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  • Artikel  (153.176)
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  • 1
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    GFZ Data Services
    Publikationsdatum: 2020-02-12
    Beschreibung: The International Geodynamics and Earth Tide Service (IGETS) was established in 2015 by the International Association of Geodesy. IGETS continues the activities of the Global Geodynamics Project (GGP) between 1997 and 2015 to provide support to geodetic and geophysical research activities using superconducting gravimeter (SG) data within the context of an international network. As a new addition to this network, the iGrav-027 superconducting gravimeter had been installed at the Borowa Gora Geodetic-Geophysical Observatory which has been established in late 1930s. Continuous time-varying gravity and atmospheric pressure data from the SGs at Borowa Gora are integrated in the IGETS data base hosted by ISDC (Information System and Data Center) at GFZ. Borowa Gora Geodetic-Geophysical Observatory is located in Poland, situated 50 km north of Warsaw (longitude: 21.0359 E, latitude: 52.2755 N, height above MSL: 109 m). The operation and maintenance of the Borowa Gora instrumentation is done by staff of the Institute of Geodesy and Cartography. The shortest distance to the Baltic Sea coastline is approx. 240 km. The area is located in a tectonically quiet zone. Geologically the situation is not well recognized, a significant size artificial reservoir is located within 1-2 km from the Observatory. The environment is a not significantly urbanized area with visible daily seismicity. The climate at this place has rough winters (up to -20 degrees Celsius) and hot summers (up to 35 degrees Celsius). The iGrav-027 is located in a specially prepared chamber in the basement of one of the Observatory buildings. It is separated from the compressor operating in a separate room. The location of the gravimeter ensures a relatively stable temperature of 21°C ±2°C throughout the year. The instrument is placed on a specially prepared concrete monument of 1.2 × 1.2 m horizontal and 1.5 m vertical dimensions (ca 1.3 m deep below floor level). The sensor of the instrument is located about 2 m below ground level, and the position and height of the instrument has been determined with a centimetre accuracy, before the installation. The iGrav-027 is co-located in the same building with the A10-020 absolute gravimeter. There are three well monumented pillars for absolute gravity determinations, which can be conducted along with the operating iGrav-027 (e.g. for the comparison with absolute gravimeters). In the vicinity of the observatory several further pillars were set up for various other geodetic antennas and instrumentation. Borowa Gora is a geodynamic observatory comprising space techniques and ground instruments. The iGrav-027 operation started at the end of April 2016, official start is assigned as from 1th of May 2016. Since that time the time series is carried out without interruption up to present. The time sampling of the raw gravity and barometric pressure data of IGETS Level 1 is 1 minute. Future plans include uploading 1s data sampling also. In addition, Borowa Gora is equipped with auxiliary data supporting the interpretation of the SG measurements, which is, however, not provided in the IGETS data base due to complexity. These are a local network of hydrological and meteorological sensors as well as two permanent GNSS (Global Navigation Satellite Systems) stations BOGO and BOGI. Additionally magnetic field variations are also recorded.
    Sprache: Englisch
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  • 2
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    GFZ Data Services
    Publikationsdatum: 2020-02-12
    Sprache: Englisch
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  • 3
    Publikationsdatum: 2020-02-12
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  • 4
    Publikationsdatum: 2020-02-12
    Beschreibung: A temporary seismic array was installed in combination with a meteorological station in the Dead Sea valley, Jordan. Within the scope of the HGF virtual institute DESERVE we operated 15 temporary seismic stations between February 2014 and February 2015 together with a nearby meteorological station close to the east coast of the Dead Sea. The main aim was to acquire data to study the influence of wind on seismic records and retrieve related meteorological parameters. The study area is scarcely populated and has ideal meteorological conditions to study periodically occurring winds.
    Sprache: Englisch
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  • 5
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    GFZ Data Services
    In:  EnMAP Technical Report
    Publikationsdatum: 2020-02-12
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/report
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  • 6
    Publikationsdatum: 2020-09-05
    Beschreibung: We describe EnMAP-like imaging spectroscopy data files to be used for mineral mapping with the EnMAPBOX software. It is simulated EnMAP satellite data, which is based on hyperspectral flight cam-paign data with the AVIRIS-NG and HyMap sensors. In preparation of the EnMAP satellite mission, an EnMAPBOX software package provides tools for visualization and scientific analysis of the data. Among many applications, the EnMAPBOX contains geological mapping tools (EnGeoMAP). Here we apply these tools to several representative test cases (Boesche, 2015; Boesche et al., 2016; Mielke et al., 2016). The test data comprise two study sites. The first scene covers the Mountain Pass open pit mine - a carbonatite deposit in California, USA. It contains calcitic rock units and rare earth element (REE) bearing minerals of the bastnaesite group, also called fluorocarbonates (Olson et al., 1954). The REE concentrations at mountain pass are 9.2% on average, among the highest in the world (Brüning and Böhmer, 2011). The high concentration and the open pit activities make Mountain Pass an ideal test site to investigate the rare earth element distribution in the surface layer. The airborne image data were collected in 2014 by Jet Propulsion Laboratory (JPL), USA, with the AVIRIS-NG sensor and form the basis for EnMAP simulations (Segl et al., 2012; Thompson et al., 2015). The second HyMap spectral image data covers part of the Miocene Cabo de Gata-Nίjar volcanic field, in southeast Spain. It comprises a subset of (Chabrillat et al., 2016) covering the Rodalquilar and Lomilla Calderas, which host the economically relevant gold-silver, lead-zinc-silver-gold and alunite deposits. It is a hydrothermal alteration complex, representing the silicic alteration, the advanced argillic alter-ation zone, which grades into the argillic and propylitic zone (Arribas et al., 1995, 1989). The image data are part of the Cabo de Gata-Nίjar HyMap imagery which was collected during the DLR HyEurope airborne campaign 2005 in the frame of the GFZ land degradation program (Chabrillat et al., 2016, 2005). We use these datasets to simulate EnMAP-like images for classification and mapping using spectro-scopic remote sensing techniques in the EnGeoMAP tools. The EnMAP end-to-end Simulation (EeteS) tool produced simulated EnMAP like data with a spatial sampling distance of 30 x 30 m and 242 spectral bands (Guanter et al., 2015; Segl et al., 2012).
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/report
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  • 7
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    GFZ Data Services
    Publikationsdatum: 2020-02-12
    Beschreibung: Abstract data objects are frequently transferred between a central computer (server) and one or more other computers (clients). The httpmsgbus (HMB) facilitates the transfer of these objects, functioning as a messaging service which runs over HTTP. These may be SeisComP data model items, or any other content. Messages sent by one client can be received by multiple clients connected to the same bus, using JSON and BSON formats for communication. Clients may limit what objects they wish to receive as part of the connection process. A bus may have multiple queues. Order of messages within a queue is preserved. A queue may have multiple topics; topic name is simply an attribute of a message. A receiving client subscribes to one or more queues and tells which topics it is interested in. Each message within a queue has a sequence number, so it is possible to resume connection without data loss, provided that the needed messages are still in the queue. A client can also select messages based on start- and end-time, and filter messages using a subset of MongoDB query language. HMB supports out-of-order messages by letting a sending client specify the sequence number when sending messages. Messages are received in order; a receiving client may ignore out-of-order messages or wait for missing messages until a timeout. httpmsgbus can be used as a standalone program or as an add-on to SeisComP 3 [1]; the code can be copied to SC3 source tree and compiled together with the rest of the SC3 using CMake or installed separately using the install.sh script. Go compiler [2] is required to compile the code; other requirements include Libpcre (pcre-devel, libpcre3-dev or similar Linux package), and Mongo DB for persistent storage. Source code is freely available for download; its use is governed by the GNU General Public License, version 3.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/other
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  • 8
    Publikationsdatum: 2020-02-12
    Beschreibung: The scope of the Science Plan is to describe the scientific background, applications, and activities related to the Environmental Mapping and Analysis Program (EnMAP) mission. Primarily, the document addresses scientists and funding institutions, but it may also be of interest for environmental stakeholders and governmental bodies. It is conceived to be a living document that will be updated throughout the entire mission. Chapter 1 provides a brief overview of the principles and current state of imaging spectroscopy. This is followed by an introduction to the EnMAP mission, including its objectives and potential impact on international programs as well as major environmental and societal challenges to their understanding and management EnMAP can contribute. Chapter 2 describes the EnMAP system together with data products and access, calibration/validation issues, and synergies with other missions. Chapter 3 gives an overview of the relevance, current lines of research, and potential contributions of EnMAP for major fields of application, such as vegetation, geology and soils, coastal and inland waters, cryosphere, urban areas, atmosphere and hazards to address the environmental and societal challenges presented in Chapter 1. Finally, Chapter 4 outlines the scientific exploitation strategy, which includes the strategy for community building and training, preparatory flight campaigns and software developments. A list of abbreviations is provided in the annex to this document, while an extended glossary of terms and abbreviations is available at the EnMAP website.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/report
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  • 9
    Publikationsdatum: 2020-02-12
    Materialart: info:eu-repo/semantics/workingPaper
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  • 10
    Publikationsdatum: 2020-02-12
    Materialart: info:eu-repo/semantics/workingPaper
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  • 11
    Publikationsdatum: 2020-02-12
    Materialart: info:eu-repo/semantics/workingPaper
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  • 12
    Publikationsdatum: 2020-02-12
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  • 13
    Publikationsdatum: 2020-02-12
    Beschreibung: The International Continental Scientific Drilling Program (ICDP) performed a dual-phase scientific drilling project to investigate mountain-building processes called Collisional Orogeny in the Scandinavian Caledonides (COSC). The borehole COSC-1 was drilled through the Lower Seve Nappe, as the first of two 2.5 km deep drill holes close to Åre, central Sweden. The recovered rocks comprise a 1650 m thick suite of high grade gneisses and amphibolites with clear Seve Nappe affinities, while the lower 850 m comprise rather homogenous mylonitic gneisses with interfingered K-rich phyllonite bands of cm to several m size and some intercalated amphibolites. The different lithologies all crosscut the core in a subhorizontal direction with foliation of gneisses and phyllonites in the same direction. Albite and garnet porphyroblasts with pressure shadows show syn-deformational growth and the same sub-horizontal alignment. The focus of this study was to detect chemical and mineralogical differences in mylonitic and host rocks and to relate these differences to either metasomatism and deformation or inherited source rock variance. Another goal of this work is to compare chemical core scanning instruments. For this purpose two different X-Ray Fluorescence (XRF) techniques, Laser Induced Breakdown Spectroscopy (LIBS) and hyperspectral imaging served to measure seven samples from the lower 850 m of the COSC-1 core. This data publication comprises the datasets gained in the course of this study. The metadata (OF WHAT?) will be presented in an additional file including XRF data from the Avaatech XRF core scanner in a txt.file as well as datasets of the other used devices in original file formats.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/workingPaper
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  • 14
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    GFZ Data Services
    Publikationsdatum: 2020-02-12
    Beschreibung: The experiments are performed down the Edward Bailey valley, in the Renland peninsula, Scoresby Sund, Greenland. General purpose: ambient seismic noise recordings are obtained to characterize the geometry/structure of the valley the geometry/structure of the glaciers the microseismicity of the glacier, the friction process, crack orientation and mechanisms the seismic activity of glacial rivers, the relation between hydrological flow and noise spectrum the localization and characterization of sub-glacial flow from surface recordings. Seismic stations were composed of 3C broadband Trillium compact seismometer, a Cube datalogger and a 12V (D-cell types, stacked) battery pack.The experiment splits into three surveys performed at three different sites, one after the other, from july to august 2016. In the first experiment, we deploy 11 stations, 9 of them on a flat sandy area covering, partly, immobile ice that seems to be blocked between the Bailey Glacier (upstream) and the Apusinikajik glacier (downstream). The 9 sensors are placed a few hundreds of meters from the Apusinikajik lateral front, the last 2 are placed on the glacier next to the collapsing front. In the second and third experiment (chronologically speaking), we deploy 10 and 8 stations, respectively. Each deployment is performed along a Bailey valley transect. The first one intercepts the front-end of the glacier and the sub-glacial river exit (flow of several m3/s). The second transect is performed some 850m upstream. Waveform data are available from the GEOFON data centre, under network code 3H, and are embargoed until summer of 2019.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/workingPaper
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  • 15
    Publikationsdatum: 2020-02-12
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  • 16
    Publikationsdatum: 2020-02-12
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  • 17
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    Publikationsdatum: 2020-02-12
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  • 18
    Publikationsdatum: 2020-02-12
    Beschreibung: This data collection contains a multitemporal series of six airborne hyperspectral image mosaics ac-quired during the growing season of 2012 over the Neusling test area near Landau a.d. Isar in Southern Germany. The airborne hyperspectral data is complemented by accompanying in-situ data acquired parallel to the overflights. The dataset is composed of a) four airborne hyperspectral image mosaics acquired during overflights on April 28th 2012, May 25th 2012, June 16th 2012 and September 8th 2012 with the AVIS-3 imaging spectrometer. The AVIS data consists of 197 spectral bands, ranging from VIS to SWIR (477 - 1704 nm); b) two airborne hyperspectral image mosaics acquired during overflights on May 8th 2012 and August 12th 2012 with a HySpex imaging spectrometer. The HySpex data consists of 332 spectral bands, ranging from VIS to SWIR (417 - 2496 nm); c) spatially comprehensive land use/land cover maps generated from in-situ observations for two time-windows during the growing season of 2012 (May and August); d) Flight-parallel in-situ point-measurements consisting of: i) non-destructively measured leaf area index of winter wheat, winter barley, sugar beet, maize and rapeseed (561 meas-urements incl. standard deviations), ii) SPAD chlorophyll measurements (522 measurements incl. standard deviations), iii) 557 soil moisture measurements incl. standard deviations iv) 539 phenological observations v) 499 measurements of canopy height incl. standard deviations and vi) 38 measurements of plant density. The dataset was collected in order to cover the seasonal dynamics in the development of agricultural crops in Southern Germany.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/report
