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  • 1
    Publikationsdatum: 2021-03-09
    Beschreibung: Mixed‐mode fluid‐filled cracks represent a common means of fluid transport within the Earth's crust. They often show complex propagation paths which may be due to interaction with crustal heterogeneities or heterogeneous crustal stress. Previous experimental and numerical studies focus on the interplay between fluid over-pressure and external stress but neglect the effect of other crack parameters. In this study, we address the role of crack length on the propagation paths in the presence of an external heterogeneous stress field. We make use of numerical simulations of magmatic dike and hydrofracture propagation, carried out using a two‐dimensional boundary element model, and analogue experiments of air‐filled crack propagation into a transparent gelatin block. We use a 3‐D finite element model to compute the stress field acting within the gelatin block and perform a quantitative comparison between 2‐D numerical simulations and experiments. We show that, given the same ratio between external stress and fluid pressure, longer fluid‐filled cracks are less sensitive to the background stress, and we quantify this effect on fluid‐filled crack paths. Combining the magnitude of the external stress, the fluid pressure, and the crack length, we define a new parameter, which characterizes two end member scenarios for the propagation path of a fluid‐filled fracture. Our results have important implications for volcanological studies which aim to address the problem of complex trajectories of magmatic dikes (i.e., to forecast scenarios of new vents opening at volcanoes) but also have implications for studies that address the growth and propagation of natural and induced hydrofractures.
    Beschreibung: Published
    Beschreibung: 2064–2081
    Beschreibung: 2V. Struttura e sistema di alimentazione dei vulcani
    Beschreibung: JCR Journal
    Schlagwort(e): Magmatic dykes ; hydrofractures ; Numerical symulations ; Analogue experiments ; 04.08. Volcanology ; 05.05. Mathematical geophysics
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 2
    Publikationsdatum: 2021-01-25
    Beschreibung: Tsunami deposits present an important archive for understanding tsunami histories and dynamics. Most research in this field has focused on onshore preserved remains, while the offshore deposits have received less attention. In 2009, during a coring campaign with theItalian Navy Magnaghi, four 1 m long gravity cores (MG cores) were sampled from the northern part of Augusta Bay, along a transect in 60 to 110 m water depth. These cores were taken in the same area where a core (MS06) was collected in 2007 about 2.3 km offshore Augusta at a water depth of 72 m below sea level. Core MS06 consisted of a 6.7 m long sequence that included 12 anomalous intervals interpreted as the primary effect of tsunami backwash waves in the last 4500 years. In this study, tsunami deposits were identified, based on sedimentology and displaced benthic foraminifera (as for core MS06) reinforced by X-ray fluorescence data. Two erosional surfaces (L1 and L2) were recognized coupled with grain size increase, abundant Posidonia oceanica seagrass remains and a significant amount of Nubecularia lucifuga, an epiphytic sessile benthic foraminifera considered to be transported from the inner shelf. The occurrence of Ti/Ca and Ti/Sr increments, coinciding with peaks in organic matter (Mo inc/coh) suggests terrestrial run-off coupled with an input of organic matter. The L1 and L2 horizons were attributed to two distinct historical tsunamis (AD 1542 and AD 1693) by indirect age-estimation methods using 210Pb profiles and the comparison of Volume Magnetic Susceptibility data between MG cores and MS06 cores. One most recent bioturbated horizon (Bh), despite not matching the above listed interpretative features, recorded an important palaeoenvironmental change that may correspond to the AD 1908 tsunami. These findings reinforce the value of offshore sediment records as an underutilized resource for the identification of past tsunamis.
    Beschreibung: Published
    Beschreibung: 1553-1576
    Beschreibung: 6T. Studi di pericolosità sismica e da maremoto
    Beschreibung: JCR Journal
    Schlagwort(e): Eastern Sicily ; tsunami ; foraminifera ; sedimentology ; XRF core scanning ; 04.04. Geology
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 3
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    Wiley
    In:  EPIC3The Ocean Floor : Bruce Heezen commemorative volume, (A Wiley-Interscience publication), Chichester, Wiley, pp. 147-163, ISBN: 0-471-10091-9
    Publikationsdatum: 2014-05-12
    Beschreibung: The sedimentation regime off Northwest Africa is shaped by: (1) structur~al factors. which result in generallv low relief on land. shelf widths between 40 and more than 120 km. and av-erage sfope inclinations between 10 30' and 30; (2) land climates. which contral the delivery of terrigenous particles to the margin: (3) water movements including boundary currents and upwelling; and (4) the post- Pleistocene sea level rise. This chapter combines published and new results arising from research into the sedimentation processes off Northwest Africa. and emphasizes particularly the activities of the Kiel marine geological group during the past few years. Reviews of cruise activities and results were given in Closs et al. (1969) (Meteor cruise 8. 1967. off Morocco) . Seibold (1972) (Meteor cmise 25 . 1971. off Sahara to Central Senegal). Seibold and Hinz (1976) (Meteor cmise 39,1975 . and Valdivia cruise 10. 1975, from Morocco to South Senegal), and Waiden et al. (1974) (Meteor cmise 30, 1973, off Sierra Leone). Some of these cmises were used for pre- or post-site surveys for the Deep-Sea Drilling Project, or to add undisturbed Quaternary cores to the Glomar Challenger cores (leg 41, ] 975; Lancelot, et al .• 1978); leg 47 A, Arthur er al .• 1979; Lutze et al., 1979). We have concentrated our geological investigations on a number of standard profiles from the shelf to the upper continental rise as given in Figure 1. The manuscript was finished May 1979.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Inbook , peerRev
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  • 4
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46(8), pp. 4288-4298, ISSN: 0094-8276
    Publikationsdatum: 2021-02-16
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 5
    Publikationsdatum: 2019-04-29
    Beschreibung: Sedimentary architecture and morphogenetic evolution of a polar bay-mouth gravel-spit system are revealed based on topographic mapping, sedimentological data, radiocarbon dating and ground-penetrating radar investigations. Data document variable rates of spit progradation in reaction to atmospheric warming synchronous to the termination of the last glacial re-advance (LGR, 0.45–0.25 ka BP), the southern hemisphere equivalent of the Little Ice Age cooling period. Results show an interruption of spit progradation that coincides with the proposed onset of accelerated isostatic rebound in reaction to glacier retreat. Spit growth resumed in the late 19th century after the rate of isostatic rebound decreased, and continues until today. The direction of modern spit progradation, however, is rotated northwards compared with the growth axis of the early post-LGR spit. This is interpreted to reflect the shift and strengthening in the regional wind field during the last century. A new concept for the interplay of polar gravel-spit progradation and glacio-isostatic adjustment is presented, allowing for the prediction of future coastal evolution in comparable polar settings.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev , info:eu-repo/semantics/article
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  • 6
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46, ISSN: 0094-8276
    Publikationsdatum: 2019-07-10
    Beschreibung: Here we evaluate five atmospheric reanalyses in an Arctic gateway during late summer. The reanalyses include ERA5, ERA-Interim, JRA-55, CFSv2 and MERRA-2. We use observations from 50 radiosondes launched in the Fram Strait around 79-80˚N, between 25 August – 11 September 2017. Crucially, data from 27 radiosondes were not transmitted to the Global Telecommunications System (GTS), and therefore not assimilated into any reanalysis. In most reanalyses, the magnitude of wind speed and humidity errors are similar for profiles with and without data assimilation. In cases without data assimilation, correlation coefficients (R) exceed 0.88 for temperature, wind speed and specific humidity, in all reanalyses. Overall, the newly released ERA5 has higher correlation coefficients than any other reanalyses as well as smaller biases and root mean square errors, for all three variables. The largest improvements identified in ERA5 are in its representation of the wind field, and temperature profiles over warm water.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 7
    Publikationsdatum: 2019-08-13
    Beschreibung: The importance of macrobenthos in benthic‐pelagic coupling and early diagenesis of organic carbon (OC) has long been recognized but has not been quantified at a regional scale. By using the southern North Sea as an exemplary area we present a modelling attempt to quantify the budget of total organic carbon (TOC) reworked by macrobenthos in seafloor surface sediments. Vertical profiles in sediments collected in the field indicate a significant but nonlinear correlation between TOC and macrobenthic biomass. A mechanistic model is used to resolve the bi‐directional interaction between TOC and macrobenthos. A novelty of this model is that bioturbation is resolved dynamically depending on variations in local food resource and macrobenthic biomass. The model is coupled to 3D hydrodynamic‐biogeochemical simulations to hindcast the mutual dependence between sedimentary TOC and macrobenthos from 1948 to 2015. Agreement with field data reveals a satisfactory model performance. Our simulations show that the preservation of TOC in the North Sea sediments is not only determined by pelagic conditions (hydrodynamic regime and primary production) but also by the vertical distribution of TOC, bioturbation intensity, and the vertical positioning of macrobenthos. Macrobenthos annually ingest 20%–35% and in addition vertically diffuse 11%–22% of the total budget of TOC in the upper‐most 30 cm sediments in the southern North Sea. This result indicates a central role of benthic animals in modulating the OC cycling at the sediment‐water interface of continental margins.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 8
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    Wiley
    In:  EPIC3Paleoceanography and Paleoclimatology, Wiley, 34, pp. 432-435
    Publikationsdatum: 2019-06-23
    Beschreibung: Age control and paleoceanographic evidence of marine sediment records might be challenged if authors solely build their stratigraphy on visual correlation to apparently well‐dated records from the same ocean basin, using, for example, highly resolved X‐ray fluorescence‐based element‐count records and correlation tools such as AnalySeries. While per se perfectly reasonable, this approach bears the risk of missing stratigraphic gaps in the sedimentary record and thus might result in imprecise and/or flawed interpretations. Here we present a unique series of 14 planktic 14C ages from a 7‐cm section of East Pacific Rise core PS75/059‐2. The ages suggest a 14‐ky‐long period of low‐to‐zero deposition during Last Glacial Maximum, mainly marked by continuous redistribution of winnowed foraminifers, probably the result of enhanced bottom currents, moreover, by some bioturbational mixing. On the basis of this data we demonstrate the impact of the hiatus on a South Pacific transect of apparent benthic ventilation ages (ΔΔ14C values) and their meaning for estimates of CO2 stored in Last Glacial Maximum Pacific deep waters.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 9
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Publikationsdatum: 2019-06-16
    Beschreibung: Satellite‐derived data suggest an increase in annual primary production following the loss of summer sea ice in the Arctic Ocean. The scarcity of field data to corroborate this enhanced algal production incited a collaborative project combining six annual cycles of sequential sediment trap measurements obtained over a 17‐year period in the Eurasian Arctic Ocean. Here we present microalgal fluxes measured at ~200 m to reflect the bulk of algal carbon production. Ice algae contributed to a large proportion of the microalgal carbon export before complete ice melt and possible detection of their production by satellites. In the northern Laptev Sea, annual microalgal carbon fluxes were lower during the 2007 minimum ice extent than in 2006. In 2012, early snowmelt led to early microalgal carbon flux in the Nansen Basin. Hence, a change in the timing of snowmelt and ice algae release may affect productivity and export over the Arctic basins.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 10
    Publikationsdatum: 2020-08-27
    Beschreibung: Sea ice dynamics determine the drift and deformation of sea ice. Nonlinear physics, usually expressed in a viscous‐plastic rheology, makes the sea ice momentum equations notoriously difficult to solve. At increasing sea ice model resolution the nonlinearities become stronger as linear kinematic features (leads) appear in the solutions. Even the standard elastic‐viscous‐plastic (EVP) solver for sea ice dynamics, which was introduced for computational efficiency, becomes computationally very expensive, when accurate solutions are required, because the numerical stability requires very short, and hence more, subcycling time steps at high resolution. Simple modifications to the EVP solver have been shown to remove the influence of the number of subcycles on the numerical stability. At low resolution appropriate solutions can be obtained with only partial convergence based on a significantly reduced number of subcycles as long as the numerical procedure is kept stable. This previous result is extended to high resolution where linear kinematic features start to appear. The computational cost can be strongly reduced in Arctic Ocean simulations with a grid spacing of 4.5 km by using modified and adaptive EVP versions because fewer subcycles are required to simulate sea ice fields with the same characteristics as with the standard EVP.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 11
    Publikationsdatum: 2019-07-15
    Beschreibung: Quaternary East Asian winter monsoon (EAWM) evolution has long been attributed to high‐latitude Northern Hemisphere climate change. However, it cannot explain the distinct relationships of the EAWM in the northern and southern East Asian marginal sea in paleoclimatic records. Here we present an EAWM record of the northern East China Sea over the past 300 ka and a transient climate simulation with the Kiel Climate Model through the Holocene. Both proxy record and simulation suggest anticorrelated long‐term EAWM evolution between the northern East China Sea and the South China Sea. We suggest that this spatial discrepancy of EAWM can be interpreted as El Niño–Southern Oscillation (ENSO)‐like controlling, which generates cyclonic/anticyclonic wind anomalies in the northern/southern East Asian marginal sea. This research explains much of the controversy in nonorbital scale variability of Quaternary EAWM records in the East Asian marginal sea and supports a potent role of tropical forcing in East Asian winter climate change.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 12
    Publikationsdatum: 2019-08-01
    Beschreibung: The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. We review the state‐of‐the art knowledge concerning the WG from an interdisciplinary perspective, uncovering critical aspects needed to understand this system's role in shaping the future evolution of oceanic heat and carbon uptake over the next decades. The main limitations in our knowledge are related to the conditions in this extreme and remote environment, where the polar night, very low air temperatures and presence of sea ice year‐round hamper field and remotely sensed measurements. We highlight the importance of winter and under‐ice conditions in the southern WG, the role that new technology will play to overcome present‐day sampling limitations, the importance of the WG connectivity to the low‐latitude oceans and atmosphere, and the expected intensification of the WG circulation as the westerly winds intensify. Greater international cooperation is needed to define key sampling locations that can be visited by any research vessel in the region. Existing transects sampled since the 1980s along the Prime Meridian and along an East‐West section at ~62°S should be maintained with regularity to provide answers to the relevant questions. This approach will provide long‐term data to determine trends and will improve representation of processes for regional, Antarctic‐wide and global modeling efforts – thereby enhancing predictions of the WG in global ocean circulation and climate.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 13
    Publikationsdatum: 2020-07-02
    Beschreibung: The East Antarctic Ice Sheet (EAIS) is underlain by a series of low‐lying subglacial sedimentary basins. The extent, geology, and basal topography of these sedimentary basins are important boundary conditions governing the dynamics of the overlying ice sheet. This is particularly pertinent for basins close to the grounding line wherein the EAIS is grounded below sea level and therefore potentially vulnerable to rapid retreat. Here we analyze newly acquired airborne geophysical data over the Pensacola‐Pole Basin (PPB), a previously unexplored sector of the EAIS. Using a combination of gravity and magnetic and ice‐penetrating radar data, we present the first detailed subglacial sedimentary basin model for the PPB. Radar data reveal that the PPB is defined by a topographic depression situated ~500 m below sea level. Gravity and magnetic depth‐to‐source modeling indicate that the southern part of the basin is underlain by a sedimentary succession 2–3 km thick. This is interpreted as an equivalent of the Beacon Supergroup and associated Ferrar dolerites that are exposed along the margin of East Antarctica. However, we find that similar rocks appear to be largely absent from the northern part of the basin, close to the present‐day grounding line. In addition, the eastern margin of the basin is characterized by a major geological boundary and a system of overdeepened subglacial troughs. We suggest that these characteristics of the basin may reflect the behavior of past ice sheets and/or exert an influence on the present‐day dynamics of the overlying EAIS.
