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  • American Geophysical Union  (17,132)
  • 2010-2014  (12,674)
  • 1995-1999  (4,458)
  • 1970-1974
  • 2014  (6,639)
  • 2011  (6,035)
  • 1999  (4,458)
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  • 2010-2014  (12,674)
  • 1995-1999  (4,458)
  • 1970-1974
Year
  • 1
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    An unloading foam model to constrain Etna’s 11–13 January 2011 lava fountaining episode (2011)
    American Geophysical Union
    Details
    Publication Date: 2021-06-09
    Description: The 11–13 January 2011 eruptive episode at Etna volcano occurred after several months of increasing ash emissions from the summit craters, and was heralded by increasing SO2 output, which peaked at ∼5000 megagrams/day several hours before the start of the eruptive activity. The eruptive episode began with a phase of Strombolian activity from a pit crater on the eastern flank of the SE‐Crater. Explosions became more intense with time and eventually became transitional between Strombolian and fountaining, before moving into a lava fountaining phase. Fountaining was accompanied by lava output from the lower rim of the pit crater. Emplacement of the resulting lava flow field, as well as associated lava fountain‐ and Strombolian‐phases, was tracked using a remote sensing network comprising both thermal and visible cameras. Thermal surveys completed once the eruptive episode had ended also allowed us to reconstruct the emplacement of the lava flow field. Using a high temporal resolution geostationary satellite data we were also able to construct a detailed record of the heat flux during the fountain‐fed flow phase and its subsequent cooling. The dense rock volume of erupted lava obtained from the satellite data was 1.2 × 106 m3; this was emplaced over a period of about 6 h to give a mean output rate of ∼55 m3 s−1. By comparison, geologic data allowed us to estimate dense rock volumes of ∼0.85 × 106 m3 for the pyroclastics erupted during the lava fountain phase, and 0.84–1.7 × 106 m3 for lavas erupted during the effusive phase, resulting in a total erupted dense rock volume of 1.7–2.5 × 106 m3 and a mean output rate of 78–117 m3 s−1. The sequence of events and quantitative results presented here shed light on the shallow feeding system of the volcano.
    Description: Published
    Description: B11207
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: partially_open
    Keywords: Etna ; lava fountains ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Turbulent times in the northern polar ionosphere? (2011)
    American Geophysical Union
    Details
    Publication Date: 2020-12-03
    Description: A model is presented of the growth rate of turbulently generated irregularities in the electron concentration of northern polar cap plasma patches. The turbulence is generated by the short‐term fluctuations in the electric field imposed on the polar cap ionosphere by electric field mapping from the magnetosphere. The model uses an ionospheric imaging algorithm to specify the state of the ionosphere throughout. The growth rates are used to estimate mean amplitudes for the irregularities, and these mean amplitudes are compared with observations of the scintillation indices S4 and s by calculating the linear correlation coefficients between them. The scintillation data are recorded by GPS L1 band receivers stationed at high northern latitudes. A total of 13 days are analyzed, covering four separate magnetic storm periods. These results are compared with those from a similar model of the gradient drift instability (GDI) growth rate. Overall, the results show better correlation between the GDI process and the scintillation indices than for the turbulence process and the scintillation indices. Two storms, however, show approximately equally good correlations for both processes, indicating that there might be times when the turbulence process of irregularity formation on plasma patches may be the controlling one.
    Description: Published
    Description: A04310
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: restricted
    Keywords: ionospheric irregularities ; scintillations ; Gradient Drift Instability ; 01. Atmosphere::01.02. Ionosphere::01.02.04. Plasma Physics ; 01. Atmosphere::01.02. Ionosphere::01.02.07. Scintillations ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
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  • 3
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    Mapping Moho depth variations in central Italy from PsMoho-P delay times: Evidence of an E-W transition in the Adriatic Moho at 42°N latitude (2014)
    American Geophysical Union
    Details
    Publication Date: 2020-12-18
    Description: Along the Italian peninsula adjoin two crustal domains, peri-Tyrrhenian and Adriatic, whose boundary is not univocal in central Italy. In this area, we attempt to map the extent of the Moho in the two terrains from variations of the travel time difference between the direct P wave and the P-to-S wave converted at the crust-mantle boundary, called PsMoho. We use teleseismic receiver functions computed at 38 broad-band stations in this and previous studies, and assigned each of the recording sites to the Adriatic or peri-Tyrrhenian terrains based on station location, geologic and geophysical data and interpretation, and consistency of delays with the regional Moho trend. The results of the present study show that the PsMoho arrival time varies from 2.3 to 4.1 s in the peri-Tyrrhenian domain and from 3.7 to 5.5 s in the Adriatic domain. As expected, the lowest time difference is observed along the Tyrrhenian coastline and the largest values are observed in the axial zone of the Apennine chain. A key new result of this study is a sharp E-W boundary in the Adriatic domain that separates a deeper Moho north of about 42 N latitude from a shallower Moho to the south. This feature is constrained for a length of about 40 km by the observations available in this study. The E-W boundary requires a revision of prior mapping of the Moho in central Italy and supports previous hypotheses of lithosphere segmentation.
    Description: Published
    Description: 3929–3938
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: open
    Keywords: teleseismic receiver functions ; Moho discontinuity ; central Italy ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
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  • 4
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    Low-temperature magnetic properties of pelagic carbonates: Oxidation of biogenic magnetite and identification of magnetosome chains (2014)
    American Geophysical Union
    Details
    Publication Date: 2021-02-17
    Description: Pelagic marine carbonates provide important records of past environmental change. We carried out detailed low-temperature magnetic measurements on biogenic magnetite-bearing sediments from the Southern Ocean (Ocean Drilling Program (ODP) Holes 738B, 738C, 689D, and 690C) and on samples containing whole magnetotactic bacteria cells. We document a range of low-temperature magnetic properties, including reversible humped low-temperature cycling (LTC) curves. Different degrees of magnetite oxidation are considered to be responsible for the observed variable shapes of LTC curves. A dipole spring mechanism in magnetosome chains is introduced to explain reversible LTC curves. This dipole spring mechanism is proposed to result from the uniaxial anisotropy that originates from the chain arrangement of biogenic magnetite, similar to published results for uniaxial stable single domain (SD) particles. The dipole spring mechanism reversibly restores the remanence during warming in LTC measurements. This supports a previous idea that remanence of magnetosome chains is completely reversible during LTC experiments. We suggest that this magnetic fingerprint is a diagnostic indicator for intact magnetosome chains, although the presence of isolated uniaxial stable SD particles and magnetically interacting particles can complicate this test. Magnetic measurements through the Eocene section of ODP Hole 738B reveal an interval with distinct magnetic properties that we interpret to originate from less oxidized biogenic magnetite and enrichment of a biogenic “hard” component. Co-occurrence of these two magnetic fingerprints during the late Eocene in the Southern Ocean indicates less oxic conditions, probably due to increased oceanic primary productivity and organic carbon burial.
    Description: Published
    Description: 6049–6065
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: pelagic carbonates ; biogenic magnetite ; rock magnetism ; environmental magnetism ; ODP ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
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  • 5
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    Sudden deep gas eruption nearby Rome's airport of Fiumicino (2014)
    American Geophysical Union
    Details
    Publication Date: 2021-03-24
    Description: On 24 August 2013 a sudden gas eruption from the ground occurred in the Tiber river delta, nearby Rome's international airport of Fiumicino. We assessed that this gas, analogous to other minor vents in the area, is dominantly composed of deep, partially mantle-derived CO2, as in the geothermal gas of the surrounding Roman Comagmatic Province. Increased amounts of thermogenic CH4 are likely sourced from Meso-Cenozoic petroleum systems, overlying the deep magmatic fluids. We hypothesize that the intersection of NE-SW and N-S fault systems, which at regional scale controls the location of the Roman volcanic edifices, favors gas uprising through the impermeable Pliocene and deltaic Holocene covers. Pressurized gas may temporarily be stored below these covers or within shallower sandy, permeable layers. The eruption, regardless the triggering cause—natural or man-made, reveals the potential hazard of gas-charged sediments in the delta, even at distances far from the volcanic edifices.
    Description: Published
    Description: 5632–5636
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: geothermal gas ; deep CO2 ; Tiber river delta ; thermogenic CH4 ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
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  • 6
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    High resolution velocity structure beneath Mount Vesuvius from seismic array data (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: A high resolution P-wave image of Mt. Vesuvius edifice has been derived from simultaneous inversion of travel times and hypocentral parameters of local earthquakes, land based shots and small aperture array data. The results give detailsdownto300 – 500m.Therelocatedlocalseismicity appears to extend down to 5 km below the central crater, distributed in a major cluster, centered at 3 km below the central crater and in a minor group, with diffuse hypocenters inside the volcanic edifice. The two clusters are separated by an anomalously high Vp region at around 1 km depth. A zone with high Vp/Vs in the upper layers is interpreted as produced by the presence of intense fluid circulation. The highest energy quakes (up to M = 3.6) are located in the deeper cluster, in a high P-wave velocity zone. Our results favor an interpretation in terms of absence of shallow magma reservoirs.
    Description: Published
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Velocity Tomography ; Mt. Vesuvius ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
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  • 7
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    Topography of the Calabria subduction zone (southern Italy): Clues for the origin of Mt. Etna (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: Calabria represents an ideal site to analyze the topography of a subduction zone as it is located on top of a narrow active Wadati-Benioff zone and shows evidence of rapid uplift. We analyzed a pattern of surface deformation using elevation data with different filters and showed the existence of a long wavelength (〉100 km) relatively positive topographic signal at the slab edges. The elevation of MIS 5.5 stage marine terraces supports this pattern, although the record is incomplete and partly masked by the variable denudation rate. We performed structural analyses along the major active or recently reactivated normal faults showing that the extensional direction varies along the Calabrian Arc and laterally switches from arc-normal, within the active portion of the slab, to arc-oblique or even arc-parallel, along the northern and southern slab edges. This surface deformation pattern was compared with a recent high resolution P wave tomographic model showing that the high seismic velocity anomaly is continuous only within the active Wadati-Benioff zone, whereas the northern and southwestern sides are marked by low velocity anomalies, suggesting that large-scale topographic bulges, volcanism, and uplift could have been produced by mantle upwelling. We present numerical simulations to visualize the three-dimensional mantle circulation around a narrow retreating slab, ideally similar to the one presently subducting beneath Calabria. We emphasize that mantle upwelling and surface deformation are expected at the edges of the slab, where return flows may eventually drive decompression melting and the Mount Etna volcanism.
    Description: Published
    Description: TC1003
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: topography ; Calabrian Arc ; subduction ; tomography ; mantle flow ; uplift ; retreat ; anisotropy ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
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  • 8
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    Water vapor sounding with the far infrared REFIR-PAD spectroradiometer from a high-altitude ground-based station during the ECOWAR campaign (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: The Radiation Explorer in the Far InfraRed-Prototype for Applications and Development (REFIR-PAD) spectroradiometer was operated from the Testa Grigia Italian-Alps station in March 2007 during the Earth Cooling by Water Vapour Radiation (ECOWAR) measurement campaign, obtaining downwelling radiance spectra in the 100–1100 cm−1 range, under clear-sky conditions and in the presence of cirrus clouds. The analysis of these measurements has proven that the instrument is capable of determining precipitable water vapor with a total uncertainty of 5–7% by using the far-infrared rotational band of water. The measurement is unaffected by the presence of cirri, whose optical depth can be instead retrieved as an additional parameter. Information on the vertical profiles of water vapor volume mixing ratio and temperature can also be retrieved for three altitude levels. The ability to measure the water vapor column with a simple, uncooled instrument, capable of operating continuously and with a time resolution of about 10 min, makes REFIR-PAD a very valuable instrument for meteorological and climatological studies for the characterization of the water vapor distribution.
    Description: Published
    Description: D02310
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 1.10. TTC - Telerilevamento
    Description: JCR Journal
    Description: reserved
    Keywords: tropospheric water vapor ; IR spectroscopy ; REFIR-PAD ; ECOWAR ; 01. Atmosphere::01.01. Atmosphere::01.01.01. Composition and Structure ; 01. Atmosphere::01.01. Atmosphere::01.01.08. Instruments and techniques
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  • 9
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    Slip Distribution of the 2003 Tokachi-oki Mw 8.1 earthquake from joint inversion of tsunami waveforms and geodetic data (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: We study the 2003 Mw 8.1 Tokachi‐oki earthquake, a great interplate event that occurred along the southwestern Kuril Trench and generated a significant tsunami. To determine the earthquake slip distribution, we perform the first joint inversion of tsunami waveforms measured by tide gauges and of coseismic displacement measured both by GPS stations and three ocean bottom pressure gauges (PG) for this event. The resolution of the different data sets on the slip distribution is assessed by means of several checkerboard tests. Results show that tsunami data constrain the slip distribution offshore, whereas GPS data constrain the slip distribution in the onshore zone. The three PG data only coarsely constrain the offshore slip, indicating that denser networks should be installed close to subduction zones. Combining the three data sets significantly improves the inversion results. Joint inversion of the 2003 Tokachi‐oki earthquake data leads to maximum slip values (∼6 m) confined at depths greater than ∼25 km, between 30 and 80 km northwest of the hypocenter, with a patch of slip (3 m) in the deepest part of the source (∼50 km depth). Slip values are very low (≤1 m) updip from the hypocenter. Furthermore, the rupture does not extend on the plate interface off Akkeshi. As a significant back slip amount (∼4 m) has accumulated there since the last 1952 earthquake, this segment could rupture during the next large interplate event along the Kuril Trench.
    Description: Published
    Description: B11313
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: tsunami ; coseismic displacement ; joint inversion ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
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  • 10
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    A relation between lava discharge rate, thermal insulation, and flow area set using lidar data (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: A simple linear relation can be used to link time averaged discharge rate (TADR) and lava flow area (A). The relation applies to given insulation conditions, as described by the characteristic flow surface temperature (Te), and will vary from case-to-case depending on rheological and topographic influences on flow spreading. Most flows have insulation conditions that change through time, modifying the relationship between TADR and area as insulation conditions evolve. Using lidar data we can define TADR, the flow area that the discharge feeds and Te, allowing generation of a case-specific relation to convert satellite-data-derived flow areas to TADR. For Etna's 2006 lava flow field we obtain a relation whereby TADR = 5.6 × 10−6 A for well insulated conditions (Te = 100°C) and TADR = 1.5 × 10−4 A for poorly insulated conditions (Te = 600°C).
    Description: Published
    Description: L20308
    Description: 1.10. TTC - Telerilevamento
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: lava flow ; discharge rate ; area ; surface temperature ; lidar ; Etna. ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 11
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    Magnetic properties of sedimentary greigite (Fe3S4): an update (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: Greigite (Fe3S4) is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction. It can also grow at any time when dissolved iron and sulfide are available during diagenesis. Greigite is important in paleomagnetic, environmental, biological, biogeochemical, tectonic, and industrial processes. Much recent progress has been made in understanding its magnetic properties. Greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites. The crystallographic c axis is the easy axis of magnetization, with magnetic properties dominated by magnetocrystalline anisotropy. Robust empirical estimates of the saturation magnetization, anisotropy constant, and exchange constant for greigite have been obtained recently for the first time, and the first robust estimate of the low‐field magnetic susceptibility is reported here. The Curie temperature of greigite remains unknown but must exceed 350°C. Greigite lacks a low‐temperature magnetic transition. On the basis of preliminary micromagnetic modeling, the size range for stable single domain behavior is 17–200 nm for cubic crystals and 17–500 nm for octahedral crystals. Gradual variation in magnetic properties is observed through the pseudo‐single‐domain size range. We systematically document the known magnetic properties of greigite (at high, ambient, and low temperatures and with alternating and direct fields) and illustrate how grain size variations affect magnetic properties. Recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite, which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records, including widespread remagnetizations.
    Description: Published
    Description: RG1002
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: greigite ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
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  • 12
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    Characterization of GPS time series at the Neapolitan volcanic area by statistical analysis (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: The GPS time series recorded at the Neapolitan volcanic area reveals a very peculiar behavior. When a clear deformation is observed, the amplitude distribution evolves from a super‐Gaussian to a broader distribution. This behavior can be characterized by evaluating the kurtosis. Spurious periodic components were evidenced by independent component analysis and then removed by filtering the original signal. The time series for all stations was modeled with a fifth‐order polynomial fit, which represents the deformation history at that place. Indeed, when this polynomial is subtracted from the time series, the distributions again become super‐Gaussian. A simulation of the deformation time evolution was performed by superposing a Laplacian noise and a synthetic deformation history. The kurtosis of the obtained signals decreases as the superposition increases, enlightening the insurgence of the deformation. The presented approach represents a contribution aimed at adding further information to the studies about the deformation at the Neapolitan volcanic area by revealing geologically relevant data.
    Description: Published
    Description: B10416
    Description: 1.3. TTC - Sorveglianza geodetica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: GPS time series ; Neapolitan volcanic ; statistical analysis ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
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  • 13
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    Intermediate-focus earthquakes under South Shetland Islands (Antarctica) (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Intermediate-focus seismicity (50〈H〈100km) related to the underplating zone of the South Shetland plate have been recorded at a small aperture seismic array set up in Deception Island, Antarctica.
    Description: Published
    Description: 531-534
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Deep earthquakes ; Antarctica ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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  • 14
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    Array tracking of the volcanic tremor source at Deception Island Antarctica (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We have found experimental evidence which shows that the volcanic tremor recorded at Deception Island (South Shetland Islands, Antarctica) is a superposition in time of overlapping hybrid events.
    Description: Published
    Description: 3069-3072
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Arrays ; volcanictremor ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 15
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    On the mechanism of seasonal and solar cycle NmF2 variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Seasonal (winter/summer) and solar cycle NmF2 variations as well as summer saturation effect in NmF2 have been analyzed using Millstone Hill incoherent scatter radar (ISR) daytime observations. A self‐consistent approach to the Ne(h) modeling has been applied to extract from ISR observations a consistent set of main aeronomic parameters and to estimate their quantitative contribution to the observed NmF2 variations. The retrieved aeronomic parameters are independent of uncertainties in thermosphere and solar EUV empirical models, and this is a distinguishing feature of the present consideration. Different temperatures in winter and in summer in the course of solar cycle overlapped on the O++N2 reaction rate coefficient temperature dependence result in different NmF2 dependences on solar activity: a steep practically linear increase with a tendency to turn up in January (contrary to international reference ionosphere prediction) and a slow increase with a tendency to saturate at high solar activity in July despite increasing solar EUV irradiation. In winter the EUV flux and thermospheric parameters provide approximately equal contributions to the NmF2 increase, while in summer the contribution of thermospheric parameters is small. Both in winter and in summer the variations of atomic oxygen [O] are small at the F2 layer peak, and its contribution is small compared to linear loss coefficient, b. It is shown that the summer saturation effect in NmF2 under high solar activity is not just reduced to O/N2 or EUV flux solar cycle variations but is determined by b via the g1 temperature dependence. A new mechanism (qualitative) to explain the December anomaly in NmF2 is proposed. It is based on the idea that the areas of atomic oxygen production and its loss are spatially separated and that time is required to transfer [O] from one area to the other where [O] associates in a three‐body collision. Therefore, under a 7% increase in the O2 dissociation rate due to the Sun‐Earth distance decrease in December–January compared to June–July, an accumulation of atomic oxygen should take place in the thermosphere in the vicinity of the December solstice resulting in a 21% NmF2 increase, which is close to the observed global December effect.