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  • 19
    Publikationsdatum: 2020-02-12
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  • 20
    Publikationsdatum: 2020-02-12
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/workingPaper
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  • 21
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    In:  EnMAP Flight Campaigns Technical Report
    Publikationsdatum: 2020-02-12
    Beschreibung: Berlin-Urban-Gradient is a ready-to-use imaging spectrometry dataset for multi-scale unmixing and hard classification analyses in urban environments. The dataset comprises two airborne HyMap scenes at 3.6 and 9 m resolution, a simulated spaceborne EnMAP scene at 30 m resolution, an im-age endmember spectral library and detailed land cover reference information. All images are pro-vided as geocoded reflectance products and cover the same subset along Berlin’s urban-rural gra-dient. The variety of land cover and land use patterns captured make the dataset an ideal play-ground for testing the transfer of methods and research approaches at multiple spatial scales.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/report
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  • 22
    Publikationsdatum: 2020-02-12
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  • 23
    Publikationsdatum: 2020-02-12
    Materialart: info:eu-repo/semantics/workingPaper
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  • 24
    Publikationsdatum: 2020-02-12
    Beschreibung: The Halmahera island belongs to the North Moluccas province (Maluku Utara), Indonesia. This K-shaped island is located in the eastern part of the Moluccas Sea, the only active arc-arc collision complex on the Earth. The western arm of the K forms a volcanic arc due to the former subduction of the Moluccas Sea plate underneath Halmahera. The region is characterized by intense seismic activity at crustal, intermediate depth, and along the subducting plate. At crustal level the Halmahera seismicity along the two eastern arms of the K show strike-slip faulting style. In November 2015 a localized intense and energetic seismic activity started around Jailolo volcano in the West Halmahera Regency. The seismic sequence intermittently lasted until February 2016 and hundreds of events were felt by the population and several buildings were destroyed and damaged by the shaking. The largest shocks of the sequence have been located by global seismicity networks (GEOFON and GCMT) showing normal faulting style. The temporal evolution of the seismicity seems to be more swarm-like type activity instead of mainshock-aftershock sequence. In spring 2016 a research project has been funded by the German's Humanitarian program in collaboration with BMKG, Indonesia, with the goal of understanding the origin of the intense seismic activity and the related hazard. In summer 2016 we instrumented the area with a dense seismic network composed of 29 short period and 6 broad-band seismometers. The instrument deployment aims at characterizing the seismicity of the Jailolo region in relationship with the 2015-2016 seismic activity. The network will help to understand the seismo-tectonic of the area and the relation between seismicity and the volcanic activity at Jailolo volcano and possible link with the 2015-2016 swarm. Should the seismic activity intensify as in November 2015, we can record it and narrow down the underlying physical mechanisms. Waveform data are available from the GEOFON data centre, under network code 7G, and are embargoed until the end of 2021.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/workingPaper
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  • 25
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    Publikationsdatum: 2020-02-12
    Beschreibung: A temporary seismic network was installed in Sri Lanka for a time period of 13 months. The stations were equipped with Earth Data EDR-210 digital recorders and Trillium 120 PA, Güralp C3E and Güralp CMG-3ESP broadband sensors. Main aim of the network is to shed light on the crustal and upper mantle structure beneath the island. Also local seismic activity is studied. Waveform data are available from the GEOFON data centre, under network code 1A, and are embargoed until July 2021.(Grant-Number: GIPP201616 ) * Description is taken from seismic metadata, and may not match the preferred title for citations.
    Sprache: Englisch
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  • 26
    Publikationsdatum: 2020-02-12
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  • 27
    Publikationsdatum: 2020-02-12
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/workingPaper
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  • 28
    Publikationsdatum: 2020-02-12
    Beschreibung: Berlin-Urban-Gradient is a ready-to-use imaging spectrometry dataset for multi-scale unmixing and hard classification analyses in urban environments. The dataset comprises two airborne HyMap scenes at 3.6 and 9 m resolution, a simulated spaceborne EnMAP scene at 30 m resolution, an image endmember spectral library and detailed land cover reference information. All images are provided as geocoded reflectance products and cover the same subset along Berlin’s urban-rural gradient. The variety of land cover and land use patterns captured make the dataset an ideal playground for testing the transfer of methods and research approaches at multiple spatial scales.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/workingPaper
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  • 29
    Publikationsdatum: 2020-02-12
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  • 30
    Publikationsdatum: 2020-02-12
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  • 31
    Publikationsdatum: 2020-02-12
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  • 32
    Publikationsdatum: 2020-02-12
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  • 33
    Publikationsdatum: 2020-02-12
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  • 34
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    Publikationsdatum: 2020-02-12
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  • 35
    Publikationsdatum: 2020-02-12
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  • 36
    Publikationsdatum: 2020-02-12
    Sprache: Englisch
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  • 37
    Publikationsdatum: 2020-02-12
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  • 38
    Publikationsdatum: 2020-02-12
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  • 39
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    In:  EnMAP Flight Campaigns Technical Report
    Publikationsdatum: 2020-02-12
    Beschreibung: Berlin-Urban-Gradient is a ready-to-use imaging spectrometry dataset for multi-scale unmixing and hard classification analyses in urban environments. The dataset comprises two airborne HyMap scenes at 3.6 and 9 m resolution, a simulated spaceborne EnMAP scene at 30 m resolution, an im-age endmember spectral library and detailed land cover reference information. All images are pro-vided as geocoded reflectance products and cover the same subset along Berlin’s urban-rural gra-dient. The variety of land cover and land use patterns captured make the dataset an ideal play-ground for testing the transfer of methods and research approaches at multiple spatial scales.
    Sprache: Englisch
    Materialart: info:eu-repo/semantics/report
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  • 40
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  • 41
    Publikationsdatum: 2020-02-12
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  • 42
    Publikationsdatum: 2020-02-12
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  • 43
    Publikationsdatum: 2020-02-12
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  • 44
    Publikationsdatum: 2020-02-12
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  • 45
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    Publikationsdatum: 2020-02-12
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  • 46
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    ISSN: 0370-2693
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Physik
    Materialart: Digitale Medien
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  • 47
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    Physics Letters B 317 (1993), S. 474-484 
    ISSN: 0370-2693
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Physik
    Materialart: Digitale Medien
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  • 48
    Publikationsdatum: 2021-05-12
    Beschreibung: Today, satellite remote sensing has reached a key role in Earth Sciences. In particular, Synthetic ApertureRadar (SAR) sensors and SAR Interferometry (InSAR) techniques are widely used for the study of dynamicprocesses occurring inside our living planet. Over the past 3 decades, InSAR has been applied for mappingtopography and deformation at the Earth’s surface. These maps are widely used in tectonics, seismology,geomorphology, and volcanology, in order to investigate the kinematics and dynamics of crustal faulting,the causes of postseismic and interseismic displacements, the dynamics of gravity driven slope failures,and the deformation associated with subsurface movement of water, hydrocarbons or magmatic fluids.
    Beschreibung: Published
    Beschreibung: 58-82
    Beschreibung: 1T. Geodinamica e interno della Terra
    Beschreibung: 4T. Fisica dei terremoti e scenari cosismici
    Beschreibung: 3V. Dinamiche e scenari eruttivi
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): SAR ; InSAR ; Earth observation ; Surface displacements ; Satellite missions ; Advanced InSAR ; Earthquake studies ; Volcanic studies ; Tectonic process ; Coseismic studies ; Soil liquefaction ; Post-seismic studies ; Interseismic studies ; Volcanic unrest ; Pre-eruptive phase ; Eruptive phase ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.03. Geodesy::04.03.06. Measurements and monitoring ; 04. Solid Earth::04.03. Geodesy::04.03.07. Satellite geodesy ; 04. Solid Earth::04.03. Geodesy::04.03.09. Instruments and techniques ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 49
    Publikationsdatum: 2018-12-19
    Beschreibung: The timing and geometry of the initial Gondwana break-up between Africa and East Antarctica is still poorly known due to missing information about the continent-ocean boundaries along the rifted margins. In this context, the Beira High off central Mozambique forms a critical geological feature of uncertain crustal fabric. Based on new wide-angle seismic and potential field data across Beira High a P-wave velocity model, supported by amplitude and gravity modelling, provides constraints on the crustal composition of this area. In the Mozambique Basin mainly normal oceanic crust of 5.5–7 km thickness with velocities of 6.5–7.0 km/s in the lower crust is present. A sharp transition towards Beira High marks the continent-ocean boundary. Here the crust thickens to 23 km at maximum. A small velocity-depth gradient and a constant increase in velocity with basal velocities of maximum 7.0 km/s are in good agreement with typical velocities of continental crust and continental fragments. The density model indicates the existence of felsicmaterial in greater depths and supports a fabric of stretched, but highly intruded continental crust below Beira High. A gradual decrease in crustal thickness characterizes the transition towards the Mozambican shelf area. Here, in the Zambezi Delta Depression 12 km of sediments cover the underlying 7 km thick crust. The presence of a high-velocity lower crustal body with velocities of 7.1–7.4 km/s indicates underplated, magmatic material in this part of the profile. However, the velocity structure in the shelf area allows no definite interpretation because of the experimental setup. Thus, the crustal nature below the Zambezi Delta and consequently the landward position of the continentocean boundary remains unknown. The difference in stretching below the margins of Beira High suggests the presence of different thinning directions and a rift jump during the early rifting stage.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 50
    Publikationsdatum: 2016-07-06
    Beschreibung: This paper presents the results of measurements of aerosol physical and chemical properties during iAREA2014 campaign that took place on Svalbard between 15th of Mar and 4th of May 2014. With respect to field area, the experiment consisted of two sites: NyeÅlesund (78�550N, 11�560E) and Longyearbyen (78�130N, 15�330E) with further integration of Aerosol Robotic Network (AERONET) station in Hornsund (77�000N, 15�330E). The subject of this study is to investigate the inesitu, passive and active remote sensing observations as well as numerical simulations to describe the temporal variability of aerosol singleescattering properties during spring season on Spitsbergen. The retrieval of the data indicates several event days with enhanced singleescattering properties due to the existence of sulphate and additional seaesalt load in the atmosphere which is possibly caused by relatively high wind speed. Optical results were confirmed by numerical simulations made by the GEMeAQ model and by chemical observations that indicated up to 45% contribution of the seaesalt to a PM10 total aerosol mass concentration. An agreement between the in-situ optical and microphysical properties was found, namely: the positive correlation between aerosol scattering coefficient measured by the nephelometer and effective radius obtained from laser aerosol spectrometer as well as negative correlation between aerosol scattering coefficient and the Ångstrom exponent indicated that slightly larger particles dominated during special events. The inesitu surface observations do not show any significant enhancement of the absorption coefficient as well as the black carbon concentration which might occur during spring. All of extensive singleescattering properties indicate a diurnal cycle in Longyearbyen, where 21:00e5:00 data stays at the background level, however increasing during the day by the factor of 3e4. It is considered to be highly connected with local emissions originating in combustion, traffic and harbour activities. On the other hand, no daily fluctuations in NyeÅlesund are observed. Mean values in NyeÅlesund are equal to 8.2, 0.8 Mm�1 and 103 ng/m3 for scattering, absorption coefficients and black carbon concentration; however in Longyearbyen (only data from 21:00e05:00 UTC) they reach 7.9, 0.6 Mm�1 as well as 83 ng/ m3 respectively. Overall, the spring 2014 was considerably clean and seaesalt was the major aerosol component
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  • 51
    Publikationsdatum: 2016-09-24
    Beschreibung: Thermokarst processes characterize a variety of ice-rich permafrost terrains and often lead to lake formation. The long-term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate, vegetation and ground conditions, including the volume of excess ground ice and its distribution. The current lake status of thermokarst-lake landscapes and their future trajectories under climatewarming are better understood in the light of their long-term development. We studied the lake-rich southern marginal upland of the Yukon Flats (northern interior Alaska) using dated lake-sediment cores, observations of river-cut exposures, and remotely-sensed data. The region features thick (up to 40 m)Quaternary deposits (mainly loess) that contain massive ground ice. Two of three studied lakes formed ~11,000–12,000 cal yr BP through inferred thermokarst processes, and fire may have played a role in initiating thermokarst development. From ~9000 cal yr BP, all lakes exhibited steady sedimentation, and pollen stratigraphies are consistentwith regional patterns. The current lake expansion rates are low (0 to b7 cmyr−1 shoreline retreat) compared with other regions (~30 cm yr−1 or more). This thermokarst lake-rich region does not showevidence of extensive landscape lowering by lake drainage, nor of multiple lake generations within a basin. However, LiDAR images reveal linear “corrugations” (N5 m amplitude), deep thermo-erosional gullies, and features resembling lake drainage channels, suggesting that highly dynamic surface processes have previously shaped the landscape. Evidently, widespread early Holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization, the latter possibly related to establishment of dense forest cover. Partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism. Holocene landscape evolution in the study area differs from that described from other thermokarst-affected regions; regional responses to future environmental change may be equally individualistic.
