportion of algal cells is retained on the glacial surface and temporal and spatial changes in pigmentation contribute to the darkening of the snow and ice surfaces. This implies that the fast, melt-induced algal growth has a high albedo reduction potential, and this may lead to a positive feedback speeding up melting processes.
    Type: info:eu-repo/semantics/article
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  • 8
    Publication Date: 2020-02-12
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  • 9
    Publication Date: 2020-02-12
    Description: Modelling the development of soils in glacier forefields is necessary in order to assess how microbial and geochemical processes interact and shape soil development in response to glacier retreat. Furthermore, such models can help us predict microbial growth and the fate of Arctic soils in an increasingly ice-free future. Here, for the first time, we combined field sampling with laboratory analyses and numerical modelling to investigate microbial community dynamics in oligotrophic proglacial soils in Svalbard. We measured low bacterial growth rates and growth efficiencies (relative to estimates from Alpine glacier forefields) and high sensitivity of bacterial growth rates to soil temperature (relative to temperate soils). We used these laboratory measurements to inform parameter values in a new numerical model and significantly refined predictions of microbial and biogeochemical dynamics of soil development over a period of roughly 120 years. The model predicted the observed accumulation of autotrophic and heterotrophic biomass. Genomic data indicated that initial microbial communities were dominated by bacteria derived from the glacial environment, whereas older soils hosted a mixed community of autotrophic and heterotrophic bacteria. This finding was simulated by the numerical model, which showed that active microbial communities play key roles in fixing and recycling carbon and nutrients. We also demonstrated the role of allochthonous carbon and microbial necromass in sustaining a pool of organic material, despite high heterotrophic activity in older soils. This combined field, laboratory, and modelling approach demonstrates the value of integrated model–data studies to understand and quantify the functioning of the microbial community in an emerging High Arctic soil ecosystem.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 10
    Publication Date: 2020-02-12
    Description: Productivity in the Southern Oceans is iron-limited, and the supply of iron dissolved from aeolian dust is believed to be the main source from outside the marine reservoir. Glacial sediment sources of iron have rarely been considered, as the iron has been assumed to be inert and non-bioavailable. This study demonstrates the presence of potentially bioavailable Fe as ferrihydrite and goethite in nanoparticulate clusters, in sediments collected from icebergs in the Southern Ocean and glaciers on the Antarctic landmass. Nanoparticles in ice can be transported by icebergs away from coastal regions in the Southern Ocean, enabling melting to release bioavailable Fe to the open ocean. The abundance of nanoparticulate iron has been measured by an ascorbate extraction. This data indicates that the fluxes of bioavailable iron supplied to the Southern Ocean from aeolian dust (0.01-0.13 Tg yr(-1)) and icebergs (0.06-0.12 Tg yr(-1)) are comparable. Increases in iceberg production thus have the capacity to increase productivity and this newly identified negative feedback may help to mitigate fossil fuel emissions.
    Language: English
    Type: info:eu-repo/semantics/article
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