    Description: Published
    Description: A03319
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: restricted
    Keywords: mid-latitude ionosphere ; thermosphere composition and chemistry ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous ; 01. Atmosphere::01.02. Ionosphere::01.02.01. Ion chemistry and composition ; 01. Atmosphere::01.02. Ionosphere::01.02.02. Dynamics
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  • 16
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    An information theory approach to the storm‐substorm relationship (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: One of the most interesting aspects of the global magnetospheric response to solar wind changes is the relationship between storms and substorms. Here we present new results on the relationship between these two different classes of magnetospheric phenomena by approaching the problem on the side of information theory. Using the Auroral Electrojet AL and SYM‐H indices as representative proxies of magnetic substorms and storms, we investigate the transfer of information by means of transfer entropy analysis (Schreiber, 2000). The obtained results seem, on average, to indicate the presence of a net transfer of information from AL to SYM‐H on time scales shorter than 10 h. On the basis of this result, geomagnetic substorms may act as a driver for the occurrence of geomagnetic storms. However, carrying out a more careful analysis which takes into account the global geomagnetic daily activity, we suggest that the direction of information flow between substorms and storms depends on the global activity level. Indeed, if it is true that a sequence of magnetospheric substorms may drive a moderate storm, it is also true that very large storms may dominate and drive the occurrence of magnetospheric substorms.
    Description: Published
    Description: A08225
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: restricted
    Keywords: Storm-substorm relationship ; Information theory ; 01. Atmosphere::01.03. Magnetosphere::01.03.02. Magnetic storms ; 01. Atmosphere::01.03. Magnetosphere::01.03.03. Magnetospheric physics ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
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    Unraveling the geometry of the New England oroclines (eastern Australia): Constraints from magnetic fabrics (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The southern New England Orogen (NEO) in eastern Australia is characterized by tight curvatures (oroclines), but the exact geometry of the oroclines and their kinematic evolution are controversial. Here we present new data on the anisotropy ofmagnetic susceptibility (AMS), which provide a petrofabric proxy for the finite strain associated with the oroclines. We focus on a series of preoroclinal Devonian-Carboniferous fore-arc basin rocks, which are aligned parallel to the oroclinal structure, and by examining structural domains, we test whether or not the magnetic fabric is consistent with the strain axes. AMS data show a first-order consistency with the shape of the oroclines, characterized, in most of structural domains, by subparallelism between magnetic lineations, “structural axis” and bedding. With the exception of the Gresford and west Hastings domains, our results are relatively consistent with the existence of the Manning and Nambucca (Hastings) Oroclines. Reconstruction of magnetic lineations to a prerotation (i.e., pre–late Carboniferous) stage, considering available paleomagnetic results, yields a consistent and rather rectilinear NE-SW predeformation fore-arc basin. This supports the validity of AMS as a strain proxy in complex orogens, such as the NEO. In the Hastings Block, magnetic lineations are suborthogonal to bedding, possibly indicating a different deformational history with respect to the rest of the NEO.
    Description: Published
    Description: 2261–2282
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: AMS data, magnetic fabric, oroclines ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.07. Tectonophysics::04.07.01. Continents ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
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  • 18
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    Paleomagnetism and magnetic fabric of the Eastern Cordillera of Colombia: Evidence for oblique convergence and non rotational reactivation of a Mesozoic intracontinental rift (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We report the paleomagnetic and magnetic fabric results of 58 sites from Cretaceous-Miocene marine and continental strata from the Eastern Cordillera (EC) and the Cucuta zone, at the junction between the Santander Massif and the Merida Andes of Colombia. The EC is an intracontinental doubly vergent range inverting a Triassic to Early Cretaceous rift zone. Twenty-three sites reveal nonsystematic tectonic rotations, including unrotated areas of the EC range with respect to stable South America. Our data show that the EC inverted a NNE oriented rift zone and that the orientation of the Mesozoic rift and the mountain chain roughly correspond. Interestingly, magnetic lineations from anisotropy of magnetic susceptibility analysis do not trend parallel to the chain but rather are oblique to the main orogenic trend. By also considering GPS evidence of a ~1 cm/yr ENE displacement of central western Colombia accommodated by the EC, we suggest that the Miocene-Recent deformation event of this belt arises from ENE oblique convergence reactivating a NNE oriented rift zone. Oblique shortening was likely partitioned into pure dip-slip shear characterizing thick-skinned frontal thrust sheets (well known along both chain fronts) and by range-parallel right-lateral strike-slip faults, which have not been identified yet, but likely exist in the axial part of the EC. Finally, the 35° ± 9° clockwise rotation observed in four post-Miocene magnetically overprinted sites from the Cucuta zone reflects late Cenozoic and ongoing right-lateral strike-slip displacement occurring along faults parallel to the Boconó fault system, possibly connected with the right-lateral faults inferred to exist along the axial part of the EC.
    Description: Published
    Description: 2233–2260
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Paleomagnetism, magnetic fabric, Eastern Cordillera ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics ; 04. Solid Earth::04.07. Tectonophysics::04.07.06. Subduction related processes ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
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  • 19
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    Bipolar climatology of GPS ionospheric scintillation at solar minimum (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: High-rate sampling data of GNSS (Global Navigation Satellite Systems) ionospheric scintillation acquired by a network of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers located in the Svalbard Islands, in Norway and in Antarctica have been analyzed. The aim is to describe the “scintillation climatology” of the high latitude ionosphere over both the poles under quiet conditions of the near-Earth environment. For climatology we mean to assess the general recurrent features of the ionospheric irregularities dynamics and temporal evolution on long data series, trying to catch eventual correspondences with scintillation occurrence. In spite of the fact that the sites are not geomagnetically conjugate, long series of data recorded by the same kind of receivers provide a rare opportunity to draw a picture of the ionospheric features characterizing the scintillation conditions over high latitudes. The method adopted is the Ground Based Scintillation Climatology, which produces maps of scintillation occurrence and of TEC relative variation to investigate ionospheric scintillations scenario in terms of geomagnetic and geographic coordinates, Interplanetary Magnetic Field conditions and seasonal variability. By means of such a novel and original description of the ionospheric irregularities, our work provides insights to speculate on the cause-effect mechanisms producing scintillations, suggesting the roles of the high latitude ionospheric trough, of the auroral boundaries and of the polar cap ionosphere in hosting those irregularities causing scintillations over both the hemispheres at high latitude. The method can constitute a first step towards the development of new algorithms to forecast the scintillations during space weather events.
    Description: Published
    Description: RS0D05
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: restricted
    Keywords: ionospheric scintillations ; climatology ; high latitude ionosphere ; space weather ; 01. Atmosphere::01.02. Ionosphere::01.02.04. Plasma Physics ; 01. Atmosphere::01.02. Ionosphere::01.02.07. Scintillations ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
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  • 20
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    Forearc extension and slow rollback of the Calabrian Arc from GPS measurements (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Here we describe the horizontal velocities of continuous GPS stations in the Calabrian Arc (CA) and surrounding regions. The appropriate reference frame to evaluate the crustal motion of the CA is considered by assessing the internal deformation and the relative motion of the crustal blocks in the foreland of the Apennines␣Ionian␣Maghrebides subduction system. We propose that the motion of CA rela- tive to the subducting Ionian lower plate is most properly assessed by minimizing the GPS velocities in Apulia. In this reference frame the significant ␣2 mm/yr southeast- ward motion of the stations on the Ionian flank of the CA shows that the arc is still moving towards the trench in agreement with the observations of active shortening in the Ioanian wedge. This southeastward migration is associated to 1.4 ± 0.3 mm/yr E␣W extension of the forearc in northern Calabria, comparable with the seismic strain averaged in the last 500 years. The limited subaerial exposure decreases the resolution on locking of the subduction interface but the distribution and direction of crustal extension along the CA impose important constraints on geodynamic interpreta- tions of the area.
    Description: Published
    Description: L17304
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: Calabrian Arc ; GPS ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 21
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    Evidence for surface faulting events along the Paganica fault prior to the 6 April 2009 L’Aquila earthquake (central Italy) (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: main article
    Description: We performed paleoseismological investigations at four sites across the normal Paganica fault (PF) (source of the 2009 Mw 6.3 L’Aquila earthquake), with the goal of reconstructing the rupture history and of contributing to the evaluation of the maximum event expected along the PF. We recognized five distinct surface faulting earthquakes (including the 2009) in the trenches. The age of the penultimate event is consistent with the 1461 earthquake; the third event back occurred around 1000 AD. The two oldest events have larger uncertainties and occurred in the interval 760 BC–670 AD and 2900–760 BC, respectively. The along‐strike vertical displacement for each paleoevent has a limited variability consistently with the fairly homogeneous slip observed in 2009 along the northern part of the rupture. Conversely, the throws change between distinct events and range between 0.15 m in 2009 (maximum estimate) and close to 0.4 (lower bound estimate) in earlier events. These paleorecords and the high fault escarpments imply that earthquakes larger than 2009 occurred on the PF, with implications for the level of hazard. Recurrence intervals also reflect a change with time, the average interval before ∼1000 AD is longer compared to that after this date. Two events occurred in the 2000– 4000 years preceding ∼1000 AD, while three events occurred since ∼1000 AD. The age uncertainties affecting the interpreted events prevent the evaluation of a unique value for interevent interval; the older events appear closely spaced in time or far apart depending on the upper or lower boundary of the age interval. We tentatively assign an average interevent time of ∼500 years for the three youngest events, whereas the time elapsed between the previous ones could be larger, in the order of 1000–2000 years. We calculate a late Pleistocene dip‐slip rate for the PF of 0.2–0.4 mm/yr, consistent with 0.25–0.5 mm/yr for the early Pleistocene. Using age and throw of individual events, we calculate a similar late Holocene average dip‐slip rate of ∼0.3–0.4 mm/yr. This suggests that the portion of the PF where the 2009 continuous surface faulting occurred has fairly a constant average slip release since late Pleistocene. Finally, we discuss different rupture scenarios and alternative models of occurrence compatible with our data and their variability.
    Description: This work was partially funded by the Italian Dipartimento della Protezione Civile in the frame of the 2007–2009 Agreement with Istituto Nazionale di Geofisica e Vulcanologia (INGV).
    Description: Published
    Description: B07308
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: 2009 L'Aquila seismic sequence ; paleoearthquakes ; Paganica fault ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
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  • 22
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    Late Quaternary sediments from deep!sea sediment drifts on the Antarctic Peninsula Pacific margin: Climatic control on provenance of minerals (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We present results of detailed paleomagnetic investigations on deep!sea cores from sediment drifts located along the Pacific continental margin of the Antarctic Peninsula. High!resolution magnetic measurements on u channel samples provide detailed age models for three cores collected from drift 7, which document an age of 122 ka for the oldest sediments recovered near the drift crest at site SED!07 and a high sedimentation rate (11 cm/kyr) at site SED!12 located close to the Alexander Channel system. Low! and high!temperature magnetic measurements in conjunction with microscopic and mineralogic observations from drifts 4, 5 and 7 indicate that pseudosingle!domain detrital titanomagnetite (partially oxidized and with limited Ti substitution) is the dominant magnetic mineral in the drift sediments. The titanomagnetite occurs in two magnetic forms: (1) a low!coercivity form similar to laboratory!synthesized titanomagnetite and (2) a high!coercivity form (Bcr 〉 60 mT). These two forms vary in amount and stratigraphic distribution across the drifts. We did not find evidence for diagenetic magnetic iron sulfides as has been previously suggested for these drift deposits. The observed change of magnetic mineralogy in sediments deposited during Heinrich events on drift 7 appears to be related to warming periods, which temporarily modified the normal glacial transport pathways of glaciogenic detritus to and along the continental rise and thus resulted in deposition of sediments with a different provenance. Understanding this sediment provenance delivery signature at a wider spatial scale should provide information about ice sheet dynamics in West Antarctica over the last !100 kyr.
    Description: Published
    Description: B06104
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: partially_open
    Keywords: Antarctic Peninsula ; Pacific margin ; sediment drift ; late Pleistocene ; Mineral magnetism ; relative palaeointensity ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
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  • 23
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    An analysis of tropical instability waves in a numerical model of the Pacific Ocean - 1. Spatial variability of the waves (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Unstable oscillations confined within the mixed layer close to the equator are generated in wind-forced experiments performed in a multilevel general circulation model configured for the tropical Pacific Ocean. The experiments indicate that the waves develop preferentially in the eastern Pacific along the northern temperature front. However, there is clear evidence of a second unstable region along the southern temperature front in the central Pacific. In both regions the instabilities propagate westward, but in the central Pacific their phase speed is considerably smaller. The differences between the wave characteristics in the eastern and central Pacific are closely correlated to the differences in the time mean conditions of the flow. The eastern instabilities have a structure with two peaks in amplitude: one located on the equator and the other a few degrees north of it. Their dispersion characteristics show many similarities to those of tropical instability waves (TIWs) observed in the Pacific Ocean, while the instabilities which grow in the central Pacific do not have any known observed correspondents. We explore the spatial variability of the simulated waves through a wavelet analysis, which provides detailed results on how the period and wavelength of the instabilities change as a function of longitude, latitude, and depth. The wavelet analysis reveals that in the eastern Pacific and close to the surface the TIWs have a phase speed of-48 cm/s, while in the central Pacific they have a phase speed of-11 cm/s. In particular, the change in the phase speed is due to a change in the dominant period of the TIWs: The period of the central Pacific instabilities is considerably longer than the period of the instabilities present in the eastern Pacific.
    Description: This work was supported by the Department of Commerce/NOAA grant NA56GP0026. One of the authors (SM) was partially supported by a NASA Global Change Fellowship NGT-30288.
    Description: Published
    Description: 29613-29635
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: restricted
    Keywords: Ocean modeling ; Equatorial Ocean ; Tropical Instability Waves ; 03. Hydrosphere::03.01. General::03.01.01. Analytical and numerical modeling
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  • 24
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    Intensity of the geomagnetic field in Europe for the last 3 ka: Influence of data quality on geomagnetic field modeling (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: One of the main challenges of paleomagnetic research is to obtain high-resolution geomagnetic field intensity reconstructions. For the last millennia, these reconstructions are mostly based on archeomagnetic data. However, the quality of the intensity data available in the databases is very variable, and the high scatter observed in the records clearly suggests that some of them might not be reliable. In this work we investigate how the geomagnetic field intensity reconstructions and, hence, our present knowledge of the geomagnetic field in the past, are affected by the quality of the data selected for modeling the Earth’s magnetic field. For this purpose we rank the European archeointensity data in four quality categories following widely accepted paleomagnetic criteria based on the methodology used during the laboratory treatment of the samples and on the number of specimens retained to calculate the mean intensities. Four geomagnetic field regional models have been implemented by applying the revised spherical cap harmonic analysis to these four groups of input data. Geomagnetic field models strongly depend on the used data set. The model built using all the available data (without any preselection) appears to be the less accurate, indicating some internal inconsistencies of the data set. In addition, some features of this model are clearly dominated by the less reliable archeointensity data, suggesting that such features might not reflect real variations of the past geomagnetic field. On the contrary, the regional model built on selected high-quality intensity data shows a very consistent intensity pattern at the European scale, confirming that the main intensity changes observed in Europe in the recent history of the geomagnetic field occurred at the continental scale.
    Description: Published
    Description: 2515–2530
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: open
    Keywords: Geomagnetism ; Paleomagnetism ; Archeomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
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  • 25
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    Ultra-thick Triassic dolomites control the rupture behavior of the central Apennine seismicity: Evidence from magnetic modeling of the L’Aquila fault zone (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: High-resolution tomography from the 2009 L’Aquila extensional seismic sequence has shown that the Mw 6.1 main shock and most of the aftershocks occurred within a high velocity body (6.6≤Vp≤6.8 Km/s), located between depths of 3 and 12 km. The nature of the high Vp-body has remained speculative, although exhumed mafic deep crustal and upper mantle rocks (serpentinites) have been favoured. We used 3D magnetic anomaly modelling to investigate the plausibility of these favoured sources for the L’Aquila body. The modelling does not support the presence of high-velocity serpentinites with a 30-50% serpentinization degree and gabbros. Accordingly, we conclude that the high Vp-body may represent non-magnetic upper Triassic and possibly lower Liassic dolomites that have been drilled in neighbouring wells for 2-4 km. This conclusion is also consistent with the lack of a coherent gravity anomaly for the body. We speculate that ultra-thick Triassic dolomites reaching a thickness of 8 km may have been deposited in syntectonic wedges formed at the northern margin of the Ionian Sea, where oceanic spreading occurred in mid-late Triassic times.
    Description: Published
    Description: 6756–6770
    Description: 7A. Geofisica di esplorazione
    Description: JCR Journal
    Description: restricted
    Keywords: L’Aquila earthquake ; seismic tomography ; magnetic anomalies ; magnetic modelling ; dolomites; ; Apennines ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies
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  • 26
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    Real-time measurements of the concentration and isotope composition of atmospheric and volcanic CO2 at Mount Etna (Italy) (2014)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: We present unprecedented data of real-time measurements of the concentration and isotope composition of CO2 in air and in fumarole-plume gases collected in 2013 during two campaigns at Mount Etna volcano, which were made using a laser-based isotope ratio infrared spectrometer. We performed approximately 360 measurements/h, which allowed calculation of the δ13C values of volcanic CO2. The fumarole gases of Torre del Filosofo (2900mabove sea level) range from 3.24 ± 0.06‰to 3.71 ± 0.09‰, comparable to isotope ratio mass spectrometry (IRMS) measurements of discrete samples collected on the same dates. Plume gases sampled more than 1 km from the craters show a δ13C= 2.2 ± 0.4‰, in agreement with the crater fumarole gases analyzed by IRMS. Measurements performed along ~17km driving track from Catania to Mount Etna show more negative δ13C values when passing through populated centers due to anthropogenic-derived CO2 inputs (e.g., car exhaust). The reported results demonstrate that this technique may represent an important advancement for volcanic and environmental monitoring.
    Description: Published
    Description: 2382–2389
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Real-time data of CO2 content and δ13C in atmospheric/volcanic gases ; This study opens new perspective for the community for volcanic surveillance ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 05. General::05.02. Data dissemination::05.02.01. Geochemical data
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  • 27
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    A new extended software package for quantitative paleoenvironmental reconstrutions (1999)
    American Geophysical Union
    In:  EPIC3EOS, Transactions of the American Geophysical Union, American Geophysical Union, 80(19), 223 p., pp. 223-223
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 28
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    Thirty years of satellite‐derived lava discharge rates at Etna: Implications for steady volumetric output (2011)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: We present a 30 year long data set of satellite‐derived time‐averaged lava discharge rates (TADR) for Mount Etna volcano (Sicily, Italy), spanning 1980–2010 and comprising 1792 measurements during 23 eruptions. We use this to classify eruptions on the basis of magnitude and intensity, as well as the shape of the TADR time series which characterizes each effusive event. We find that while 1983–1993 was characterized by less frequent but longer‐duration effusive eruptions at lower TADRs, 2000–2010 was characterized by more frequent eruptions of shorter duration and higher TADRs. However, roughly the same lava volume was erupted during both of these 11 year long periods, so that the volumetric output was linear over the entire 30 year period, increasing at a rate of 0.8 m3 s−1 between 1980 and 2010. The cumulative volume record can be extended back in time using data available in the literature. This allows us to assess Etna’s output history over 5 centuries and to place the current trend in historical context. We find that output has been stable at this rate since 1971. At this time, the output rate changed from a low discharge rate phase, which had characterized the period 1759 to 1970, to a high discharge rate phase. This new phase had the same output rate as the high discharge rate phase that characterized the period 1610–1669. The 1610–1669 phase ended with the most voluminous eruption of historic times.