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  • 14
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Publikationsdatum: 2019-09-16
    Repository-Name: EPIC Alfred Wegener Institut
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  • 15
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46(8), pp. 4413-4420, ISSN: 0094-8276
    Publikationsdatum: 2019-10-07
    Beschreibung: The Red Sea is a deep marine basin often considered as small‐scale version of the global ocean. Hydrographic observations and ocean‐atmosphere modeling indicate Red Sea deep water was episodically renewed by wintertime open‐ocean deep convections during 1982–2001, suggesting a renewal time on the order of a decade. However, the long‐term pacing of Red Sea deep water renewals is largely uncertain. We use an annually resolved coral oxygen isotope record of winter surface water conditions to show that the late twentieth century deep water renewals were probably unusual in the context of the preceding ~100 years. More frequent major events are detected during the late Little Ice Age, particularly during the early nineteenth century characterized by large tropical volcanic eruptions. We conclude that Red Sea deep water renewal time is on the order of a decade up to a century, depending on the mean climatic conditions and large‐scale interannual climate forcing.
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  • 16
    Publikationsdatum: 2020-01-07
    Beschreibung: Ocean heat transport through the Barents Sea Opening (BSO) has strong impacts on the Barents Sea ice extent and the climate. In this paper we quantified the contributions from different atmospheric forcing components to the trend and interannual variability of the BSO heat transport. Ocean‐ice model simulations were conducted in which the interannual variation of atmospheric forcing was maintained only in or outside the Arctic in two different simulations. The sum of their BSO heat transport anomalies reasonably replicated the trend and variability from a hindcast simulation. The upward trend of the BSO heat transport mainly stems from the increasing ocean temperature in the subpolar North Atlantic. For the interannual variability, the local wind and upstream forcing are similarly important. The location of the Atlantic Water boundary current in the Nordic Seas, influenced by the cyclonic atmospheric circulation, is crucial in determining part of the BSO inflow variability.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev , info:eu-repo/semantics/article
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  • 17
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    Wiley
    In:  EPIC3Ecology and Evolution, Wiley, 9(15), pp. 1-12
    Publikationsdatum: 2019-12-28
    Beschreibung: Kelps are important providers and constituents of marine ecological niches, the coastal kelp forests. Kelp species have differing distribution ranges, but mainly thrive in temperate and arctic regions. Although the principal factors determining biogeographic distribution ranges are known, genomics could provide additional answers to this question. We sequenced DNA from two Laminaria species with contrasting distribution ranges, Laminaria digitata and Laminaria solidungula. Laminaria digitata is found in the Northern Atlantic with a southern boundary in Brittany (France) or Massachusetts (USA) and a northern boundary in the Arctic, whereas L. solidungula is endemic to the Arctic only. From the raw reads of DNA, we reconstructed both chloroplast genomes and annotated them. A concatenated data set of all available brown algae chloroplast sequences was used for the calculation of a robust phylogeny, and sequence variations were analyzed. The two Laminaria chloroplast genomes are collinear to previously analyzed kelp chloroplast genomes with important exceptions. Rearrangements at the inverted repeat regions led to the pseudogenization of ycf37 in L. solidungula, a gene possibly required under high light conditions. This defunct gene might be one of the reasons why the habitat range of L. solidungula is restricted to lowlight sublittoral sites in the Arctic. The inheritance pattern of single nucleotide polymorphisms suggests incomplete lineage sorting of chloroplast genomes in kelp species. Our analysis of kelp chloroplast genomes shows that not only evolutionary information could be gleaned from sequence data. Concomitantly, those sequences can also tell us something about the ecological conditions which are required for species well‐being.
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  • 18
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    Wiley
    In:  EPIC3Biologie in unserer Zeit, Wiley, 49(6), pp. 436-442, ISSN: 0045-205X
    Publikationsdatum: 2019-12-20
    Repository-Name: EPIC Alfred Wegener Institut
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  • 19
    Publikationsdatum: 2021-02-16
    Beschreibung: A new global climate model setup using FESOM2.0 for the sea ice‐ocean component and ECHAM6.3 for the atmosphere and land surface has been developed. Replacing FESOM1.4 by FESOM2.0 promises a higher efficiency of the new climate setup compared to its predecessor. The new setup allows for long‐term climate integrations using a locally eddy‐resolving ocean. Here it is evaluated in terms of (1) the mean state and long‐term drift under preindustrial climate conditions, (2) the fidelity in simulating the historical warming, and (3) differences between coarse and eddy‐resolving ocean configurations. The results show that the realism of the new climate setup is overall within the range of existing models. In terms of oceanic temperatures, the historical warming signal is of smaller amplitude than the model drift in case of a relatively short spin‐up. However, it is argued that the strategy of “de‐drifting” climate runs after the short spin‐up, proposed by the HighResMIP protocol, allows one to isolate the warming signal. Moreover, the eddy‐permitting/resolving ocean setup shows notable improvements regarding the simulation of oceanic surface temperatures, in particular in the Southern Ocean.
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  • 20
    Publikationsdatum: 2020-01-27
    Beschreibung: The Central Asian Pamir Mountains (Pamirs) are a high‐altitude region sensitive to climatic change, with only few paleoclimatic records available. To examine the glacial‐interglacial hydrological changes in the region, we analyzed the geochemical parameters of a 31‐kyr record from Lake Karakul and performed a set of experiments with climate models to interpret the results. δD values of terrestrial biomarkers showed insolation‐driven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive δD shifts driven by changes in precipitation seasonality were observed at ca. 31–30, 28–26, and 17–14 kyr BP. Multiproxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer evaporation, triggered higher lake levels during those episodes, possibly synchronous to northern hemispheric rapid climate events. We conclude that seasonal changes in precipitation‐evaporation balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant.
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  • 21
    Publikationsdatum: 2020-06-03
    Beschreibung: - We provide the first isotopic geochronological constraints on brittle deformation in the NA by illite K-Ar dating of brittle fault rocks - A combined structural-geochronological approach constrains a Late Miocene-Early Pliocene regional compressive stress state
    Beschreibung: The Northern Apennines (NA) orogenic wedge formed during Oligocene-Miocene convergence and westward subduction of Adria beneath the European Plate. Extension ensued in the Mid-Late Miocene in response to Adria roll-back, causing opening of the back-arc Northern Tyrrhenian Sea. Whether extension continues uninterrupted since the Mid-Late Miocene or it was punctuated by short-lived compressional events, remains, however, uncertain. We used the K-Ar method to date a set of brittle-ductile and brittle deformation zones from the Island of Elba to contribute to this debate. We dated the low-angle Zuccale Fault (ZF), the Capo Norsi-Monte Arco Thrust (CN-MAT), and the Calanchiole Shear Zone (CSZ). The CN-MAT and CSZ are moderately west dipping, top-to-the-east thrusts in the immediate footwall of the ZF. The CSZ slipped 6.14 ± 0.64 Ma (〈0.1 μm fraction) and the CN-MAT 4.90 ± 0.27 Ma ago (〈0.4 μm fraction). The ZF, although cutting the two other faults, yielded an older age of 7.58 ± 0.11 Ma (〈0.1 μm fraction). The ZF gouge, however, contains an illitic detrital contaminant from the Paleozoic age flysch deformed in its hanging wall and the age thus is a maximum faulting age. Removal of ~1% of a 300-Ma-old contaminant brings the ZF faulting age to 〈4.90 Ma. Our results provide the first direct dating of brittle deformation in the Apennines, constraining Late Miocene-Early Pliocene regional compression. They call for a refinement of current NA geodynamic models in the framework of the Northern Tyrrhenian Sea extension.
    Beschreibung: Published
    Beschreibung: 3229–3243
    Beschreibung: 1T. Struttura della Terra
    Beschreibung: JCR Journal
    Schlagwort(e): K-Ar dating fault gouge ; Northern Apennines ; Elba Island ; Neogene geodynamics
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 22
    Publikationsdatum: 2019-03-06
    Beschreibung: On behalf of the authors and readers of Reviews of Geophysics, the American Geophysical Union, and the broader scientific community, the Editors wish to wholeheartedly thank those who reviewed the manuscripts for Reviews of Geophysics in 2017. The journal could not exist without your investment of time and effort, lending your expertise to ensure that the papers published in this journal meet the standards that the research community expects for it. We sincerely appreciate all that you do, and we are very grateful for your willingness and readiness to serve in this role.
    Beschreibung: Published
    Beschreibung: 566
    Beschreibung: 1VV. Altro
    Beschreibung: JCR Journal
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  • 23
    Publikationsdatum: 2019-09-12
    Beschreibung: Changes in water level are commonly reported in regions struck by a seismic event. The sign and amplitude of such changes depend on the relative position of measuring points with respect to the hypocenter, and on the poroelastic properties of the rock. We apply a porous media flow model (TOUGH2) to describe groundwater flow and water‐level changes associated with the first ML5.9 mainshock of the 2012 seismic sequence in Emilia (Italy). We represent the earthquake as an instantaneous pressure step, whose amplitude was inferred from the properties of the seismic source inverted from geodetic data. The results are consistent with the evolution recorded in both deep and shallow water wells in the area and suggest that our description of the seismic event is suitable to capture both timing and magnitude of water‐level changes. We draw some conclusions about the influence of material heterogeneity on the pore pressure evolution, and we show that to reproduce the observed maximum amplitude it is necessary to take into account compaction in the shallow layer.
    Beschreibung: Published
    Beschreibung: 452–463
    Beschreibung: 4T. Sismicità dell'Italia
    Beschreibung: JCR Journal
    Schlagwort(e): 2012 Emilia earthquake ; groundwaters ; isotropic stress ; permeability ; porosity ; water wells ; Solid Earth
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  • 24
    Publikationsdatum: 2019-10-28
    Beschreibung: On behalf of the authors and readers of Reviews of Geophysics, the American Geophysical Union (AGU), and the broader scientific community, the Editors wish to wholeheartedly thank those who reviewed the manuscripts for Reviews of Geophysics in 2018. Reviews of Geophysics is the top rated journal in Geophysics and Geochemistry and it could not exist without your investment of time and effort, lending your expertise to ensure that the papers published in this journal meet the standards that the research community expects for it. We sincerely appreciate the time spent reading and commenting on manuscripts, and we are very grateful for your willingness and readiness to serve in this role. Reviews of Geophysics published 20 review papers and an editorial in 2018, covering most of the AGU Section topics, and for this we were able to rely on the efforts of 85 dedicated reviewers from 20 countries. Many reviewers answered the call multiple times. Thank you again. We look forward to a 2019 of exciting advances in the field and communicating those advances to our community and to the broader public.
    Beschreibung: Published
    Beschreibung: 4
    Beschreibung: 5TM. Informazione ed editoria
    Beschreibung: JCR Journal
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  • 25
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    Wiley
    In:  EPIC3The Ocean Floor, The Ocean Floor, Wiley, pp. 147-163
    Publikationsdatum: 2016-03-17
    Repository-Name: EPIC Alfred Wegener Institut
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  • 26
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    Wiley
    In:  EPIC3Journal of Geophysical Research-Earth Surface, Wiley, ISSN: 0148-0227
    Publikationsdatum: 2019-04-03
    Beschreibung: Peat plateaus and palsas are characteristic morphologies of sporadic permafrost, and the transition from permafrost to permafrost‐free ground typically occurs on spatial scales of meters. They are particularly vulnerable to climate change and are currently degrading in Fennoscandia. Here we present a spatially distributed data set of ground surface temperatures for two peat plateau sites in northern Norway for the year 2015–2016. Based on these data and thermal modeling, we investigate how the snow depth and water balance modulate the climate signal in the ground. We find that mean annual ground surface temperatures are centered around 2 to 2.5 °C for stable permafrost locations and 3.5 to 4.5 °C for permafrost‐free locations. The surface freezing degree days are characterized by a noticeable threshold around 200 °C.day, with most permafrost‐free locations ranging below this value and most stable permafrost ones above it. Freezing degree day values are well correlated to the March snow cover, although some variability is observed and attributed to the ground moisture level. Indeed, a zero curtain effect is observed on temperature time series for saturated soils during winter, while drained peat plateaus show early freezing surface temperatures. Complementarily, modeling experiments allow identifying a drainage effect that can modify 1‐m ground temperatures by up to 2 °C between drained and water accumulating simulations for the same snow cover. This effect can set favorable or unfavorable conditions for permafrost stability under the same climate forcing.
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  • 27
    Publikationsdatum: 2019-05-21
    Repository-Name: EPIC Alfred Wegener Institut
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  • 28
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    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 124(2), pp. 858-869, ISSN: 0148-0227
    Publikationsdatum: 2019-02-25
    Beschreibung: We characterize the differences in the upward planetary‐scale wave propagation during observed weak polar vortex (WPV) events between heavy‐ and light‐sea‐ice years in the Barents‐Kara Sea based on a composite analysis for the period of 1979–2015. Upward wave propagation during WPV events in heavy‐ice years is dominated by the wavenumber 1 component. In contrast, WPV events occurring in light‐ice years are characterized by stronger wavenumber 2 propagation, which is caused by the tropospheric wavenumber 2 response to sea‐ice reduction in the Barents‐Kara Sea. The above observed features are supported by an Atmospheric General Circulation Model experiment. Thus, under present climate conditions, Arctic sea‐ice loss is a possible factor modulating the wave propagation during the WPV events. We also find that the WPV events in light‐ice years have stronger stratosphere‐troposphere coupling, followed by colder midlatitude surface conditions particularly over Eurasia.
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  • 29
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    Wiley
    In:  EPIC3Journal of Geophysical Research-Earth Surface, Wiley, 124, pp. 216-228, ISSN: 0148-0227
    Publikationsdatum: 2019-08-14
    Beschreibung: This study assesses the response on ice dynamics of Petermann Glacier, a major outlet glacier in northern Greenland, to the 2012 and a possible future calving event. So far Petermann Glacier has been believed to be dynamically stable as another large calving event in 2010 had no significant impact on flow velocity or grounding line retreat. By analyzing a time series of remotely sensed surface velocities, we find an average acceleration of 10% between winter 2011/2012 and winter 2016/2017. This increase in surface velocity is not linear but can be separated into two parts, starting in 2012 and 2016 respectively. By conducting modeling experiments, we show that the first speedup can be directly connected to the 2012 calving event, while the second speedup is not captured. However, on recent remote sensing imagery newly developing fractures are clearly visible ∼12 km upstream from the terminus, propagating from the eastern fjord wall to the center of the ice tongue, indicating a possible future calving event. By including these fracture zones as a new terminus position in the modeling domain, we are able to reproduce the second speedup, suggesting that surface velocities remain on the 2016/2017 level after the anticipated calving event. This indicates that, from a dynamical point of view, the terminus region has already detached from the main ice tongue.
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  • 30
    Publikationsdatum: 2019-11-25
    Beschreibung: The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community‐sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate data sets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive‐specific properties and distinguished reporting standards for new versus legacy data sets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate data sets. Since such goals are at odds with present practices, we discuss a transparent path toward implementing or revising these recommendations in the near future, using both bottom‐up and top‐down approaches.
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  • 31
    Publikationsdatum: 2019-09-10
    Beschreibung: Microalgae are capable of acclimating to dynamic light environments, as they have developed mechanisms to optimize light harvesting and photosynthetic electron transport. When absorption of light exceeds photosynthetic capacity, various physiological protective mechanisms prevent damage of the photosynthetic apparatus. Xanthophyll pigments provide one of the most important photoprotective mechanisms to dissipate the excess light energy and prevent photoinhibition. In this study, we coupled a mechanistic model for phytoplankton photoinhibition with the global biogeochemical model Regulated Ecosystem Model version 2. The assumption that photoinhibition is small in phytoplankton communities acclimated to ambient light allowed us to predict the photoprotective needs of phytoplankton. When comparing the predicted photoprotective needs to observations of pigment content determined by high‐performance liquid chromatography, our results showed that photoprotective response seems to be mediated in most parts of the ocean by a variable ratio of xanthophyll pigments to chlorophyll. The variability in the ratio appeared to be mainly driven by changes in phytoplankton community composition. Exceptions appeared at high latitudes where other energy dissipating mechanisms seem to play a role in photoprotection and both taxonomic changes and physiological acclimation determine community pigment signature. Understanding the variability of community pigment signature is crucial for modeling the coupling of light absorption to carbon fixation in the ocean. Insights about how much of this variability is attributable to changes in community composition may allow us to improve the match between remotely sensed optical data and the underlying phytoplankton community.