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  • 52
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    Elsevier
    In:  EPIC3Sedimentary Geology, Elsevier, 340, pp. 25-37, ISSN: 00370738
    Publikationsdatum: 2016-09-23
    Beschreibung: Thermokarst lakes develop as a result of the thaw and collapse of ice-rich, permanently frozen ground (permafrost). Of particular sedimentological importance are thermokarst lakes forming in late Pleistocene icy silt (yedoma),which dramatically alter the land surface by lowering surface elevation and redistributing upland sediment into lower basins. Our study provides the first description of yedoma thermokarst lake sedimentology based on the crossbasin sampling of an existing lake. We present lake sediment facies descriptions based on data from sediment cores from two thermokarst lakes of medium depth, Claudi and Jaeger (informal names), which formed in previously non thermokarst-affected upland yedoma on the northern Seward Peninsula, Alaska. We identify four prominent facies using sedimentological, biogeochemical, and macrofossil indicators: a massive silt lacking aquatic macrofossils and other aquatic indicators situated below a sub-lacustrine unconformity (Facies 1); two basal deposits: interbedded organic silt and chaotic silt (Facies 2–3); and a silt-rich mud (Facies 4). Facies 1 is interpreted as yedoma that has thawed during lake formation. Facies 3 formed adjacent to the margin due to thaw and collapse events from the lake shore. Material from Facies 3 was reworked by wave action to form Facies 2 in a medium energy margin environment. Facies 4 formed in a lower energy environment toward the lake basin center. This facies classification and description should enhance our ability (i) to interpret the spatial and temporal development of lakes and (ii) to reconstruct long-term patterns of landscape change.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 53
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    Unbekannt
    Elsevier
    In:  EPIC3Fate and Impact of Microplastics in Marine Ecosystems, Fate and Impact of Microplastics in Marine Ecosystems, Elsevier, 1 p., pp. 162-163, ISBN: 978-0-12-812271-6
    Publikationsdatum: 2017-06-21
    Beschreibung: Since the 1950s more than 6.1 billion tons of plastics have been produced. It has been estimated that about 10% of this amount will be deposited long-term in theOceans. The problem is highlighted by several currentstudies using different environmental sampling protocols and analytical methods. Effects of this anthropogenic litter on the environment and organisms are heavily on debate, emphasizing the need to transfer this knowledge to young educated people and to fuel educational programs. The school lab OPENSEA at the Alfred-Wegener-Institute on Helgoland started a joint high school project on marine plastic litter in cooperation with the experts of the marine microplastics group at AWI to link science and education more closely. Based on the OSPAR protocol for beach monitoring of marine litter we developed an experimental set up focusing on sampling and identification of plastic litter on beaches, shores and in sediments in the course of the OPENSEA science and education program for grammar and high school scholars. This monitoring provides environmental data on marine plastic litter and will be integrated in a long term data monitoring program in the course of a citizen science study. In addition we plan to integrate also smaller plastic particles into the project. Fractionated sediment samples will be screened for particles 〉 0.5mm, which then will be analyzed by ATR-FT-IR. These educational activities, with a strong link to the latest science and to sophisticated technology will raise the awareness of younger people for the marine litter problematic. We aim at increasingtheir concerns after taking part in this program. We will present background information, sampling strategies, identification efforts and results based on this scholar science project.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 54
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    Unbekannt
    Elsevier
    In:  EPIC3Fate and Impact of Microplastics in Marine Ecosystems, Elsevier
    Publikationsdatum: 2017-05-29
    Beschreibung: The pollution of the oceans with plastic particles smaller than 5 mm, called microplastics is moving into the focus of science and governments. To determine the amount of microplastics several steps are necessary, starting with the sampling, work up and finally analysis. Each step has its own challenges due to small size of the particles. For analysis the imaging with µFTIR microscopy is a powerful tool allowing the analysis of complete filters. Systematic screening for optimal conditions and filter materials have already been performed. This method has a high time demand regarding the measurement and data interpretation. While the measurement is performed mostly by the spectrometer, the interpretation has to be made by hand on the basis of false color images. To overcome the manual part we developed a novel approach based on the Bruker OPUS© Software to decrease the high time demand for the analysis of microplastics. With this approach it was possible to analyze measurement files from focal plane array (FPA) FTIR mapping containing up to 1.8 million single spectra. These spectra were compared with a database of different synthetic and natural polymers by various methods. By benchmark tests their performance was monitored with the focus on accuracy and data quality. After optimization high quality data was generated, which allowed image analysis. Based on these results an approach for image analysis was developed, giving information for the particle size distribution for each polymer type, particle distribution on the filter and polymer distribution for the particles. It was possible to collect all data with relative ease even for complex sample matrices. This approach has significantly decreased the time demand for the interpretation of FTIR-imaging data and increased the generated data quality.
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  • 55
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    Elsevier
    In:  EPIC3Remote Sensing of Environment, Elsevier, 187, pp. 30-48, ISSN: 0034-4257
    Publikationsdatum: 2017-01-20
    Beschreibung: Research on processes leading to formation, maintenance, and disappearance of polynyas in the Polar Regions benefits significantly from the use of different types of remote sensing data. The Sentinels of the European Space Agency (ESA), together with other satellite missions, provide a variety of data from different parts of the electromagnetic spectrum, at different spatial scales, and with different temporal resolutions. In a case study we demonstrate the advantage of merging data from different spaceborne instruments for analysing ice conditions and ice dynamics in and around the frequently occurring Terra Nova Bay Polynya (TNBP) in the Ross Sea in the Antarctic. Starting with a list of polynya parameters that are typically retrieved from satellite images, we assess the usefulness of different sensor types. On regional scales (several 100 km), passive microwave radiometers provide a view on the mutual influence of the three Ross Sea polynyas on sea ice drift and deformation patterns. Optical sensors with meter-scale resolution, on the other hand, allow very localized analyses of different polynya zones. The combination of different ranges of the electromagnetic spectrum is essential for recognition and classification of ice types and structures. Radar images together with data from thermal infrared sensors, operated at tens to hundreds of meters resolution, improve the separation of the outlet zone of the polynya from the adjacent pack ice. The direct comparison of radar and passive microwave images reveals the visibility of deformed ice zone in the latter. A sequence of radar images was employed to retrieve ice drift around the TNB, which allows analysing the temporal changes of the polynya area and the extension and structure of the outlet zone as well as ice movements and deformation that are influenced by the katabatic winds.
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  • 56
    Publikationsdatum: 2016-10-10
    Repository-Name: EPIC Alfred Wegener Institut
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  • 57
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    Elsevier
    In:  EPIC3Climate Change, Ocean Current Changes, Amsterdam, Elsevier, pp. 253-269
    Publikationsdatum: 2016-12-05
    Repository-Name: EPIC Alfred Wegener Institut
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  • 58
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    Elsevier
    In:  EPIC3Deep Sea Research Part I: Oceanographic Research Papers, Elsevier, 107, pp. 70-81
    Publikationsdatum: 2019-08-19
    Beschreibung: The Weddell Sea plays an important role for the global oceans and climate by being one of the biggest production and export areas of Antarctic Bottom Water (AABW). Circumpolar Deep Water (CDW) enters the Weddell Gyre (WG) at its eastern boundary. Then called Warm Deep Water (WDW), it is a major contributor to the formation of deep and bottom waters due to ocean-ice shelf interactions in the southern and soutwestern Weddell Sea. Hydrographic data collected between 0 and 30°E on the RV Polarstern cruise ANT XX/2 reveals a two-core structure for the eastern inflow of warm water at roughly 20°E but not further downstream at the Greenwich meridian (GM). Model results and climatological fields suggest that the two cores represent two separate modes of warm inflow. One mode is driven by eddy mixing in the northeastern corner of the WG and the other one is an advective mode, forming the southern branch of the inflow which extends beyond 30°E before turning westward. Both pathways are likely to carry waters from different origins within the Antarctic Circumpolar Current (ACC), where more ventilated CDW is found at the Southern Boundary (SB) compared to the centre. The southern route shows considerable interannual variability in the model. A variable inflow of two types of CDW together with admixed recirculated and cooler waters from the Weddell Sea can potentially contribute to the observed variability and warming trend of WDW over the last decade at the GM.
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  • 59
    Publikationsdatum: 2019-07-17
    Beschreibung: Microcystis are known for their potential ability to synthesize toxins, mainly microcystins (MCs). In order to evaluate the effects of temperature on chlorophyll a (Chl a), growth, physiological responses and toxin production of a native Microcystis aeruginosa, we exposed the cells to low (23 °C) and high (29 °C) temperature in addition to a 26 °C control treatment. Exponential growth rate was significantly higher at 29 °C compared to 23 °C and control, reaching 0.43, 0.32 and 0.33 day−1 respectively. In addition, there was a delay of the start of exponential growth at 23 °C. However, the intracellular concentration of Chl a decreased significantly due to temperature change. A significant increase in intracellular ROS was observed in coincidence with the activation of enzymatic antioxidant catalase (CAT) during the first two days of exposure to 23° and 29 °C in comparison to the control experiment, decreasing thereafter to nearly initial values. Five MCs were determined by LC-MS/MS analysis. In the experiments, the highest MC concentration, 205 fg [Leu1] MC-LR.cell− 1 expressed as MC-LR equivalent was measured in the beginning of the experiment and subsequently declined to 160 fg.cell− 1 on day 2 and 70 fg.cell− 1 on day 4 in cells exposed to 29 °C. The same trend was observed for all other MCs except for the least abundant MC-LR which showed a continuous increase during exposure time. Our results suggest a high ability of M. aeruginosa to perceive ROS and to rapidly initiate antioxidant defenses with a differential response on MC production.