    Description: This contribution is in support of the LMV‐based (PI: Franck Donnadieu) TerMex‐MYSTRALS project “Contribution à l’évaluation des risques associés aux activités éruptives majeures de l’Etna: approche multidisciplinaire des processus et précurseurs.”
    Description: Published
    Description: B08204
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: partially_open
    Keywords: Etna ; time averaged effusion rate ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
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  • 29
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    Shallow structure of Mt. Vesuvius volcano, Italy, from seismic array analysis (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-05-23
    Description: SPAC method applied to data from a small aperture seismic array on Mt. Vesuvius gives the shallow velocity model.
    Description: Published
    Description: 481-484
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Array analysis ; shallow structure ; SPAC method ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
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  • 30
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    Source Mechanism of Long Period events recorded by a high density seismic network during the 2008 eruption on Mt Etna (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: 129 Long Period (LP) events, divided in two families were recorded by 50 stations deployed on Mount Etna within an eruptive context in the second half of June 2008. In order to understand the mechanisms of these events, we perform moment tensor inversion. Numerical tests show that unconstrained inversion leads to reliable moment tensor solutions because of the close proximity of numerous stations to the source positions. However, single forces cannot be accurately determined as they are very sensitive to uncertainities in the velocity model. These tests emphasize the importance of using stations located as close as possible to the source in the inversion of LP events. Inversion of LP signals is initially unconstrained, in order to estimate the most likely mechanism. Constrained inversions then allow us to accurately determine the structural orientations of the mechanisms. Inversions for both families show mechanisms with strong volumetric components. These events are generated by cracks striking SW-NE for both families and dipping 70± SE (fam. 1) and 50± NW (fam. 2). The geometries of the cracks are different from the structures obtained by the location of these events. The orientation of the cracks is consistent with the local tectonic context on Mount Etna. The LP events seem to be a response to the lava fountain occuring on the 10th of May, 2008.
    Description: In press
    Description: (38)
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: Long-Period events ; earthquake source mechanism ; Etna Volcano ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 31
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    Kinematics and source zone properties of the 2004 Sumatra-Andaman earthquake and tsunami: Nonlinear joint inversion of tide gauge, satellite altimetry, and GPS data (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We (re)analyzed the source of the 26 December 2004 Sumatra-Andaman earthquake and tsunami through a nonlinear joint inversion of an inhomogeneous data set made up of tide gauges, satellite altimetry, and far-field GPS recordings. The purpose is twofold: (1) the retrieval of the main kinematics rupture parameters (slip, rake, and rupture velocity) and (2) the inference of the rigidity of the source zone. We independently estimate the slip from tsunami data and the seismic moment from geodetic data to derive the rigidity. Our results confirm that the source of the 2004 Sumatra-Andaman earthquake has a complex geometry, constituted by three main slip patches, with slip peaking at ~30 m in the southern part of the source. The rake direction rotates counterclockwise at the northern part of the source, according to the direction of convergence along the trench. The rupture velocity is higher in the deeper than in the shallower part of the source, consistent with the expected increase of rigidity with depth. It is also lower in the northern part, consistent with known variations of the incoming plate properties and shear velocity. Our model features a rigidity (20–30 GPa) that is lower than the preliminary reference Earth model (PREM) average for the seismogenic volume. The source rigidity is one of the factors controlling the tsunami genesis: for a given seismic moment, the lower the rigidity, the higher the induced seafloor displacement. The general consistence between our source model and previous studies supports the effectiveness of our approach to the joint inversion of geodetic and tsunami data for the rigidity estimation.
    Description: Published
    Description: B02304
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Source process ; Sumatra ; Tsunami ; Joint Inversion ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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    Seismoacoustic investigations of paroxysmal activity at Mt. Etna volcano: New insights into the 16 November 2006 eruption (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: On 16 November 2006, a 1 day long paroxysmal eruption occurred at the summit craters of Mt. Etna volcano. A multiparametric approach, consisting of analyzing infrasonic, seismic, and video camera recordings, was carried out to follow its evolution. Volcanological and geophysical observations identified three eruptive phases. In the first phase, infrasonic and seismic characteristics reflected the highly explosive nature of the activity. Waveform characterization of infrasound events confirmed the activity of the several explosive vents at the summit of Southeast Crater (SEC). During the second phase, results highlighted the decoupling between seismic and infrasonic sources, which was due to the decrease in explosive activity and the reactivation of effusive vents located south of Bocca Nuova and on the saddle between Bocca Nuova and SEC. The third phase was the most intense and was characterized by various volcanic phenomena (pyroclastic flows, jets of dark ash, and white steam). The very high radiated infrasonic energy, together with infrasound event features, led us to infer a gas enrichment of the shallow magma column, preceding by a few minutes and likely related to the pyroclastic flows in the SEC area. After the eruption at SEC, variations in infrasound events related to the activity of Northeast Crater (NEC) were found. The observed spectral changes and the source mechanism modeling of the NEC infrasound events suggest the existence of a link in the plumbing system feeding the two craters.
    Description: Published
    Description: B09301
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Etna ; Infrasound ; volcanic tremor ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 33
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    FORMOSAT-3/COSMIC E region observations and daytime foE at middle latitudes (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Ionosonde observations at Rome and Gibilmanna (Sicily) for some months of 2006–2007 were analyzed in the connection with recent COSMIC NmE results. Italy was completely located in the NmE enhanced zone according to COSMIC observations for the periods in question. COSMIC‐observed NmE values in the NmE enhanced zone do not coincide with NmE scaled from ionograms in accordance with the URSI Recommendations, but the IRI model correctly describes monthly median NmE contrary to the Chu et al. (2009) conclusion. Three month averaged COSMIC NmE values turn out to be close to monthly median NmE corresponding to the blanketing frequency fbEs. A conclusion is made that sporadic E practically permanently existing during daytime hours in summer strongly contributes to NmE observed by COSMIC. Possible reasons for the occurrence of the NmE enhanced zones at middle latitudes are discussed.
    Description: Published
    Description: A06307
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: JCR Journal
    Description: restricted
    Keywords: mid-latitude ionosphere ; sporadic E layer ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous ; 01. Atmosphere::01.02. Ionosphere::01.02.02. Dynamics
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  • 34
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    The failed eruption of Mt. Etna in December 2005: evidence from volcanic tremor analyses (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Strong changes in seismic radiation, comparable to those preceding and/or accompanying eruptive activity in recent years, were recorded at Mt. Etna volcano, Italy, from November 2005 to January 2006. The amplitude of volcanic tremor peaked in mid-December 2005 after a continuous, slow increase from August 2005 onwards, during which neither effusive nor paroxysmal activity was observed by volcanologists and alpine guides. During this time span, the centroid locations of volcanic tremor moved towards the surface, more and more clustered below the summit craters. The application of pattern classification analysis based on Self-Organizing Maps and fuzzy clustering to volcanic tremor data highlighted variations in the frequency domain as well. These changes were temporally associated with ground deformation variations, as indicative of a mild inflation of the summit of the volcano, and with a conspicuous increase in the SO2 plume-flux emission. Overall, we interpret this evidence as the result of recharging of the volcanic feeder at depth (〉 3 km below sea level) during which magma did not reach the shallow plumbing system.
    Description: Published
    Description: 4989–5005
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: embargoed_20140606
    Keywords: time series analysis ; volcano seismology ; volcano monitoring ; neural network and fuzzy logic ; seismic tomography ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 35
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    Probabilistic modeling of future volcanic eruptions at Mount Etna (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The statistical analysis of volcanic activity at Mt Etna was conducted with the twofold aim of (1) constructing a probability map for vent opening of future flank eruptions and (2) forecasting the expected number of eruptive events at the summit craters. The spatiotemporal map of new vent opening at Etna volcano is based on the analysis of spatial locations and frequency of flank eruptions starting from 1610. Thanks to the completeness and accuracy of historical data over the last four centuries, we examined in detail the spatial and temporal distribution of flank eruptions showing that effusive events follow a nonhomogenous Poisson process with space-time varying intensities. After demonstrating the spatial nonhomogeneity and the temporal nonstationarity of flank eruptions at Etna, we calculated the recurrence rates (events expected per unit area per unit time) and produced different spatiotemporal probability maps of new vent opening in the next 1, 10 and 50 years. These probabilistic maps have an immediate use in evaluating the future timing and areas of Etna prone to volcanic hazards. Finally, the results of the analysis of the persistent summit activity during the last 110 years indicate that the hazard rate for eruptive events is not constant with time, differs for each summit crater of Mt Etna, highlighting a general increase in the eruptive frequency starting from the middle of last century and particularly from 1971, when the SE crater was formed.
    Description: This work was developed in the frame of the TecnoLab, the Laboratory for the Technological Advance in Volcano Geophysics organized by INGV-CT, DIEES-UNICT, and DMI-UNICT.
    Description: Published
    Description: 1925-1935
    Description: 1V. Storia e struttura dei sistemi vulcanici
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 3V. Dinamiche e scenari eruttivi
    Description: 4V. Vulcani e ambiente
    Description: 3IT. Calcolo scientifico e sistemi informatici
    Description: JCR Journal
    Description: restricted
    Keywords: Etna ; probabilistic modeling ; eruption ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous ; 04. Solid Earth::04.07. Tectonophysics::04.07.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 05. General::05.01. Computational geophysics::05.01.02. Cellular automata, fuzzy logic, genetic alghoritms, neural networks ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis ; 05. General::05.01. Computational geophysics::05.01.05. Algorithms and implementation ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
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  • 36
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    Ocean, sea-ice, atmosphere oscillations in the Southern Ocean as simulated by the SINTEX coupled model (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: 1This study evaluates the Antarctic Circumpolar Wave (ACW) as simulated by the SINTEX coupled model. We found evidence that sea-ice treatment plays a crucial role on simulating the ACW. In particular, SST anomalies at interannual time scales describe a propagating ACW-like pattern when a dynamic thermodynamic sea-ice model is coupled with the ocean, but when sea-ice is relaxed to climatology, anomalies occur as zonally symmetric patterns that do not propagate in longitude. Moreover, from the experiment with an active sea-ice component we saw that ACW-like oscillations are strongly modulated by low frequency variability. Our result adds some extra confidence to previous studies based on relatively short series of observed data.
    Description: This research was supported by the PREDICATE EU project (EVK2 – CT-1999 – 0020,). First author was supported by the PRISM EU project (EVR1 – CT-2001 – 40012).
    Description: Published
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: restricted
    Keywords: Antarctic Circumpolar Wave ; General Circulation Models ; air-ice-sea interactions ; 02. Cryosphere::02.04. Sea ice::02.04.01. Atmosphere/sea ice/ocean interaction
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 37
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    An analysis of tropical instability waves in a numerical model of the Pacific Ocean - 2. Generation and energetics of the waves (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The instability processes which generate unstable waves with chara- cteristics similar to observed tropical instability waves in the Pacific Ocean are examined through a local energy analysis based on deviations from the time mean flow. Numerical experiments indicate that the waves develop preferentially in the eastern Pacific along the northern temperature front and have a westward phase speed and a structure with two peaks in amplitude: one located on the equator and the other a few degrees north of it. The energy analysis shows that the "two-peak" structure of the eastern waves is explained by two different instability processes which occur at different latitudes. In the time mean sense the region north of the equator is baroclinically unstable, while barotropic instability prevails at the equator. The life cycle of the waves is revealed by the time evolution of the energetics. Baroclinic instability is the dominant triggering mechanism which induces growth of the waves along the northern temperature front. The eddy pressure fluxes radiate energy south of the equator where the rneridional shear between the Equatorial Undercurrent and the South Equatorial Current becomes barotropically unstable. From the numerical simulations, there is evidence of a second unstable region in the central Pacific south of the equator where the instabilities have a lower phase speed. The energy analysis also shows that these waves grow from both barotropic and baroclinic conversions.
    Description: This work was supported by the Department of Com- merce/NOAA under grant NA56GP0026. One of the au- thors (SM) was partially supported by a NASA Global Change Fellowship NGT-30288. Another author (AB) was supported by a UCAR Postdoctoral Fellowship
    Description: Published
    Description: 29637-29661
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: restricted
    Keywords: Ocean modeling ; Equatorial Ocean ; Tropical Instability Waves ; Ocean wave generation ; Ocean wave energetics ; 03. Hydrosphere::03.01. General::03.01.01. Analytical and numerical modeling
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  • 38
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    Seismo-tectonic behavior of the Pernicana Fault System (Mt Etna): A gauge for volcano flank instability? (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Flank instability at basaltic volcanoes is often related to repeated dike intrusions along rift zones and accompanied by surface fracturing and seismicity. These processes have been mostly studied during specific events, and the lack of longer-term observations hinders their better understanding. Here we analyze ~20 years of deformation of the Pernicana Fault System (PFS), the key structure controlling the instability of the eastern flank of Mt. Etna. We exploit East-West and vertical components of mean deformation velocity, as well as corresponding time series, computed from ERS/ENVISAT (1992–2010) and COSMO-SkyMed (2009–2011) satellite radar sensors via Synthetic Aperture Radar Interferometry techniques. We then integrate and compare this information with field, seismic, and leveling data, collected between 1980 and 2012. We observe transient displacements accompanied by seismicity, overprinted on a long-term background eastward motion (~2 cm/yr). In the last decades, these transient events were preceded by a constant amount of accumulated strain near the PFS. The time of strain accumulation varies between a few years and a few decades, also depending on magma emplacement within the nearby North East Rift, which may increase the strain along the PFS. These results suggest that the amount of deformation near the PFS may be used as a gauge to forecast the occurrence of instability transients on the eastern flank of Etna. In this context, the PFS may provide an ideal, small-scale structure to test the relations between strain accumulation, stress loading, and seismic energy release.
    Description: This work has been partially supported by the Italian Space Agency (ASI) within the SAR4Volcanoes project, agreement I/ 034/11/0.
    Description: Published
    Description: 4398-4409
    Description: 1T. Geodinamica e interno della Terra
    Description: 2T. Tettonica attiva
    Description: 3T. Pericolosità sismica e contributo alla definizione del rischio
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: 5T. Sorveglianza sismica e operatività post-terremoto
    Description: 1V. Storia e struttura dei sistemi vulcanici
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 3V. Dinamiche e scenari eruttivi
    Description: 4V. Vulcani e ambiente
    Description: 6A. Monitoraggio ambientale, sicurezza e territorio
    Description: JCR Journal
    Description: restricted
    Keywords: Volcano flank instability ; Pernicana fault ; Etna ; 04. Solid Earth::04.01. Earth Interior::04.01.99. General or miscellaneous ; 04. Solid Earth::04.03. Geodesy::04.03.99. General or miscellaneous ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 04. Solid Earth::04.07. Tectonophysics::04.07.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 05. General::05.01. Computational geophysics::05.01.99. General or miscellaneous ; 05. General::05.02. Data dissemination::05.02.99. General or miscellaneous ; 05. General::05.08. Risk::05.08.99. General or miscellaneous
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  • 39
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    Complete seismic release of tectonic strain and earthquake recurrence in the Apennines (Italy) (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Here I compare estimates of tectonic strain rates from dense Global Positioning System measurements with the seismicity released in the last ~500 years in the Apennines (Italy). The rates of seismic moment accumulation from geodesy and of historical seismic release by earthquakes agree within the uncertainties, ruling out significant aseismic deformation. Within the considered 400 km long section of the Apennines, this balance yields an average recurrence interval of 30–75 years for MW≥6.5 events without requiring a future earthquake larger than those observed historically (MW~7). A minimum estimate of unreleased strain allows MW≥6.5 and MW≥6.9 events to be released in ~35% and ~10% of the central-southern Apennines, respectively. The definition of the seismic potential for smaller events is more uncertain, and their occurrence remains a significant threat throughout the Apennines.
    Description: Published
    Description: 1155–1162
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: restricted
    Keywords: Crustal deformation ; Earthquakes ; GPS ; Apennines ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 40
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    Long-term stress-strain analysis of volcano flank instability: The eastern sector of Etna from 1980 to 2012 (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We investigated the evolution of seismicity and deformation in the unstable eastern flank of Etna volcano over a 30 year period (from 1980 to 2012). A significant temporal correlation has been revealed between periods of flank acceleration and intensified seismic activity by comparing seismicity along the northern border (Pernicana fault system) of the sliding flank and the deformation of the eastern flank. Two marked phases have been observed in 1984-1986 and in the years following 2002. These two phases are separated by an intermediate phase from 1987 to 2001, in which the flank sliding slowed down and the seismicity dropped drastically. This common temporal evolution in the deformation rate and seismic release supports the hypothesis that the seismicity in the northern border can be viewed as a marker of the response to accommodate the stress exerted by the traction of the eastern flank sliding. This interplay has also been corroborated by finite element method numerical computations that highlight a good correlation between the seismicity pattern and areas of positive stress changes induced by the sliding surface. The two intense phases of flank acceleration are representative of two main different sources: volcano flank instability stretching the eastern sector in the first 1984-1986 phase and magmatic intrusions pushing the eastern flank seaward since the 2002-2003 eruption. Establishing the relationship between flank acceleration and seismic activation therefore contributes to understanding Etna's mechanical behavior and provides insights into the processes regulating the unstable flank response.