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  • 32
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 115(52), (2018): E12275-E12284. doi: 10.1073/pnas.1805243115.
    Beschreibung: Diatoms are prominent eukaryotic phytoplankton despite being limited by the micronutrient iron in vast expanses of the ocean. As iron inputs are often sporadic, diatoms have evolved mechanisms such as the ability to store iron that enable them to bloom when iron is resupplied and then persist when low iron levels are reinstated. Two iron storage mechanisms have been previously described: the protein ferritin and vacuolar storage. To investigate the ecological role of these mechanisms among diatoms, iron addition and removal incubations were conducted using natural phytoplankton communities from varying iron environments. We show that among the predominant diatoms, Pseudo-nitzschia were favored by iron removal and displayed unique ferritin expression consistent with a long-term storage function. Meanwhile, Chaetoceros and Thalassiosira gene expression aligned with vacuolar storage mechanisms. Pseudo-nitzschia also showed exceptionally high iron storage under steady-state high and low iron conditions, as well as following iron resupply to iron-limited cells. We propose that bloom-forming diatoms use different iron storage mechanisms and that ferritin utilization may provide an advantage in areas of prolonged iron limitation with pulsed iron inputs. As iron distributions and availability change, this speculated ferritin-linked advantage may result in shifts in diatom community composition that can alter marine ecosystems and biogeochemical cycles.
    Beschreibung: We thank the captain and crew of the R/V Melville and the CCGS J. P. Tully as well as the participants of the IRNBRU (MV1405) cruise for the California-based data, particularly K. Ellis [University of North Carolina (UNC)], T. Coale (University of California, San Diego), F. Kuzminov (Rutgers), H. McNair [University of California, Santa Barbara (UCSB)], and J. Jones (UCSB). W. Burns (UNC), S. Haines (UNC), and S. Bargu (Louisiana State University) assisted with sample processing and analysis. This work was funded by the National Science Foundation Grants OCE-1334935 (to A.M.), OCE-1334632 (to B.S.T.), OCE-1333929 (to K.T.), OCE-1334387 (to M.A.B.), OCE-1259776 (to K.W.B), and DGE-1650116 (Graduate Research Fellowship to R.H.L).
    Beschreibung: 2019-06-11
    Schlagwort(e): phytoplankton ; iron limitation ; Pseudo-nitzschia ; ferritin ; metatranscriptomics
    Repository-Name: Woods Hole Open Access Server
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  • 33
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    Wiley
    In:  EPIC3Journal of Geophysical Research-Solid Earth, Wiley, 124, pp. 7699-7724, ISSN: 0148-0227
    Publikationsdatum: 2019-10-10
    Beschreibung: Understanding the patterns and characteristics of sedimentary deposits on the conjugate Australian‐Antarctic margins is critical to reveal the Cretaceous‐Cenozoic tectonic, oceanographic, and climatic conditions in the basin. However, unraveling its evolution has remained difficult due to the different seismic stratigraphic interpretations on each margin and sparse drill sites. Here, for the first time, we collate all available seismic reflection profiles on both margins and use newly available offshore drilling data to develop a consistent seismic stratigraphic framework across the Australian‐Antarctic basins. We find sedimentation patterns similar in structure and thickness, prior to the onset of Antarctic glaciation, enabling the basinwide correlation of four major sedimentary units and their depositional history. We interpret that during the warm and humid Late Cretaceous (~83–65 Ma), large onshore river systems on both Australia and Antarctica resulted in deltaic sediment deposition offshore. We interpret that the onset of clockwise bottom currents during the early Paleogene (~58–48 Ma) formed prominent sediment drift deposits along both continental rises. We suggest that these currents strengthened and progressed farther east through the Eocene. Coevally, global cooling (〈48 Ma) and progressive aridification led to a large‐scale decrease in sediment input from both continents. Two major Eocene hiatuses recovered by the Integrated Ocean Discovery Program site U1356A at the Antarctic continental slope likely formed during this preglacial phase of low sedimentation and strong bottom currents. Our results can be used to constrain future paleo‐oceanographic modeling of this region and aid the understanding of the oceanographic changes accompanying the transition from a greenhouse to icehouse world.
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  • 34
    Publikationsdatum: 2019-09-18
    Beschreibung: Increasing sea surface temperatures (SST) and blooms of lipid‐poor, filamentous cyanobacteria can change mesozooplankton metabolism and foraging strategies in marine systems. Lipid shortage and imbalanced diet may challenge the build‐up of energy pools of lipids and proteins, and access to essential fatty acids (FAs) and amino acids (AAs) by copepods. The impact of cyanobacterial blooms on individual energy pools was assessed for key species temperate Temora longicornis and boreal Pseudo‐/Paracalanus spp. that dominated field mesozooplankton communities isolated by sea‐sonal stratification in the central Baltic Sea during the hot and the cold summer. We looked at (a) total lipid and protein levels, (b) FA trophic markers and AA composition, and (c) compound‐specific stable carbon isotopes (δ13C) in bulk mesozooplankton and in a subset of parameters in particulate organic matter. Despite lipid‐poor cyanobacterial blooms, the key species were largely able to cover both energy pools, yet a tendency of lipid reduction was observed in surface animals. Omni‐ and car‐nivory feeding modes, FA trophic makers, and δ13C patterns in essential compounds emphasized that cyanobacterial FAs and AAs have been incorporated into meso‐zooplankton mainly via feeding on mixo‐ and heterotrophic (dino‐) flagellates and detrital complexes during summer. Foraging for essential highly unsaturated FAs from (dino‐) flagellates may have caused night migration of Pseudo‐/Paracalanus spp. from the deep subhalocline waters into the upper waters. Only in the hot summer (SST〉19.0°C) was T. longicornis submerged in the colder subthermocline water (~4°C). Thus, the continuous warming trend and simultaneous feeding can eventually lead to competition on the preferred diet by key copepod species below the thermocline in stratified systems. A comparison of δ13C patterns of essential AAs in surface meso‐zooplankton across sub‐basins of low and high cyanobacterial biomasses revealed the potential of δ13C‐AA isoscapes for studies of commercial fish feeding trails across the Baltic Sea food webs.
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  • 35
    Publikationsdatum: 2019-10-25
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  • 36
    Publikationsdatum: 2020-09-01
    Beschreibung: In the Northern Patagonian gulfs of Argentina (Golfo Nuevo and Golfo San José), blooms of toxigenic microalgae and the detection of their associated phycotoxins are recurrent phenomena. The present study evaluated the transfer of phycotoxins from toxigenic microalgae to mesozooplankton in Golfo Nuevo and Golfo San José throughout an annual cycle (December 2014–2015 and January 2015–2016, respectively). In addition, solid-phase adsorption toxin tracking (SPATT) samplers were deployed for the first time in these gulfs, to estimate the occurrence of phycotoxins in the seawater between the phytoplankton samplings. Domoic acid was present throughout the annual cycle in SPATT samplers, whereas no paralytic shellfish poisoning toxins were detected. Ten toxigenic species were identified: Alexandrium catenella, Dinophysis acuminata, Dinophysis acuta, Dinophysis tripos, Dinophysis caudata, Prorocentrum lima, Pseudo-nitzschia australis, Pseudo-nitzschia calliantha, Pseudo-nitzschia fraudulenta, and Pseudo-nitzschia pungens. Lipophilic and hydrophilic toxins were detected in phytoplankton and mesozooplankton from both gulfs. Pseudo-nitzschia spp. were the toxigenic species most frequent in these gulfs. Consequently, domoic acid was the phycotoxin most abundantly detected and transferred to upper trophic levels. Spirolides were detected in phytoplankton and mesozooplankton for the first time in the study area. Likewise, dinophysistoxins were found in mesozooplankton from both gulfs, and this is the first report of the presence of these phycotoxins in zooplankton from the Argentine Sea. The dominance of calanoid copepods indicates that they were the primary vector of phycotoxins in the pelagic trophic web.
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  • 37
    Publikationsdatum: 2019-10-25
    Beschreibung: Climate warming in regions of ice‐rich permafrost can result in widespread thermokarst development, which reconfigures the landscape and damages infrastructure. We present multisite time series observations which couple ground temperature measurements with thermokarst development in a region of very cold permafrost. In the Canadian High Arctic between 2003 and 2016, a series of anomalously warm summers caused mean thawing indices to be 150–240% above the 1979–2000 normal resulting in up to 90 cm of subsidence over the 12‐year observation period. Our data illustrate that despite low mean annual ground temperatures, very cold permafrost (〈−10 °C) with massive ground ice close to the surface is highly vulnerable to rapid permafrost degradation and thermokarst development. We suggest that this is due to little thermal buffering from soil organic layers and near‐surface vegetation, and the presence of near‐surface ground ice. Observed maximum thaw depths at our sites are already exceeding those projected to occur by 2090 under representative concentration pathway version 4.5.
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  • 38
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, (46), pp. 9474-9482, ISSN: 0094-8276
    Publikationsdatum: 2019-10-02
    Beschreibung: In the South Atlantic, a reorganization of the Mid‐Atlantic Ridge began before anomaly C34n (83.6 Ma) and ended before anomaly C30n (66.4 Ma), complicating tectonics of Rio Grande Rise and older Walvis Ridge (WR), which formed together at the Mid‐Atlantic Ridge. This reorganization is poorly understood because magnetic anomalies C30n‐C34n are poorly defined near WR. We interpreted these anomalies along westernWRto improve knowledge of Rio Grande Rise‐WRtectonic development. Anomaly trends indicate that Valdivia Bank has an E‐W age progression, perpendicular to that predicted by hot spot models. Anomaly spacing and width is irregular and anomalous near WR, implying a series of ridge jumps and possibly a microplate between anomalies C34n and C32n. Eastward ridge jumps transferred microplate lithosphere to the South American plate. This study shows that Late Cretaceous tectonic evolution of the Rio Grande Rise‐WRlarge igneous provinces was more complex than previously understood.
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  • 39
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46(14), pp. 8289-8299, ISSN: 0094-8276
    Publikationsdatum: 2019-10-07
    Beschreibung: The last interglacial (LIG; Marine Isotope Substage 5e, ~127–117 ka) experienced globally warmer than modern temperatures; however, profound differences in regional climate occurred that are relevant to the assessment of future climate change scenarios. Tropical Atlantic sea surface temperature (SST) and hydrology are intrinsic to the spatiotemporal evolution of past and future climate. We present eight monthly resolved coral Sr/Ca and δ18O records (130–118 ka) to reconstruct mean western tropical Atlantic SST and seawater δ18O changes during the LIG. Cooler and fresher than modern surface waters are indicated for the middle of the LIG at ~126 ka. This was followed by a rapid transition to modern‐like SSTs and salinities that characterized the remaining part of the LIG. Our results, which account for differences found among corals, proxies, and SST calibration uncertainties, agree with western tropical Atlantic sediment records. Together, they suggest that an oceanic regime existed that differed from today.
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  • 40
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    Wiley
    In:  EPIC3Geochemistry Geophysics Geosystems, Wiley, 20, ISSN: 1525-2027
    Publikationsdatum: 2019-12-12
    Beschreibung: Ultraslow spreading ridges are poorly understood plate boundaries consisting of magmatic and amagmatic segments that expose mostly mantle peridotite and only traces of basalt and gabbro. The slowest part of the global spreading system is represented by the eastern Gakkel Ridge in the Central Arctic Ocean, where crustal accretion is characterized by extreme focusing of melt to discrete magmatic centers. Close to its eastern tip lies the unusual 5,310 m deep Gakkel Rift Deep (GRD) with limited sediment infill, which is in strong contrast to the broader sediment-filled rift valleys to the east and west. Here, we report an 40Ar/39Ar age of 3.65±0.01 Ma for a pillow basalt from a seamount located on the rim the GRD confirming ultraslow spreading rates of ~7 mm/yr close to the Laptev Sea as suggested from aeromagnetic data. Its geochemistry points to an alkaline lava, attributed to partial melting of a source that underwent prior geochemical enrichment. We note that the GRD extracts compositionally similar melts as the sparsely magmatic zone further west but at much slower spreading velocities of only ~6-7 mm/yr, indicating the widespread occurrence of similarly fertile mantle in the High Arctic. This enriched source differs from sub-continental lithospheric mantle that influences magmatism along the Western Volcanic Zone (Goldstein et al. 2008) and is similar to metasomatized mantle - shown to influence melt genesis along the Eastern Volcanic Zone.
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  • 41
    Publikationsdatum: 2019-11-18
    Repository-Name: EPIC Alfred Wegener Institut
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  • 42
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46, ISSN: 0094-8276
    Publikationsdatum: 2019-09-16
    Beschreibung: Coupled subseasonal forecast systems with dynamical sea ice have the potential of providing important predictive information in polar regions. Here, we evaluate the ability of operational ensemble prediction systems to predict the location of the sea ice edge in Antarctica. Compared to the Arctic, Antarctica shows on average a 30% lower skill, with only one system remaining more skillful than aclimatological benchmark up to ∼30 days ahead. Skill tends to be highest in the west Antarctic sectorduring the early freezing season. Most of the systems tend to overestimate the sea ice edge extent and fail to capture the onset of the melting season. All the forecast systems exhibit large initial errors. We conclude that subseasonal sea ice redictions could provide marginal support for decision-making only in selected seasons and regions of the Southern Ocean. However, major progress is possible through investments in model development, forecast initialization and calibration.
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  • 43
    Publikationsdatum: 2021-11-09
    Beschreibung: The Neotethyan oceanic Diamante-Terranova unit (DIATU; southern Apennines–Calabria–Peloritani Terrane system) includes basic rocks that during the Cenozoicwere subducted and metamorphosed to lawsonite-blueschist facies conditions.Petrological and structural observations (both at the meso- and micro-scale) showthat lawsonite growth was continuous during three distinctive ductile deformationstages (D1–D3).....
    Beschreibung: Published
    Beschreibung: 691-714
    Beschreibung: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Beschreibung: JCR Journal
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 44
    Publikationsdatum: 2022-10-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Proceedings of the National Academy of Sciences.of the United States of America 116(36), (2019): 17666-17672. doi:10.1073/pnas.1907871116.
    Beschreibung: The conditions of methane (CH4) formation in olivine-hosted secondary fluid inclusions and their prevalence in peridotite and gabbroic rocks from a wide range of geological settings were assessed using confocal Raman spectroscopy, optical and scanning electron microscopy, electron microprobe analysis, and thermodynamic modeling. Detailed examination of 160 samples from ultraslow- to fast-spreading midocean ridges, subduction zones, and ophiolites revealed that hydrogen (H2) and CH4 formation linked to serpentinization within olivine-hosted secondary fluid inclusions is a widespread process. Fluid inclusion contents are dominated by serpentine, brucite, and magnetite, as well as CH4(g) and H2(g) in varying proportions, consistent with serpentinization under strongly reducing, closed-system conditions. Thermodynamic constraints indicate that aqueous fluids entering the upper mantle or lower oceanic crust are trapped in olivine as secondary fluid inclusions at temperatures higher than ∼400 °C. When temperatures decrease below ∼340 °C, serpentinization of olivine lining the walls of the fluid inclusions leads to a near-quantitative consumption of trapped liquid H2O. The generation of molecular H2 through precipitation of Fe(III)-rich daughter minerals results in conditions that are conducive to the reduction of inorganic carbon and the formation of CH4. Once formed, CH4(g) and H2(g) can be stored over geological timescales until extracted by dissolution or fracturing of the olivine host. Fluid inclusions represent a widespread and significant source of abiotic CH4 and H2 in submarine and subaerial vent systems on Earth, and possibly elsewhere in the solar system.