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  • 60
    Publikationsdatum: 2016-10-01
    Repository-Name: EPIC Alfred Wegener Institut
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  • 61
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    Elsevier
    In:  EPIC3MICRO 2016. Fate and Impact of Microplastics in Marine Ecosystems, MICRO 2016. Fate and Impact of Microplastics in Marine Ecosystems, Elsevier, 1 p., pp. 120-120, ISBN: 9780128122716
    Publikationsdatum: 2016-12-12
    Repository-Name: EPIC Alfred Wegener Institut
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  • 62
    Publikationsdatum: 2017-06-07
    Beschreibung: Over the past ~ 5000 years, amplified dust generation and deposition in the American West has been linked to human activity. In recent decades, intensified rates of agriculture and livestock grazing have been correlated with greater dust production detected on seasonal to annual timescales. The combination of land use intensification and climate change (i.e. increased drought frequency) in North America highlights the importance of characterizing the sources of dust both before and after the influence of anthropogenic activity. We apply high-precision geochemical and isotopic (Sr and Nd isotopes) techniques to an ice core from the Upper Fremont Glacier (Wyoming, USA) to produce the first glacial dataset from the American West. Our Sr-Nd isotopic composition data indicates the evolving dust provenance to the Upper Fremont Glacier (UFG) from a long-range transport of mineral dust to a local source. This increasing input of dust from a local source is supported by a rise in average dust particle diameter combined with greater average dust concentration throughout the record. The greater presence of dust particles smaller than 2.5 μm in the most recent samples from UFG ice core record support existing satellite and sediment core data regarding the effects of anthropogenic activity upon dust sources and pathways in the American West. Although the Sr-Nd isotope database in North America needs be expanded, our results provide a survey of windborne dust through the past 270 years.
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  • 63
    Publikationsdatum: 2019-07-17
    Beschreibung: Reactive iron (oxyhydr)oxide minerals preferentially undergo early diagenetic redox cycling which can result in the production of dissolved Fe(II), the adsorption of Fe(II) onto particle surfaces, and the formation of authigenic Fe minerals. The partitioning of iron in sediments has traditionally been studied by applying sequential extractions that target operationally-defined iron phases. Here, we complement an existing sequential leaching method by developing a sample processing protocol for δ56Fe analysis, which we subsequently use to study Fe phase-specific fractionation related to dissimilatory iron reduction in a modern marine sediment. Carbonate-Fe was extracted by acetate, easily reducible oxides (e.g. ferrihydrite and lepidocrocite) by hydroxylamine–HCl, reducible oxides (e.g. goethite and hematite) by dithionite–citrate, and magnetite by ammonium oxalate. Subsequently, the samples were repeatedly oxidized, heated and purified via Fe precipitation and column chromatography. The method was applied to surface sediments collected from the North Sea, south of the island of Helgoland. The acetate-soluble fraction (targeting siderite and ankerite) showed a pronounced downcore δ56Fe trend. This iron pool was most depleted in 56Fe close to the sediment–water interface, similar to trends observed for pore-water Fe(II). We interpret this pool as surface-reduced Fe(II), rather than siderite or ankerite, that was open to electron and atom exchange with the oxide surface. Common extractions using 0.5 M HCl or Na-dithionite alone may not resolve such trends, as they dissolve iron from isotopically distinct pools leading to a mixed signal. Na-dithionite leaching alone, for example, targets the sum of reducible Fe oxides that potentially differ in their isotopic fingerprint. Hence, the development of a sequential extraction Fe isotope protocol provides a new opportunity for detailed study of the behavior of iron in a wide range of environmental settings.
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  • 64
    Publikationsdatum: 2016-02-12
    Beschreibung: The focus of this research has been on detecting changes in lake areas, vegetation, land surface temperatures, and the area covered by snow, using data from remote sensing. The study area covers the main (central) part of the Lena River catchment in the Yakutia region of Siberia (Russia), extending from east of Yakutsk to the central Siberian Plateau, and from the southern Lena River to north of the Vilyui River. Approximately 90% of the area is underlain by continuous permafrost. Remote sensing products were used to analyze changes in water bodies, land surface temperature (LST), and leaf area index (LAI), as well as the occurrence and extent of forest fires, and the area and duration of snow cover. The remote sensing analyses (for LST, snow cover, LAI, and fire) were based on MODIS–derived NASA products (250–1000 m) for 2000 to 2011. Changes in water bodies were calculated from two mosaics of (USGS) Landsat (30 m) satellite images from 2002 and 2009. Within the study area's 315,000 km2 the total area covered by lakes increased by 17.9% between 2002 and 2009, but this increase varied in different parts of the study area, ranging between 11% and 42%. The land surface temperatures showed a consistent warming trend, with an average increase of about 0.12 °C/year. The average rate of warming during the April–May transition period was 0.17 °C/year and 0.19 °C/year in the September–October period, but ranged up to 0.49 °C/year during September–October. Regional differences in the rates of land surface temperature change, and possible reasons for the temperature changes, are discussed with respect to changes in the land cover. Our analysis of a broad spectrum of variables over the study area suggests that the spring warming trend is very likely to be due to changes in the area covered by snow. The warming trend observed in fall does not, however, appear to be directly related to any changes in the area of snow cover, or to the atmospheric conditions, or to the proportion of the land surface that is covered by water (i.e., to wetting and drying). Supplementary data (original data, digitized version of the maps, metadata) are archived under PANGAEA (http://dx.doi.org/10.1594/PANGAEA.855124).
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  • 65
    Publikationsdatum: 2016-06-23
    Beschreibung: The Southern Ocean (SO) is a major sink for anthropogenic atmospheric carbon dioxide (CO2), potentially harbouring even greater potential for additional sequestration of CO2 through enhanced phytoplankton productivity. In the SO, primary productivity is primarily driven by bottom up processes (physical and chemical conditions) which are spatially and temporally heterogeneous. Due to a paucity of trace metals (such as iron) and high variability in light, much of the SO is characterised by an ecological paradox of high macronutrient concentrations yet uncharacteristically low chlorophyll concentrations. It is expected that with increased anthropogenic CO2 emissions and the coincident warming, the major physical and chemical process that govern the SO will alter, influencing the biological capacity and functioning of the ecosystem. This review focuses on the SO primary producers and the bottom up processes that underpin their health and productivity. It looks at the major physico-chemical drivers of change in the SO, and based on current physiological knowledge, explores how these changes will likely manifest in phytoplankton, specifically, what are the physiological changes and floristic shifts that are likely to ensue and how this may translate into changes in the carbon sink capacity, net primary productivity and functionality of the SO.
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  • 66
    Publikationsdatum: 2017-06-14
    Beschreibung: We compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub-polar marine ecosystems. Circulation patterns differ strikingly between the north and south. Meridional circulation in the north provides connections between the sub-Arctic and Arctic despite the presence of encircling continental landmasses, whereas annular circulation patterns in the south tend to isolate Antarctic surface waters from those in the north. These differences influence fundamental aspects of the polar ecosystems from the amount, thickness and duration of sea ice, to the types of organisms, and the ecology of zooplankton, fish, seabirds and marine mammals. Meridional flows in both the North Pacific and the North Atlantic oceans transport heat, nutrients, and plankton northward into the Chukchi Sea, the Barents Sea, and the seas off the west coast of Greenland. In the North Atlantic, the advected heat warms the waters of the southern Barents Sea and, with advected nutrients and plankton, supports immense biomasses of fish, seabirds and marine mammals. On the Pacific side of the Arctic, cold waters flowing northward across the northern Bering and Chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there. Southward flow of cold Arctic waters into sub-Arctic regions of the North Atlantic occurs mainly through Fram Strait with less through the Barents Sea and the Canadian Archipelago. In the Pacific, the transport of Arctic waters and plankton southward through Bering Strait is minimal. In the Southern Ocean, the Antarctic Circumpolar Current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub-Antarctic waters, with the consequent evolution of Antarctic zooplankton and fish species largely occurring in isolation from those to the north. The Antarctic Circumpolar Current also disperses biota throughout the Southern Ocean, and as a result, the biota tends to be similar within a given broad latitudinal band. South of the Southern Boundary of the ACC, there is a large-scale divergence that brings nutrient-rich water to the surface. This divergence, along with more localized upwelling regions and deep vertical convection in winter, generates elevated nutrient levels throughout the Antarctic at the end of austral winter. However, such elevated nutrient levels do not support elevated phytoplankton productivity through the entire Southern Ocean, as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters. However, coastal regions, with the upward mixing of iron, maintain greatly enhanced rates of production, especially in coastal polynyas. In these coastal areas, elevated primary production supports large biomasses of zooplankton, fish, seabirds, and mammals. As climate warming affects these advective processes and their heat content, there will likely be major changes in the distribution and abundance of polar biota, in particular the biota dependent on sea ice.
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  • 67
    Publikationsdatum: 2016-03-17
    Beschreibung: Forests worldwide are threatened by various environmental and anthropogenic hazards, especially tropical forests. Knowledge on the impacts of these hazards on forest structure and dynamics has been compiled in empirical studies. However, the results of these studies are often not sufficient for long-term projections and extrapolations to large spatial scales especially for unprecedented environmental conditions, which require both the identification and understanding of key underlying processes. Forest models bridge this gap by incorporating multiple ecological processes in a dynamic framework (i.e. including a realistic model structure) and addressing the complexity of forest ecosystems. Here, we describe the evolution of the individual-based and process-based forest gap model FORMIND and its application to tropical forests. At its core, the model includes physiological processes on tree level (photosynthesis, respiration, tree growth, mortality, regeneration, competition). During the past two decades, FORMIND has been used to address various scientific questions arising from different forest types by continuously extending the model structure. The model applications thus provided understanding in three main aspects: (1) the grouping of single tree species into plant functional types is a successful approach to reduce complexity in vegetation models, (2) structural realism was necessary to analyze impacts of natural and anthropogenic disturbances such as logging, fragmentation, or drought, and (3) complex ecological processes such as carbon fluxes in tropical forests – starting from the individual tree level up to the entire forest ecosystem – can be explored as a function of forest structure, species composition and disturbance regime. Overall, this review shows how the evolution of long-term modelling projects not only provides scientific understanding of forest ecosystems, but also provides benefits for ecological theory and empirical study design.
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  • 68
    Publikationsdatum: 2016-05-02
    Beschreibung: Recent declines in ice shelf and sea ice extent experienced in polar regions highlight the importance of evaluating variations in local weather patterns in response to climate change. Airborne mineral particles (dust) transported through the atmosphere and deposited on ice sheets and glaciers in Antarctica and Greenland can provide a robust set of tools for resolving the evolution of climatic systems through time. Here we present the first high time resolution radiogenic isotope (strontium and neodymium) data for Holocene dust in a coastal East Antarctic ice core, accompanied by rare earth element composition, dust concentration, and particle size distribution during the last deglaciation. We aim to use these combined ice core data to determine dust provenance, with variations indicative of shifts in either dust production, sources, and/or transport pathways. We analyzed a series of 17 samples from the Taylor Dome (77◦47'47''S, 158◦43'26''E) ice core, 113–391m in depth from 1.1–31.4ka. Radiogenic isotopic and rare earth element compositions of dust during the last glacial period are in good agreement with previously measured East Antarctic ice core dust records. In contrast, the Holocene dust dataset displays a broad range in isotopic and rare earth element compositions, suggesting a shift from long-range transported dust to a more variable, local input that may be linked to the retreat of the Ross Ice Shelf during the last deglaciation. Observed changes in the dust cycle inferred from a coastal East Antarctic ice core can thus be used to infer an evolving local climate.
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  • 69
    Publikationsdatum: 2022-05-25
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Continental Shelf Research 124 (2016): 165-181, doi:10.1016/j.csr.2016.06.005.