    Description: Published
    Description: 5098-5108
    Description: 1V. Storia e struttura dei sistemi vulcanici
    Description: JCR Journal
    Description: restricted
    Keywords: Pernicana ; fault ; volcano-tectonics ; flank instability ; seismicity and deformation ; stress and strain ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
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  • 41
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    Magma flow between summit and Pu‘u ‘O‘o at Kılauea Volcano, Hawai‘i (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Volcanic eruptions are often accompanied by spatiotemporal migration of ground deformation, a consequence of pressure changes within magma reservoirs and pathways. We modeled the propagation of pressure variations through the east rift zone (ERZ) of K" ılauea Volcano, Hawai‘i, caused by magma " o-Kupaianaha withdrawal during the early eruptive episodes (1983–1985) of the ongoing Pu‘u ‘ O‘" " eruption. Eruptive activity at the Pu‘u ‘ O‘" o vent was typically accompanied by abrupt deflation that lasted for several hours and was followed by a sudden onset of gradual inflation once the eruptive episode had ended. Similar patterns of deflation and inflation were recorded at K" ılauea’s summit, approximately 15 km to the northwest, albeit with time delays of hours. These delay times can be reproduced by modeling the spatiotemporal changes in magma pressure and flow rate within an elastic-walled dike that traverses K" ılauea’s ERZ. Key parameters that affect the behavior of the magma-dike system are the dike dimensions, the elasticity of the wall rock, the magma viscosity, and to a lesser degree the magnitude and duration of the pressure variations themselves. Combinations of these parameters define a transport efficiency and a pressure diffusivity, which vary somewhat from episode to episode, resulting in variations in delay times. The observed variations in transport efficiency are most easily explained by small, localized changes to the geometry of the magma pathway
    Description: Published
    Description: 2232–2246
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: magma flow ; dikes ; Kilauea ; elastic rock ; magma-rock coupling ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
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  • 42
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    The coupling between very long period seismic events, volcanic tremor, and degassing rates at Mount Etna volcano (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: From December 2005 to January 2006, an anomalous degassing episode was observed at Mount Etna, well-correlated with an increase in volcanic tremor, and in the almost complete absence of eruptive activity. In the same period, more than 10,000 very long period (VLP) events were detected. Through moment tensor inversion analyses of the VLP pulses, we obtained quantitative estimates of the volumetric variations associated with these events. This allowed a quantitative investigation of the relationship between VLP seismic activity, volcanic tremor, and gas emission rate at Mount Etna. We found a statistically significant positive correlation between SO2 gas flux and volcanic tremor, suggesting that tremor amplitude can be used as a first-order proxy for the background degassing activity of the volcano. VLP volumetric changes and SO2 gas flux are correlated only for the last part of our observations, following a slight change in the VLP source depth. We calculate that the gas associated with VLP signal genesis contributed less than 5% of the total gas emission. The existence of a linear correlation between VLP and degassing activities indicates a general relationship between these two processes. The effectiveness of such coupling appears to depend upon the particular location of the VLP source, suggesting that conduit geometry might play a significant role in the VLP-generating process. These results are the first report on Mount Etna of a quantitative relationship between the amounts of gas emissions directly estimated through instrumental flux measurements and the quantities of gas mass inferred in the VLP source inversion.
    Description: Published
    Description: 4910-4921
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Very Long Period seismicity ; UV scanners network ; Etna Volcano ; volcano monitoring ; 04. Solid Earth::04.02. Exploration geophysics::04.02.06. Seismic methods ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 43
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    Interaction between magma intrusion and flank dynamics at Mt. Etna in 2008, imaged by integrated dense GPS and DInSAR data (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Global positioning system (GPS) and differential interferometric synthetic aperture radar (DInSAR) data, collected from July 2007 to July 2008 on Mt. Etna, are analyzed to define the dynamics preceding and accompanying the onset of the eruption on 13 May 2008. Short- and long-term comparisons have been made on both GPS and radar data, covering similar time windows. Thanks to the availability of three GPS surveys the year before the eruption onset, an increase in the seaward movement of the NE flank of the volcano has been detected in the few months before the dike intrusion. The GPS ground deformation pattern also shows a slight inflation centered on the western side of the volcano in the preeruptive long-term comparison (from July 2007 to May 2008). The GPS has been integrated with DInSAR data by the SISTEM approach, to take advantage of the different methodologies and provide high spatial sampling of the 3-D ground displacement pattern. We inverted the SISTEM results to model the pressure source causing the observed preeruptive inflation. The subsequent emplacement of the eruptive dike was imaged by two GPS surveys carried out on a dense network over the uppermost part of the volcano on 6 and 13 May, i.e., a few days before and a few hours after the beginning of the eruption. We inverted this comparison to define the position, geometry, and kinematics of the dike. The dike intrusion was also imaged by DInSAR data with temporal baselines of 2-3 months, which confirm strong displacements localized on the summit area, rapidly decreasing toward the middle flanks of the volcano, as detected by very short-term GPS data; furthermore, the comparison between DInSAR and GPS data highlighted the presence of a depressurizing source localized beneath the upper southwestern area, acting just after the dike intrusion. Finally, the long-period (1 year) GPS and DInSAR data were integrated by SISTEM to finely depict the 3-D ground deformation pattern with the highest spatial resolution. The long-period data allowed the complex kinematics of the volcano to be finely imaged and highlighting the interaction between flank dynamics and magma injection.
    Description: Published
    Description: 2818-2835
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: flank dynamics ; eruption ; volcano-tectonics ; GPS ; DInSAR ; data integration ; Etna ; deformation ; volcano ; fault ; 04. Solid Earth::04.03. Geodesy::04.03.07. Satellite geodesy
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  • 44
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    New data from borehole strainmeters to infer lava fountain sources (Etna 2011-2012) (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: In January 2011 eruptive activity resumed at Etna producing a new phase with frequent lava fountain episodes until April 2012. In November 2011, the first two borehole strainmeters were installed, which detected negative strain changes (~ 0.15 - 0.8 strain) during the paroxysmal events. A Finite Element Model was set up to estimate accurately the tilt and volumetric strain, taking into account the real profile of the volcano and the elastic medium heterogeneity. The numerical computations indicated an elongated depressurizing source located at 0 km b.s.l., which underwent a volume change of ~2 x 106 m3 which is the most of the magma volume erupted while a smaller remaining part is accommodated by the magma compressibility. This shallow source cannot accumulate large magma volumes and, thus, favours short term periodic eruptive events with a fairly constant balance between the refilling and the erupted magma.
    Description: Published
    Description: 3579-3584
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: embargoed_20150613
    Keywords: Etna volcano ; lava fountain eruptions ; shallow plumbing system ; borehole strainmeters ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
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  • 45
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    Interseismic coupling, seismic potential, and earthquake recurrence on the southern front of the Eastern Alps (NE Italy) (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Here we use continuous GPS observations to document the geodetic strain accumulation across the South-Eastern Alps (NE Italy). We estimate the interseismic coupling on the intracontinental collision thrust fault and discuss the seismic potential and earthquake recurrence. We invert the GPS velocities using the back slip approach to simultaneously estimate the relative angular velocity and the degree of interseismic coupling on the thrust fault that separates the Eastern Alps and the Venetian-Friulian plain. Comparison between the rigid rotation predicted motion and the shortening observed across the area indicates that the South-Eastern Alpine thrust front absorbs about 70% of the total convergence between the Adria and Eurasia plates. The coupling is computed on a north dipping fault following the continuous external seismogenic thrust front of the South-Eastern Alps. The modeled thrust fault is currently locked from the surface to a depth of ≈10 km. The transition zone between locked and creeping portions of the fault roughly corresponds with the belt of microseismicity parallel and to the north of the mountain front. The estimated moment deficit rate is 1.3 ± 0.4 × 1017 Nm/yr. The comparison between the estimated moment deficit and that released historically by the earthquakes suggests that to account for the moment deficit the following two factors or their combination should be considered: (1) a significant part of the observed interseismic coupling is released aseismically and (2) infrequent “large” events with long return period (〉 1000 years) and with magnitudes larger than the value assigned to the largest historical events (Mw≈ 6.7).
    Description: Published
    Description: 4448-4468
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: restricted
    Keywords: Eastern Alps; interseismic coupling; seismotectonics; seismic potential; recurrence time; GPS ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk ; 04. Solid Earth::04.07. Tectonophysics::04.07.01. Continents ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 46
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    An active oblique-contractional belt at the transition between the Southern Apennines and Calabrian Arc: The Amendolara Ridge, Ionian Sea, Italy (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: High-resolution, single-channel seismic and multibeam bathymetry data collected at the Amendolara Ridge, a key submarine area marking the junction between the Apennine collision belt and the Calabrian subduction forearc, reveal active deformation in a supposedly stable crustal sector. New data, integrated with existing multichannel seismic profiles calibrated with oil-exploratory wells, show that middle to late Pleistocene sediments are deformed in growth folds above blind oblique-reverse faults that bound a regional pop-up. Data analysis indicates that ~10 to 20 km long banks that top the ~80 km long, NW-SE trending ridge are structural culminations above en echelon fault segments. Numeric modeling of bathymetry and stratigraphic markers suggests that three 45° dipping upper crustal (2–10 km) fault segments underlie the ridge, with slip rates up to ~0.5 mm/yr. Segments may be capable with M ~ 6.1–6.3 earthquakes, although an unknown fraction of aseismic slip undoubtedly contributes to deformation. The fault array that bounds the southern flank of the ridge (Amendolara Fault System) parallels a belt of Mw 〈 4.7 strike-slip and thrust earthquakes, which suggest current left-oblique reverse motion on the array. The eastern segment of the array shows apparent morphologic evidence of deformation and might be responsible for Mw ≤ 5.2 historic events. Late Pliocene-Quaternary growth of the oblique contractional belt is related to the combined effects of stalling of Adriatic slab retreat underneath the Apennines and subduction retreat of the Ionian slab underneath Calabria. Deformation localization was controlled by an inherited mechanical interface between the thick Apulian (Adriatic) platform crust and the attenuated Ionian Basin crust.
    Description: Published
    Description: 2169–2194
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: partially_open
    Keywords: Active compression ; Growth strata modeling ; High-resolution seismic ; Multibeam bathymetry ; Jonian Sea ; 04. Solid Earth::04.02. Exploration geophysics::04.02.06. Seismic methods ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology ; 04. Solid Earth::04.04. Geology::04.04.04. Marine geology ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy
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  • 47
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    The initial phases of the 2008–2009 Mount Etna eruption: A multidisciplinary approach for hazard assessment (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Between 2007 and early 2008, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) monitoring networks on Etna volcano recorded a recharging phase that climaxed with a new effusive eruption on 13 May 2008 and lasted about 14 months. A dike‐forming intrusion was accompanied by a violent seismic swarm, with more than 230 events recorded in the first 6 h, the largest being ML = 3.9. In the meanwhile, marked ground deformation was recorded by the permanent tilt and GPS networks, and sudden changes in the summit area were detected by five continuously recording magnetic stations. Poor weather conditions did not allow direct observation of the eruptive events, but important information was provided by infrared satellite images that detected the start of lava fountains from the eruptive fissure, feeding a lava flow. This flow spread within the Valle del Bove depression, covering 6.4 km on the southeastern flank of the volcano in a few hours. The seismicity and deformation pattern indicated that the dike‐forming intrusion was propagating northward. It produced a dry fracture field, which generated concern for the possibility that the eruptive fissures could expand downslope toward populated areas. Monitoring and modeling of the multidisciplinary data, together with the simulations of ash dispersal and lava flows, allowed us both to infer the eruptive mechanisms and to provide correct interpretation of the ongoing phenomena, furnishing useful information for civil defense purposes. We describe how this approach of feedback between monitoring and research provides critical support to risk evaluation.
    Description: We wish to thank all our colleagues from INGV Sezione di Catania for data collection, for the maintenance of the monitoring networks during the whole eruption, and for the many discussions about the interpretation of the eruptive events; the Etna Guides, the Funivia dell’Etna, and especially Alfio Mazzaglia and Nino Mazzaglia for the prompt information pertaining any news about the summit eruptive activity at Mount Etna; the Italian Civil Defense (DPC) for the close and efficient collaboration built up during the last height years of activity at Etna and other Sicilian volcanoes. We obtained MODIS data from NASA and SEVIRI data from EUMETSAT. We are indebted to Paul Davis for his B03203 BONACCORSO ET AL.: ETNA MULTIDISCIPLINARY HAZARD ASSESSMENT B03203 17 of 19 positive and encouraging comments. We thank the Associate Editor Michael P. Ryan, who helped greatly in improving the form of the manuscript. This study was undertaken with partial financial support from the INGV‐DPC 2007–2009 Agreement. Scientific papers funded by DPC do not represent its official opinion and politics. We thank Stephen Conway for revising the English language of this manuscript.
    Description: Published
    Description: B03203
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: reserved
    Keywords: Etna ; effusive eruption ; hazard evaluation ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 48
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    Wave-guide effects in very high rate GPS record of the 6 April 2009, Mw 6.1 L'Aquila, central Italy earthquake (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: A 10 Hz sampling frequency GPS station was installed near L'Aquila a few days before the 6 April 2009 Mw 6.1 earthquake. It recorded displacement waveforms during the main shock and the largest Mw 5.4 aftershock of 7 April. The horizontal components of the main shock contain a high-amplitude (43 cm peak-to-peak) nearly harmonic (1 Hz) wave train not evident in other nearby instrumental records. The persistency of this feature during aftershocks recorded by a temporarily colocated seismological station highlights a local site effect. Traditional models based on near-surface velocity structure and topography variations fail to reproduce the size and frequency band of the observed amplified motion. The amplified wave train can be explained by a low-velocity fault zone layer below the station. This model fits the delay of the large-amplitude nearly harmonic wave train after the S wave phase and is consistent with the variation in the fault excitation efficiency between the two shocks in relation to their different source depth and location. Synthetic calculation of trapped waves in a model consisting of two quarter spaces separated by a 650 m wide low-velocity zone with 50% velocity reduction and Q value of 20 fit well the observed anomalous record. The parameters of the model fault zone layer are consistent with geological evidence of a broad damage zone adjacent to the station and a similar site response found in this crustal zone with ambient noise. Results of shallow seismic surveys and sonic logs from deep wells provide independent constraints on the host rock velocities.
    Description: This work has partially benefited from the activities performed in the NERA project (Network of European Research infrastructures for earthquake risk Assessment and mitigation, 262330), funded by the European Commission FP7 program, and in the FIRB-Abruzzo project, funded by the Italian Ministery of Education, University and Research.
    Description: Published
    Description: 490–501
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: restricted
    Keywords: High-rate GPS ; Transient deformation ; L'Aquila earthquake ; fault-guided waves ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
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  • 49
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    Investigation of the complex dynamics and structure of the 2010 Eyjafjallajökull volcanic ash cloud using multispectral images and numerical simulations (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We investigated the structure and evolution of the 2010 Eyjafjallajökull volcanic cloud and its dispersal over Iceland and Europe integrating satellite multispectral images and numerical simulations. Data acquired by Medium Resolution Imaging Spectrometer (MERIS)and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) have been analyzed to quantify the cloud extent and composition. The VOL-CALPUFF dispersal code was applied to reconstruct the transient and 3-D evolution of the cloud. Source parameters estimated on the base of available a posteriori volcanological data sets have been used. Quantitative comparisons between satellite retrievals and modeling results were performed for two selected instants of time during the first and third eruptive phases on a regional scale. Sensitivity of the model to initial volcanological conditions has been analyzed at continental scale. Several complex non intuitive features of cloud dynamics have been highlighted and strengths and limitations of the adopted methods identified. The main findings are: the level of quantitative agreement between satellite observations and numerical results depends on ash cloud composition (particle sizes and concentration) with better agreement for smaller particles and higher concentrations; the agreement between observations and modeling outcomes also depends on the temporal stability of volcanological conditions and the complexity of the meteorological wind field; the irregular dispersion of ash, as reconstructed from satellite data and numerical modeling, can be well explained by the different response of particle sizes to strong vertical wind-shear, and by resuspension processes acting at ground level; eruptive source conditions are the main source of uncertainty in modeling, especially during an ongoing crisis and at long-range scales.
    Description: Published
    Description: 4729–4747
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Volcanic ash cloud ; Satellite retrieval ; Numerical modelling ; Eyjafjallajokull ; Ash dispersal and deposition ; 01. Atmosphere::01.01. Atmosphere::01.01.07. Volcanic effects
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  • 50
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    Vertical GPS ground motion rates in the Euro-Mediterranean region: New evidence of velocity gradients at different spatial scales along the Nubia-Eurasia plate boundary (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We use 2.5 to 14 years long position time series from 〉800 continuous Global Positioning System (GPS) stations to study vertical deformation rates in the Euro-Mediterranean region. We estimate and remove common mode errors in position time series using a principal component analysis, obtaining a significant gain in the signal-to-noise ratio of the displacements data. Following the results of a maximum likelihood estimation analysis, which gives a mean spectral index ~ 0.7, we adopt a power law + white noise stochastic model in estimating the final vertical rates and find 95% of the velocities within ±2 mm/yr, with uncertainties from filtered time series ~40% smaller than from the unfiltered ones. We highlight the presence of statistically significant velocity gradients where the stations density is higher. We find undulations of the vertical velocity field at different spatial scales both in tectonically active regions, like eastern Alps, Apennines, and eastern Mediterranean, and in regions characterized by a low or negligible tectonic activity, like central Iberia and western Alps. A correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area. Glacial isostatic adjustment and weathering processes do not completely explain the measured rates, and a combination of active tectonics and deep-seated geodynamic processes must be invoked. Excluding areas where localized processes are likely, or where subduction processes may be active, mantle dynamics is the most likely process, but regional mantle modeling is required for a better understanding.
    Description: Published
    Description: 6003–6024
    Description: 1T. Geodinamica e interno della Terra
    Description: 2T. Tettonica attiva
    Description: 1R. Reti di monitoraggio e Osservazioni
    Description: JCR Journal
    Description: restricted
    Keywords: GPS ; Geodynamics ; Mediterranean ; Vertical deformation ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.03. Geodesy::04.03.06. Measurements and monitoring ; 04. Solid Earth::04.03. Geodesy::04.03.07. Satellite geodesy ; 04. Solid Earth::04.07. Tectonophysics::04.07.01. Continents ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics ; 04. Solid Earth::04.07. Tectonophysics::04.07.06. Subduction related processes
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  • 51
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    Deep structure and tectonics of the northern-central Apennines as seen by regional-scale tomography and 3-D located earthquakes (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: In this study we present new high-resolution, regional-scale, Vp and Vp/Vs models of the northern-central Apennines along with accurate 3-D locations of a large set of local earthquakes. The main velocity anomalies are consistent with the surface geology in the shallow layers and present evidence for fluids stored within the basement at greater depths beneath the extensional belt. The Adria and Tyrrhenian mantle are defined by positive velocity anomalies below 30 km depth, while a low-Vp, high-Vp/Vs region in between indicates the existence of a hydrated wedge. The results yield new constraints on active processes in the Apennines and more generally envisage the evolution of a postcollisional belt. Velocity anomalies and earthquakes are consistent with a complex system of delamination and sinking of the Adria continental lithosphere, with the peeling of the crust identified by intermediate-depth seismicity. Change of seismicity and structural patterns along the belt indicates that this tectonic process is diachronous and that fluids, released by sunken lithosphere, are stored within the crust, conditioning the occurrence of seismicity and the onset of extension.
    Description: Published
    Description: 5391-5403
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: Local earthquake tomography ; tectonic of Apennines ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
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  • 52
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    Eruptive processes leading to the most explosive lava fountain at Etna volcano: The 23 November 2013 episode (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The 23 November 2013 lava fountain at Etna volcano was the most explosive of the last 44 episodes that have occurred at Etna in 2011–2013. We infer the total magma volume erupted by thermal images analysis and show that it was characterized by a very high time-averaged-discharge-rate (TADR) of ~360m3 s 1, having erupted ~1.6 × 106m3 of dense-rock equivalent magma volume in just 45 min, which is more than 3 times the TADR observed during previous episodes. Two borehole dilatometers confirmed the eruption dynamics inferred from the thermal images. When compared to the other lava fountains, this episode can be considered as the explosive end-member. However, the erupted volume was still comparable to the other lava fountain events. We interpret that the 23 November explosive end-member event was caused by more primitive and gas-rich magma entering the system, as demonstrated by the exceptional height reached by the lava fountain.