    Beschreibung: We are indebted to J. Eckert for his support with FE-EMPA; to K. Aquinho and E. Codillo for providing samples from Zambales; to K. Aquinho for Raman analysis of some of the samples from Zambales and Mt. Dent; to H. Dick for providing access to his thin section collection; to the curators of the IODP core repositories for providing access to Ocean Drilling Program (ODP) and Integrated Ocean Drilling Program (IODP) samples; and to the captains and crews of the many cruises without whom the collection of these samples would not have been possible. Reviews by Peter Kelemen and an anonymous referee greatly improved this manuscript. This study is supported with funds provided by the National Science Foundation (NSF-OCE Award 1634032 to F.K. and J.S.S.).
    Beschreibung: 2020-02-19
    Schlagwort(e): Abiotic methane ; Fluid inclusions ; Serpentinization ; Methane seeps ; Carbon cycling
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  • 45
    Publikationsdatum: 2022-10-26
    Beschreibung: Author Posting. © The Author(s), 2019. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 116(20), (2019):9925-9930, doi:10.1073/pnas.1818349116.
    Beschreibung: Microbial capacity to metabolize arsenic is ancient, arising in response to its pervasive presence in the environment, which was largely in the form of As(III) in the early anoxic ocean. Many biological arsenic transformations are aimed at mitigating toxicity; however, some microorganisms can respire compounds of this redox-sensitive element to reap energetic gains. In several modern anoxic marine systems concentrations of As(V) are higher relative to As(III) than what would be expected from the thermodynamic equilibrium, but the mechanism for this discrepancy has remained unknown. Here we present evidence of a complete respiratory arsenic cycle, consisting of dissimilatory As(V) reduction and chemoautotrophic As(III) oxidation, in the pelagic ocean. We identified the presence of genes encoding both subunits of the respiratory arsenite oxidase AioA and the dissimilatory arsenate reductase ArrA in the Eastern Tropical North Pacific (ETNP) oxygen-deficient zone (ODZ). The presence of the dissimilatory arsenate reductase gene arrA was enriched on large particles (〉30 um), similar to the forward bacterial dsrA gene of sulfate-reducing bacteria, which is involved in the cryptic cycling of sulfur in ODZs. Arsenic respiratory genes were expressed in metatranscriptomic libraries from the ETNP and the Eastern Tropical South Pacific (ETSP) ODZ, indicating arsenotrophy is a metabolic pathway actively utilized in anoxic marine water columns. Together these results suggest arsenic-based metabolisms support organic matter production and impact nitrogen biogeochemical cycling in modern oceans. In early anoxic oceans, especially during periods of high marine arsenic concentrations, they may have played a much larger role.
    Beschreibung: We thank John Baross and Rika Anderson for helpful discussions and feedback on this project. We also thank the chief scientists of the research cruise, Al Devol and Bess Ward, as well as the captain and crew of the R/V Thomas G. Thompson. This work was supported through a NASA Earth and Space Sciences Graduate Research Fellowship to J.K.S. and National Science Foundation Grant OCE-1138368 (to G.R.).
    Beschreibung: 2019-10-29
    Schlagwort(e): Oxygen deficient zones ; Arsenic ; Chemoautotrophy ; Dissimilatory arsenate reduction ; Marine metagenome
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  • 46
    Publikationsdatum: 2022-10-26
    Beschreibung: Author Posting. © National Academy of Sciences, 2019. This article is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 116 (24), (2019):11646-11651, doi:10.1073/pnas.1900371116.
    Beschreibung: Measurements show large decadal variability in the rate of CO2 accumulation in the atmosphere that is not driven by CO2 emissions. The decade of the 1990s experienced enhanced carbon accumulation in the atmosphere relative to emissions, while in the 2000s, the atmospheric growth rate slowed, even though emissions grew rapidly. These variations are driven by natural sources and sinks of CO2 due to the ocean and the terrestrial biosphere. In this study, we compare three independent methods for estimating oceanic CO2 uptake and find that the ocean carbon sink could be responsible for up to 40% of the observed decadal variability in atmospheric CO2 accumulation. Data-based estimates of the ocean carbon sink from pCO2 mapping methods and decadal ocean inverse models generally agree on the magnitude and sign of decadal variability in the ocean CO2 sink at both global and regional scales. Simulations with ocean biogeochemical models confirm that climate variability drove the observed decadal trends in ocean CO2 uptake, but also demonstrate that the sensitivity of ocean CO2 uptake to climate variability may be too weak in models. Furthermore, all estimates point toward coherent decadal variability in the oceanic and terrestrial CO2 sinks, and this variability is not well-matched by current global vegetation models. Reconciling these differences will help to constrain the sensitivity of oceanic and terrestrial CO2 uptake to climate variability and lead to improved climate projections and decadal climate predictions.
    Beschreibung: We thank Rebecca Wright and Erik Buitenhuis at University of East Anglia, Norwich, for providing updated runs from the NEMO-PlankTOM5 model. T.D. was supported by NSF Grant OCE-1658392. C.L.Q. thanks the UK Natural Environment Research Council for supporting the SONATA Project (Grant NE/P021417/1). P.L. was supported by the Max Planck Society for the Advancement of Science. J.H. was supported under Helmholtz Young Investigator Group Marine Carbon and Ecosystem Feedbacks in the Earth System (MarESys) Grant VH-NG-1301. S.B. and R.S. were supported by the H2020 project CRESCENDO “Coordinated Research in Earth Systems and Climate: Experiments, Knowledge, Dissemination and Outreach,” which received funding from the European Union’s Horizon 2020 research and innovation program under Grant No 641816. SOCAT is an international effort, endorsed by the International Ocean Carbon Coordination Project, the Surface Ocean-Lower Atmosphere Study, and the Integrated Marine Biosphere Research program, to deliver a uniformly quality-controlled surface ocean CO2 database. The many researchers and funding agencies responsible for the collection of data and quality control are thanked for their contributions to SOCAT.
    Beschreibung: 2019-11-28
    Schlagwort(e): Carbon dioxide ; Ocean carbon sink ; Terrestrial carbon sink ; Climate variability ; Carbon budget
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  • 47
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Proceedings of the National Academy of Sciences.of the United States of America 116(36), (2019): 17934-17942, doi:10.1073/pnas.1910121116.
    Beschreibung: Plastid endosymbiosis has been a major force in the evolution of eukaryotic cellular complexity, but how endosymbionts are integrated is still poorly understood at a mechanistic level. Dinoflagellates, an ecologically important protist lineage, represent a unique model to study this process because dinoflagellate plastids have repeatedly been reduced, lost, and replaced by new plastids, leading to a spectrum of ages and integration levels. Here we describe deep-transcriptomic analyses of the Antarctic Ross Sea dinoflagellate (RSD), which harbors long-term but temporary kleptoplasts stolen from haptophyte prey, and is closely related to dinoflagellates with fully integrated plastids derived from different haptophytes. In some members of this lineage, called the Kareniaceae, their tertiary haptophyte plastids have crossed a tipping point to stable integration, but RSD has not, and may therefore reveal the order of events leading up to endosymbiotic integration. We show that RSD has retained its ancestral secondary plastid and has partitioned functions between this plastid and the kleptoplast. It has also obtained genes for kleptoplast-targeted proteins via horizontal gene transfer (HGT) that are not derived from the kleptoplast lineage. Importantly, many of these HGTs are also found in the related species with fully integrated plastids, which provides direct evidence that genetic integration preceded organelle fixation. Finally, we find that expression of kleptoplast-targeted genes is unaffected by environmental parameters, unlike prey-encoded homologs, suggesting that kleptoplast-targeted HGTs have adapted to posttranscriptional regulation mechanisms of the host.
    Beschreibung: We are grateful to Martin Kolisko and Fabien Burki for helpful discussion about and comments on the phylogenetic analysis; and Filip Husnik and Vittorio Boscaro for valuable comments on the manuscript. This work was supported by a grant from the National Science Foundation to R.J.G. and P.J.K. (PLR-1341362) and from the Natural Sciences and Engineering Research Council of Canada to P.J.K. (RGPIN-2014-03994).
    Beschreibung: 2020-02-19
    Schlagwort(e): plastid endosymbiosis ; kleptoplasty ; dinoflagellates ; plastid integration
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  • 48
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in [citation], doi:[doi]. Johnson, W. M., Longnecker, K., Soule, M. C. K., Arnold, W. A., Bhatia, M. P., Hallam, S. J., Van Mooy, B. A. S., & Kujawinski, E. B. Metabolite composition of sinking particles differs from surface suspended particles across a latitudinal transect in the South Atlantic. Limnology and Oceanography, (2019), doi:10.1002/lno.11255.
    Beschreibung: Marine sinking particles transport carbon from the surface and bury it in deep‐sea sediments, where it can be sequestered on geologic time scales. The combination of the surface ocean food web that produces these particles and the particle‐associated microbial community that degrades them creates a complex set of variables that control organic matter cycling. We use targeted metabolomics to characterize a suite of small biomolecules, or metabolites, in sinking particles and compare their metabolite composition to that of the suspended particles in the euphotic zone from which they are likely derived. These samples were collected in the South Atlantic subtropical gyre, as well as in the equatorial Atlantic region and the Amazon River plume. The composition of targeted metabolites in the sinking particles was relatively similar throughout the transect, despite the distinct oceanic regions in which they were generated. Metabolites possibly derived from the degradation of nucleic acids and lipids, such as xanthine and glycine betaine, were an increased mole fraction of the targeted metabolites in the sinking particles relative to surface suspended particles, while algal‐derived metabolites like the osmolyte dimethylsulfoniopropionate were a smaller fraction of the observed metabolites on the sinking particles. These compositional changes are shaped both by the removal of metabolites associated with detritus delivered from the surface ocean and by production of metabolites by the sinking particle‐associated microbial communities. Furthermore, they provide a basis for examining the types and quantities of metabolites that may be delivered to the deep sea by sinking particles.
    Beschreibung: The authors would like to thank the captain and crew of the R/V Knorr and R/V Atlantic Explorer, as well as Justin Ossolinski, Catherine Carmichael, and Sean Sylva for helping to make this data set possible. Special thanks to Colleen Durkin for sharing her data and providing feedback on the manuscript. Funding for this work came from the National Science Foundation (NSF Grant OCE‐1154320 to EBK and KL) and a WHOI Ocean Ventures Fund award to WMJ. The instruments in the WHOI FT‐MS Facility were purchased with support from the Gordon & Betty Moore Foundation and NSF. Support for WMJ was provided by a National Defense Science and Engineering Fellowship. Sequencing was performed under the auspices of the US Department of Energy (DOE) JGI Community Science Program (CSP) project (CSP 1685) supported by the Office of Science of US DOE Contract DE‐AC02‐ 05CH11231. Additional work related to sample collection and processing was supported by the G. Unger Vetlesen and Ambrose Monell Foundations, the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Institute for Advanced Study (CIFAR), and the Canada Foundation for Innovation through grants awarded to SJH. MPB was supported by a CIFAR Global Scholarship and NSERC postdoctoral fellowship.
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  • 49
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Long, M. H., Sutherland, K., Wankel, S. D., Burdige, D. J., & Zimmerman, R. C. Ebullition of oxygen from seagrasses under supersaturated conditions. Limnology and Oceanography, (2019), doi:10.1002/lno.11299.
    Beschreibung: Gas ebullition from aquatic systems to the atmosphere represents a potentially important fraction of primary production that goes unquantified by measurements of dissolved gas concentrations. Although gas ebullition from photosynthetic surfaces has often been observed, it is rarely quantified. The resulting underestimation of photosynthetic activity may significantly bias the determination of ecosystem trophic status and estimated rates of biogeochemical cycling from in situ measures of dissolved oxygen. Here, we quantified gas ebullition rates in Zostera marina meadows in Virginia, U.S.A. using simple funnel traps and analyzed the oxygen concentration and isotopic composition of the captured gas. Maximum hourly rates of oxygen ebullition (3.0 mmol oxygen m−2 h−1) were observed during the coincidence of high irradiance and low tides, particularly in the afternoon when oxygen and temperature maxima occurred. The daily ebullition fluxes (up to 11 mmol oxygen m−2 d−1) were roughly equivalent to net primary production rates determined from dissolved oxygen measurements indicating that bubble ebullition can represent a major component of primary production that is not commonly included in ecosystem‐scale estimates. Oxygen content comprised 20–40% of the captured bubble gas volume and correlated negatively with its δ18O values, consistent with a predominance of mixing between the higher δ18O of atmospheric oxygen in equilibrium with seawater and the lower δ18O of oxygen derived from photosynthesis. Thus, future studies interested in the metabolism of highly productive, shallow water ecosystems, and particularly those measuring in situ oxygen flux, should not ignore the bubble formation and ebullition processes described here.
    Beschreibung: Two anonymous reviewers provided thoughtful contributions that improved this manuscript. We thank Miraflor Santos, Victoria Hill, David Ruble, Jeremy Bleakney, and Brian Collister for assistance in the field and the staff of the Anheuser‐Busch Coastal Research Center for logistical support. This work was supported by NSF OCE grants 1633951 (to MHL) and 1635403 (to RCZ and DJB), NASA Fellowship NESSF NNX15AR62H (to KS), and a fellowship from the Hansewissenschaftskolleg (Institute for Advanced Studies; to SDW).
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  • 50
    Publikationsdatum: 2022-10-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Diaz, J. M., Plummer, S., Hansel, C. M., Andeer, P. F., Saito, M. A., & McIlvin, M. R. NADPH-dependent extracellular superoxide production is vital to photophysiology in the marine diatom Thalassiosira oceanica. Proceedings of the National Academy of Sciences of the United States of America, 116 (33), (2019): 16448-16453, doi: 10.1073/pnas.1821233116.
    Beschreibung: Reactive oxygen species (ROS) like superoxide drive rapid transformations of carbon and metals in aquatic systems and play dynamic roles in biological health, signaling, and defense across a diversity of cell types. In phytoplankton, however, the ecophysiological role(s) of extracellular superoxide production has remained elusive. Here, the mechanism and function of extracellular superoxide production by the marine diatom Thalassiosira oceanica are described. Extracellular superoxide production in T. oceanica exudates was coupled to the oxidation of NADPH. A putative NADPH-oxidizing flavoenzyme with predicted transmembrane domains and high sequence similarity to glutathione reductase (GR) was implicated in this process. GR was also linked to extracellular superoxide production by whole cells via quenching by the flavoenzyme inhibitor diphenylene iodonium (DPI) and oxidized glutathione, the preferred electron acceptor of GR. Extracellular superoxide production followed a typical photosynthesis-irradiance curve and increased by 30% above the saturation irradiance of photosynthesis, while DPI significantly impaired the efficiency of photosystem II under a wide range of light levels. Together, these results suggest that extracellular superoxide production is a byproduct of a transplasma membrane electron transport system that serves to balance the cellular redox state through the recycling of photosynthetic NADPH. This photoprotective function may be widespread, consistent with the presence of putative homologs to T. oceanica GR in other representative marine phytoplankton and ocean metagenomes. Given predicted climate-driven shifts in global surface ocean light regimes and phytoplankton community-level photoacclimation, these results provide implications for future ocean redox balance, ecological functioning, and coupled biogeochemical transformations of carbon and metals.