    Beschreibung: A new hydrographic climatology has been created for the continental shelf region, extending from the Labrador shelf to the Mid-Atlantic Bight. The 0.2-degree climatology combines all available observations of surface and bottom temperature and salinity collected between 1950 and 2010 along with the location, depth and date of these measurements. While climatological studies of surface and bottom temperature and salinity have been presented previously for various regions along the Canadian and U.S. shelves, studies also suggest that all these regions are part of one coherent system. This study focuses on the coherent structure of the mean seasonal cycle of surface and bottom temperature and salinity and its variation along the shelf and upper slope. The seasonal cycle of surface temperature is mainly driven by the surface heat flux and exhibits strong dependency on latitude (r≈−0.9). The amplitude of the seasonal cycle of bottom temperature is rather dependent on the depth, while the spatial distribution of bottom temperature is correlated with latitude. The seasonal cycle of surface salinity is influenced by several components, such as sea-ice on the northern shelves and river discharge in the Gulf of St. Lawrence. The bottom salinity exhibits no clear seasonal cycle, but its spatial distribution is highly correlated with bathymetry, thus Slope Water and its intrusion on the shelf can be identified by its relatively high salinity compared to shallow, fresher shelf water. Two different regimes can be identified, especially on the shelf, separated by the Laurentian Channel: advection influences the phasing of the seasonal cycle of surface salinity and bottom temperature to the north, while in the southern region, river runoff and air-sea heat flux forcing are dominant, especially over the shallower bathymetry.
    Beschreibung: Support from NSF OCE PO to Y-OK (OCE-1242989 and OCE-1435602) and SJL (OCE-1332666).
    Schlagwort(e): Seasonal climatology ; Temperature ; Salinity ; Dataset ; Shelf
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  • 70
    Publikationsdatum: 2022-05-25
    Beschreibung: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Quaternary Geochronology 30 (2015): 114–131, doi:10.1016/j.quageo.2015.09.001.
    Beschreibung: The ages of recent effusive eruptions on Erebus volcano, Antarctica are poorly known. Published 40Ar/39Ar ages of the 10 youngest “post-caldera” lava flows are unreliable because of the young ages of the flows (〈10 ka) and the presence of excess 40Ar. Here we use cosmogenic 3He and 36Cl to provide new ages for the 10 youngest flows and 3 older summit flows, including a newly recognized flow distinguished by its exposure age. Estimated eruption ages of the post-caldera flows, assuming no erosion or prior snow cover, range from 4.52 ± 0.08 ka to 8.50 ± 0.19 ka, using Lifton et al. (2014) to scale cosmogenic production rates. If the older Lal (1991)/Stone (2000) model is used to scale production rates, calculated ages are older by 16–25%. Helium-3 and chlorine-36 exposure ages measured on the same samples show excellent agreement. Helium-3 ages measured on clinopyroxene and olivine from the same samples are discordant, probably due in part to lower-than-expected 3He production rates in the Fe-rich olivine. Close agreement of multiple clinopyroxene 3He ages from each flow indicates that the effects of past snow coverage on the exposure ages have been minimal. The new cosmogenic ages differ considerably from published 40Ar/39Ar and 36Cl ages and reveal that the post-caldera flows were erupted during relatively brief periods of effusive activity spread over an interval of ∼4 ka. The average eruption rate over this interval is estimated to be 0.01 km3/ka. Because the last eruption was at least 4 ka ago, and the longest repose interval between the 10 youngest eruptions is ∼1 ka, we consider the most recent period of effusive activity to have ended.
    Beschreibung: This research was supported by grant ANT-1142083 from the National Science Foundation, Division of Polar Programs.
    Schlagwort(e): Erebus volcano ; Cosmogenic nuclides ; Exposure age ; Helium-3 ; Chlorine-36
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  • 71
    Publikationsdatum: 2022-05-25
    Beschreibung: This paper is not subject to U.S. copyright. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 132 (2016): 263–264, doi:10.1016/j.dsr2.2016.08.001.
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  • 72
    Publikationsdatum: 2022-05-25
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Methods in Oceanography 17 (2016): 264-281, doi:10.1016/j.mio.2016.09.004.
    Beschreibung: Understanding intrusive exchange at oceanic water mass fronts may depend on building data-constrained models of the processes, but obtaining the needed representative and comprehensive data is challenging. Acoustic imaging (remote sensing) is an attractive method for mapping the three-dimensional intrusion geometry to enable the required focused in situ sampling of the mixing processes in intrusions. The method depends on backscatter of sound from sharp interfaces and from microstructure resulting from double-diffusive instability (DDI), a probable occurrence at intrusions. The potential of the method is evaluated using data collected using established methods in a field of intrusions south of New England. Above and beneath warm and salty intrusions may lie diffusive–convective DDI microstructure and salt-fingering microstructure, respectively, marking the intrusion boundaries, providing the backscattering features. The data show that both types of microstructure can occur in close proximity within intrusions, but the question of whether this is common or not is unanswered by the modest amount of data, as are questions about continuity of DDI-microstructure in intrusions (to facilitate intrusion acoustic imaging) and variability of DDI-driven heat, salt and buoyancy fluxes. Analysis here shows that detectable backscatter from DDI-microstructure will occur, and can be easily measured when plankton scattering is low enough. Interface scattering is also likely to be detectable. The DDI-linked microstructure data used here are inherently interesting in their own right and are presented in some detail.
    Beschreibung: The data were collected under Office of Naval Research grant N00014-03-1-0335. Acoustic analysis was done under grant N00014-14-1-0223/N00014-16-1-2372.
    Schlagwort(e): Intrusions ; Double-diffusive microstructure ; Ocean mixing ; Acoustic backscatter ; Echosounder ; South New England shelf
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  • 73
    Publikationsdatum: 2022-05-25
    Beschreibung: This paper is not subject to U.S. copyright. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 451 (2016): 73-83, doi:10.1016/j.palaeo.2016.03.018.
    Beschreibung: Sea-level records from atolls, potentially spanning the Cenozoic, have been largely overlooked, in part because the processes that control atoll form (reef accretion, carbonate dissolution, sediment transport, vertical motion) are complex and, for many islands, unconstrained on million-year timescales. Here we combine existing observations of atoll morphology and corelog stratigraphy from Enewetak Atoll with a numerical model to (1) constrain the relative rates of subsidence, dissolution and sedimentation that have shaped modern Pacific atolls and (2) construct a record of sea level over the past 8.5 million years. Both the stratigraphy from Enewetak Atoll (constrained by a subsidence rate of ~ 20 m/Myr) and our numerical modeling results suggest that low sea levels (50–125 m below present), and presumably bi-polar glaciations, occurred throughout much of the late Miocene, preceding the warmer climate of the Pliocene, when sea level was higher than present. Carbonate dissolution through the subsequent sea-level fall that accompanied the onset of large glacial cycles in the late Pliocene, along with rapid highstand constructional reef growth, likely drove development of the rimmed atoll morphology we see today.
    Beschreibung: Support for this work was provided through a Jackson School Distinguished Postdoctoral Fellowship to Michael Toomey.
    Schlagwort(e): Reef ; Coral ; Dissolution ; Late Miocene ; Oxygen isotope stack
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  • 74
    Publikationsdatum: 2022-05-25
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Neurobiology of Aging 47 (2016): 113–126, doi:10.1016/j.neurobiolaging.2016.07.015.
    Beschreibung: Misfolded tau proteins are characteristic of tauopathies, but the isoform composition of tau inclusions varies by tauopathy. Using aggregates of the longest tau isoform (containing 4 microtubule-binding repeats and 4-repeat tau), we recently described a direct mechanism of toxicity that involves exposure of the N-terminal phosphatase-activating domain (PAD) in tau, which triggers a signaling pathway that disrupts axonal transport. However, the impact of aggregation on PAD exposure for other tau isoforms was unexplored. Here, results from immunochemical assays indicate that aggregation-induced increases in PAD exposure and oligomerization are common features among all tau isoforms. The extent of PAD exposure and oligomerization was larger for tau aggregates composed of 4-repeat isoforms compared with those made of 3-repeat isoforms. Most important, aggregates of all isoforms exhibited enough PAD exposure to significantly impair axonal transport in the squid axoplasm. We also show that PAD exposure and oligomerization represent common pathological characteristics in multiple tauopathies. Collectively, these results suggest a mechanism of toxicity common to each tau isoform that likely contributes to degeneration in different tauopathies.
    Beschreibung: This work was supported by NIH grants R01 AG044372 (Nicholas M. Kanaan), R01 NS082730 (Nicholas M. Kanaan and Scott T. Brady), BrightFocus Foundation (A2013364S, Nicholas M. Kanaan), the Jean P. Schultz Biomedical Research Endowment (Nicholas M. Kanaan), the Secchia Family Foundation (Nicholas M. Kanaan) and NS066942A (Gerardo Morfini).
    Schlagwort(e): Tauopathy ; Alzheimer's disease ; Oligomer ; Axon ; Aggregation ; Microtubule-associated protein ; Pathological conformations
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  • 75
    Publikationsdatum: 2022-05-25
    Beschreibung: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Chemistry 177 (2015): 366–373, doi:10.1016/j.marchem.2015.06.012.
    Beschreibung: Metabolomics is the study of small molecules, or ‘metabolites’, that are the end products of biological processes. While -omics technologies such as genomics, transcriptomics, and proteomics measure the metabolic potential of organisms, metabolomics provides detailed information on the organic compounds produced during metabolism and found within cells and in the environment. Improvements in analytical techniques have expanded our understanding of metabolomics and developments in computational tools have made metabolomics data accessible to a broad segment of the scientific community. Yet, metabolomics methods have only been applied to a limited number of projects in the marine environment. Here, we review analysis techniques for mass spectrometry data and summarize the current state of metabolomics databases. We then describe a boutique database developed in our laboratory for efficient data analysis and selection of mass spectral targets for metabolite identification. The code to implement the database is freely available on GitHub (https://github.com/joefutrelle/domdb). Data organization and analysis are critical, but often under-appreciated, components of metabolomics research. Future advances in environmental metabolomics will take advantage of continued development of new tools that facilitate analysis of large metabolomics datasets.
    Beschreibung: The field data populating the database comes from scientific cruises funded by grants from the National Science Foundation to EBK and KL (Atlantic Ocean, OCE-1154320) and E.V. Armbrust (Pacific Ocean, OCE-1205233). The laboratory experiment with coastal seawater was funded by a grant from the Gulf of Mexico Research Initiative to EBK and H.K. White. The laboratory experiments with microbial isolates and the database development are funded by the Gordon and Betty Moore Foundation through Grant GBMF3304 to EBK.
    Schlagwort(e): Metabolomics ; Data analysis ; Database design
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  • 76
    Publikationsdatum: 2022-05-25
    Beschreibung: This paper is not subject to U.S. copyright. The definitive version was published in Marine Geology 381 (2016): 42–53, doi:10.1016/j.margeo.2016.08.008.
    Beschreibung: Behavior of coastal systems on time scales ranging from single storm events to years and decades is controlled by both small-scale sediment transport processes and large-scale geologic, oceanographic, and morphologic processes. Improved understanding of coastal behavior at multiple time scales is required for refining models that predict potential erosion hazards and for coastal management planning and decision-making. Here we investigate the primary controls on shoreline response along a geologically-variable barrier island on time scales resolving extreme storms and decadal variations over a period of nearly one century. An empirical orthogonal function analysis is applied to a time series of shoreline positions at Fire Island, NY to identify patterns of shoreline variance along the length of the island. We establish that there are separable patterns of shoreline behavior that represent response to oceanographic forcing as well as patterns that are not explained by this forcing. The dominant shoreline behavior occurs over large length scales in the form of alternating episodes of shoreline retreat and advance, presumably in response to storms cycles. Two secondary responses include long-term response that is correlated to known geologic variations of the island and the other reflects geomorphic patterns with medium length scale. Our study also includes the response to Hurricane Sandy and a period of post-storm recovery. It was expected that the impacts from Hurricane Sandy would disrupt long-term trends and spatial patterns. We found that the response to Sandy at Fire Island is not notable or distinguishable from several other large storms of the prior decade.