    Description: Published
    Description: 4912–4919
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Etna eruption ; paroxysmal explosive eruption ; lava fountain ; strainmeters ; lava fountain volume ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 53
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    Progression of spontaneous in-plane shear faults from sub-Rayleigh to compressional wave rupture speeds (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We investigate numerically the passage of spontaneous, dynamic in-plane shear ruptures from initiation to their final rupture speed, using very fine grids. By carrying out more than 120 simulations, we identify two different mechanisms controlling supershear transition. For relatively weaker faults, the rupture speed always passes smoothly and continuously through the range of speeds between the Rayleigh and shear wave speeds (the formerly considered forbidden zone of rupture speeds). This, however, occurs in a very short time, before the ruptures reach the compressional wave speed. The very short time spent in this range of speeds may explain why a jump over these speeds was seen in some earlier numerical and experimental studies and confirms that this speed range is an unstable range, as predicted analytically for steady state, singular cracks. On the other hand, for relatively stronger faults, we find that a daughter rupture is initiated by the main (mother) rupture, ahead of it. The mother rupture continues to propagate at sub-Rayleigh speed and eventually merges with the daughter rupture, whose speed jumps over the Rayleigh to shear wave speed range. We find that this daughter rupture is essentially a “pseudorupture,” in that the two sides of the fault are already separated, but the rupture has negligible slip and slip velocity. After the mother rupture merges with it, the slip, the slip velocity, and the rupture speed become dominated by those of the mother rupture. The results are independent of grid sizes and of methods used to nucleate the initial rupture.
    Description: Published
    Description: 8331–8345
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: open
    Keywords: Seismic source ; Supershear ruptures ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
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  • 54
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    Paleomagnetic evidence for a post-Eocene 90° CCW rotation of internal Apennine units: A linkage with Corsica-Sardinia rotation? (2014)
    American Geophysical Union
    Details
    Publication Date: 2017-10-06
    Description: We report on an extensive paleomagnetic study (36 sites) of the Tuscan Nappe succession from the Northern Apennines Arc, aimed to reconstruct the tectonic evolution of the internal sector of this chain. We analyzed Eocene pelagic foreland ramp deposits (Scaglia Toscana Formation) and Oligocene–lower Miocene siliciclastic turbidites (Macigno and Falterona Formations). Paleomagnetic results show that the internal sector of the Northern Apennines underwent large counterclockwise (CCW) rotations with respect to the Adria-Africa foreland. A decrease in the rotation magnitude was observed from the southern to the northern sector of the arc (from 91 to 36°). This trend is opposite to that observed in the more external units of Northern Apennines and demonstrates that the oroclinal bending model, which has been proposed for the external units of the chain, is not appropriate to explain the evolution of the internal sector of the arc. On the basis of the observed paleomagnetic pattern, we propose a new tectonic model in which the Tuscan and Falterona-Cervarola units in the southern area were first rotated CCW along with the Corsica-Sardinia block during its lower Miocene rotational drifting and were later involved in the main phases of rotational emplacement and translation toward the outermost sector (Umbria domain), thus yielding the final curved shape of the Northern Apennines chain. Data from this study represent the first paleomagnetic evidence of the influence of the Corsica-Sardinia CCW rotation in the Apennines orogenic wedge deformation, in the general framework of the geodynamic evolution of the Central Mediterranean subduction system.
    Description: Published
    Description: 374-392
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: paleomagnetism, Apennines, Tuscany ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
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  • 55
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    Seismovolcanic signals at Deception Island volcano,Antarctica: Wave field analysis and source modeling (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-11-17
    Description: Island (Antarctica), recorded during three Antarctic summers (1994- 1995, 1995-1996 and 1996-1997), are analyzed using a dense small-aperture (500 m) seismic array. The visual and spectral classification of the seismic events shows the existence of long-period and hybrid isolated seismic events, and of low-frequency, quasi-monochromatic and spasmodic continuous tremors, All spectra have the highest amplitudes in the frequency band between 1 and 4 Hz, while hybrids and spasmodic tremors have also significant amplitudes in the high-frequency band (4-10 Hz). The array analysis indicates that almost all the well-correlated low-frequency signals share similar array parameters (slowness and back azimuth) and have the same source area, close to the array site. The polarization analysis shows that phases at high-frequency are mostly composed of P waves, and those phases dominated by low frequencies can be interpreted as surface waves. No clear shear waves are evidenced. From the energy evaluation, we have found that the reduced displacement values for surface and body waves are confined in a narrow interval. Volcano-tectonic seismicity is located close to the array, at a depth shallower than 1 km. The wave-field properties of the seismovolcanic signals allow us to assume a unique source model, a shallow resonating fluid-filled crack system at a depth of some hundreds of meters. All of the seismic activity is interpreted as the response of a reasonably stable stationary geothermal process. The differences observed in the back azimuth between low and high frequencies are a near-field effect. A few episodes of the degassification process in an open conduit were observed and modeled with a simple organ pipe.
    Description: Published
    Description: 13905-13931
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Long Period Events ; Deception Island ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 56
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    A Holocene paleosecular variation record from the northwestern Barents Sea continental margin (2011)
    American Geophysical Union
    Details
    Publication Date: 2019-06-17
    Description: A high‐resolution paleomagnetic and rock magnetic study has been carried out on sediment cores collected in glaciomarine silty‐clay sequences from the continental shelf and slope of the southern Storfjorden trough‐mouth fan, on the northwestern Barents Sea continental margin. The Storfjorden sedimentary system was investigated during the SVAIS and EGLACOM cruises, when 10 gravity cores, with a variable length from 1.03 m to 6.41 m, were retrieved. Accelerator mass spectrometry (AMS) 14C analyses on 24 samples indicate that the cores span a time interval that includes the Holocene, the last deglaciation phase and in some cores the last glacial maximum. The sediments carry a well‐defined characteristic remanent magnetization and have a valuable potential to reconstruct the paleosecular variation (PSV) of the geomagnetic field, including relative paleointensity (RPI) variations. The paleomagnetic data allow reconstruction of past dynamics and amplitude of the geomagnetic field variations at high northern latitudes (75°–76° N). At the same time, the rock magnetic and paleomagnetic data allow a high‐resolution correlation of the sedimentary sequences and a refinement of their preliminary age models. The Holocene PSV and RPI records appear particularly sound, since they are consistent between cores and they can be correlated to the closest regional stacking curves (UK PSV, FENNOSTACK and FENNORPIS) and global geomagnetic model for the last 7 ka (CALS7k.2). The computed amplitude of secular variation is lower than that outlined by some geomagnetic field models, suggesting that it has been almost independent from latitude during the Holocene.
    Description: Published
    Description: Q11Z33
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Barents Sea ; Holocene ; Storfjorden ; geomagnetic paleosecular variation ; relative paleointensity ; 04. Solid Earth::04.05. Geomagnetism::04.05.01. Dynamo theory ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
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  • 57
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    Explosive expansion of a slowly-decompressed magma analog:evidence of delayed bubble nucleation (2014)
    American Geophysical Union
    Details
    Publication Date: 2019-12-05
    Description: While ascending in the plumbing system of volcanoes, magma undergoes decompression at rates spanning several orders of magnitude and set by a number of factors internal and external to the volcano. Slow decompression generally results in an effusive or mildly explosive expansion of the magma, but counterexamples of sudden switches from effusive to explosive eruptive behaviour have been documented at various volcanoes worldwide. The mechanisms involved in this behavior are currently debated, in particular regarding basaltic magmas. Here, we explore the interplay between decompression rate and vesiculation vigour by decompressing a magma analog obtained by dissolving pine resin into acetone in varying proportions. Our mixtures contain solid particles and upon decompression experience the nucleation of acetone bubbles. We find mixtures high in acetone, containing smaller and fewer solid particles, experience strong supersaturation and fragment for very slow decompressions, despite having low viscosity, while mixtures low in acetone, with more and larger solid particles degas efficiently. We interpret our results in terms of delayed bubble nucleation due to a lack of efficient nucleation sites. We discuss how a similar mechanism might induce violent, explosive expansion in volatile-rich and poorly crystalline low-silica magmas, by analogy to previous inferences for rhyolitic magmas.
    Description: Published
    Description: 3067-3084
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: embargoed_20150613
    Keywords: Magma fragmentation ; basaltic magma ; analog laboratory experiments ; slow decompression ; bubble nucleation ; explosive volcanic eruptions ; 04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism
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  • 58
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    Laboratory measurements of the frictional properties of the Zuccale low-angle normal fault, Elba Island, Italy (2011)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: Using a case study from the island of Elba, Italy, we seek to test the hypothesis that the presence of minerals with low frictional strengths can explain prolonged slip on low-angle normal faults. The central core of the Zuccale low-angle normal fault contains a distinctive fault rock zonation that developed during progressive exhumation. Most fault rock components preserve microstructural evidence for having accommodated deformation entirely, or partly, by frictional mechanisms. One millimeter thick sample powders of all the major fault rock components were deformed in a triaxial deformation apparatus under water-saturated conditions, at room temperature, and at constant effective normal stresses of 25, 50, and 75 MPa. Pore fluid pressure was maintained at 50 MPa throughout. Overall, the coefficient of friction (m) of the fault rocks varies between 0.25 and 0.8, emphasizing the marked strength heterogeneity that may exist within natural fault zones. Also, m is strongly dependent on fault rock mineralogy and is 〈0.45 for fault rocks containing talc, chlorite, and kaolinite and 〉0.6 for fault rocks dominated by quartz, dolomite, calcite, and amphibole. Localization of frictional slip within talc-rich portions of the fault core can potentially explain movements along the Zuccale fault over a wide range of depths within the upper crust, although the mechanical importance of the talc-bearing fault rocks likely decreased following their dismemberment into a series of poorly connected fault rock lenses. Additionally, slip within clay-bearing fault gouges with m between 0.4 and 0.5 may have facilitated movements in the uppermost (〈2 km) crust. For several other fault rock components, m varies between 0.5 and 0.8, and mineralogical weakening alone is insufficient to account for low-angle slip. In the latter fault rock components, other weakening mechanisms such as the development of high fluid pressures, or dissolution-precipitation creep, may have been particularly important in reducing fault strength.
    Description: Published
    Description: B02407
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: Friction ; Low-Angle Normal Fault ; Elba ; Zuccale Fault ; Microstructure ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 59
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    Comment on “The winter anomaly in the middlelatitude F region during the solar minimum period observed by the Constellation Observing System for Meteorology, Ionosphere, and Climate” by W. K. Lee, H. Kil, Y.-S. Kwak, Q. Wu, S. Cho, and J. U. Park (2014)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: Seasonal or winter anomaly in the F2 layer has been known since the beginning of regular ionospheric observations [e.g., Berkner and Wells, 1938, and references therein], and one may be sure that such a fundamental feature of this phenomenon as its height extent has been analyzed. However, Lee et al. [2011] using radio occultation Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Ne(h) observations have decided to reconsider this problem starting from the very beginning without any analyses of previous investigations and comparisons to earlier obtained results as if ionospheric F2 layer physics has started with them. Besides, the authors have done some incorrect statements which contradict the present theory of the ionospheric F2 layer. They claim that “The topside plasma density is greater in the summer hemisphere than in the winter hemisphere; … the electron density below the F peak at middle latitudes is also greater during summer than during winter; Therefore, the seasonal anomalous behavior is a phenomenon only near the F-peak height in the Northern Hemisphere; The question is why the seasonal behavior of the ionosphere near the F-peak height is different from the behavior below and above the F peak. ….there was no explanation for the different seasonal behaviors of electron density in the lower F region and at F-peak height”. This is the main contents and results of the paper. Let us consider what was known about winter anomaly before the paper by Lee et al. [2011].
    Description: Published
    Description: 7972–7978
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Description: restricted
    Keywords: December anomaly, ionosphere ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous
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  • 60
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    Increase in radon emission due to rock failure: An experimental study (2011)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: Radon anomalies are commonly observed prior to dynamic failure in the crust and are interpreted as cracking of the medium, thus attracting considerable attention in understanding the precursory phenomena of earthquakes and volcanic activity. In this study we have compared the starting radon emissions from low porosity crystalline lava (phonolite) samples with those from damaged and failed samples. The damaged sample was loaded up to just beyond the end of the linear elastic phase, as evidenced by the output of AE energy, the increase in total porosity and a decrease in P‐wave and S‐wave velocity relative to the intact sample. Whereas, the failed sample showed deformation behaviour characteristically brittle with increasing values of AE output and porosity as the sample approached macroscopic failure. Radon measurements have evidenced that dilatational microcracking of deformed sample produced no significant variation in radon emanation with respect to the intact sample. In contrast, after macroscopic failure, radon emanation drastically increased. Therefore, major finding from this study is that, in the case of low porosity and relatively high strength crystalline lavas, the development of a macroscopic fracture provides new large exhaling surface resulting in a substantial increase in radon emission rate.
    Description: Published
    Description: L14304
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: reserved
    Keywords: Radon ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
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  • 61
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    Multidisciplinary Approach Yields Insight into Mt. Etna 2001 Eruption (2014)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: On July 17,2001, lava began pouring down the slopes of Mt. Etna in Sicily signaling the start of the volcano's first flank eruption in nearly 10 years. Etna typically experiences long periods of explosive and effusive activity at the summit, which lies 3350 m a.s.l., interspersed with shorter flank eruptions. During the latter, large volumes of lava can threaten local populations. The Catania Section of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) routinely monitors the volcano with an array of integrated multidisciplinary techniques. During the 2001 flank eruption, researchers obtained the deepest insight yet into the mechanisms that control this fascinating volcano. In particular, by studying ground deformation, seismicity, gravity changes, and geomagnetism, researchers were able to forecast 3 to 4 days in advance the intrusion of a new feeder dike in the upper part of the volcano and follow the propagation of dike emplacement and fissure opening, as well as estimate the volume of the intrusion. During the eruption, volcanology gas geochemistry and petrology were used to distinguish two different magmas erupting at the same time from both this new feeder dike and the summit feeding system, which has been active since January 2001. Effusion rate measurements and thermal mapping of the flow field provided insight into the maximum length the lava flow could reach from the lower vent, and researchers were able to follow the process of tube formation along this flow. The previous flank eruption on Etna occurred between 1991 and 1993, when 235 million of lava poured from within the Valle del Bove (VDB) and formed a lava flow field over 8.5 km long that threatened the town of Zafferana. Since then, eruptive activity at Etna has been restricted to the summit area. A progressive increase in the activity occurred between June 1998 and February 1999, with a succession of 21 paroxysmal episodes from the Southeast Cone (SEC). Then, on February 1999, a fire fountain episode from the SEC indicated the start of the 1999 summit eruption, which produced two lava flow fields. During 2000, there were 66 fire fountain events from the SEC accompanied by small lava flows. Lava flow emission started again from the north base of the SEC in January 2001, and on May 9,2001, small fire fountaining episodes were observed on the summit and northern flank of the SEC.This activity gradually increased in frequency and intensity before the 2001 flank eruption.
    Description: Published
    Description: 653-656
    Description: 3V. Dinamiche e scenari eruttivi
    Description: N/A or not JCR
    Description: restricted
    Keywords: Etna eruption ; volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 62
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    A method for foF2 short-term (1–24 h) forecast using both historical and real-time foF2 observations over European stations: EUROMAP model (2014)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: A method for foF2 short-term forecast over Europe has been developed and implemented in the EUROMAP model. The input-driving parameters are 3 h ap indices (converted to ap(τ)), effective ionospheric T index, and real-time foF2 observations. The method includes local (for each station) regression storm models to describe strong negative disturbances under ap(τ)〉30 and training models to describe foF2 variations under ap(τ) ≤ 30. The derived model was tested in two regimes: descriptive when observed 3 h ap indices were used and real forecast when predicted daily Ap were used instead of 3 h ap indices—. In the case of strong negative disturbances the EUROMAP model demonstrates on average the improvement over the lnternational Reference Ionosphere STORM-time correction model (IRI(STORM)) model: 40% in winter, 24% in summer, and 39% in equinox. The average improvement over climatology is 41% in winter, 59% in summer, and 55% in equinox. In the majority of cases this difference is statistically significant. In the case of strong positive disturbances, higher-latitude stations also manifest a significant difference between the twomodels but this difference is insignificant at lower latitude stations. The substitution of 3 h ap input indices for the predicted daily Ap ones decreases the foF2 prediction accuracy in the case of negative disturbances but practically has no effect with positive disturbances. In both cases the proposed method manifests better accuracy than the IRI(STORM) model provides. The obtained results show a real opportunity to provide foF2 forecast with the (1–24 h) lead time on the basis of predicted Ap indices
    Description: Published
    Description: 253-270
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Description: restricted
    Keywords: forecast ; 01. Atmosphere::01.02. Ionosphere::01.02.03. Forecasts
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  • 63
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    Modeling the spreading of glacial meltwater from the Amundsen and Bellingshausen Seas (2014)
    American Geophysical Union
    In:  EPIC3Geophysical Research Letters, American Geophysical Union, 41(22), pp. 7942-7949, ISSN: 00948276
    Details
    Publication Date: 2019-07-16
    Description: It has been suggested that an increased melting of continental ice in the Amundsen Sea (AS) and Bellingshausen Sea (BS) is a likely source of the observed freshening of Ross Sea (RS) water. To test this hypothesis, we simulate the spreading of glacial meltwater using the Finite Element Sea Ice/Ice Shelf/Ocean Model. Based on the spatial distribution of simulated passive tracers, most of the basal meltwater from AS ice shelves flows toward the RS with more than half of the melt originating from the Getz Ice Shelf. Further, the model results show that a slight increase of the basal mass loss can substantially intensify the transport of meltwater into the RS due to a strengthening of the melt-driven shelf circulation and the westward flowing coastal current. This supports the idea that the basal melting of AS and BS ice shelves is one of the main sources for the RS freshening.
    Repository Name: EPIC Alfred Wegener Institut
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  • 64
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    A Mid-Holocene Shift and Millennial-Scale Variations in North Pacific Intermediate Water Oxygenation and Upper Ocean Hydrography (2014)
    American Geophysical Union
    In:  EPIC3American Geophysical Union Fall Meeting, San Francisco, CA, USA, 2014-12-15-2014-12-19Washington, D. C., USA, American Geophysical Union
    Details
    Publication Date: 2015-01-05
    Description: The subarctic North Pacific and its marginal seas constitute a key area in which rapid environmental changes over the past decades have been observed in instrumental records, like sea ice decreases, or alterations of nutrient inventories and oxygenation of mid-depth water masses. However, knowledge about the past climatic and oceanographic variability beyond instrumental time series in the subarctic North Pacific and its marginal seas is limited. Few temporally and spatially well-resolved high-resolution and spatially well datasets exist, with spatial and temporal coverage being insufficient to gain a detailed picture of past variations. Our proxydata-based study focuses on a collection of sediment records from the Okhotsk Sea as major source area for well ventilated North Pacific Intermediate Water (NPIW) that cover the last ca. 12,000 years with high temporal and adequate spatial resolution. We decipher rapid changes in NPIW ventilation patterns on centennial to millennial time scales and show that the current ventilation of the mid-depth North Pacific has likely only been prevalent for the last 2 ka. We further provide evidence for a Mid-Holocene shift in mid-depth NPIW ventilation characteristics. Additionally, changes in North Atlantic Deep Water flow speed and patterns are reflected in our records of North Pacific mid-depth water mass dynamics, thus indicating a hemispheric-wide connection between the Atlantic and Pacific regions during the Holocene. Planktic oxygen isotope data suggest a high variability in the stratification of local surface water masses and the formation of sea ice, influencing the formation of new, well ventilated water masses near to our core sites. We compare the main Holocene baseline changes evidenced in our proxy reconstructions to Early Holocene and Pre-Industrial time slice results from the fully-coupled MPI-ESM (COSMOS) Earth System Model, with a focus on the Pacific Ocean to better understand NPIW and upper ocean dynamic changes.
