2,081 research outputs found

    CLIVAR Exchanges No. 54

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    State Borders in Africa

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    Aerospace medicine and biology: A continuing bibliography with indexes (supplement 388)

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    This bibliography lists 132 reports, articles and other documents introduced into the NASA Scientific and Technical Information Database. Subject coverage includes: aerospace medicine and physiology, life support systems and man/system technology, protective clothing, exobiology and extraterrestrial life, planetary biology, and flight crew behavior and performance

    Detection of Tephra Layers in Antarctic Sediment Cores with Hyperspectral Imaging

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    Tephrochronology uses recognizable volcanic ash layers (from airborne pyroclastic deposits, or tephras) in geological strata to set unique time references for paleoenvironmental events across wide geographic areas. This involves the detection of tephra layers which sometimes are not evident to the naked eye, including the so-called cryptotephras. Tests that are expensive, time-consuming, and/or destructive are often required. Destructive testing for tephra layers of cores from difficult regions, such as Antarctica, which are useful sources of other kinds of information beyond tephras, is always undesirable. Here we propose hyperspectral imaging of cores, Self-Organizing Map (SOM) clustering of the preprocessed spectral signatures, and spatial analysis of the classified images as a convenient, fast, non-destructive method for tephra detection. We test the method in five sediment cores from three Antarctic lakes, and show its potential for detection of tephras and cryptotephras.info:eu-repo/semantics/publishedVersio

    Modelling microbial diversity in Antarctic soils

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    PhD ThesisMicroorganisms play a crucial role in supporting biodiversity, maintaining marine and terrestrial ecosystems at the crux of the nutrient cycle. They are the most diverse and abundant of all living creatures, yet little is understood about their distribution or their intimate relationship with the environment. Antarctic ecosystems are among the most simple on Earth; with basic trophic structuring and the absence of many taxonomic groups, they are also isolated geographically with small patchy areas of nutrient inputs. In this instance, Antarctica becomes a pristine laboratory to examine the ecological paradigms already applied to macro-organisms, to determine if common biological laws govern the distribution of biology globally. The decline of biodiversity with increasing latitude is one such observation in the distribution of macro-organisms. In this study, soil microbial community samples were retrieved over a latitude of 56 to 72 °S across the Antarctic Peninsula region. This is a region of special interest due to a rapidly warming climate with mean temperatures increasing at several times the rate of mean global warming. Sites were biologically and environmentally profiled and data used in a variety of multivariate analysis in order to identify spatial trends and infer mechanisms that may be driving Antarctic terrestrial food webs; or where this was not possible, the areas where focus was needed to increase the information profile to allow this. Results indicate a lack of linear latitudinal gradient in microbial diversity, but do show a correlation with environmental heterogeneity; analysis of site diversity identified a gradient between warmer wetter areas, and areas synonymous with cold desert environment at 66⁰S, supported by both phylum composition and indicative soil chemistry. This was confirmed through principal co-ordinates of neighbours’ matrices analysis (PCNM), with distinct regions of community composition being identified when viewed with respect to environmental variables. Considering an overview of diversity with respect to environmental variables provided additional structure to test hypotheses about nutrient webs through structural equation modelling (SEM), and inferred that areas of patchy nutrient input exist and by means of ornithogenic guano additions promote higher C and N availability, increasing microbial abundance and richness.NERC

    Do bacteria thrive when the ocean acidifies? Results from an off-­shore mesocosm study

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    Marine bacteria are the main consumers of the freshly produced organic matter. In order to meet their carbon demand, bacteria release hydrolytic extracellular enzymes that break down large polymers into small usable subunits. Accordingly, rates of enzymatic hydrolysis have a high potential to affect bacterial organic matter recycling and carbon turnover in the ocean. Many of these enzymatic processes were shown to be pH sensitive in previous studies. Due to the continuous rise in atmospheric CO2 concentration, seawater pH is presently decreasing at a rate unprecedented during the last 300 million years with so-far unknown consequences for microbial physiology, organic matter cycling and marine biogeochemistry. We studied the effects of elevated seawater pCO2 on a natural plankton community during a large-scale mesocosm study in a Norwegian fjord. Nine 25m-long Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS) were adjusted to different pCO2 levels ranging from ca. 280 to 3000 µatm by stepwise addition of CO2 saturated seawater. After CO2 addition, samples were taken every second day for 34 days. The first phytoplankton bloom developed around day 5. On day 14, inorganic nutrients were added to the enclosed, nutrient-poor waters to stimulate a second phytoplankton bloom, which occurred around day 20. Our results indicate that marine bacteria benefit directly and indirectly from decreasing seawater pH. During both phytoplankton blooms, more transparent exopolymer particles were formed in the high pCO2 mesocosms. The total and cell-specific activities of the protein-degrading enzyme leucine aminopeptidase were elevated under low pH conditions. The combination of enhanced enzymatic hydrolysis of organic matter and increased availability of gel particles as substrate supported higher bacterial abundance in the high pCO2 treatments. We conclude that ocean acidification has the potential to stimulate the bacterial community and facilitate the microbial recycling of freshly produced organic matter, thus strengthening the role of the microbial loop in the surface ocean
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