    Beschreibung: This work was supported by a postdoctoral fellowship from the Ford Foundation (to J.M.D.), the National Science Foundation (NSF) under grants OCE 1225801 (to J.M.D.) and OCE 1246174 (to C.M.H.), a Junior Faculty Seed Grant from the University of Georgia Research Foundation (to J.M.D.), and a National Science Foundation Graduate Research Fellowship (to S.P.). The FIRe was purchased through a NSF equipment improvement grant (1624593).The authors thank Melissa Soule for assistance with LC/MS/MS analysis of peptide samples.
    Schlagwort(e): Reactive oxygen species ; Photosynthesis ; Oxidative stress ; Biogeochemistry
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  • 51
    Publikationsdatum: 2022-10-20
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Baumgartner, M. F., Bonnell, J., Van Parijs, S. M., Corkeron, P. J., Hotchkin, C., Ball, K., Pelletier, L., Partan, J., Peters, D., Kemp, J., Pietro, J., Newhall, K., Stokes, A., Cole, T. V. N., Quintana, E., & Kraus, S. D. Persistent near real-time passive acoustic monitoring for baleen whales from a moored buoy: System description and evaluation. Methods in Ecology and Evolution, 10(9), (2019): 1476-1489, doi: 10.1111/2041-210X.13244.
    Beschreibung: 1. Managing interactions between human activities and marine mammals often relies on an understanding of the real‐time distribution or occurrence of animals. Visual surveys typically cannot provide persistent monitoring because of expense and weather limitations, and while passive acoustic recorders can monitor continuously, the data they collect are often not accessible until the recorder is recovered. 2. We have developed a moored passive acoustic monitoring system that provides near real‐time occurrence estimates for humpback, sei, fin and North Atlantic right whales from a single site for a year, and makes those occurrence estimates available via a publicly accessible website, email and text messages, a smartphone/tablet app and the U.S. Coast Guard's maritime domain awareness software. We evaluated this system using a buoy deployed off the coast of Massachusetts during 2015–2016 and redeployed again during 2016–2017. Near real‐time estimates of whale occurrence were compared to simultaneously collected archived audio as well as whale sightings collected near the buoy by aerial surveys. 3. False detection rates for right, humpback and sei whales were 0% and nearly 0% for fin whales, whereas missed detection rates at daily time scales were modest (12%–42%). Missed detections were significantly associated with low calling rates for all species. We observed strong associations between right whale visual sightings and near real‐time acoustic detections over a monitoring range 30–40 km and temporal scales of 24–48 hr, suggesting that silent animals were not especially problematic for estimating occurrence of right whales in the study area. There was no association between acoustic detections and visual sightings of humpback whales. 4. The moored buoy has been used to reduce the risk of ship strikes for right whales in a U.S. Coast Guard gunnery range, and can be applied to other mitigation applications.
    Beschreibung: We thank Annamaria Izzi, Danielle Cholewiak and Genevieve Davis of the NOAA NEFSC for assistance in developing the analyst protocol. We are grateful to the NOAA NEFSC aerial survey observers (Leah Crowe, Pete Duley, Jen Gatzke, Allison Henry, Christin Khan and Karen Vale) and the NEAq aerial survey observers (Angela Bostwick, Marianna Hagbloom and Paul Nagelkirk). Danielle Cholewiak and three anonymous reviewers provided constructive criticism on earlier drafts of the manuscript. Funding for this project was provided by the NOAA NEFSC, NOAA Advanced Sampling Technology Work Group, Environmental Security Technology Certification Program of the U.S. Department of Defense, the U.S. Navy's Living Marine Resources Program, Massachusetts Clean Energy Center and the Bureau of Ocean Energy Management. Funding from NOAA was facilitated by the Cooperative Institute for the North Atlantic Region (CINAR) under Cooperative Agreement NA14OAR4320158.
    Schlagwort(e): Acoustics ; Autonomous ; Buoy ; Conservation ; Mitigation ; Real‐time ; Ship strikes ; Whale
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  • 52
    Publikationsdatum: 2022-10-26
    Beschreibung: Author Posting. © National Academy of Sciences, 2019. This article is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 116(27), (2019): 13233-13238, doi: 10.1073/pnas.1904087116.
    Beschreibung: The overturning circulation of the global ocean is critically shaped by deep-ocean mixing, which transforms cold waters sinking at high latitudes into warmer, shallower waters. The effectiveness of mixing in driving this transformation is jointly set by two factors: the intensity of turbulence near topography and the rate at which well-mixed boundary waters are exchanged with the stratified ocean interior. Here, we use innovative observations of a major branch of the overturning circulation—an abyssal boundary current in the Southern Ocean—to identify a previously undocumented mixing mechanism, by which deep-ocean waters are efficiently laundered through intensified near-boundary turbulence and boundary–interior exchange. The linchpin of the mechanism is the generation of submesoscale dynamical instabilities by the flow of deep-ocean waters along a steep topographic boundary. As the conditions conducive to this mode of mixing are common to many abyssal boundary currents, our findings highlight an imperative for its representation in models of oceanic overturning.
    Beschreibung: The DynOPO project is supported by the UK Natural Environment Research Council (grants NE/K013181/1 and NE/K012843/1) and the US National Science Foundation (grants OCE-1536453 and OCE-1536779). A.C.N.G. acknowledges the support of the Royal Society and the Wolfson Foundation. S.L. acknowledges the support of award NA14OAR4320106 from the National Oceanic and Atmospheric Administration, US Department of Commerce. The statements, findings, conclusions, and recommendations are those of the authors, and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration, or the US Department of Commerce. We are grateful to the scientific party, crew, and technicians on the RRS James Clark Ross for their hard work during data collection.
    Beschreibung: 2019-12-18
    Schlagwort(e): Ocean mixing ; Overturning circulation ; Submesoscale instabilities ; Turbulence
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  • 53
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    Wiley
    In:  EPIC3Journal of Geophysical Research-Earth Surface, Wiley, 124(4), pp. 920-937, ISSN: 0148-0227
    Publikationsdatum: 2022-08-12
    Beschreibung: Thawing of subsea permafrost can impact offshore infrastructure, affect coastal erosion, and release permafrost organic matter. Thawing is usually modeled as the result of heat transfer, although salt diffusion may play an important role in marine settings. To better quantify nearshore subsea permafrost thawing, we applied the CryoGRID2 heat diffusion model and coupled it to a salt diffusion model. We simulated coastline retreat and subsea permafrost evolution as it develops through successive stages of a thawing sequence at the Bykovsky Peninsula, Siberia. Sensitivity analyses for seawater salinity were performed to compare the results for the Bykovsky Peninsula with those of typical Arctic seawater. For the Bykovsky Peninsula, the modeled ice‐bearing permafrost table (IBPT) for ice‐rich sand and an erosion rate of 0.25 m/year was 16.7 m below the seabed 350 m offshore. The model outputs were compared to the IBPT depth estimated from coastline retreat and electrical resistivity surveys perpendicular to and crossing the shoreline of the Bykovsky Peninsula. The interpreted geoelectric data suggest that the IBPT dipped to 15–20 m below the seabed at 350 m offshore. Both results suggest that cold saline water forms beneath grounded ice and floating sea ice in shallow water, causing cryotic benthic temperatures. The freezing point depression produced by salt diffusion can delay or prevent ice formation in the sediment and enhance the IBPT degradation rate. Therefore, salt diffusion may facilitate the release of greenhouse gasses to the atmosphere and considerably affect the design of offshore and coastal infrastructure in subsea permafrost areas.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , NonPeerReviewed , info:eu-repo/semantics/article
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  • 54
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    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 46, ISSN: 0094-8276
    Publikationsdatum: 2022-08-12
    Beschreibung: Permafrost is thawing extensively due to climate warming. When permafrost thaws, previously frozen organic carbon (OC) is converted into carbon dioxide (CO2) or methane, leading to further warming. This process is included in models as gradual deepening of the seasonal non‐frozen layer. Yet, models neglect abrupt OC mobilization along rapidly eroding Arctic coastlines. We mimicked erosion in an experiment by incubating permafrost with seawater for an average Arctic open‐water season. We found that CO2 production from permafrost OC is as efficient in seawater as without. For each gram (dry weight) of eroding permafrost, up to 4.3 ± 1.0 mg CO2 will be released and 6.2 ± 1.2% of initial OC mineralized at 4 °C. Our results indicate that potentially large amounts of CO2 are produced along eroding permafrost coastlines, onshore and within nearshore waters. We conclude that coastal erosion could play an important role in carbon cycling and the climate system.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 55
    Publikationsdatum: 2022-06-06
    Beschreibung: We present the results of geological and structural investigation documenting the interaction between hydrothermal fluids and host rock leading to a vein-type ore mineralization at shallow crustal depths (〈7 km) in the mining district of the eastern Island of Elba (Italy). Sulfide- and iron-rich veins and breccia in addition to minor massive iron-ore bodies form the mineralized system. Structural mapping and analysis of vein systems, fractures, faults and associated fault rocks as well as fracture opening modes show that the main factors controlling the formation and distribution of the mineralization are lithology, deformation style and deformation intensity. Their interplay led to a positive feedback between the evolution of pore pressure through time, strain localization and the resulting mineralization. Inversion of fault and vein data defines an E-W extensional stress field at the time of faulting, which favoured fluid ingress and pervasive flow within the porous host sandstone, interstitial sulfide precipitation and reduction of the primary bulk porosity. Subsequently, cyclic channelized fluid flow during repeated fluid ingresses caused extensive veining and numerous episodes of breccia formation.
    Beschreibung: Published
    Beschreibung: 210-230
    Beschreibung: 1T. Struttura della Terra
    Beschreibung: JCR Journal
    Schlagwort(e): Hydrothermalism ; Upper crust ; Faulting ; Fluids Island of Elba ; Structural analysis ; Island of Elba ; Northern Apennines ; deformation and hydrothermal fluid circulation in upper crust
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 56
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Reid, E. C., DeCarlo, T. M., Cohen, A. L., Wong, G. T. F., Lentz, S. J., Safaie, A., Hall, A., & Davis, K. A. Internal waves influence the thermal and nutrient environment on a shallow coral reef. Limnology and Oceanography, 64(5), (2019): 1949-1965, doi:10.1002/lno.11162.
    Beschreibung: Internal waves can influence water properties in coastal ecosystems through the shoreward transport and mixing of subthermocline water into the nearshore region. In June 2014, a field experiment was conducted at Dongsha Atoll in the northern South China Sea to study the impact of internal waves on a coral reef. Instrumentation included a distributed temperature sensing system, which resolved spatially and temporally continuous temperature measurements over a 4‐km cross‐reef section from the lagoon to 50‐m depth on the fore reef. Our observations show that during summer, internal waves shoaling on the shallow atoll regularly transport cold, nutrient‐rich water shoreward, altering near‐surface water properties on the fore reef. This water is transported shoreward of the reef crest by tides, breaking surface waves and wind‐driven flow, where it significantly alters the water temperature and nutrient concentrations on the reef flat. We find that without internal wave forcing on the fore reef, temperatures on the reef flat could be up to 2.0°C ± 0.2°C warmer. Additionally, we estimate a change in degree heating weeks of 0.7°C‐weeks warmer without internal waves, which significantly increases the probability of a more severe bleaching event occurring at Dongsha Atoll. Furthermore, using nutrient samples collected on the fore reef during the study, we estimated that instantaneous onshore nitrate flux is about four‐fold higher with internal waves than without internal waves. This work highlights the importance of internal waves as a physical mechanism shaping the nearshore environment, and likely supporting resilience of the reef.
    Beschreibung: We are grateful for the support of the Dongsha Atoll Research Station and the Dongsha Atoll Marine National Park, whose efforts made this research possible. The authors would also like to thank G. Lohmann from Woods Hole Oceanographic Institution and L. Hou, F. Shiah, and K. Lee from Academia Sinica for providing logistical and field support. We thank S. Tyler, and J. Selker from the Center for Transformative Environmental Monitoring Programs, funded by the National Science Foundation (EAR awards 1440596 and 1440506), for timely and effective provision of experimental design support, logistical support, and equipment for the project. We thank R. Branch, University of Washington, and X. Pan, Ocean University of China, for their guidance and SST data that informed this study. Support to G. T. F. Wong is from the Ministry of Science and Technology, Taiwan, grant NSC98‐2611‐M‐001‐004‐MY3 and NSC100‐2611‐M‐001‐001 and from the Academia Sinica through grants titled “Atmospheric Forcing on Ocean Biogeochemistry (AFOBi)” and “Dongsha Ocean Acidification Study (DOcS)”. Support for S. Lentz is from National Science Foundation grant OCE‐1558343. Support for A. Cohen from NSF Grant No. 1220529, by the Academia Sinica (Taiwan) through a thematic project grant to G. Wong and A. Cohen. Support for E. Reid, A. Safaie, and K. A. Davis is from National Science Foundation grant OCE‐1753317, and support to E. Reid from the Environmental Engineering Henry Samueli Endowed Fellowship and the UCI Oceans Graduate Fellowship.
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  • 57
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Johns, C. T., Grubb, A. R., Nissimov, J. I., Natale, F., Knapp, V., Mui, A., Fredricks, H. F., Van Mooy, B. A. S., & Bidle, K. D. The mutual interplay between calcification and coccolithovirus infection. Environmental Microbiology, 21(6), (2019): 1896-1915, doi:10.1111/1462-2920.14362.
    Beschreibung: Two prominent characteristics of marine coccolithophores are their secretion of coccoliths and their susceptibility to infection by coccolithoviruses (EhVs), both of which display variation among cells in culture and in natural populations. We examined the impact of calcification on infection by challenging a variety of Emiliania huxleyi strains at different calcification states with EhVs of different virulence. Reduced cellular calcification was associated with increased infection and EhV production, even though calcified cells and associated coccoliths had significantly higher adsorption coefficients than non‐calcified (naked) cells. Sialic acid glycosphingolipids, molecules thought to mediate EhV infection, were generally more abundant in calcified cells and enriched in purified, sorted coccoliths, suggesting a biochemical link between calcification and adsorption rates. In turn, viable EhVs impacted cellular calcification absent of lysis by inducing dramatic shifts in optical side scatter signals and a massive release of detached coccoliths in a subpopulation of cells, which could be triggered by resuspension of healthy, calcified host cells in an EhV‐free, ‘induced media’. Our findings show that calcification is a key component of the E. huxleyi‐EhV arms race and an aspect that is critical both to the modelling of these host–virus interactions in the ocean and interpreting their impact on the global carbon cycle.
    Beschreibung: We thank Liti Haramaty for her guidance and assistance in culturing and infection experiments. This research was funded by the Gordon and Betty Moore Foundation (GBMF3301 to BVM and KDB and GBMF3789 to KDB) and the National Science Foundation (OCE‐1537951 and OCE‐1559179 to KDB).
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  • 58
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © The Author(s), 2019. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 116(25), (2019):12343-12352, doi:10.1073/pnas.1901080116.