    Beschreibung: Funding for this research was provided by the USGS Coastal and Marine Geology Program and the USGS Natural Resource Preservation Program.
    Schlagwort(e): Shoreline change ; Coastal evolution ; Storm response ; Empirical orthogonal function ; Fire Island
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  • 77
    Publikationsdatum: 2022-05-25
    Beschreibung: This paper is not subject to U.S. copyright. The definitive version was published in Marine Geology 380 (2016): 284–289, doi:10.1016/j.margeo.2016.04.008.
    Beschreibung: Rivers have long been recognized for their ability to shape reef-bound volcanic islands. On the time-scale of glacial–interglacial sea-level cycles, fluvial incision of exposed barrier reef lagoons may compete with constructional coral growth to shape the coastal geomorphology of ocean islands. However, overprinting of Pleistocene landscapes by Holocene erosion or sedimentation has largely obscured the role lowstand river incision may have played in developing the deep lagoons typical of modern barrier reefs. Here we use high-resolution seismic imagery and core stratigraphy to examine how erosion and/or deposition by upland drainage networks has shaped coastal morphology on Tahaa, a barrier reef-bound island located along the Society Islands hotspot chain in French Polynesia. At Tahaa, we find that many channels, incised into the lagoon floor during Pleistocene sea-level lowstands, are located near the mouths of upstream terrestrial drainages. Steeper antecedent topography appears to have enhanced lowstand fluvial erosion along Tahaa's southwestern coast and maintained a deep pass. During highstands, upland drainages appear to contribute little sediment to refilling accommodation space in the lagoon. Rather, the flushing of fine carbonate sediment out of incised fluvial channels by storms and currents appears to have limited lagoonal infilling and further reinforced development of deep barrier reef lagoons during periods of highstand submersion.
    Beschreibung: This project was supported by a Jackson School Distinguished Postdoctoral Fellowship to Michael Toomey and the WHOI Coastal Ocean Institute and Ocean and Climate Change Institute.
    Schlagwort(e): Coral ; Island ; Lagoon ; Dissolution ; Morphology
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  • 78
    Publikationsdatum: 2016-09-23
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochimica et Cosmochimica Acta 179 (2016): 123-141, doi:10.1016/j.gca.2016.01.023.
    Beschreibung: The carbonate clumped isotope thermometer is a promising tool for determining past ocean temperatures. It is based on the temperature dependence of rare isotopes ‘clumping’ into the same carbonate ion group in the carbonate mineral lattice. The extent of this clumping effect is independent of the isotope composition of the water from which carbonate precipitates, providing unique advantages over many other paleotemperature proxies. Existing calibrations of this thermometer in cold-water and warm-water corals suggest clumped isotope ‘vital effects’ are negligible in cold-water corals but may be significant in warm-water corals. Here, we test the calibration of the carbonate clumped isotope thermometer in cold-water corals with a recently collected and well characterised sample set spanning a range of coral genera (Balanophyllia, Caryophyllia, Dasmosmilia, Desmophyllum, Enallopsammia and Javania). The clumped isotope compositions (Δ47) of these corals exhibit systematic dependences on their growth temperatures, confirming the basis of the carbonate clumped isotope thermometer. However, some cold-water coral genera show Δ47 values that are higher than the expected equilibrium values by up to 0.05‰ (equivalent to underestimating temperature by ∼9 °C) similar to previous findings for some warm-water corals. This finding suggests that the vital effects affecting corals Δ47 are common to both warm- and cold-water corals. By comparison with models of the coral calcification process we suggest that the clumped isotope offsets in these genera are related to the kinetic isotope effects associated with CO2 hydration/hydroxylation reactions in the corals’ calcifying fluid. Our findings complicate the use of the carbonate clumped isotope thermometer in corals, but suggest that species- or genus-specific calibrations could be useful for the future application of this paleotemperature proxy.
    Beschreibung: This work was supported by a British National Environment Research Council studentship to P. Spooner (NE/K500823/1), National Science Foundation Grant NSF-ANT-1246387 and The Penzance Endowed Fund in Support of Assistant Scientists (WHOI) to W. Guo, and by funds from the European Research Council, the Leverhulme Trust and a Marie Curie Reintegration grant.
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  • 79
    facet.materialart.
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    Elsevier
    In:  EPIC3Global and Planetary Change, Elsevier, 146, pp. 10-21, ISSN: 09218181
    Publikationsdatum: 2021-08-20
    Beschreibung: The impact of observed changes in air temperature and precipitation from 1969 to 2013 and climate projections for 2050 and 2080 at Ny-Ålesund, an arctic research station on Spitzbergen Island in the Svalbard Archipelago on snow hydrological processes, were analyzed using snow accumulation and ablation algorithms in the physically based Cold Regions HydrologicalModelling platform(CRHM). The climate projectionswere obtained from phase 5 of the Coupled Model Intercomparison Project (CMIP5), with a focus on the snow-dominated period (October to June). To identify the potential effects of increasing temperature and precipitation, a model sensitivity analysis (1 °C to 5 °C), with and without a 25% increase in precipitation, was run on CRHM snow processes. The results indicated that the greatest observed warming was during the early snow season (October–February), with increases of 0.8 and 0.9 °C decade−1 for maximum (Tmax) and minimum (Tmin) temperatures, respectively. Therewas also a significant increase in annual and winter precipitation (24mmdecade−1). The late snowseason (March–June) also had a marked increase in temperature (0.5 and 0.69 °C decade−1 for Tmax and Tmin respectively), but no significant change in precipitation. These changes lead to a significant increase in the number of dayswith rainfall rather than snowfall. The sensitivity analysis indicated that mean snowwater equivalent snowpack will decrease by 10.2% (early snow season) and 11.1% (late snow season) per degree of increased air temperature. For each degree of temperature increase, the modelled peak snow-water-equivalent (SWE) declined by 6.9%, duration of snowpack declined 11 days, and the number of days with rain increased 43% for the early snow season and 12.8% for the late snowseason. Awarmer climate also leads to markedly decreased surface snowsublimation and the fraction of snowfall eroded and transported by blowing snow. For most snowpack parameters analyzed, the response to warming accelerates with increased warming, especially above 3 °C. A 25% increase in precipitation partially counteracted the response to warming, with the greatest effect on peak SWE.
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  • 80
    facet.materialart.
    Unbekannt
    Elsevier
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences 57 (2016): 129-136, doi:10.1016/j.shpsc.2016.02.003.
    Beschreibung: Embryos have different meanings for different people and in different contexts. Seen under the microscope, the biological embryo starts out as one cell and then becomes a bunch of cells. Gradually these divide and differentiate to make up the embryo, which in humans becomes a fetus at eight weeks, and then eventually a baby. At least, that happens in those cases that carry through normally and successfully. Yet a popular public perception imagines the embryo as already a little person in the very earliest stages of development, as if it were predictably to become an adult. In actuality, cells can combine, pull apart, and recombine in a variety of ways and still produce embryos, whereas most embryos never develop into adults at all. Biological embryos and popular imaginations of embryos diverge. This paper looks at some of the historical reasons for and social implications of that divergence.
    Beschreibung: Thanks to the National Science Foundation for support through a series of grants.
    Schlagwort(e): Embryos ; Microscopes ; Science and society ; Bioethics ; Science policy
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  • 81
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biochemical Pharmacology 110-111 (2016): 117-129, doi:10.1016/j.bcp.2016.04.012.
    Beschreibung: 6-Formylindolo[3,2-b]carbazole (FICZ) is a potent aryl hydrocarbon receptor (AHR) agonist that is efficiently metabolized by AHR-regulated cytochrome P4501 enzymes. FICZ is a proposed physiological AHR ligand that induces its own degradation as part of a regulatory negative feedback loop. In vitro studies in cells show that CYP1 inhibition in the presence of FICZ results in enhanced AHR activation, suggesting that FICZ accumulates in the cell when its metabolism is blocked. We used zebrafish (Danio rerio) embryos to investigate the in vivo effects of FICZ when CYP1A is knocked down or inhibited. Embryos were injected with morpholino antisense oligonucleotides targeting CYP1A (CYP1A-MO), Ahr2, or a combination of both. FICZ exposure of non-injected embryos or embryos injected with control morpholino had little effect. In CYP1A-MO-injected embryos, however, FICZ dramatically increased mortality, incidence and severity of pericardial edema and circulation failure, reduced hatching frequency, blocked swim bladder inflation, and strongly potentiated expression of Ahr2-regulated genes. These effects were substantially reduced in embryos with a combined knockdown of Ahr2 and CYP1A, indicating that the toxicity was mediated at least partly by Ahr2. Co-exposure to the CYP1 inhibitor alpha-naphthoflavone (αNF) and FICZ had similar effects as the combination of CYP1A-MO and FICZ. HPLC analysis of FICZ-exposed embryos showed increased levels of FICZ after concomitant CYP1A-MO injection or αNF co-exposure. Together, these results show that a functioning CYP1/AHR feedback loop is crucial for regulation of AHR signaling by a potential physiological ligand in vivo and further highlights the role of CYP1 enzymes in regulating biological effects of FICZ.
    Beschreibung: This work was supported by Swedish Research Council Formas grants 2011-963 (EW) and 2008-1249 (MJ), by a European Commission Horizon 2020 grant, Project ID 634880 (MJ), by a National Institute of Environmental Health Sciences (NIEHS) grant P42ES007381 (JJS and MEH), R01ES006272 (MEH) and F32ES017585 (ART-L), by Japan Society for the Promotion of Science Postdoctoral Fellowship for Research Abroad194313 (AK), by Grant-in-Aids for Research Activity Start-up26881001 (AK) and for Young Scientists (A)15H05334 (AK).
    Schlagwort(e): Aryl hydrocarbon receptor ; Cytochrome P4501 ; 6-Formylindolo[3,2-b]carbazole ; Enzyme inhibition ; Zebrafish embryo toxicity ; Synergistic receptor activation
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  • 82
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Protist 167 (2016): 106–120, doi:10.1016/j.protis.2016.01.003.
    Beschreibung: Arranging organisms into functional groups aids ecological research by grouping organisms (irrespective of phylogenetic origin) that interact with environmental factors in similar ways. Planktonic protists traditionally have been split between photoautotrophic “phytoplankton” and phagotrophic “microzooplankton”. However, there is a growing recognition of the importance of mixotrophy in euphotic aquatic systems, where many protists often combine photoautotrophic and phagotrophic modes of nutrition. Such organisms do not align with the traditional dichotomy of phytoplankton and microzooplankton. To reflect this understanding, we propose a new functional grouping of planktonic protists in an eco-physiological context: (i) phagoheterotrophs lacking phototrophic capacity, (ii) photoautotrophs lacking phagotrophic capacity, (iii) constitutive mixotrophs (CMs) as phagotrophs with an inherent capacity for phototrophy, and (iv) non-constitutive mixotrophs (NCMs) that acquire their phototrophic capacity by ingesting specific (SNCM) or general non-specific (GNCM) prey. For the first time, we incorporate these functional groups within a foodweb structure and show, using model outputs, that there is scope for significant changes in trophic dynamics depending on the protist functional type description. Accordingly, to better reflect the role of mixotrophy, we recommend that as important tools for explanatory and predictive research, aquatic food-web and biogeochemical models need to redefine the protist groups within their frameworks.
    Beschreibung: This work was funded by grants to KJF and AM from the Leverhulme Trust (International Network Grant F00391 V) and NERC (UK) through its iMARNET programme NE/K001345/1.
    Schlagwort(e): Plankton functional types (PFTs) ; Phagotroph ; Phototroph ; Mixotroph ; Phytoplankton ; Microzooplankton
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  • 83
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Chemistry 177 (2015): 1-8, doi:10.1016/j.marchem.2015.04.005.
    Beschreibung: The GEOTRACES Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The IDP2014 covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The TEI data in the IDP2014 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including ASCII spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the IDP2014 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2014 data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes.