    Repository Name: EPIC Alfred Wegener Institut
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  • 65
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    Modeling Earth Dynamics: Complexity, Uncertainty, and Validation (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: 28th IUGG Conference on Mathematical Geophysics; Pisa, Italy, 7–11 June 2010; The capabilities and limits of mathematical models applied to a variety of geophysical processes were discussed during the 28th international Conference on Mathematical Geophysics, held in Italy (see the conference Web site (http://cmg2010.pi.ingv.it), which includes abstracts). The conference was organized by the International Union of Geodesy and Geophysics (IUGG) Commission on Mathematical Geophysics (CMG) and the Istituto Nazionale di Geofisica e Vulcanologia and was cosponsored by the U.S. National Science Foundation. The meeting was attended by more than 160 researchers from 26 countries and was dedicated to the theme “Modelling Earth Dynamics: Complexity, Uncertainty, and Validation.” Many talks were dedicated to illustration of the complexities affecting geophysical processes. Novel applications of geophysical fluid dynamics were presented, with specific reference to volcanological and ­subsurface/surface flow processes. In most cases, investigations highlighted the need for multidimensional and multiphase flow models able to describe the nonlinear effects associated with the nonhomogeneous nature of the matter. Fluid dynamic models of atmospheric, oceanic, and environmental systems also illustrated the fundamental role of nonlinear couplings between the different subsystems. Similarly, solid Earth models have made it possible to obtain the first tomographies of the planet; to formulate nonlocal and dynamic damage models of rocks; to investigate statistically the triggering, clustering, and synchronization of faults; and to develop realistic simulators of the planetary dynamo, plate tectonics, and gravity and magnetic fields.
    Description: Published
    Description: 506
    Description: 3.6. Fisica del vulcanismo
    Description: N/A or not JCR
    Description: reserved
    Keywords: mathematical models ; geophysics ; uncertainty ; validation ; 05. General::05.01. Computational geophysics::05.01.99. General or miscellaneous ; 05. General::05.05. Mathematical geophysics::05.05.99. General or miscellaneous
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  • 66
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    Remote sensing for monitoring of land surface hydrology at high latitudes within the framework of the ESA DUE Permafrost and STSE ALANIS-Methane projects (GC41C-0820 Poster) (2011)
    American Geophysical Union
    In:  EPIC32011 AGU Fall Meeting, San Francisco, USA, 2011-12-05-2011-12-09San Francisco, American Geophysical Union
    Details
    Publication Date: 2019-07-17
    Description: Time series of a wide range of biogeophysical parameters from satellite data are available to date on a global scale. A few initiatives focus on their improvement and validation in high latitudes. For example the DUE Permafrost and STSE ALANIS-Methane, which are activities funded by the European Space Agency, focus on this issue. ALANIS Methane is a research project to produce and use a suite of relevant earth observation (EO) derived information to validate and improve one of the next generation land-surface models and thus reduce current uncertainties in wetland-related CH4 emissions. The task of the ESA DUE Permafrost project is to build up an Earth observation service for high-latitudinal permafrost applications. Results which are shown in this paper contribute to both. Microwave sensors are of special interest in this context due to their independence on cloud conditions and illumination of the Earth Surface. They can be used for derivation of land surface temperature, snow properties and land surface hydrology. The latter includes near surface soil moisture and inundation. Such parameters are of importance for studies on e.g. permafrost and land-atmosphere exchange. Datasets derived from active microwave instruments operating in C-band have been analysed with respect to their usability at high latitudes. Several examples from western Siberia are discussed.
    Repository Name: EPIC Alfred Wegener Institut
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    ESA DUE PERMAFROST: Remote Sensing Service for Permafrost - Adaption for Models (GC41B-0798 Poster) (2011)
    American Geophysical Union
    In:  EPIC32011 AGU Fall Meeting, San Francisco, USA, 2011-12-05-2011-12-09San Francisco, USA, American Geophysical Union
    Details
    Publication Date: 2019-07-16
    Description: The ESA DUE Permafrost project (2009-2011) is developing a suite of parameters indicative of the subsurface phenomenon permafrost using satellite remote sensing: Land Surface Temperature (LST), Surface Soil Moisture (SSM), Surface Frozen and Thawed State (Freeze/Thaw), Terrain, Land Cover (LC), and Surface Water (SW). Snow parameters (Snow Extent and Snow Water Equivalent) are being developed through the DUE GlobSnow project, Global Snow Monitoring for Climate Research (2008-2011). The final DUE Permafrost remote sensing products cover the years 2007 to 2011 with a circumpolar coverage that will soon be released (early 2012), and then be used to analyze the temporal dynamics and map the spatial patterns of indicators. Further information is available at www.ipf.tuwien.ac.at/ permafrost. Since the beginning, scientific stakeholders and the International Permafrost Association (IPA) have been involved in the science and implementation plan. Interactive international user workshops took place in 2010 at the Technical University of Vienna, Vienna (AT), and in 2011 at the International Arctic Research Center (IARC), Fairbanks, Alaska (US). This involvement and the ongoing evaluation of the indicators derived from remote sensing for the high-latitude permafrost regions make the DUE Permafrost products trustworthy for the permafrost and the climate research community. The adaption of the remote sensing products for the permafrost and climate modelling is experimental and highly dependent on the users’ involvement. For a few years already, the Geophysical Institute Permafrost Laboratory (GIPL), University of Alaska Fairbanks, US, (http://www.gi.alaska.edu/research/snowicepermafrost/Permafrost) has successfully demonstrated the value of using LST derived from remote sensing data for driving its permafrost models. Further experimental testing of the DUE Permafrost products for use by the modeling community (permafrost and climate) will range from (i) the evaluation of external data of the models, with modifying or providing new external data (e.g. tundra land cover, surface water ratio, soil distribution), to (ii) new drivers for regional models derived from remote sensing (e.g., LST), to (iii) the evaluation of the output data from the models (e.g. spatial patterns of moisture and temperature).
    Repository Name: EPIC Alfred Wegener Institut
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    ESA DUE Permafrost: Evaluation of remote sensing derived products using ground data from the Global Terrestrial Network of Permafrost (GTN-P) (2011)
    American Geophysical Union
    In:  EPIC3AGU 2011 Fall Meeting, San Francisco, 2011-12-05-2011-12-09SanFrancisco, American Geophysical Union
    Details
    Publication Date: 2019-07-16
    Description: The task of the ESA DUE Permafrost project is to build up an Earth observation service for high-latitudinal permafrost applications with extensive involvement of the permafrost research community. The DUE Permafrost products derived from remote sensing are land surface temperature (LST), surface soil moisture (SSM), surface frozen and thawed state (freeze/ thaw), terrain, land cover, and surface waters. Weekly and monthly averages for most of the DUE Permafrost products will be made available for the years 2007-2010. The DUE Permafrost products are provided for the circumpolar permafrost area (north of 55°N) with 25 km spatial resolution. In addition, regional products with higher spatial resolution (300-1000 m/ pixel) were developed for five case study regions. These regions are: (1) the Laptev Sea and Eastern Siberian Sea Region (RU, continuous very cold permafrost/ tundra), (2) the Yakutsk Region (RU, continuous cold permafrost/ taiga), (3) the Western Siberian transect including Yamal Peninsula and Ob Region (RU, continuous to discontinuous/ taiga-tundra), (4) the Alaska Highway Transect (US, continuous to discontinuous/ taiga-tundra), and (5) the Mackenzie Delta and Valley Transect (CA, continuous to discontinuous/ taiga-tundra). The challenge of the programme is to adapt remote sensing products that are well established and tested in agricultural low and mid-latitudinal areas for highly heterogeneous taiga/ tundra permafrost landscapes in arctic regions. Ground data is essential for the evaluation of DUE Permafrost products and is provided by user groups and global networks. A major part of the DUE Permafrost core user group is contributing to GTN-P, the Global Terrestrial Network of Permafrost. Its main programmes, the Circumpolar Active Layer Monitoring (CALM) and the Thermal State of Permafrost (TSP) have been thoroughly overhauled during the last International Polar Year (2007-2008). Their spatial coverage has been extended to provide a true circumpolar network. Ground data ranges from active layer- and snow depths, to air-, ground-, and borehole temperature data as well as soil moisture measurements and the description of landform and vegetation. The GTN-P sites, with their position in different permafrost zones in the DUE Permafrost case study regions, are highly suitable for the evaluation of DUE Permafrost remote sensing products. Air and surface temperatures with high-temporal resolution are available for three GTN-P sites in Siberia and compared to LST products. Daily average GTN-P borehole- and air temperature data for 22 sites in Alaska and 6 sites in Western Siberia were used to validate surface frozen and thawed state. The preliminary results are promising. In addition, landform and vegetation descriptions of circumpolar GTN-P sites are used for the evaluation of global ‘landcover’ remote-sensing datasets like GlobeCover, Landcover2000 and EcoClimap – global datasets used as input for climate modeling.
    Repository Name: EPIC Alfred Wegener Institut
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  • 69
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    Liquid water in snow (2014)
    American Geophysical Union
    In:  EPIC3Workshop at the Institute for Snow and Avalanche Research, EOS, Davos, Switzerland, American Geophysical Union
    Details
    Publication Date: 2019-07-17
    Description: From 2-4 April 2014 about 50 researchers attended the workshop „Liquid water in snow – measurements techniques and modeling approaches“ that took place at the Institute for Snow and Avalanche Research (SLF) in Davos, Switzerland – the first one since 1982 in Innsbruck, Austria. This is the report thereof.
    Repository Name: EPIC Alfred Wegener Institut
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    The Opening of the Arctic-Atlantic Gateway: Tectonic, Oceanographic and Climatic Dynamics - an IODP Initiative (2014)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, San Francisco, 2014-12-15-2014-12-19American Geophysical Union
    Details
    Publication Date: 2014-08-03
    Description: The modern polar cryosphere reflects an extreme climate state with profound temperature gradients towards high-latitudes. It developed in association with stepwise Cenozoic cooling, beginning with ephemeral glaciations and the appearance of sea ice in the late middle Eocene. The polar ocean gateways played a pivotal role in changing the polar and global climate, along with declining greenhouse gas levels. The opening of the Drake Passage finalized the oceanographic isolation of Antarctica, some 40 Ma ago. The Arctic Ocean was an isolated basin until the early Miocene when rifting and subsequent sea-floor spreading started between Greenland and Svalbard, initiating the opening of the Fram Strait / Arctic-Atlantic Gateway (AAG). Although this gateway is known to be important in Earth’s past and modern climate, little is known about its Cenozoic development. However, the opening history and AAG’s consecutive widening and deepening must have had a strong impact on circulation and water mass exchange between the Arctic Ocean and the North Atlantic. To study the AAG’s complete history, ocean drilling at two primary sites and one alternate site located between 73°N and 78°N are proposed. These sites will provide unprecedented sedimentary records that will unveil (1) the history of shallow-water exchange between the Arctic Ocean and the North Atlantic, and (2) the development of the AAG to a deep-water connection and its influence on the global climate system. The specific overarching goals of our proposal are to study: • the influence of distinct tectonic events in the development of the AAG and the formation of deep water passage on the North Atlantic and Arctic paleoceanography, and • the role of the AAG in the climate transition from the Paleogene greenhouse to the Neogene icehouse for the long-term (~50 Ma) climate history of the northern North Atlantic.
    Repository Name: EPIC Alfred Wegener Institut
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    Drilling constraints on lithospheric accretion and evolution at Atlantis Massif, Mid-Atlantic Ridge 30°N (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B07103, doi:10.1029/2010JB007931.
    Description: Expeditions 304 and 305 of the Integrated Ocean Drilling Program cored and logged a 1.4 km section of the domal core of Atlantis Massif. Postdrilling research results summarized here constrain the structure and lithology of the Central Dome of this oceanic core complex. The dominantly gabbroic sequence recovered contrasts with predrilling predictions; application of the ground truth in subsequent geophysical processing has produced self-consistent models for the Central Dome. The presence of many thin interfingered petrologic units indicates that the intrusions forming the domal core were emplaced over a minimum of 100–220 kyr, and not as a single magma pulse. Isotopic and mineralogical alteration is intense in the upper 100 m but decreases in intensity with depth. Below 800 m, alteration is restricted to narrow zones surrounding faults, veins, igneous contacts, and to an interval of locally intense serpentinization in olivine-rich troctolite. Hydration of the lithosphere occurred over the complete range of temperature conditions from granulite to zeolite facies, but was predominantly in the amphibolite and greenschist range. Deformation of the sequence was remarkably localized, despite paleomagnetic indications that the dome has undergone at least 45° rotation, presumably during unroofing via detachment faulting. Both the deformation pattern and the lithology contrast with what is known from seafloor studies on the adjacent Southern Ridge of the massif. There, the detachment capping the domal core deformed a 100 m thick zone and serpentinized peridotite comprises ∼70% of recovered samples. We develop a working model of the evolution of Atlantis Massif over the past 2 Myr, outlining several stages that could explain the observed similarities and differences between the Central Dome and the Southern Ridge.
    Keywords: Atlantis Massif ; Integrated Ocean Drilling Program ; Oceanic Core Complex
    Repository Name: Woods Hole Open Access Server
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    Net exchanges of CO2, CH4, and N2O between China's terrestrial ecosystems and the atmosphere and their contributions to global climate warming (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): G02011, doi:10.1029/2010JG001393.
    Description: China's terrestrial ecosystems have been recognized as an atmospheric CO2 sink; however, it is uncertain whether this sink can alleviate global warming given the fluxes of CH4 and N2O. In this study, we used a process-based ecosystem model driven by multiple environmental factors to examine the net warming potential resulting from net exchanges of CO2, CH4, and N2O between China's terrestrial ecosystems and the atmosphere during 1961–2005. In the past 45 years, China's terrestrial ecosystems were found to sequestrate CO2 at a rate of 179.3 Tg C yr−1 with a 95% confidence range of (62.0 Tg C yr−1, 264.9 Tg C yr−1) while emitting CH4 and N2O at rates of 8.3 Tg C yr−1 with a 95% confidence range of (3.3 Tg C yr−1, 12.4 Tg C yr−1) and 0.6 Tg N yr−1 with a 95% confidence range of (0.2 Tg N yr−1, 1.1 Tg N yr−1), respectively. When translated into global warming potential, it is highly possible that China's terrestrial ecosystems mitigated global climate warming at a rate of 96.9 Tg CO2eq yr−1 (1 Tg = 1012 g), substantially varying from a source of 766.8 Tg CO2eq yr−1 in 1997 to a sink of 705.2 Tg CO2eq yr−1 in 2002. The southeast and northeast of China slightly contributed to global climate warming; while the northwest, north, and southwest of China imposed cooling effects on the climate system. Paddy land, followed by natural wetland and dry cropland, was the largest contributor to national warming potential; forest, followed by woodland and grassland, played the most significant role in alleviating climate warming. Our simulated results indicate that CH4 and N2O emissions offset approximately 84.8% of terrestrial CO2 sink in China during 1961–2005. This study suggests that the relieving effects of China's terrestrial ecosystems on climate warming through sequestering CO2 might be gradually offset by increasing N2O emission, in combination with CH4 emission.
    Description: This study has been supported by NASA LCLUC Program (NNX08AL73G_S01) , NASA IDS Program (NNG04GM39C), and China’s Ministry of Science and Technology (MOST) 973 Program (2002CB412500).
    Keywords: Carbon dioxide ; China ; Global warming potential ; Methane ; Nitrous oxide
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    Detecting aseismic strain transients from seismicity data (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B06305, doi:10.1029/2010JB007537.
    Description: Aseismic deformation transients such as fluid flow, magma migration, and slow slip can trigger changes in seismicity rate. We present a method that can detect these seismicity rate variations and utilize these anomalies to constrain the underlying variations in stressing rate. Because ordinary aftershock sequences often obscure changes in the background seismicity caused by aseismic processes, we combine the stochastic Epidemic Type Aftershock Sequence model that describes aftershock sequences well and the physically based rate- and state-dependent friction seismicity model into a single seismicity rate model that models both aftershock activity and changes in background seismicity rate. We implement this model into a data assimilation algorithm that inverts seismicity catalogs to estimate space-time variations in stressing rate. We evaluate the method using a synthetic catalog, and then apply it to a catalog of M ≥ 1.5 events that occurred in the Salton Trough from 1990 to 2009. We validate our stressing rate estimates by comparing them to estimates from a geodetically derived slip model for a large creep event on the Obsidian Buttes fault. The results demonstrate that our approach can identify large aseismic deformation transients in a multidecade long earthquake catalog and roughly constrain the absolute magnitude of the stressing rate transients. Our method can therefore provide a way to detect aseismic transients in regions where geodetic resolution in space or time is poor.
    Description: This work was supported by NSF EAR grant 0738641 and USGS NEHRP grant G10AP00004.
    Keywords: ETAS model ; Rate-state model ; Earthquake triggering
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    Domains of depleted mantle : new evidence from hafnium and neodymium isotopes (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q08001, doi:10.1029/2011GC003617.
    Description: Isotope systematics of basalts provide information on the distribution of mantle components and the length scale of mantle heterogeneity. To obtain this information, high data and sampling density are crucial. We present hafnium and neodymium isotope data on more than 400 oceanic volcanics. Over length scales of several hundred to over one thousand kilometers hafnium and neodymium isotopes of mid-ocean ridge basalts are correlated and form an array of parallel trends on a global scale. On a larger scale these domains differ in the amount of highly depleted mantle material with radiogenic hafnium and neodymium isotope ratios. Compared to the Atlantic and Indian Ocean basins the asthenosphere of the Pacific basin seems to have a more uniform and a less radiogenic Hf isotopic composition for a given Nd isotopic composition. The parallel arrays of mid-ocean ridge basalts provide strong constraints on the makeup of the MORB mantle and are evidence for the presence of a highly depleted and highly radiogenic neodymium and hafnium component. This component, because of its highly depleted character, is unrecognized in the strontium-neodymium-lead isotope systems alone. Alternatively, the parallel arrays can have an ancient origin of systematic variations in the degree of depletion. Each array then represents the variations in this fossil melting regime. Individual ocean island basalt suites display different slopes in hafnium-neodymium isotope space, which are also best explained by varying amounts of highly residual mantle rather than isotopic differences in enriched mantle components as previously invoked. The ocean island basalt arrays diverge at the depleted end and project to radiogenic compositions that are similar to those of the asthenosphere through which they travel. This is strong evidence that the plume material interacts with its surrounding mantle as it ascends. The isotopic compositions of the ocean island and ridge basalts suggest that their systematics are influenced by a heretofore unrecognized depleted component.