    Beschreibung: Genes encoding cytochrome P450 (CYP; P450) enzymes occur widely in the Archaea, Bacteria, and Eukarya, where they play important roles in metabolism of endogenous regulatory molecules and exogenous chemicals. We now report that genes for multiple and unique P450s occur commonly in giant viruses in the Mimiviridae, Pandoraviridae, and other families in the proposed order Megavirales. P450 genes were also identified in a herpesvirus (Ranid herpesvirus 3) and a phage (Mycobacterium phage Adler). The Adler phage P450 was classified as CYP102L1, and the crystal structure of the open form was solved at 2.5 Å. Genes encoding known redox partners for P450s (cytochrome P450 reductase, ferredoxin and ferredoxin reductase, and flavodoxin and flavodoxin reductase) were not found in any viral genome so far described, implying that host redox partners may drive viral P450 activities. Giant virus P450 proteins share no more than 25% identity with the P450 gene products we identified in Acanthamoeba castellanii, an amoeba host for many giant viruses. Thus, the origin of the unique P450 genes in giant viruses remains unknown. If giant virus P450 genes were acquired from a host, we suggest it could have been from an as yet unknown and possibly ancient host. These studies expand the horizon in the evolution and diversity of the enormously important P450 superfamily. Determining the origin and function of P450s in giant viruses may help to discern the origin of the giant viruses themselves.
    Beschreibung: We thank Dr. David Nes (Texas Tech University) for providing sterols and Dr. Matthieu Legendre and Dr. Chantal Abergel (CNRS, Marseille) for access to the P. celtis sequences. Drs. Irina Arkhipova, Mark Hahn, Judith Luborsky, and Ann Bucklin commented on the manuscript. The research was supported by a USA-UK Fulbright Scholarship and a Royal Society grant (to D.C.L.), the Boston University Superfund Research Program [NIH Grant 5P42ES007381 (to J.J.S. and J.V.G.) and NIH Grant 5U41HG003345 (to J.V.G.)], the European Regional Development Fund and Welsh Government Project BEACON (S.L.K.), the Woods Hole Center for Oceans and Human Health [NIH Grant P01ES021923 and National Science Foundation Grant OCE-1314642 (to J.J.S.)], and NIH Grant R01GM53753 (to T.L.P.).
    Beschreibung: 2019-12-05
    Schlagwort(e): cytochrome P450 ; virus ; evolution ; domains of life ; redox partner
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  • 59
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Staudinger, M. D., Mills, K. E., Stamieszkin, K., Record, N. R., Hudak, C. A., Allyn, A., Diamond, A., Friedland, K. D., Golet, W., Henderson, M. E., Hernandez, C. M., Huntington, T. G., Ji, R., Johnson, C. L., Johnson, D. S., Jordaan, A., Kocik, J., Li, Y., Liebman, M., Nichols, O. C., Pendleton, D., Richards, R. A., Robben, T., Thomas, A. C., Walsh, H. J., & Yakola, K. It's about time: a synthesis of changing phenology in the Gulf of Maine ecosystem. Fisheries Oceanography, 28(5), (2019): 532-566, doi: 10.1111/fog.12429.
    Beschreibung: The timing of recurring biological and seasonal environmental events is changing on a global scale relative to temperature and other climate drivers. This study considers the Gulf of Maine ecosystem, a region of high social and ecological importance in the Northwest Atlantic Ocean and synthesizes current knowledge of (a) key seasonal processes, patterns, and events; (b) direct evidence for shifts in timing; (c) implications of phenological responses for linked ecological‐human systems; and (d) potential phenology‐focused adaptation strategies and actions. Twenty studies demonstrated shifts in timing of regional marine organisms and seasonal environmental events. The most common response was earlier timing, observed in spring onset, spring and winter hydrology, zooplankton abundance, occurrence of several larval fishes, and diadromous fish migrations. Later timing was documented for fall onset, reproduction and fledging in Atlantic puffins, spring and fall phytoplankton blooms, and occurrence of additional larval fishes. Changes in event duration generally increased and were detected in zooplankton peak abundance, early life history periods of macro‐invertebrates, and lobster fishery landings. Reduced duration was observed in winter–spring ice‐affected stream flows. Two studies projected phenological changes, both finding diapause duration would decrease in zooplankton under future climate scenarios. Phenological responses were species‐specific and varied depending on the environmental driver, spatial, and temporal scales evaluated. Overall, a wide range of baseline phenology and relevant modeling studies exist, yet surprisingly few document long‐term shifts. Results reveal a need for increased emphasis on phenological shifts in the Gulf of Maine and identify opportunities for future research and consideration of phenological changes in adaptation efforts.
    Beschreibung: This work was supported by the Department of the Interior Northeast Climate Adaptation Science Center (G14AC00441) for MDS, AJ, and KY; the National Science Foundation's Coastal SEES Program (OCE‐1325484) for KEM, ACT, MEH, and AA; the National Aeronautics and Space Administration (NNX16 AG59G) for ACT, KEM, NRR, and KSS; the USGS Climate Research and Development Program for TGH; National Science & Engineering Research Council of Canada, University of New Brunswick, Environment Canada, Sir James Dunn Wildlife Research Centre, and New Brunswick Wildlife Trust Fund for AD. We also thank the Regional Association for Research on the Gulf of Maine for support, and the Gulf of Maine Research Institute for hosting and providing in kind resources for a two day in‐person workshop in August 2016. We greatly appreciate contributions from K. Alexander, G. Calandrino, C. Feurt, I. Mlsna, N. Rebuck, J. Seavey, and J. Sun for helping shape the initial scope of the manuscript. We thank J. Weltzin and two anonymous reviewers for their constructive comments. The contents of this paper are solely the responsibility of the authors and do not necessarily represent the views of the Northeast Climate Adaptation Science Center, U.S. Geological Survey, National Oceanographic and Atmospheric Administration, Fisheries and Oceans Canada or the US Environmental Protection Agency. This manuscript is submitted for publication with the understanding that the United States Government is authorized to reproduce and distribute reprints for Governmental purposes. None of the authors have conflicts of interest to declare in association with the contents of this manuscript.
    Schlagwort(e): coastal ; fish ; Gulf of Maine ; life cycle ; marine ; marine invertebrates ; marine mammals ; migration ; phenology ; phytoplankton ; seabirds ; seasonal ; timing ; zooplankton
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  • 60
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schall, E., Di Iorio, L., Berchok, C., Filun, D., Bedrinana-Romano, L., Buchan, S. J., Van Opzeeland, I., Sears, R., & Hucke-Gaete, R. Visual and passive acoustic observations of blue whale trios from two distinct populations. Marine Mammal Science, (2019): 1-10, doi:10.1111/mms.12643.
    Beschreibung: Blue whale populations from both hemispheres are thought to undertake annual migrations between high latitude feeding grounds and low latitude breeding grounds (Mackintosh, 1966). For individuals of some populations these predetermined movements to and from wintering areas where calving occurs have been confirmed through photo‐identification, satellite‐tracking, and passive acoustic monitoring (Burtenshaw et al., 2004; Mate, Lagerquist, & Calambokidis, 1999; Sears & Perrin, 2002; Stafford, Nieukirk, & Fox, 1999a). However, for many blue whale populations no clear migratory behavior has been reported and locations of respective breeding grounds remain unclear (e.g., Hucke‐Gaete, Osman, Moreno, Findlay, & Ljungblad, 2004; Samaran et al., 2013; Stafford, Chapp, Bohnenstiel, & Tolstoy, 2011; Thomisch et al., 2016). On feeding grounds in the Gulf of St. Lawrence and along the coast of California, blue whales have been observed to form female–male pairs during summer, which can remain stable up to over several weeks, with the number of pairs increasing towards the end of summer (Sears & Perrin, 2002; Calambokidis, unpublished data;1 RS, unpublished data). These pairs are sometimes joined by a second male, forming a blue whale trio, which often is observed to engage in surface active behaviors lasting several minutes (Sears & Perrin, 2002; RS, unpublished data). The formation of blue whale trios is probably related to reproductive competition between male escorts and female choice (RS, unpublished data). Blue whale males produce population‐specific songs likely functioning as reproductive advertisement (Edds‐Walton, 1997; Oleson et al. 2007a; Stafford, Fox, & Clark, 1998). Several studies have reported song year‐round in low‐, mid‐, and high‐latitude waters, frequently with high song production rates during summer on the feeding grounds (e.g., Barlow et al., 2018; Buchan, Stafford, & Hucke‐Gaete, 2015; Samaran, Adam, & Guinett, 2010; Širović et al., 2004; Stafford, Nieukirk, & Fox, 1999b; Thomisch et al., 2016). Therefore, breeding activities in blue whales may be more opportunistic, i.e., not restricted to the breeding season or to a specific habitat.
    Beschreibung: ES thanks Prof. Dr. Per J. Palsbøll for the supervision of the initial Master research project, the Marco Polo fund, and the University Groningen for covering travel expenses. We thank the Melimoyu Ecosystem Research Institute, SNP Patagonia Sur, and the company Teledyne Reson for partially funding the acoustic data collection in southern Chile. RHG is thankful to WWF‐Germany/Chile for partially funding fieldwork through grants to Centro Ballena Azul. CLB thanks the team of the Mingan Island Cetacean Study for their logistical support of boats and lodging, access to the North Atlantic blue whale database, and field assistance; Yvon Bélanger for opening his home to her and RS's field crews; for financial support from the National Science Foundation (Graduate Fellowship), National Defense Industrial Association, American Museum of Natural History (Lerner Gray Fund for Marine Research Grant), Penn State Applied Research Laboratory, and private donors Jeff and Lynn Kraus; and graduate advisors at Penn State University David L. Bradley, Thomas B. Gabrielson, and Diana McCammon. LDI thanks the Croisières du Grand Héron and Center Mériscope for allowing and supporting fieldwork, the Animal Behavior Department of the University of Zurich (Switzerland), the Bioacoustics Research Program at Cornell University (USA) and Prof. M. Manser and C. W. Clark for supervising LDI's Ph.D. The work was supported by grants to LDI for her PhD from the Forschungskommission der Universität Zürich, Züricher Tierschutz, Basler Stiftung für Biologische Forschung, SCNAT, Zangger‐Weber‐Stiftung, SSVA. SJB thanks the Center for Oceanographic Research COPAS Sur‐Austral, CONICYT PIA PFB31, the Office of Naval Research Global (awards N62909‐16‐2214 and N00014‐17‐2606), and a grant to the Centro de Estudios Avanzados en Zonas Áridas from Programa Regional CONICYT R16A10003 for support during manuscript writing. We would like to thank the field crews (F. Viddi, J. Ruiz, A. Carpentier, M. Lessard, A. Liebschner, C. Ramp, S. Angel, K. Aucrenaz, T. Doniol‐Valcroze, J. LeBreus, B. Kot, and J. Puschock) for their immense commitment to blue whale research.
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  • 61
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sutherland, K. M., Coe, A., Gast, R. J., Plummer, S., Suffridge, C. P., Diaz, J. M., Bowman, J. S., Wankel, S. D., & Hansel, C. M. Extracellular superoxide production by key microbes in the global ocean. Limnology and Oceanography, (2019), doi:10.1002/lno.11247.
    Beschreibung: Bacteria and eukaryotes produce the reactive oxygen species superoxide both within and outside the cell. Although superoxide is typically associated with the detrimental and sometimes fatal effects of oxidative stress, it has also been shown to be involved in a range of essential biochemical processes, including cell signaling, growth, differentiation, and defense. Light‐independent extracellular superoxide production has been shown to be widespread among many marine heterotrophs and phytoplankton, but the extent to which this trait is relevant to marine microbial physiology and ecology throughout the global ocean is unknown. Here, we investigate the dark extracellular superoxide production of five groups of organisms that are geographically widespread and represent some of the most abundant organisms in the global ocean. These include Prochlorococcus, Synechococcus, Pelagibacter, Phaeocystis, and Geminigera. Cell‐normalized net extracellular superoxide production rates ranged seven orders of magnitude, from undetectable to 14,830 amol cell−1 h−1, with the cyanobacterium Prochlorococcus being the lowest producer and the cryptophyte Geminigera being the most prolific producer. Extracellular superoxide production exhibited a strong inverse relationship with cell number, pointing to a potential role in cell signaling. We demonstrate that rapid, cell‐number–dependent changes in the net superoxide production rate by Synechococcus and Pelagibacter arose primarily from changes in gross production of extracellular superoxide, not decay. These results expand the relevance of dark extracellular superoxide production to key marine microbes of the global ocean, suggesting that superoxide production in marine waters is regulated by a diverse suite of marine organisms in both dark and sunlit waters.
    Beschreibung: The authors would like to acknowledge their funding sources including NASA NESSF NNX15AR62H (K.M.S.), NASA Exobiology grant NNX15AM04G to S.D.W. and C.M.H., NSF‐OCE grant 1355720 to C.M.H., NSF‐OPP 1641019 (J.S.B), and Simons Foundation SCOPE Award ID 329108 (Sallie W. Chisholm). The authors would also like to thank the Harvey lab (Skidaway Institute of Oceanography) for use of their flow cytometer in this study. We thank Stephen Giovannoni and Sallie Chisholm for providing bacteria strains and laboratory facilities. Additional thanks to Marianne Acker, Rogier Braakman, and Aldo Arellano for assistance in lab and helpful conversations.
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  • 62
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © National Academy of Sciences, 2019. This article is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 116 (35), (2019): 17187-17192, doi:10.1073/pnas.1903067116.
    Beschreibung: Mesoscale eddies are critical components of the ocean’s “internal weather” system. Mixing and stirring by eddies exerts significant control on biogeochemical fluxes in the open ocean, and eddies may trap distinctive plankton communities that remain coherent for months and can be transported hundreds to thousands of kilometers. Debate regarding how and why predators use fronts and eddies, for example as a migratory cue, enhanced forage opportunities, or preferred thermal habitat, has been ongoing since the 1950s. The influence of eddies on the behavior of large pelagic fishes, however, remains largely unexplored. Here, we reconstruct movements of a pelagic predator, the blue shark (Prionace glauca), in the Gulf Stream region using electronic tags, earth-observing satellites, and data-assimilating ocean forecasting models. Based on 〉2,000 tracking days and nearly 500,000 high-resolution time series measurements collected by 15 instrumented individuals, we show that blue sharks seek out the interiors of anticyclonic eddies where they dive deep while foraging. Our observations counter the existing paradigm that anticyclonic eddies are unproductive ocean “deserts” and suggest anomalously warm temperatures in these features connect surface-oriented predators to the most abundant fish community on the planet in the mesopelagic. These results also shed light on the ecosystem services provided by mesopelagic prey. Careful consideration will be needed before biomass extraction from the ocean twilight zone to avoid interrupting a key link between planktonic production and top predators. Moreover, robust associations between targeted fish species and oceanographic features increase the prospects for effective dynamic ocean management.
    Beschreibung: We thank D. McGillicuddy, G. Lawson, and G. Flierl for helpful discussions while developing this work and 2 anonymous reviewers whose feedback significantly improved the manuscript. We also thank C. Fischer and the OCEARCH team for their support of this research. This work was funded by awards to C.D.B. from the Martin Family Society of Fellows for Sustainability Fellowship at the Massachusetts Institute of Technology; the Grassle Fellowship and Ocean Venture Fund at the Woods Hole Oceanographic Institution; and the National Aeronatics and Space Administration (NASA) Earth and Space Science Fellowship. C.D.B. and P.G. acknowledge support from the NASA New Investigator Program Award 80NSSC18K0757, and P.G. acknowledges support from NSF Award OCE-1558809. This research is partially supported by funding to S.R.T. as part of the Audacious Project, a collaborative endeavor, housed at TED. We thank donors to the Woods Hole Oceanographic Institution (WHOI) ProjectWHOI crowdfunding campaign: The Secret Lives of Sharks. Computational support was provided by the Amazon Web Services Cloud Credits for Research program. Funding for the development of HYCOM has been provided by the National Ocean Partnership Program and the Office of Naval Research.
    Beschreibung: 2020-02-06
    Schlagwort(e): remote sensing ; oceanographic model ; satellite telemetry ; marine predator ; mesopelagic
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  • 63
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © National Academy of Sciences, 2019. This article is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 116 (35), (2019): 17207-17212, doi:10.1073/pnas.1900325116.