    Beschreibung: We gratefully acknowledge financial support by the Scientific Committee on Oceanic Research (SCOR) through grants from the U.S. National Science Foundation, including grants OCE-0608600, OCE-0938349, and OCE-1243377. Financial support was also provided by the UK Natural Environment Research Council, the Ministry of Earth Science of India, the Centre National de Recherche Scientifique, l'Université Paul Sabatier de Toulouse, the Observatoire Midi-Pyrénées Toulouse, the Universitat Autònoma de Barcelona, the Kiel Excellence Cluster The Future Ocean, the Swedish Museum of Natural History, The University of Tokyo, The University of British Columbia, The Royal Netherlands Institute for Sea Research, the GEOMAR-Helmholtz Centre for Ocean Research Kiel, and the Alfred Wegener Institute.
    Schlagwort(e): GEOTRACES ; Trace elements ; Isotopes ; Electronic atlas
    Repository-Name: Woods Hole Open Access Server
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  • 84
    Publikationsdatum: 2022-05-26
    Beschreibung: This paper is not subject to U.S. copyright. The definitive version was published in Journal of Volcanology and Geothermal Research 314 (2016): 142-155, doi:10.1016/j.jvolgeores.2015.07.037.
    Beschreibung: Autonomous underwater vehicles were used to conduct a high-resolution water column survey of Lake Rotomahana using temperature, pH, turbidity, and oxidation–reduction potential (ORP) to identify active hydrothermal discharge zones within the lake. Five areas with active sublacustrine venting were identified: (1) the area of the historic Pink Terraces; (2) adjacent to the western shoreline subaerial “Steaming Cliffs,” boiling springs and geyser; (3) along the northern shoreline to the east of the Pink Terrace site; (4) the newly discovered Patiti hydrothermal system along the south margin of the 1886 Tarawera eruption rift zone; and (5) a location in the east basin (northeast of Patiti Island). The Pink Terrace hydrothermal system was active prior to the 1886 eruption of Mount Tarawera, but venting along the western shoreline, in the east basin, and the Patiti hydrothermal system appear to have been initiated in the aftermath of the eruption, similar to Waimangu Valley to the southwest. Different combinations of turbidity, pH anomalies (both positive and negative), and ORP responses suggest vent fluid compositions vary over short distances within the lake. The seasonal period of stratification limits vertical transport of heat to the surface layer and the hypolimnion temperature of Lake Rotomahana consequently increases with an average warming rate of ~ 0.010 °C/day due to both convective hydrothermal discharge and conductive geothermal heating. A sudden temperature increase occurred during our 2011 survey and was likely the response to an earthquake swarm just 11 days prior.
    Beschreibung: Funding was provided by GNS Strategic Development Fund.
    Schlagwort(e): Lake Rotomahana ; Hydrothermal venting ; pH ; Turbidity ; Oxidation–reduction potential ; Freshwater lakes
    Repository-Name: Woods Hole Open Access Server
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  • 85
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochimica et Cosmochimica Acta 176 (2016): 227–238, doi:10.1016/j.gca.2015.12.027.
    Beschreibung: Measurements of Xe isotope ratios in ocean island basalts (OIB) suggest that Earth’s mantle accreted heterogeneously, and that compositional remnants of accretion are sampled by modern, high-3He/4He OIB associated with the Icelandic and Samoan plumes. If so, the high-3He/4He source may also have a distinct oxygen isotopic composition from the rest of the mantle. Here, we test if the major elements of the high-3He/4He source preserve any evidence of heterogeneous accretion using measurements of three oxygen isotopes on olivine from a variety of high-3He/4He OIB locations. To high precision, the Δ17O value of high-3He/4He olivines from Hawaii, Pitcairn, Baffin Island and Samoa, are indistinguishable from bulk mantle olivine (Δ17OBulk Mantle − Δ17OHigh 3He/4He olivine = −0.002 ± 0.004 (2 × SEM)‰). Thus, there is no resolvable oxygen isotope evidence for heterogeneous accretion in the high-3He/4He source. Modelling of mixing processes indicates that if an early-forming, oxygen-isotope distinct mantle did exist, either the anomaly was extremely small, or the anomaly was homogenised away by later mantle convection. The δ18O values of olivine with the highest 3He/4He ratios from a variety of OIB locations have a relatively uniform composition (∼5‰). This composition is intermediate to values associated with the depleted MORB mantle and the average mantle. Similarly, δ18O values of olivine from high-3He/4He OIB correlate with radiogenic isotope ratios of He, Sr, and Nd. Combined, this suggests that magmatic oxygen is sourced from the same mantle as other, more incompatible elements and that the intermediate δ18O value is a feature of the high-3He/4He mantle source. The processes responsible for the δ18O signature of high-3He/4He mantle are not certain, but δ18O–87Sr/86Sr correlations indicate that it may be connected to a predominance of a HIMU-like (high U/Pb) component or other moderate δ18O components recycled into the high-3He/4He source.
    Repository-Name: Woods Hole Open Access Server
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  • 86
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ocean Modelling 105 (2016): 1-12, doi:10.1016/j.ocemod.2016.02.009
    Beschreibung: The sea state of the Beaufort and Chukchi seas is controlled by the wind forcing and the amount of ice-free water available to generate surface waves. Clear trends in the annual duration of the open water season and in the extent of the seasonal sea ice minimum suggest that the sea state should be increasing, independent of changes in the wind forcing. Wave model hindcasts from four selected years spanning recent conditions are consistent with this expectation. In particular, larger waves are more common in years with less summer sea ice and/or a longer open water season, and peak wave periods are generally longer. The increase in wave energy may affect both the coastal zones and the remaining summer ice pack, as well as delay the autumn ice-edge advance. However, trends in the amount of wave energy impinging on the ice-edge are inconclusive, and the associated processes, especially in the autumn period of new ice formation, have yet to be well-described by in situ observations. There is an implicit trend and evidence for increasing wave energy along the coast of northern Alaska, and this coastal signal is corroborated by satellite altimeter estimates of wave energy.
    Beschreibung: This work was supported by the Office of Naval Research, Code 322, “Arctic and Global Prediction”, directed by Drs. Martin Jeffries and Scott Harper. (Grant numbers and Principal Investigators are: Ackley, N000141310435; Babanin, N000141310278; Doble, N000141310290; Fairall, N0001413IP20046; Gemmrich, N000141310280; Girard-Ardhuin and Ardhuin, N000141612376; Graber, N000141310288; Guest, N0001413WX20830; Holt, N0001413IP20050; Lehner, N000141310303; Maksym, N000141310446; Perrie, N00014-15-1-2611; Rogers, N0001413WX20825; Shen, N000141310294; Squire, N000141310279; Stammerjohn, N000141310434; Thomson, N000141310284; Wadhams, N000141310289.)
    Schlagwort(e): Sea ice ; Arctic Ocean ; Ocean surface waves
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 87
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochimica et Cosmochimica Acta 179 (2016): 123-141, doi:10.1016/j.gca.2016.01.023.
    Beschreibung: The carbonate clumped isotope thermometer is a promising tool for determining past ocean temperatures. It is based on the temperature dependence of rare isotopes ‘clumping’ into the same carbonate ion group in the carbonate mineral lattice. The extent of this clumping effect is independent of the isotope composition of the water from which carbonate precipitates, providing unique advantages over many other paleotemperature proxies. Existing calibrations of this thermometer in cold-water and warm-water corals suggest clumped isotope ‘vital effects’ are negligible in cold-water corals but may be significant in warm-water corals. Here, we test the calibration of the carbonate clumped isotope thermometer in cold-water corals with a recently collected and well characterised sample set spanning a range of coral genera (Balanophyllia, Caryophyllia, Dasmosmilia, Desmophyllum, Enallopsammia and Javania). The clumped isotope compositions (Δ47) of these corals exhibit systematic dependences on their growth temperatures, confirming the basis of the carbonate clumped isotope thermometer. However, some cold-water coral genera show Δ47 values that are higher than the expected equilibrium values by up to 0.05‰ (equivalent to underestimating temperature by ∼9 °C) similar to previous findings for some warm-water corals. This finding suggests that the vital effects affecting corals Δ47 are common to both warm- and cold-water corals. By comparison with models of the coral calcification process we suggest that the clumped isotope offsets in these genera are related to the kinetic isotope effects associated with CO2 hydration/hydroxylation reactions in the corals’ calcifying fluid. Our findings complicate the use of the carbonate clumped isotope thermometer in corals, but suggest that species- or genus-specific calibrations could be useful for the future application of this paleotemperature proxy.
    Beschreibung: This work was supported by a British National Environment Research Council studentship to P. Spooner (NE/K500823/1), National Science Foundation Grant NSF-ANT-1246387 and The Penzance Endowed Fund in Support of Assistant Scientists (WHOI) to W. Guo, and by funds from the European Research Council, the Leverhulme Trust and a Marie Curie Reintegration grant.
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  • 88
    Publikationsdatum: 2022-05-26
    Beschreibung: This paper is not subject to U.S. copyright. The definitive version was published in Earth and Planetary Science Letters 449 (2016): 332–344, doi:10.1016/j.epsl.2016.05.023.
    Beschreibung: The recent discovery of active methane venting along the US northern and mid-Atlantic margin represents a new source of global methane not previously accounted for in carbon budgets from this region. However, uncertainty remains as to the origin and history of methane seepage along this tectonically inactive passive margin. Here we present the first isotopic analyses of authigenic carbonates and methanotrophic deep-sea mussels, Bathymodiolus sp., and the first direct constraints on the timing of past methane emission, based on samples collected at the upper slope Baltimore Canyon (∼385 m water depth) and deepwater Norfolk (∼1600 m) seep fields within the area of newly-discovered venting. The authigenic carbonates at both sites were dominated by aragonite, with an average View the MathML sourceδC13 signature of −47‰−47‰, a value consistent with microbially driven anaerobic oxidation of methane-rich fluids occurring at or near the sediment–water interface. Authigenic carbonate U and Sr isotope data further support the inference of carbonate precipitation from seawater-derived fluids rather than from formation fluids from deep aquifers. Carbonate stable and radiocarbon (View the MathML sourceδC13 and View the MathML sourceΔC13) isotope values from living Bathymodiolus sp. specimens are lighter than those of seawater dissolved inorganic carbon, highlighting the influence of fossil carbon from methane on carbonate precipitation. U–Th dates on authigenic carbonates suggest seepage at Baltimore Canyon between 14.7±0.6 ka14.7±0.6 ka to 15.7±1.6 ka15.7±1.6 ka, and at the Norfolk seep field between 1.0±0.7 ka1.0±0.7 ka to 3.3±1.3 ka3.3±1.3 ka, providing constraint on the longevity of methane efflux at these sites. The age of the brecciated authigenic carbonates and the occurrence of pockmarks at the Baltimore Canyon upper slope could suggest a link between sediment delivery during Pleistocene sea-level lowstand, accumulation of pore fluid overpressure from sediment compaction, and release of overpressure through subsequent venting. Calculations show that the Baltimore Canyon site probably has not been within the gas hydrate stability zone (GHSZ) in the past 20 ka, meaning that in-situ release of methane from dissociating gas hydrate cannot be sustaining the seep. We cannot rule out updip migration of methane from dissociation of gas hydrate that occurs farther down the slope as a source of the venting at Baltimore Canyon, but consider that the history of rapid sediment accumulation and overpressure may play a more important role in methane emissions at this site.
    Beschreibung: Funding for this project (sponsored by the National Oceanographic Partnership Program) included USGS Terrestrial, Freshwater, and Marine Environments Program through the Outer Continental shelf study, Coastal and Marine Geology Program, and the Bureau of Ocean Energy Management (BOEM) contract number M10PC00100 (contracted to CSA Ocean Sciences, Inc.). C.R. was supported by USGS–DOE Interagency Agreements DE-FE000291 and 0023495.
    Schlagwort(e): Authigenic carbonate ; Cold seep ; AOM ; Chemosynthesis ; Mid-Atlantic margin ; Isotope geochemistry
    Repository-Name: Woods Hole Open Access Server
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  • 89
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth and Planetary Science Letters 449 (2016): 372-381, doi:10.1016/j.epsl.2016.05.016.