    Description: This work was supported by NSF grants EAR 0635864 and OCE0648484 to V.S. and OCE0351437 to S.H.
    Keywords: MORB ; Hafnium ; Isotopes ; Neodymium
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    The influence of crosswind tidal currents on Langmuir circulation in a shallow ocean (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C08005, doi:10.1029/2011JC006971.
    Description: Langmuir circulation (LC) is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum, heat, and mass in the oceanic surface layer. On the coastal shelves the largest-scale LC span the whole water column and thus couple the surface and bottom boundary layers and enhance turbulent mixing. Observations and large eddy simulations (LES) of a shallow coastal ocean demonstrate that these relatively large scale Langmuir cells are strongly influenced by crosswind tidal currents. Two mechanisms by which crosswind tidal shear may distort and disrupt Langmuir cells are proposed. The first mechanism involves cell shearing due to differential advection across the whole cell. For the second mechanism, middepth vertical LC currents advect sheared mean crosswind current, leading to the attraction of upwelling and downwelling regions, so that LC cells are unsustainable when both regions overlap. Scaling arguments indicate that LC cells are more susceptible to crosswind shear distortion for smaller LC surface velocity convergence and greater cell aspect ratio (vertical to horizontal LC scale), which is consistent with the results obtained from the observations and LES. These results imply that scaling of LC characteristics in a coastal ocean differs from that in the open ocean, which has important practical implications for parameterizing enhanced mixing due to LC.
    Description: This research was supported by the Office of Naval Research through grant N00014‐06‐1‐0178 (A.P., J.T.). Author T.K. received support from Faculty Startup Funds of the University of Delaware College of Earth, Ocean, and Environment.
    Keywords: Langmuir circulation ; Boundary layer dynamics ; Tides
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    Moist synoptic transport of CO2 along the mid-latitude storm track (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L09804, doi:10.1029/2011GL047238.
    Description: Atmospheric mixing ratios of CO2 are strongly seasonal in the Arctic due to mid-latitude transport. Here we analyze the seasonal influence of moist synoptic storms by diagnosing CO2 transport from a global model on moist isentropes (to represent parcel trajectories through stormtracks) and parsing transport into eddy and mean components. During winter when northern plants respire, warm moist air, high in CO2, is swept poleward into the polar vortex, while cold dry air, low in CO2, that had been transported into the polar vortex earlier in the year is swept equatorward. Eddies reduce seasonality in mid-latitudes by ∼50% of NEE (∼100% of fossil fuel) while amplifying seasonality at high latitudes. Transport along stormtracks is correlated with rising, moist, cloudy air, which systematically hides this CO2 transport from satellites. We recommend that (1) regional inversions carefully account for meridional transport and (2) inversion models represent moist and frontal processes with high fidelity.
    Description: This research is supported by the National Aeronautics and Space Administration contracts NNX08AT77G, NNX06AC75G, and NNX08AM56G.
    Keywords: Atmospheric transport ; Carbon cycle ; Inversion ; Isentropic coordinates ; Synoptic weather ; Tracer modeling
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    Changes in micronutrient supply to the surface Southern Ocean (Atlantic sector) across the glacial termination (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q09007, doi:10.1029/2011GC003691.
    Description: Major deepwater masses upwell and reach the surface in the Southern Ocean, forming an important conduit supplying nutrients and micronutrients to the surface and playing a key role in the regulation of global climate through ocean-atmosphere gas exchange. Here, we reconstruct changes in micronutrient distribution in this region in response to past changes in upwelling, oceanic mixing, and sea-ice seasonality. We present two downcore (Zn/Si)opal records from the Scotia Sea and Drake Passage region, which we interpret in the context of micronutrient distribution in the Atlantic sector of the Southern Ocean over the last glacial termination. Previous work shows that micronutrient availability in the surface waters in the South Atlantic appear to be controlled dominantly by upwelling and mixing of micronutrient rich deepwaters, which are additionally fuelled by the terrestrial sediment sources of the Scotia Arc and South Georgia. This is supported by our reconstructions, which show micronutrient availability to the west of the Scotia Arc and South Georgia are consistently lower than to the east over the last glacial termination due to downstream transport and mixing into surface waters of continentally derived material in the Antarctic Circumpolar Current. Micronutrient availability in this region was at a minimum from 20 to 25 ky BP, coinciding with maximum sea-ice coverage, and increased due to an expansion of the seasonal sea-ice zone and increased mixing of subsurface waters. Our findings are consistent with largely diminished upwelling of micronutrients during the maximum glacial extent, and reduced mixing due to the presence of persistent sea-ice. During the deglacial there was an increase in micronutrient availability, as well as other nutrients and inorganic carbon, within the Antarctic Circumpolar Current as a result of an increase in deep oceanic upwelling, mixing and strengthened zonal transport.
    Description: This work was funded by NERC/S/A/2004/12390 and the Antarctic Funding Initiative grant AFI4–02.
    Keywords: Deglaciation ; Diatom opal ; Westerlies ; Zinc
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    Nitrogen fixation in the South Atlantic Gyre and the Benguela Upwelling System (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L16608, doi:10.1029/2011GL048315.
    Description: Dinitrogen (N2) fixation is recognized as an important input of new nitrogen (N) to the open ocean gyres, contributing to the export of organic matter from surface waters. However, very little N2-fixation research has focused on the South Atlantic Gyre, where dust deposition of iron (Fe), an important micronutrient for diazotrophs, is seasonally low. Recent modeling efforts suggest that N2-fixation may in fact be closely coupled to, and greatest in, areas of denitrification, as opposed to the oceanic gyres. One of these areas, the Benguela Upwelling System, lies to the east of the South Atlantic Gyre. In this study we show that N2-fixation in surface waters across the South Atlantic Gyre was low overall (〈1.5 nmol N l−1 d−1) with highest rates seen in or near the Benguela Upwelling System (up to ∼8 nmol N l−1 d−1). Surface water dissolved Fe (dFe) concentrations were very low in the gyre (∼0.3 nM or lower), while soluble reactive phosphorus (SRP) concentrations were relatively high (∼0.15 μM). N2-fixation rates across the entire sampling area were significantly positively correlated to dFe, but also to SRP and NO3−. Thus, high NO3− concentrations did not exclude N2-fixation in the upwelling region, which provides evidence that N2-fixation may be occurring in previously unrecognized waters, specifically near denitrification zones. However the gene encoding for a nitrogenase component (nifH) was not detected from known diazotrophs at some stations in or near the upwelling where N2-fixation was greatest, suggesting the presence of unknown diazotrophs in these waters.
    Description: Funding for this research was provided by NSF grants OCE‐0452883 (to E.A.W. and M.A.S.), OCE‐0825922 (to E.A.W.), and The Gordon and Betty Moore Foundation (JPZ).
    Keywords: Diazotrophs ; Nitrogen fixation
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    Gravity and seismic study of crustal structure along the Juan de Fuca Ridge axis and across pseudofaults on the ridge flanks (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q05008, doi:10.1029/2010GC003439.
    Description: Variations in topography and seismic structure are observed along the Juan de Fuca (JdF) Ridge axis and in the vicinity of pseudofaults on the ridge flanks left by former episodes of ridge propagation. Here we analyze gravity data coregistered with multichannel seismic data from the JdF Ridge and flanks in order to better understand the origin of crustal structure variations in this area. The data were collected along the ridge axis and along three ridge-perpendicular transects at the Endeavor, Northern Symmetric, and Cleft segments. Negative Mantle Bouguer anomalies of −21 to −28 mGal are observed at the axis of the three segments. Thicker crust at the Endeavor and Cleft segments is inferred from seismic data and can account for the small differences in axial gravity anomalies (3–7 mGal). Additional low densities/elevated temperatures within and/or below the axial crust are required to explain the remaining axial MBA low at all segments. Gravity models indicate that the region of low densities is wider beneath the Cleft segment. Gravity models for pseudofaults crossed along the three transects support the presence of thinner and denser crust within the pseudofault zones that we attribute to iron-enriched crust. On the young crust side of the pseudofaults, a 10–20 km wide zone of thicker crust is found. Reflection events interpreted as subcrustal sills underlie the zones of thicker crust and are the presumed source for the iron enrichment.
    Description: This work was supported by the National Science Foundation grants OCE‐0648303 to Lamont‐Doherty Earth Observatory, OCE‐0648923 to Woods Hole Oceanographic Institution.
    Keywords: Mid-ocean ridges ; Propagation ; Juan de Fuca Ridge ; Gravity
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    Sharp thermal transition in the forearc mantle wedge as a consequence of nonlinear mantle wedge flow (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L13308, doi:10.1029/2011GL047705.
    Description: In the forearc mantle wedge, the thermal field depends strongly on slab-driven mantle wedge flow. The flow is in turn affected by the thermal field via the temperature dependence of mantle rheology. Using thermal modeling, we show that the nonlinear feedback between the thermal and flow fields always leads to complete stagnation of the mantle wedge over a shallow, weakened part of the slab-mantle interface and an abrupt onset of mantle flow further down-dip. The abrupt increase in flow velocity leads to a sharp thermal transition from a cold stagnant to a hot flowing part of the wedge. This sharp thermal transition is inherent to all subduction zones, explaining a commonly observed sharp arc-ward increase in seismic attenuation.
    Description: This research was partially supported by National Science Foundation through a MARGINS postdoctoral fellowship (NSF OCE‐0840800) and by Natural Environment Research Council.
    Keywords: Mantle rheology ; Mantle wedge ; Seismic attenuation ; Subduction zone ; Thermal structure
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    Bio-optical footprints created by mesoscale eddies in the Sargasso Sea (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L13608, doi:10.1029/2011GL047660.
    Description: We investigate the bio-optical footprints made by mesoscale eddies in the Sargasso Sea and the processes that create them through an eddy-centric approach. Many (〉10,000) eddies are identified and followed in time using satellite altimetry observations and the spatial ocean color patterns surrounding each eddy are assessed. We find through a sequence of statistical hypothesis tests that not one but several mechanisms (i.e., eddy pumping, eddy advection and eddy-Ekman pumping) are responsible for the spatial-temporal ocean color patterns following individual eddies. Both eddy pumping and the eddy-Ekman pumping mechanisms alter subsurface nutrient distributions thereby driving biogeochemical cycles, while the eddy advection mechanism to first order stirs existing horizontal gradients in bio-optical properties. This work illustrates both the promise and some of the limitations of satellite observations for assessing the biogeochemical impacts of mesoscale eddies.
    Description: We would like to acknowledge the support of the National Science Foundation and NASA.
    Keywords: Bio-physical coupling ; Eddy pumping ; Mesoscale eddies ; Ocean color remote sensing
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    Surface freshening in the Arctic Ocean's Eurasian Basin : an apparent consequence of recent change in the wind-driven circulation (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C00D03, doi:10.1029/2011JC006975.
    Description: Data collected by an autonomous ice-based observatory that drifted into the Eurasian Basin between April and November 2010 indicate that the upper ocean was appreciably fresher than in 2007 and 2008. Sea ice and snowmelt over the course of the 2010 drift amounted to an input of less than 0.5 m of liquid freshwater to the ocean (comparable to the freshening by melting estimated for those previous years), while the observed change in upper-ocean salinity over the melt period implies a freshwater gain of about 0.7 m. Results of a wind-driven ocean model corroborate the observations of freshening and suggest that unusually fresh surface waters observed in parts of the Eurasian Basin in 2010 may have been due to the spreading of anomalously fresh water previously residing in the Beaufort Gyre. This flux is likely associated with a 2009 shift in the large-scale atmospheric circulation to a significant reduction in strength of the anticyclonic Beaufort Gyre and the Transpolar Drift Stream.
    Description: This work was funded by the National Science Foundation Office of Polar Programs Arctic Sciences Section under awards ARC‐0519899, ARC‐0856479, and ARC‐ 0806306.
    Keywords: Arctic Ocean ; Circulation ; Fresh water
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    Is the northern high-latitude land-based CO2 sink weakening? (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 25 (2011): GB3018, doi:10.1029/2010GB003813.
    Description: Studies indicate that, historically, terrestrial ecosystems of the northern high-latitude region may have been responsible for up to 60% of the global net land-based sink for atmospheric CO2. However, these regions have recently experienced remarkable modification of the major driving forces of the carbon cycle, including surface air temperature warming that is significantly greater than the global average and associated increases in the frequency and severity of disturbances. Whether Arctic tundra and boreal forest ecosystems will continue to sequester atmospheric CO2 in the face of these dramatic changes is unknown. Here we show the results of model simulations that estimate a 41 Tg C yr−1 sink in the boreal land regions from 1997 to 2006, which represents a 73% reduction in the strength of the sink estimated for previous decades in the late 20th century. Our results suggest that CO2 uptake by the region in previous decades may not be as strong as previously estimated. The recent decline in sink strength is the combined result of (1) weakening sinks due to warming-induced increases in soil organic matter decomposition and (2) strengthening sources from pyrogenic CO2 emissions as a result of the substantial area of boreal forest burned in wildfires across the region in recent years. Such changes create positive feedbacks to the climate system that accelerate global warming, putting further pressure on emission reductions to achieve atmospheric stabilization targets.
    Description: This study was supported through grants provided as part of the Arctic System Science Program (NSF OPP‐ 0531047), the North American Carbon Program (NASA NNG05GD25G), and the Bonanza Creek Long‐Term Ecological Program (funded jointly by NSF grant DEB‐0423442 and USDA Forest Service, Pacific Northwest Research Station grant PNW01‐JV11261952‐231).
    Keywords: Carbon cycle ; High-latitude ecosystems ; Modeling
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    The impact of the North Atlantic Oscillation on the uptake and accumulation of anthropogenic CO2 by North Atlantic Ocean mode waters (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 25 (2011): GB3022, doi:10.1029/2010GB003892.
    Description: The North Atlantic Ocean accounts for about 25% of the global oceanic anthropogenic carbon sink. This basin experiences significant interannual variability primarily driven by the North Atlantic Oscillation (NAO). A suite of biogeochemical model simulations is used to analyze the impact of interannual variability on the uptake and storage of contemporary and anthropogenic carbon (Canthro) in the North Atlantic Ocean. Greater winter mixing during positive NAO years results in increased mode water formation and subsequent increases in subtropical and subpolar Canthro inventories. Our analysis suggests that changes in mode water Canthro inventories are primarily due to changes in water mass volumes driven by variations in water mass transformation rates rather than local air-sea CO2 exchange. This suggests that a significant portion of anthropogenic carbon found in the ocean interior may be derived from surface waters advected into water formation regions rather than from local gas exchange. Therefore, changes in climate modes, such as the NAO, may alter the residence time of anthropogenic carbon in the ocean by altering the rate of water mass transformation. In addition, interannual variability in Canthro storage increases the difficulty of Canthro detection and attribution through hydrographic observations, which are limited by sparse sampling of subsurface waters in time and space.
    Description: We would like to acknowledge funding from the NOAA Climate Program under the Office of Climate Observations and Global Carbon Cycle Program (NOAA‐NA07OAR4310098), NSF (OCE‐0623034), NCAR, the WHOI Ocean Climate Institute, a National Defense Science and Engineering Graduate Fellowship and an Environmental Protection Agency STAR graduate fellowship. NCAR is sponsored by the National Science Foundation.
    Keywords: North Atlantic Oscillation ; Anthropogenic carbon ; Carbon cycle ; Climate change ; Global climate model ; Mode waters
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    Simulating the impacts of disturbances on forest carbon cycling in North America : processes, data, models, and challenges (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): G00K08, doi:10.1029/2010JG001585.
    Description: Forest disturbances greatly alter the carbon cycle at various spatial and temporal scales. It is critical to understand disturbance regimes and their impacts to better quantify regional and global carbon dynamics. This review of the status and major challenges in representing the impacts of disturbances in modeling the carbon dynamics across North America revealed some major advances and challenges. First, significant advances have been made in representation, scaling, and characterization of disturbances that should be included in regional modeling efforts. Second, there is a need to develop effective and comprehensive process-based procedures and algorithms to quantify the immediate and long-term impacts of disturbances on ecosystem succession, soils, microclimate, and cycles of carbon, water, and nutrients. Third, our capability to simulate the occurrences and severity of disturbances is very limited. Fourth, scaling issues have rarely been addressed in continental scale model applications. It is not fully understood which finer scale processes and properties need to be scaled to coarser spatial and temporal scales. Fifth, there are inadequate databases on disturbances at the continental scale to support the quantification of their effects on the carbon balance in North America. Finally, procedures are needed to quantify the uncertainty of model inputs, model parameters, and model structures, and thus to estimate their impacts on overall model uncertainty. Working together, the scientific community interested in disturbance and its impacts can identify the most uncertain issues surrounding the role of disturbance in the North American carbon budget and develop working hypotheses to reduce the uncertainty.
    Description: Liu’s work is supported by USGS Geographic Analysis and Monitoring Program, Climate Change R&D Program, and Climate Effects Network Program.
    Keywords: Carbon ; Disturbances ; Forest ; Modeling
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    Distributed deformation ahead of the Cocos-Nazca Rift at the Galapagos triple junction (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q11003, doi:10.1029/2011GC003689.
    Description: The Galapagos triple junction is not a simple ridge-ridge-ridge (RRR) triple junction. The Cocos-Nazca Rift (C-N Rift) tip does not meet the East Pacific Rise (EPR). Instead, two secondary rifts form the link: Incipient Rift at 2°40′N and Dietz Deep volcanic ridge, the southern boundary of the Galapagos microplate (GMP), at 1°10′N. Recently collected bathymetry data are used to investigate the regional tectonics prior to the establishment of the GMP (∼1.5 Ma). South of C-N Rift a band of northeast-trending cracks cuts EPR-generated abyssal hills. It is a mirror image of a band of cracks previously identified north of C-N Rift on the same age crust. In both areas, the western ends of the cracks terminate against intact abyssal hills suggesting that each crack initiated at the EPR spreading center and cut eastward into pre-existing topography. Each crack formed a short-lived triple junction until it was abandoned and a new crack and triple junction initiated nearby. Between 2.5 and 1.5 Ma, the pattern of cracking is remarkably symmetric about C-N Rift providing support for a crack interaction model in which crack initiation at the EPR axis is controlled by stresses associated with the tip of the westward-propagating C-N Rift. The model also shows that offsets of the EPR axis may explain times when cracking is not symmetric. South of C-N Rift, cracks are observed on seafloor as old as 10.5 Ma suggesting that this triple junction has not been a simple RRR triple junction during that time.
    Description: HS was supported by the U.S. National Science Foundation (NSF) grant OCE‐0751831, DS by NSF grant OCE‐1028537, WZ by NSF grant EAR‐1056317, and LM by NSF grant EAR‐0911151.
    Description: 2012-05-08
    Keywords: East Pacific Rise ; Galapagos triple junction ; Crack propagation ; Triple junction
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  • 87
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    Comparison of shear measurements and mixing predictions with a direct observation of diapycnal mixing in the Atlantic thermocline (2011)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 1995. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 100 no.C7 (1995): 13481–13498, doi:10.1029/95JC01023.