    Beschreibung: It has been hypothesized that the overall size of—or efficiency of carbon export from—the biosphere decreased at the end of the Great Oxidation Event (GOE) (ca. 2,400 to 2,050 Ma). However, the timing, tempo, and trigger for this decrease remain poorly constrained. Here we test this hypothesis by studying the isotope geochemistry of sulfate minerals from the Belcher Group, in subarctic Canada. Using insights from sulfur and barium isotope measurements, combined with radiometric ages from bracketing strata, we infer that the sulfate minerals studied here record ambient sulfate in the immediate aftermath of the GOE (ca. 2,018 Ma). These sulfate minerals captured negative triple-oxygen isotope anomalies as low as ∼ −0.8‰. Such negative values occurring shortly after the GOE require a rapid reduction in primary productivity of 〉80%, although even larger reductions are plausible. Given that these data imply a collapse in primary productivity rather than export efficiency, the trigger for this shift in the Earth system must reflect a change in the availability of nutrients, such as phosphorus. Cumulatively, these data highlight that Earth’s GOE is a tale of feast and famine: A geologically unprecedented reduction in the size of the biosphere occurred across the end-GOE transition.
    Beschreibung: Olivia M. J. Dagnaud assisted during fieldwork. S. V. Lalonde and E. A. Sperling provided helpful comments on an early version of the manuscript. We thank N. J. Planavsky and an anonymous reviewer for their constructive feedback. M.S.W.H. was supported by an NSERC PGS-D and student research grants from National Geographic, the APS Lewis and Clark Fund, Northern Science Training Program, McGill University Graduate Research Enhancement and Travel Awards, Geological Society of America, Mineralogical Association of Canada, and Stanford University. P.W.C. acknowledges support from the University of Colorado Boulder, the Agouron Institute Geobiology postdoctoral Fellowship program, a Natural Sciences and Engineering Council of Canada Postgraduate Scholarship–Doctoral Program scholarship, and the NSTP. Y.P. was supported by the Strategic Priority Research Program of CAS (XDB26000000). T.J.H. thanks Maureen E. Auro for laboratory assistance and the NSF for supporting isotope research in the NIRVANA Labs.
    Beschreibung: 2020-02-12
    Schlagwort(e): Proterozoic ; primary productivity ; Great Oxidation Event ; triple-oxygen isotopes ; nutrient limitation
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  • 64
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © National Academy of Sciences, 2019. This article is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 116(45), (2019): 22518-22525, doi:10.1073/pnas.1913714116.
    Beschreibung: The Ganges–Brahmaputra (G-B) River system transports over a billion tons of sediment every year from the Himalayan Mountains to the Bay of Bengal and has built the world’s largest active sedimentary deposit, the Bengal Fan. High sedimentation rates drive exceptional organic matter preservation that represents a long-term sink for atmospheric CO2. While much attention has been paid to organic-rich fine sediments, coarse sediments have generally been overlooked as a locus of organic carbon (OC) burial. However, International Ocean Discovery Program Expedition 354 recently discovered abundant woody debris (millimeter- to centimeter-sized fragments) preserved within the coarse sediment layers of turbidite beds recovered from 6 marine drill sites along a transect across the Bengal Fan (∼8°N, ∼3,700-m water depth) with recovery spanning 19 My. Analysis of bulk wood and lignin finds mostly lowland origins of wood delivered episodically. In the last 5 My, export included C4 plants, implying that coarse woody, lowland export continued after C4 grassland expansion, albeit in reduced amounts. Substantial export of coarse woody debris in the last 1 My included one wood-rich deposit (∼0.05 Ma) that encompassed coniferous wood transported from the headwaters. In coarse layers, we found on average 0.16 weight % OC, which is half the typical biospheric OC content of sediments exported by the modern G-B Rivers. Wood burial estimates are hampered by poor drilling recovery of sands. However, high-magnitude, low-frequency wood export events are shown to be a key mechanism for C burial in turbidites.
    Beschreibung: This work was funded by National Science Foundation Grants OCE-1401217 and COL-T354A55 to S.J.F. and OCE-1400805 to V.G. Graduate student participation in the project received support from University of Southern California Provost’s Fellowship to H.L. Samples were provided by the International Ocean Discovery Program. We are grateful for the efforts of the Expedition 354 Science Party, Carl Johnson, and Zongguang Liu. C.F.-L. and A.G. were supported by IODP-France. We thank Colin Osborne and Maria Vorontsova for helpful discussions.
    Beschreibung: 2020-04-21
    Schlagwort(e): carbon cycle ; wood ; lignin ; Himalaya ; Bengal Fan
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  • 65
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    In:  EPIC3German Research, Wiley, 41(2), pp. 8-13, ISSN: 0172-1526
    Publikationsdatum: 2024-01-22
    Beschreibung: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉Plate tectonics, volcanic activity and ocean floor spreading in the Arctic: Following several complex research expeditions and earthquake measurements, the Emmy Noether group MOVE has obtained some surprising findings about the formation and structure of the ocean lithosphere. A look at the results so far〈/jats:p〉
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  • 66
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4665-4670 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Positron annihilation lifetime spectroscopy is a powerful method for characterizing free volumes in a variety of materials. Correlations between positron annihilation rates and the size of free-volume regions in which o-Ps localizes are well described. Unfortunately, difficulties in the analysis of positron annihilation lifetime data have limited the approach to the determination of average lifetimes and average free volumes. Recent advances in the development of numerical integral transform methods now make it possible to extract continuous distributions of positron annihilation rates. The application of these methods to the determination of free-volume distributions is described. The variable transformations required to convert positron annihilation rate probability density functions (PDF) to the corresponding lifetime, radius, and free-volume PDFs are given and the approach is illustrated by application to positron annihilation lifetime data for amorphous polytetrafluoroethylene.
    Materialart: Digitale Medien
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  • 67
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4671-4678 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Photon-gated persistent spectral hole burning was observed for metal-free tetraphenylporphine with halogenated anthracene derivatives in poly(methylmethacrylate) or poly(ethylene) at liquid-helium temperatures. The hole formation yield was markedly dependent on the polymer matrices and the sample composition as well as on the gating wavelength. The irreversible broadening of holes in the systems measured by temperature cycling experiment was smaller than that by proton tautomerization of tetraphenylporphine. We concluded that the hole formation mechanism is donor-acceptor electron transfer on the basis of combined analysis of the matix and acceptor concentration dependence of hole formation yield, the action spectrum of the gating photon and the photoproduct spectrum.
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  • 68
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4694-4696 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: ArF(B-X) laser emission has been observed under long pulse electron-beam excitation at relatively low pump rate. ArF lasing only occurred with Ne buffered gas mixtures. Optimum performance of 1.93 J/l at an intrinsic efficiency of 1.35% occurred with an Ar/F2 mixture of 1/0.075% using a Ne buffer to 4.0 amagats. Total energy of 290 mJ in a 2-cm2 beam with a 1.0-μs full width at half maximum pulse width was recorded.
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  • 69
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4708-4714 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is shown that the resultant in-plane acceleration sensitivity of contoured quartz resonators symmetrically supported along rectangular edges always vanishes. This result is a consequence of symmetry and applies to any shape for which the support system is symmetric with respect to the center of the mode shape. When the active plate is supported on one side only, a state of flexure is induced in the resonator which degrades the in-plane sensitivity. This emphasizes the importance of a symmetric support system to achieve low acceleration sensitivities. The extensional and induced in-plane flexural biasing deformations are determined by means of our variational approximation procedure using the variational principles in which all conditions appear as natural conditions. The resulting biasing states are employed in an existing perturbation equation along with the mode shapes of the contoured resonators to calculate the nonvanishing acceleration sensitivities when the resonator is supported on one side only.
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  • 70
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4741-4755 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A low-resistance electrical contact is provided by a liquid metal in a small gap between the perimeter of a rotating disk (rotor) and a static surrounding surface (stator). The liquid metal extends radially inward on both sides of the rotor to free surfaces with an inert cover gas, and there is a strong axial magnetic field. This paper presents results for the shape of the free surface and for the liquid-metal velocity and pressure adjacent to the free surface. The results depend on the magnetic-field strength, the surface tension, the wetting angle at the free-surface–solid intersections, and the voltage difference between the stator and rotor. The copper stator and rotor are perfect conductors compared to the liquid metal. Two cases are considered, with and without electrically insulating coatings on the sides of the rotor.
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  • 71
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4770-4778 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The threading dislocation morphologies and characteristics in In-doped 3-μm-thick GaAs films grown by molecular-beam epitaxy on Si (100) substrates tilted toward the [110] orientation by 2° have been examined mainly using cross-sectional transmission electron microscopy. Most of the observed threading dislocations are 30°- and 60°-type dislocations along the 〈211〉 and 〈110〉 directions on inclined {111} planes. Also, screw-type dislocations running parallel to the [001] growth direction are frequently detected. No appreciable effect of homogeneous In doping throughout the films with a content between 2×1019 and 2×1020 atoms/cm3 on the reduction of threading dislocation generation is observed. However, an In content of 2×1020/cm3 (a misfit of 7.5×10−4) in GaAs films doped in the middle of growth is found to be effective for changing the dislocation direction on the {111} planes.
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  • 72
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4790-4796 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In most theoretical and experimental investigations into the shock response of underdense solid media, the influence of the medium's mesostructure on the resulting pressure and degree of compaction has not been taken into account. In typical cases examined, shock pressures are well in excess of 1 GPa and this approach is clearly justified. However, at low pressures, calculations show that the distribution of void sizes can affect the final state achieved upon shocking the medium from a given initial porosity. This paper analyzes the response of porous aluminum to low pressure shocking and demonstrates a dependence of the final shocked state on the distribution of void sizes.
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  • 73
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4797-4807 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Fracto-emission is the emission of particles and photons during and after fracture of materials. The observed emissions include electrons, ±ions, neutral species in both ground states and in excited states, and visible photons. Here we examine primarily photon and electron emission during failure of axially loaded stainless-steel fixtures (e.g., rods) embedded in epoxy. The observed signals provide time resolved information on the sequence of events involving interfacial fracture preceding pullout. In addition, we examine the emissions during frictional pullout following debonding. Over a large range of strain rates this pullout exhibits stick-slip behavior. These effects model the processes of fiber/matrix debonding and fiber pullout in a brittle matrix composite.
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  • 74
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4823-4826 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A quantitative determination of the contributions of the triply negatively charged Ga vacancies (V3−Ga) and of the doubly positively charged Ga self-interstitials (I2+Ga) to the Ga self-diffusion coefficient in GaAs has been carried out. Under thermal equilibrium and intrinsic conditions, the V3−Ga contribution is characterized by an activation enthalpy of 6 eV for As-rich crystals and of 7.52 eV for Ga-rich crystals, while the I2+Ga contribution is characterized by an activation enthalpy of 4.89 eV for As-rich crystals and of 3.37 eV for Ga-rich crystals.
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  • 75
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4842-4845 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The viscosity of Pd77Cu6.5Si16.5 was measured from 995 to 1183 K by capillary flow method. In the experiment, fluxing of the molten specimen by boron oxide was necessary in order to inhibit the formation of crystallites at temperatures near its liquidus. It was found that the viscosity can be described very well by the following Vogel–Fulcher equation: ln η=−3.764+938.543/(T−726), where T is in K. No discontinuity in viscosity was observed at the thermodynamic melting temperature. Recently Tsao and Spaepen [Amorphous Materials: Modeling of Structure and Properties, edited by V. Vitek (The Metallurgical Society of AIME, New York, 1983), p. 323] determined the equilibrium viscosity of the same system near the glass transition temperature. It turned out that the viscosity data from the two regimes cannot be joined together by a single Vogel–Fulcher equation of constant parameters. Finally the present results were compared with those earlier viscosity data of Pd40Ni40P20 and Au77Ge13.6Si9.4 [D. E. Polk and D. Turnbull, Acta Metall. 20, 493 (1972)] to test the validity of the principle of corresponding states for atomic transport properties.
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  • 76
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4870-4876 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Multilayers of Fe0.33Zr0.67, prepared by electron beam evaporation, have been characterized by conversion electron Mössbauer spectroscopy, Rutherford backscattering spectroscopy, and x-ray diffraction. Two phases, one amorphous and another crystalline (FeZr3), occur by solid-state reaction. For temperatures of 350 and 500 °C and annealing times ranging from 10 min to 72 h the growth rates of both phases had been obtained. From these results we suggest a model to describe the phase growth kinetics of the amorphous-crystalline Fe0.33Zr0.67 multilayer thin film.
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  • 77
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4890-4893 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Epitaxial thin films of ErAs were grown by molecular beam epitaxy on (100) GaAs. The lattice mismatch induced strain and subsequent lattice relaxation were studied using Rutherford backscattering spectrometry and ion channeling. The channeling results showed a strong thickness dependence for the backscattered minimum yield. Channeled angular scans showed the thin films to be fully strained up to 15 nm in thickness. Thicker films were found to relax with full relaxation not being reached until the 100-nm thickness range. The thick films were found to tilt up to 0.26° with respect to the crystal axes of the substrate. The tilt is apparently a result of the strain relaxation mechanism.
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  • 78
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4903-4908 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An unconventional analytical/empirical approach was used to determine the intrinsic stress in thin films of hydrogenated amorphous carbon (a-C:H) from measurements at room temperature of total stress on glass. The a-C:H was deposited through the decomposition of methane in an rf plasma over a range of conditions defined by two parameters; namely, the self-bias voltage on the substrate support electrode, Vb, and the pressure of methane in the deposition chamber, P. The intrinsic stress was found to differ from the total stress at room temperature by a thermal stress introduced by the deposition process. Over the range of deposition conditions investigated, 400 ≤ Vb ≤ 1600 V and 1≤P≤16 mTorr, the intrinsic stress was compressive, high in level (varying only slightly between 1–3×1010 dynes/cm2) and proportional to a function of the deposition parameters, Vb−1/4P1/8. Over the same range of conditions, the thermal stress (at ∼20 °C) was tensile and proportional to Vb3/2P1/4. At the highest values of Vb and P investigated, 1600 V and 16 mTorr, respectively, the level of the thermal stress (∼0.8×1010 dynes/cm2) exceeded the level of the total stress (∼0.3×1010 dynes/cm2) by a significant margin. Implications are discussed.
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  • 79
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4931-4937 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The changes in electrical properties of n-GaAs as a result of irradiations with fast neutrons have been studied. Epitaxial layers doped with Si at concentrations in the range 1.35×1015 to 1.599×1016 cm−3 were irradiated with reactor neutron fluences up to 1.31×1015 cm−2. When the changes in carrier concentration, Hall mobility, and resistivity were more than 25% of their initial values, nonlinear dependence on neutron fluence was apparent. New theory is proposed which explains the changes in electrical properties in terms of rates of trapping and release of charges. A theoretical relationship is derived for the change in carrier concentration as a function of neutron fluence and doping level. A linear relationship between neutron fluence and Fermi level shift was found to be consistent with the observed changes in carrier concentration.
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  • 80
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4946-4949 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We studied nonradiative recombination centers in undoped (AlxGa1−x)0.5In0.5Pgrown by metalorganic vapor phase epitaxy using transient capacitance spectroscopy. We found three deep energy levels, including a mid-gap level. We drew an equation to get a capture cross section for minority carriers, and obtained it using isothermal capacitance transient spectroscopy measurement. The mid-gap level had an electron capture cross section of 2 × 10−10 cm2 and a hole capture cross section of 1 × 10−15 cm2. The time constant of nonradiative recombination through the mid-gap level was found to be comparable to that of radiative recombination. We concluded that the mid-gap level is an effective nonradiative recombination center that reduces photoluminescence intensity.