    Beschreibung: Although boron and uranium to calcium ratios (B/Ca, U/Ca) in planktonic foraminifera have recently received much attention as potential proxies for ocean carbonate chemistry, the extent of a carbonate chemistry control on these ratios remains contentious. Here, we use bi-weekly sediment trap samples collected from the subtropical North Atlantic in combination with measured oceanographic data from the same location to evaluate the dominant oceanographic controls on B/Ca and U/Ca in three depth-stratified species of planktonic foraminifera. We also test the control of biological, growth-related, processes on planktonic foraminiferal B and U incorporation by using foraminifer test area density (μg/μm2)(μg/μm2) (a monitor of test thickness) and test size from the same samples. B/Ca and U/Ca show little or no significant correlation with carbonate system parameters both within this study and in comparison with other published works. We provide the first evidence for a strong positive relationship between area density (test thickness) and B/Ca, and reveal that this is consistent in all species studied, suggesting a likely role for calcification in controlling boron partitioning into foraminiferal calcite. This finding is consistent with previous observations of less efficient discrimination against trace element ‘impurities’ (such as B), at higher calcification rates. We observe little or no dependency of B/Ca on test size. In marked contrast, we find that U/Ca displays a strong species-specific dependency on test size in all species, but no relationship with test thickness, implicating some other biological control (possibly related to growth), rather than a calcification control, on U incorporation into foraminiferal calcite. Our results caution against the use of B/Ca and U/Ca in planktonic foraminifera as reliable proxies for the ocean carbonate system and recommend that future work should concentrate on improving the mechanistic understanding of how planktonic foraminifer calcification and growth rates regulate boron and uranium incorporation into the test.
    Beschreibung: This research was funded through the U.K. Ocean Acidification Research Program by Natural Environment Research Council grant to P. Anand and P. Sexton (grant NE/I019891/1). K.S. thanks the Cushman Foundation for their financial support through the Johanna Resig Foraminifera Fellowship. We acknowledge the National Science Foundation for its support of the Oceanic Flux Program time-series (most recently by grant OCE-1234292) and the Bermuda Atlantic Time Series (most recently by grant OCE-0801991).
    Schlagwort(e): Planktonic foraminifera ; Boron ; Uranium ; Proxy ; Sediment trap
    Repository-Name: Woods Hole Open Access Server
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  • 90
    Publikationsdatum: 2016-07-12
    Beschreibung: We present experimental results obtained under normal gravity on the dynamics of solid particles in periodic oscillatory thermocapillary-driven flows in a non-isothermal liquid bridge made of decane. Inertial particles of different densities and in the size range approximately 0.75 − 75 μ m are able to form stable coherent structures (particle accumulation structures, or PASs). Two image processing techniques were developed and successfully applied to compute time required for an ensemble of particles to form a structure. It is shown that the formation time grows with the decrease of the Stokes number. The observations indicate the probable irrelevance of the memory term for these experiments. Two types of PAS were observed—single (SL-I) and double-loop (SL-II)—which sometimes co-existed. Only large or very dense particles may form an SL-II type structure. A number of novel features of the system were perceived. In some cases, intermittently stable structures emerged (their dynamics is characterized by alternating time intervals during which a structure exists and is destroyed). Whereas in most experiments we observed a conventional symmetric and centered PAS, there were cases when a long-term stable asymmetric structure appeared. Experiments wherein two different types of PAS-forming particles were used simultaneously revealed the destructive role of collisions between the particles on formation of structures.
    Print ISSN: 1054-1500
    Digitale ISSN: 1089-7682
    Thema: Physik
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  • 91
    Publikationsdatum: 2016-07-12
    Beschreibung: A three-dimensional model is presented to investigate helium plasma generated by microwave under atmospheric pressure in this paper, which includes the physical processes of electromagnetic wave propagation, electron and heavy species transport, gas flow, and heat transfer. The model is based on the fluid approximation calculation and local thermodynamic equilibrium assumption. The simulation results demonstrate that the maxima of the electron density and gas temperature are 4.79 × 10 17  m −3 and 1667 K, respectively, for the operating conditions with microwave power of 500 W, gas flow rate of 20 l/min, and initial gas temperature of 500 K. The electromagnetic field distribution in the plasma source is obtained by solving Helmholtz equation. Electric field strength of 2.97 × 10 4  V/m is obtained. There is a broad variation on microwave power, gas flow rate, and initial gas temperature to obtain deeper information about the changes of the electron density and gas temperature.
    Print ISSN: 1070-664X
    Digitale ISSN: 1089-7674
    Thema: Physik
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  • 92
    Publikationsdatum: 2016-07-12
    Beschreibung: The paper analyzes the dielectric breakdown properties of N 2 –O 2 mixtures at different O 2 concentrations and gas pressures, taking into account electron detachments from negative ions. The reduced effective ionization coefficients α(eff)/N in N 2 –O 2 mixtures at different O 2 concentrations and gas pressures were calculated and analyzed, by considering electron detachments. The critical reduced electric fields (E/N) cr and the critical electron temperature T b were then determined. The result indicates a clear enhancement of α(eff)/N by collisional detachments, which causes a reduction in the (E/N) cr . In addition, a synergistic effect in the N 2 –O 2 mixture was also observed in both (E/N) cr and T b . The value of T b was decreased by the increase of pd product, however, T b tended to be constant at relatively high pd products.
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    Thema: Physik
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  • 93
    Publikationsdatum: 2016-07-11
    Beschreibung: Publication date: Available online 9 July 2016 Source: Geodesy and Geodynamics Author(s): Ruisha Li, Xi Zhang, Shouwen Gong, Hongtao Tang, Peng Jia The equation for determining cross-fault representative value is calculated based on hanging wall and foot wall reference level surfaces. The cross-fault data reliability are analyzed base on the stability of reference datum and observation points, thereby facilitating plotting of the representative value curves after removing interference. The spatial and temporal characteristics of fault deformation abnormalities before the 2016 Menyuan M s6.4 earthquake, as well as the fault-movement characteristics reflected by representative value, are summarized. The results show that many site trends had changed 1–3 years before the Menyuan M s6.4 earthquake in the Qilian Fault, reflecting certain background abnormalities. The short-term abnormalities centrally had appeared in the 6 months to 1 year period before the earthquake near and in the neighborhood of the source region, demonstrating a significantly increased number of short-term abnormalities. Many sites near and in the neighborhood of the source region had strengthened inverse activities or had changed from positive to inverse activities in the most recent 2–3 years, which reflect stress-field enhancements or adjustment features.
    Print ISSN: 1674-9847
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geologie und Paläontologie
    Publiziert von Elsevier
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  • 94
    Publikationsdatum: 2016-07-13
    Beschreibung: In semiconductors almost all heat is conducted by phonons (lattice vibrations), which is limited by their quasi-particle lifetimes. Phonon-phonon interactions represent scattering mechanisms that produce thermal resistance. In thermoelectric materials, this resistance due to anharmonicity should be maximised for optimal performance. We use a first-principles lattice-dynamics approach to explore the changes in lattice dynamics across an isostructural series where the average atomic mass is conserved: ZnS to CuGaS 2 to Cu 2 ZnGeS 4 . Our results demonstrate an enhancement of phonon interactions in the multernary materials and confirm that lattice thermal conductivity can be controlled independently of the average mass and local coordination environments.
    Digitale ISSN: 2166-532X
    Thema: Maschinenbau
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  • 95
    Publikationsdatum: 2016-07-13
    Beschreibung: In this contribution, we present a highly accurate approach for thickness measurements of multi-layered automotive paints using terahertz time domain spectroscopy in reflection geometry. The proposed method combines the benefits of a model-based material parameters extraction method to calibrate the paint coatings, a generalized Rouard's method to simulate the terahertz radiation behavior within arbitrary thin films, and the robustness of a powerful evolutionary optimization algorithm to increase the sensitivity of the minimum thickness measurement limit. Within the framework of this work, a self-calibration model is introduced, which takes into consideration the real industrial challenges such as the effect of wet-on-wet spray in the painting process.
    Print ISSN: 0003-6951
    Digitale ISSN: 1077-3118
    Thema: Physik
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  • 96
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    American Institute of Physics (AIP)
    Publikationsdatum: 2016-07-13
    Beschreibung: Based on electromagnetic scattering theory, a model of superscatterer enhanced distant wireless power transfer (WPT) device has designed and analyzed with the concept of transformation optics. The numerical results obtained through a series expansion method reveal that a properly designed ss-WPT has high efficiency for long transfer distances as well as a wide transfer range. The transfer distance can be further enlarged by fine tuning of the design. These effects can be explained qualitatively through the study of magnetic flux.
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    Thema: Physik
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  • 97
    Publikationsdatum: 2016-07-13
    Beschreibung: In this work, we report enhanced power conversion efficiency (PCE) of bulk heterojunction polymer solar cells by Förster resonance energy transfer (FRET) from samarium-doped luminescent gadolinium orthovanadate (GdVO 4 :Sm 3+ ) quantum dots (QDs) to polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) polymer. The photoluminescence emission spectrum of GdVO 4 :Sm 3+ QDs overlaps with the absorption spectrum of PTB7, leading to FRET from GdVO 4 :Sm 3+ to PTB7, and significant enhancements in the charge-carrier density of excited and polaronic states of PTB7 are observed. This was confirmed by means of femtosecond transient absorption spectroscopy. The FRET from GdVO 4 :Sm 3+ QDs to PTB7 led to a remarkable increase in the power conversion efficiency (PCE) of PTB7:GdVO 4 :Sm 3+ :PC 71 BM ([6,6]-phenyl-C 71 -butyric acid methyl ester) polymer solar cells. The PCE in optimized ternary blend PTB7:GdVO 4 :Sm 3+ :PC 71 BM (1:0.1:1.5) is increased to 8.8% from 7.2% in PTB7:PC 71 BM. This work demonstrates the potential of rare-earth based luminescent QDs in enhancing the PCE of polymer solar cells.
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    Thema: Physik
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  • 98
    Publikationsdatum: 2016-07-13
    Beschreibung: We fabricate planar graphene field-effect transistors with self-aligned side-gate at 100 nm from the 500 nm wide graphene conductive channel, using a single lithographic step. We demonstrate side-gating below 1 V with conductance modulation of 35% and transconductance up to 0.5 mS/mm at 10 mV drain bias. We measure the planar leakage along the SiO 2 /vacuum gate dielectric over a wide voltage range, reporting rapidly growing current above 15 V. We unveil the microscopic mechanisms driving the leakage, as Frenkel-Poole transport through SiO 2 up to the activation of Fowler-Nordheim tunneling in vacuum, which becomes dominant at higher voltages. We report a field-emission current density as high as 1  μ A/ μ m between graphene flakes. These findings are important for the miniaturization of atomically thin devices.
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  • 99
    Publikationsdatum: 2016-07-13
    Beschreibung: The nanoscale resistive switching in hafnium oxide stack is investigated by the conductive atomic force microscopy (C-AFM). The initial oxide stack is insulating and electrical stress from the C-AFM tip induces nanometric conductive filaments. Multimode resistive switching can be observed in consecutive operation cycles at one spot. The different modes are interpreted in the framework of a low defect quantum point contact theory. The model implies that the optimization of the conductive filament active region is crucial for the future application of nanoscale resistive switching devices.
    Print ISSN: 0003-6951
    Digitale ISSN: 1077-3118
    Thema: Physik
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  • 100
    Publikationsdatum: 2016-07-13
    Beschreibung: We report on the fabrication and characterization of a Schottky diode made using 2D germanane (hydrogenated germanene). When compared to germanium, the 2D structure has higher electron mobility, an optimal band-gap, and exceptional stability making germanane an outstanding candidate for a variety of opto-electronic devices. One-atom-thick sheets of hydrogenated puckered germanium atoms have been synthesized from a CaGe 2 framework via intercalation and characterized by XRD, Raman, and FTIR techniques. The material was then used to fabricate Schottky diodes by suspending the germanane in benzonitrile and drop-casting it onto interdigitated metal electrodes. The devices demonstrate significant rectifying behavior and the outstanding potential of this material.
    Print ISSN: 0003-6951
    Digitale ISSN: 1077-3118
    Thema: Physik
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