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  • 81
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4950-4957 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Capacitance and conductance measurements are presented for dc-driven Au/ZnS:Mn/p-Si electroluminescence metal-insulator-semiconductor (MIS) devices, where the ZnS:Mn films are deposited by radio frequency sputtering. Stable dc operation is achieved by introducing oxygen into the film during deposition and subsequently annealing. The effect of the post-deposition annealing upon the density of states at the ZnS:Mn/p-Si interface is investigated. As deposited, the devices show unusual MIS C-V characteristics, that indicate a very high interface state density. Annealing at 700 °C, normal C-V characteristics are observed, indicating that the very high density of states is greatly reduced. For these films the conductance technique has been used to measure the density of states at the interface between the ZnS:Mn and p-Si. The statistical model is found to describe most accurately the interface state conductance response. The interface state density consists of a tail of states that varies between 3.7×1013 cm−2 eV−1 at the silicon Fermi level and 1.1×1013 cm−2 eV−1 at the silicon mid-gap. A small peak is superimposed upon this tail at (−0.16±0.01) eV below mid-gap. The tail of states is believed to be intrinsic to the ZnS:Mn/p-Si interface, but evidence suggests that the small peak is due to the presence of oxygen, which is shown by secondary-ion mass spectrometry analysis to accumulate at the interface after annealing at 700 °C. It seems likely that the very high density of interface states in as deposited devices is a consequence of a plasma damage to the silicon surface during growth, creating defects such as silicon dangling bonds. One possible explanation for the decrease in this density is that by annealing at 700 °C, oxygen in the bulk of the film diffuses to the interface, where it mops up these defects by forming compounds such as SiOx. A simpler model of interface recrystallization is also suggested. The doping density in the depletion region of the silicon is calculated as (7.5±0.5)×1014 cm−3, and the interface state capture cross section for holes is found to have mean value of approximately 10−15 cm−2.
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  • 82
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The correlations between structural quality and superconducting behavior in 1000-A(ring)-thick Ba2YCu3O7−δ (BYCO) films grown on LaAlO3(100) from the coevaporation of BaF2, Y, and Cu, followed by an optimized ex situ annealing process are reported. Epitaxial films with smooth, laminar morphology and excellent crystallinity can be grown to have critical current density Jc values nearly identical to single crystals. This finding contrasts with the typical observation that Jc values in thin films of BYCO are very high compared to those of single crystals. This is attributed to a greater density of flux pinning sites due to structural defects within the films. The most crystalline films presented here have penetration length λ∼2000 A(ring) with temperature dependencies described well by the Bardeen–Cooper–Schrieffer (BCS) theory. Material disorder of two types can be controlled by the high-temperature stage Ta of the annealing process. The first type is point defects and dislocations the same size or smaller than the coherence length ξab, which Rutherford backscattering/channeling suggests decrease in number with increasing Ta. The second is crevices, pinholes, and microcracks, which are at least one to two orders of magnitude larger than ξab. At Ta 〈 850 °C, crevices, which create areas of nonuniform thickness, occur due to incomplete epitaxial growth and correlate with the presence of weak links. Hence film resistivity is high, Tc is low, and λ is large. As Ta is increased, the film morphology becomes smoother and all electrical properties improve, except for Jc in nonzero applied magnetic fields, since the improved epitaxy correlates with reduced flux pinning. By Ta= 900 °C, the BYCO films are similar to single crystals in both cation alignment and Jc behavior. Above this annealing temperature, pinholes and microcracks develop and increase in both size and density with increasing Ta. Although these relatively large defects do not act as weak links, they do affect magnetic screening (and hence λ), to result in an anomalous temperature dependence that masks the intrinsic BCS behavior.
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  • 83
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5010-5017 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The changes in the real index of refraction and the optical absorption for conduction intersubband transitions in AlxGa1−xAs/GaAs/AlxGa1−xAs quantum wells are examined as a function of the carrier density. Various values for the input optical field and quantum well width are considered in the calculations. The linear contribution due to χ(1) as well as the nonlinear contribution from χ(3) is included. The relationship of the results to device applications such as waveguides and optical modulators is discussed.
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  • 84
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5040-5044 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In0.32Ga0.68P epitaxial layers doped with Te and Zn were grown on (100) GaAs0.61P0.39 epitaxial substrates by liquid-phase epitaxy using a supercooling method. The electrical properties of doped layers were determined by C-V measurements at 300 K. Room-temperature carrier concentrations ranging from 9×1016 to 2×1018 cm−3 for n-type and from 3×1016 to 6×1018 cm−3 for p-type dopants are obtained reproducibly. The full width at half maximum value of the 300 K photoluminescent spectrum increases with carrier concentration for Te- and Zn-doped layers. The relative intensity of 300-K photoluminescent peak presents the maximum values at 1×1018 and 6×1017 cm−3 for electron and hole concentrations, respectively. The 100-K photoluminescent spectra show three distinctive peaks and their relative intensities change with hole concentrations. Finally, the relationship between the acceptor ionization energy and hole concentration is described.
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  • 85
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5076-5084 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The oxidation of alloys of Si1−xGex differs significantly from that of pure Si in both the thermodynamics of the process and in the kinetics of the oxidation reaction. In this paper these fundamental differences are explored and are used to explain experimental observations of Si1−xGex oxidation that are presented herein and elsewhere in the literature. Alloys of Si1−xGex (with x=5.4, 11.6, and 17 at. %) approximately 200 nm thick were oxidized using the following two processes: (i) dry oxygen at 680 atm at a temperature of 550 °C and (ii) conventional, 1-atm steam at 800 °C. The wet oxidation conditions were chosen to produce an oxide thickness comparable (≈100 nm for xGe=11.6 at. %) to that obtained during high-pressure oxidation at 550 °C. Auger sputter depth profiling, x-ray photoelectron spectroscopy (XPS), and cross-sectional transmission electron microscopy were used to characterize the as-grown oxides. XPS studies reveal that high-pressure oxides formed from alloys of Si1−xGex chemically incorporate Ge directly into the oxide. In contrast, atmospheric oxidation of the same alloy composition produces oxides with no Ge incorporation that is detectable using XPS. It is shown that the selective removal of Si from alloys of Si1−xGex is predicted from Si-Ge-O ternary-phase equilibrium considerations. High-pressure oxidation conditions, however, allow the growth of oxides at much lower temperatures which minimizes Si-Ge interdiffusion and, as a consequence, prevents the selective oxidation of Si from the alloy. These results have direct significance to future device fabrication in Si1−xGex and to the issues of oxidation of multicomponent systems in general.
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  • 86
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5085-5089 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The uniform deposition of the oxide nitride oxide (ONO) film on the tunnel-structured polysilicon electrodes was examined by measuring the electrical characteristics of the capacitor and by using transmission electron microscopy. The conventional low pressure chemical vapor deposition method was adopted for the deposition of the nitride film of the ONO. The tunnel length is varied from 1.6 to 15.6 μm. The ONO film deposited over the entire tunnel of 15.6 μm showed good electrical characteristics, and the thickness uniformity as well. In addition to the maximum tunnel length which can accommodate the uniform ONO deposition, the growth mechanism of the ONO film inside of the tunnel is discussed.
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  • 87
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5108-5110 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Superconducting YBa2Cu3O7−x films have been deposited in situ onto III-V superlattice substrates. The substrates were GaAs/AlAs superlattices grown by molecular beam epitaxy onto GaAs substrates. For 5000-A(ring) -thick YBCO films grown at 615 °C substrate temperature, we have obtained Tc of 73 K. For thinner films the Tc's are lower, indicating poor interfaces. However, the onset of the superconducting transition is 90 K in all cases. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy (TEM) show these films to be polycrystalline. TEM shows an interaction layer of about 1000 A(ring) at the interface. Low-temperature cathodoluminescence measurements of the substrate show that atomic interdiffusion has intruded at least 5000 A(ring) below the interface.
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  • 88
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5119-5121 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The optical absorption of hydrogenated amorphous carbon films (a-C:H) was measured by spectroscopic ellipsometry. The a-C:H films were deposited at different substrate temperatures by rf-plasma of methane. A volume distribution of graphitic cluster size was assumed to reproduce the experimental spectra of the absorption coefficient. The changes in the absorption coefficient and the optical gap, induced by deposition temperature, have been interpreted in terms of changes in the graphitic cluster size of the network. The increase in the deposition temperature produces an increase in the size of the graphitic clusters.
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  • 89
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5125-5127 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have measured the tensor components c1111 and c1221 of third-order nonlinear optical susceptibility of two nematic liquid crystals, MBBA (p-methoxy-benzylidene p-n-butylaniline) and EBBA (p-ethoxy-benzylidene p-n-butylaniline), in the picosecond regime. We observed that the molecule with ethoxy group (EBBA) has a larger third-order nonlinearity than the one with methoxy group (MBBA) and present a model to explain this effect.
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  • 90
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5122-5124 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The thermally stimulated discharge current (TSD) behavior of native (dark rested) and irradiated amorphous selenium films (∼100 μm) has been studied in the temperature range 295–385 K. The TSD spectra of these films shows, in addition to the already reported relaxation at 310 K, a new relaxation peak in the temperature range 370–380 K. The origin of this relaxation is attributed to the trapping of charge carriers i.e., electron and holes at deep intrinsic and irradiation induced photostructural defect levels lying at ∼1.6 and 1.7 eV, respectively.
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  • 91
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5147-5149 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: MeV He ion implantation is used to produce optical waveguides in KTa1−xNbxO3 (x=0.37). The detailed refractive index profiles of the implanted planar waveguides are reconstructed from the measured mode spectra at the wavelength of 632.8 nm. The absorption and the tunneling losses of the lowest mode of the waveguides are determined. Ionic collision is proposed to be the mechanism which causes the observed variation of the refractive index.
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  • 92
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5090-5094 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Insulated gate Ga0.47In0.53As/Al0.48In0.52As heterojunction field-effect transistors have been prepared using SiOx and SrF2 insulation and dilute acid and O2 plasma surface cleaning. The leakage current-gate voltage characteristics at different temperatures are analyzed by thermionic and field emission theories to extract the effective barrier heights. The transistor pinch-off characteristics and effective barrier height results are compared with elemental depth profiles obtained from Auger electron spectroscopy. It is concluded that O2 plasma cleaning followed by SiOx gate insulation, is the most suitable technique for fabricating devices and leads to an effective barrier height of 0.3±0.1 V. With refinement this fabrication route should lead to satisfactory room-temperature operation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 93
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5095-5100 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: This paper reports a current transport study on the P+/N AlxGa1−xAs homojunction diodes with the AlAs mole fraction, x, ranging from 0 to 0.66. From the 2-kT surface recombination current behavior, the surface state density is nearly independent of x as x is smaller than 0.2. On the other hand, as x is larger than 0.2, the surface state density decreases as x increases. A photocurrent-aided method is proposed to extract the embedded 1-kT current out of the series resistance effect. It is found that the 1-kT current follows Shockley diffusion theory, and the hole diffusion length has a drastic change in the transition region from direct to indirect band. A three-band diffusion model considering the Γ-band-electron-concentration-dependent hole lifetime has been proposed to explain the experimental results successfully.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Results of combined ac capacitance and conductance measurements on two-terminal metal-oxide-semiconductor-oxide-semiconductor capacitors fabricated in a silicon-on-insulator substrate formed by oxygen implantation are presented for the first time. We demonstrate the efficiency of the technique to investigate the presence of bulk traps presumably caused by metallic contaminants introduced during the high-energy oxygen implantation, as well as to determine the interface trap density at the buried oxide/Si substrate interface.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4332-4335 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electron mobility and the two-dimensional electron gas (2DEG) concentration in different indium compositions (0.1〈x〈0.6) δ-doped GaAs/InxGa1−xAs/GaAs pseudomorphic structures grown by low-pressure metalorganic chemical vapor deposition are studied. The electron mobilities of a δ-doped GaAs layer are comparable to those of previous reports. Furthermore, the maximum mobility (5500 and 33 000 cm2/V s at 300 and 77 K, respectively) of the proposed pseudomorphic structure appears at x=0.37. Taking into account of strain and quantum effects, the variation trends of calculated 2DEG concentrations are in good agreement with the experimental results.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4357-4361 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: General variational expressions for the calculation of the binding energies of the low-lying bound states of an anisotropic donor in a quantum well (QW) are presented. To demonstrate the utilization of these expressions the binding energies of anisotropic donor states in a stepped quantum well are studied theoretically. The variations of the binding energies of the anisotropic donor states as a function of impurity position are presented for different values of the anisotropy factor γ=m*⊥(large-closed-square)m*(parallel), where m*⊥ and m*(parallel) represent the effective electron mass perpendicular to and parallel to the z axis (perpendicular to the interfaces of the QW), respectively. The peak position of the binding energy curves shifts to the deep side of the stepped well. The smaller the γ, the larger the peak shift. The peak shift and the maximum in the binding energies are also dependent on the potential V2 of the step barrier. For the 2p0-like state the corresponding binding energy curve exhibits double peaks, different from the s- and 2p±-like states.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4383-4391 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The critical parameters in the single-target magnetron sputtering of YBa2Cu3O7 have been identified and sufficiently optimized to allow the reproducible deposition of films with Tc's of (approximately-greater-than)90 K and Jc's of (very-much-greater-than) 106 A/cm2 at 77 K. It was found that during film growth the bombardment of the YBa2Cu3O7 by energetic particles must be minimized and also a stronger oxidizing agent than molecular oxygen must be present to obtain films with these properties. Otherwise, films are deposited that, by x-ray diffraction and energy dispersive x-ray spectroscopy analyses, are indistinguishable from the highest-Tc 1:2:3 stoichiometric material but which have critical temperatures of (very-much-less-than)90 K. Films need not have 1:2:3 overall stoichiometry to have optimum superconducting properties. In such cases the excess elements are present as second-phase particles.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4431-4438 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The remanent magnetization of fine particle media of perpendicular anisotropy is known to exhibit a time decay of pseudologarithmic form. The viscous properties are to a large extent determined by the magnetostatic particle interaction and the particle size. A mean-field model of a perfectly aligned ensemble of Stoner–Wohlfarth particles is presented that gives a qualitative description of the hysteretic and time-dependent properties of particulate perpendicular media. The time decay of the remanent magnetization of Alumite media after initial magnetic saturation was measured. The decay was found to be logarithmic within the measuring period, and a coefficient of magnetic viscosity was obtained. Although the reversal mechanism for the particles in Alumite media is known to be incoherent, a good qualitative agreement between the theoretical model and the measurements was found by introducing a reduced effective volume acting as a scaling factor that accounts for the discrepancy in reversal mechanisms.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4460-4464 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: FeSi multilayered films (MLFs) with intermediate SiO2 or Ni80Fe20 layers have been found to have superior corrosion resistance, as well as excellent soft magnetic properties. Corrosion resistance for the MLFs depends on the intermediate layer material, intermediate layer thickness, and FeSi layer thickness. In the MLFs with appropriate intermediate layers, oxygen diffusion is restricted to only 20 nm depth from the surface, which is less than the FeSi layer thickness, and no rust is observed after 600 h exposure in 60 °C and 90% relative humidity conditions. In contrast, in FeSi single-layered films, oxygen spreads throughout the entire film, and a reddish brown rust of Fe2O3 was observed. Due to the high saturation magnetization and high corrosion resistance, the FeSi MLFs are forseen to be soft magnetic materials applicable for higher density magnetic recording heads.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4476-4479 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We investigate the influence of interaction between dispersed particles to ac conductivity of suspension of charged particles immersed in electrolyte solution. Using the Rayleigh technique, we establish an identity for charged suspensions, and derive a formula for effective complex conductivity of the systems. A useful scheme for computation of effective constants of composite media is proposed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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