    Description: Four sets of velocity and density profiles have been measured with an autonomous profiler during an upper ocean intentional‐tracer (SF6) diapycnal diffusivity measurement, the North Atlantic Tracer Release Experiment (NATRE). The tracer was injected near 310 m depth in the Canary Basin. Two profile sets were collected 6 months after tracer release, and two were collected 1 year after release, all within the horizontal boundaries of the SF6 patch. Shear and strain can be combined with turbulent kinetic energy dissipation and diffusivity measurements (published elsewhere) to test existing expressions for dissipation and diffusivity due to shear‐induced turbulence. These expressions arise from internal‐wave decay modeling. One expression of dissipation parameterized in terms of shear, based on stochastic nonlinear internal‐wave interaction, has fared well empirically; its extension to estimate diffusivity is evaluated. Shear variance of the first two data sets was about 1.6 times GM76, and 2.5 to 3.0 times GM76 in the later sets. The average parameterized mixing estimate computed using all of the temporally limited shear measurements overestimates annual mean NATRE diffusivity, 1.5 × 10−5 m2 s−1, by a factor of 1.2. A modified parameterization gives an underestimate. To first order, this supports the present understanding of open‐ocean diffusivity in terms of fine‐scale shear and internal‐wave decay, that is, the slow diapycnal mixing was not a consequence of unusually low shear. Adjustment of the shear‐induced mixing models to better fit the data is not warranted because of the lack of direct comparability between the various measurements, the expected natural variability of the shear, and sampling errors.
    Description: This work was supported by National Science Foundation grant OCE-9216204.
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  • 88
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    Stress transfer among en echelon and opposing thrusts and tear faults : triggering caused by the 2003 Mw = 6.9 Zemmouri, Algeria, earthquake (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B03305, doi:10.1029/2010JB007654.
    Description: The essential features of stress interaction among earthquakes on en echelon thrusts and tear faults were investigated, first through idealized examples and then by study of thrust faulting in Algeria. We calculated coseismic stress changes caused by the 2003 Mw = 6.9 Zemmouri earthquake, finding that a large majority of the Zemmouri afterslip sites were brought several bars closer to Coulomb failure by the coseismic stresses, while the majority of aftershock nodal planes were brought closer to failure by an average of ∼2 bars. Further, we calculated that the shallow portions of the adjacent Thenia tear fault, which sustained ∼0.25 m slip, were brought 〉2 bars closer to failure. We calculated that the Coulomb stress increased by 1.5 bars on the deeper portions of the adjacent Boumerdes thrust, which lies just 10–20 km from the city of Algiers; both the Boumerdes and Thenia faults were illuminated by aftershocks. Over the next 6 years, the entire south dipping thrust system extending 80 km to the southwest experienced an increased rate of seismicity. The stress also increased by 0.4 bar on the east Sahel thrust fault west of the Zemmouri rupture. Algiers suffered large damaging earthquakes in A.D. 1365 and 1716 and is today home to 3 million people. If these shocks occurred on the east Sahel fault and if it has a ∼2 mm/yr tectonic loading rate, then enough loading has accumulated to produce a Mw = 6.6–6.9 shock today. Thus, these potentially lethal faults need better understanding of their slip rate and earthquake history.
    Description: Funding by the U.S. Office of Foreign Disaster Assistance of the U.S. Agency for International Development is gratefully acknowledged. Additional funding was provided by the INSU research project ACI Cat‐Nat Risque Sismique de la Région d’Alger. S. Belabbes was supported by the Algerian Ministry of Higher Education and Research.
    Keywords: Earthquake triggering ; Stress transfer ; Zemmouri ; Algeria ; Thrust faults ; Northern Africa
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  • 89
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    In situ enrichment of ocean crust microbes on igneous minerals and glasses using an osmotic flow-through device (2011)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q06007, doi:10.1029/2010GC003424.
    Description: The Integrated Ocean Drilling Program (IODP) Hole 1301A on the eastern flank of Juan de Fuca Ridge was used in the first long-term deployment of microbial enrichment flow cells using osmotically driven pumps in a subseafloor borehole. Three novel osmotically driven colonization systems with unidirectional flow were deployed in the borehole and incubated for 4 years to determine the microbial colonization preferences for 12 minerals and glasses present in igneous rocks. Following recovery of the colonization systems, we measured cell density on the minerals and glasses by fluorescent staining and direct counting and found some significant differences between mineral samples. We also determined the abundance of mesophilic and thermophilic culturable organotrophs grown on marine R2A medium and identified isolates by partial 16S or 18S rDNA sequencing. We found that nine distinct phylotypes of culturable mesophilic oligotrophs were present on the minerals and glasses and that eight of the nine can reduce nitrate and oxidize iron. Fe(II)-rich olivine minerals had the highest density of total countable cells and culturable organotrophic mesophiles, as well as the only culturable organotrophic thermophiles. These results suggest that olivine (a common igneous mineral) in seawater-recharged ocean crust is capable of supporting microbial communities, that iron oxidation and nitrate reduction may be important physiological characteristics of ocean crust microbes, and that heterogeneously distributed minerals in marine igneous rocks likely influence the distribution of microbial communities in the ocean crust.
    Description: The subseafloor flow cell enrichment chambers were funded by a small grant from the Ocean Drilling Program. This work was also funded by NASA grant NNX08AO22G, NSF OCE 0727119 to C.G.W., NSF OCE 0452333 to S.M.S., and OCE‐0550713 and OCE‐0727952 to A.T.F., PSU, and OSU.
    Keywords: Juan de Fuca ; Basalt ; Iron oxidizers ; Nitrate reducers ; Olivine ; Subseafloor
    Repository Name: Woods Hole Open Access Server
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  • 90
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    Separation of river network–scale nitrogen removal among the main channel and two transient storage compartments (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Water Resources Research 47 (2011): W00J10, doi:10.1029/2010WR009896.
    Description: Transient storage (TS) zones are important areas of dissolved inorganic nitrogen (DIN) processing in rivers. We assessed sensitivities regarding the relative impact that the main channel (MC), surface TS (STS), and hyporheic TS (HTS) have on network denitrification using a model applied to the Ipswich River in Massachusetts, United States. STS and HTS connectivity and size were parameterized using the results of in situ solute tracer studies in first- through fifth-order reaches. DIN removal was simulated in all compartments for every river grid cell using reactivity derived from Lotic Intersite Nitrogen Experiment (LINX2) studies, hydraulic characteristics, and simulated discharge. Model results suggest that although MC-to-STS connectivity is greater than MC-to-HTS connectivity at the reach scale, at basin scales, there is a high probability of water entering the HTS at some point along its flow path through the river network. Assuming our best empirical estimates of hydraulic parameters and reactivity, the MC, HTS, and STS removed approximately 38%, 21%, and 14% of total DIN inputs during a typical base flow period, respectively. There is considerable uncertainty in many of the parameters, particularly the estimates of reaction rates in the different compartments. Using sensitivity analyses, we found that the size of TS is more important for DIN removal processes than its connectivity with the MC when reactivity is low to moderate, whereas TS connectivity is more important when reaction rates are rapid. Our work suggests a network perspective is needed to understand how connectivity, residence times, and reactivity interact to influence DIN processing in hierarchical river systems.
    Description: This work was supported by the National Science Foundation through DEB- 0614282, BCS-0709685 and the Plum Island Long Term Ecological Research site (NSF OCE-0423565).
    Keywords: Biogeochemistry ; Denitrification ; Hydraulics ; Modeling ; River network ; Transient storage
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  • 91
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    A novel approach for direct estimation of fresh groundwater discharge to an estuary (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Geophysical Research Letters 38 (2011): L11402, doi:10.1029/2011GL047718.
    Description: Coastal groundwater discharge is an important source of freshwater and nutrients to coastal and estuarine systems. Directly quantifying the spatially integrated discharge of fresh groundwater over a coastline is difficult due to spatial variability and limited observational methods. In this study, I applied a novel approach to estimate net freshwater discharge from a groundwater-fed tidal creek over a spring-neap cycle, with high temporal resolution. Acoustic velocity instruments measured tidal water fluxes while other sensors measured vertical and lateral salinity to estimate cross-sectionally averaged salinity. These measurements were used in a time-dependent version of Knudsen's salt balance calculation to estimate the fresh groundwater contribution to the tidal creek. The time-series of fresh groundwater discharge shows the dependence of fresh groundwater discharge on tidal pumping, and the large difference between monthly mean discharge and instantaneous discharge over shorter timescales. The approach developed here can be implemented over timescales from days to years, in any size estuary with dominant groundwater inputs and well-defined cross-sections. The approach also directly links delivery of groundwater from the watershed with fluxes to the coastal environment.
    Description: Funding was provided by the USGS Coastal and Marine Geology Program.
    Keywords: Estuarine processes ; Nutrient loading ; Submarine groundwater discharge ; Tidal pumping
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  • 92
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    Summertime cooling of the shallow continental shelf (2011)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C07015, doi:10.1029/2010JC006744.
    Description: In summer on the shallow New England continental shelf, near the coast the water temperature is much cooler than the observed surface heat flux suggests. Using depth-integrated heat budgets in 12 and 27 m water depth calculated from observed surface heat flux, water temperature, and velocity, we demonstrate that on time scales of weeks to months the water is persistently cooled due to a mean upwelling circulation. Because the mean wind is weak, that mean circulation is likely not wind driven; it is partly a tidal residual circulation. A feedback exists between the cross-shelf and surface heat fluxes: the two fluxes remain nearly in balance for months, so the water temperature is nearly constant in spite of strong surface heating (the heat budget is two-dimensional). A conceptual model explains the feedback mechanism: the short flushing time of the shallow shelf produces a near steady state heat balance, regardless of the exact form of the circulation, and the feedback is via the influence of surface heating on temperature stratification. Along-shelf heat flux divergence is apparently small compared to the surface and cross-shelf heat flux divergences on time scales of weeks to months. Heat transport due to Stokes drift from surface gravity waves is substantial, warms the shallow shelf in summer, and was previously ignored. In winter, the surface heat flux dominates and the observed water temperature is close to the temperature predicted from surface cooling (the heat budget is one-dimensional); weak winter stratification makes the cross-shelf heat flux small even during strong cross-shelf circulation.
    Description: This research was funded by National Aeronautics and Space Administration Headquarters grant NNG04GL03G and Earth System Science Fellowship Grant NNG04GQ14H; Woods Hole Oceanographic Institution through Academic Programs Fellowship Funds and MVCO; National Science Foundation grants OCE‐0241292, OCE‐0548961, and OCE‐0337892; the Jewett/ EDUC/Harrison Foundation; and Office of Naval Research contracts N00014‐01‐1‐0029 and N00014‐05‐10090 for the Low‐Wind Component of the Coupled Boundary Layers Air‐Sea Transfer Experiment.
    Keywords: Continental shelf ; Heat budget ; Inner shelf ; Seasonal cycle
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  • 93
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    Mechanisms controlling dissolved iron distribution in the North Pacific : a model study (2011)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): G03005, doi:10.1029/2010JG001541.
    Description: Mechanisms controlling the dissolved iron distribution in the North Pacific are investigated using the Biogeochemical Elemental Cycling (BEC) model with a resolution of approximately 1° in latitude and longitude and 60 vertical levels. The model is able to reproduce the general distribution of iron as revealed in available field data: surface concentrations are generally below 0.2 nM; concentrations increase with depth; and values in the lower pycnocline are especially high in the northwestern Pacific and off the coast of California. Sensitivity experiments changing scavenging regimes and external iron sources indicate that lateral transport of sedimentary iron from continental margins into the open ocean causes the high concentrations in these regions. This offshore penetration only appears under a scavenging regime where iron has a relatively long residence time at high concentrations, namely, the order of years. Sedimentary iron is intensively supplied around continental margins, resulting in locally high concentrations; the residence time with respect to scavenging determines the horizontal scale of elevated iron concentrations. Budget analysis for iron reveals the processes by which sedimentary iron is transported to the open ocean. Horizontal mixing transports sedimentary iron from the boundary into alongshore currents, which then carry high iron concentrations into the open ocean in regions where the alongshore currents separate from the coast, most prominently in the northwestern Pacific and off of California.
    Description: This work was supported by the U.S. National Science Foundation (EF‐0424599).
    Keywords: Pacific ; Iron ; Modeling
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  • 94
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    Wave-angle control of delta evolution (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L13405, doi:10.1029/2011GL047630.
    Description: Wave-influenced deltas, with large-scale arcuate shapes and demarcated beach ridge complexes, often display an asymmetrical form about their river channel. Here, we use a numerical model to demonstrate that the angles from which waves approach a delta can have a first-order influence upon its plan-view morphologic evolution and sedimentary architecture. The directional spread of incoming waves plays a dominant role over fluvial sediment discharge in controlling the width of an active delta lobe, which in turn affects the characteristic rates of delta progradation. Oblique wave approach (and a consequent net alongshore sediment transport) can lead to the development of morphologic asymmetry about the river in a delta's plan-view form. This plan-form asymmetry can include the development of discrete breaks in shoreline orientation and the appearance of self-organized features arising from shoreline instability along the downdrift delta flank, such as spits and migrating shoreline sand waves—features observed on natural deltas. Somewhat surprisingly, waves approaching preferentially from one direction tend to increase sediment deposition updrift of the river. This ‘morphodynamic groin effect’ occurs when the delta's plan-form aspect ratio is sufficiently large such that the orientation of the shoreline on the downdrift flank is rotated past the angle of maximum alongshore sediment transport, resulting in preferential redirection of fluvial sediment updrift of the river mouth.
    Description: This research was supported by NSF grants EAR‐0952146 and OCE‐0623766, the Exxon‐Mobil Upstream Research Company, and the WHOI‐USGS postdoctoral fellowship.
    Keywords: Depositional asymmetry ; Large-scale coastal evolution ; Numerical modeling ; Plan-view delta evolution
    Repository Name: Woods Hole Open Access Server
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  • 95
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    Modeling sulfate reduction in methane hydrate-bearing continental margin sediments : does a sulfate-methane transition require anaerobic oxidation of methane? (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q07006, doi:10.1029/2011GC003501.
    Description: The sulfate-methane transition (SMT), a biogeochemical zone where sulfate and methane are metabolized, is commonly observed at shallow depths (1–30 mbsf) in methane-bearing marine sediments. Two processes consume sulfate at and above the SMT, anaerobic oxidation of methane (AOM) and organoclastic sulfate reduction (OSR). Differentiating the relative contribution of each process is critical to estimate methane flux into the SMT, which, in turn, is necessary to predict deeper occurrences of gas hydrates in continental margin sediments. To evaluate the relative importance of these two sulfate reduction pathways, we developed a diagenetic model to compute the pore water concentrations of sulfate, methane, and dissolved inorganic carbon (DIC). By separately tracking DIC containing 12C and 13C, the model also computes δ13C-DIC values. The model reproduces common observations from methane-rich sediments: a well-defined SMT with no methane above and no sulfate below and a δ13C-DIC minimum at the SMT. The model also highlights the role of upward diffusing 13C-enriched DIC in contributing to the carbon isotope mass balance of DIC. A combination of OSR and AOM, each consuming similar amounts of sulfate, matches observations from Site U1325 (Integrated Ocean Drilling Program Expedition 311, northern Cascadia margin). Without AOM, methane diffuses above the SMT, which contradicts existing field data. The modeling results are generalized with a dimensional analysis to the range of SMT depths and sedimentation rates typical of continental margins. The modeling shows that AOM must be active to establish an SMT wherein methane is quantitatively consumed and the δ13C-DIC minimum occurs. The presence of an SMT generally requires active AOM.
    Keywords: Anaerobic oxidation of methane ; Reaction-transport modeling ; Sulfate reduction
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    Modeling surf zone tracer plumes : 2. Transport and dispersion (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C11028, doi:10.1029/2011JC007211.
    Description: Five surf zone dye tracer releases from the HB06 experiment are simulated with a tracer advection diffusion model coupled to a Boussinesq surf zone model (funwaveC). Model tracer is transported and stirred by currents and eddies and diffused with a breaking wave eddy diffusivity, set equal to the breaking wave eddy viscosity, and a small (0.01 m2 s−1) background diffusivity. Observed and modeled alongshore parallel tracer plumes, transported by the wave driven alongshore current, have qualitatively similar cross-shore structures. Although the model skill for mean tracer concentration is variable (from negative to 0.73) depending upon release, cross-shore integrated tracer moments (normalized by the cross-shore tracer integral) have consistently high skills (≈0.9). Modeled and observed bulk surf zone cross-shore diffusivity estimates are also similar, with 0.72 squared correlation and skill of 0.4. Similar to the observations, the model bulk (absolute) cross-shore diffusivity is consistent with a mixing length parameterization based on low-frequency (0.001–0.03 Hz) eddies. The model absolute cross-shore dispersion is dominated by stirring from surf zone eddies and does not depend upon the presence of the breaking wave eddy diffusivity. Given only the bathymetry and incident wave field, the coupled Boussinesq-tracer model qualitatively reproduces the observed cross-shore absolute tracer dispersion, suggesting that the model can be used to study surf zone tracer dispersion mechanisms.
    Description: This research was supported by SCCOOS, CA Coastal Conservancy, NOAA, NSF, ONR, and CA Sea Grant.
    Description: 2012-05-18
    Keywords: Dispersion ; Mixing ; Surf zone ; Tracer
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  • 97
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    Sea ice and its effect on CO2 flux between the atmosphere and the Southern Ocean interior (2011)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C11019, doi:10.1029/2010JC006509.
    Description: The advance and retreat of sea ice produces seasonal convection and stratification, dampens surface waves and creates a separation between the ocean and atmosphere. These are all phenomena that can affect the air-sea gas transfer velocity (k660), and therefore it is not straightforward to determine how sea ice cover modulates air-sea flux. In this study we use field estimates k660 to examine how sea ice affects the net gas flux between the ocean and atmosphere. An inventory of salinity, 3He, and CFC-11 in the mixed layer is used to infer k660 during the drift of Ice Station Weddell in 1992. The average of k660 is 0.11 m d−1 across nearly 100% ice cover. In comparison, the only prior field estimates of k660 are disproportionately larger, with average values of 2.4 m d−1 across 90% sea ice cover, and 3.2 m d−1 across approximately 70% sea ice cover. We use these values to formulate two scenarios for the modulation of k660 by the fraction of sea ice cover in a 1-D transport model for the Southern Ocean seasonal ice zone. Results show the net CO2 flux through sea ice cover represents 14–46% of the net annual air-sea flux, depending on the relationship between sea ice cover and k660. The model also indicates that as much as 68% of net annual CO2 flux in the sea ice zone occurs in the springtime marginal ice zone, which demonstrates the need for accurate parameterizations of gas flux and primary productivity under partially ice-covered conditions.
    Description: Support for this work was provided by the Climate Center at the Lamont‐Doherty Earth Observatory, an NSF IGERT Fellowship and a NOAA Climate and Global Change Postdoctoral Fellowship to BL, and NSF grant OPP 01‐25523/ANT 04‐40825 (PS).
    Description: 2012-05-15
    Keywords: CO2 ; Southern Ocean ; Carbon cycle ; Gas exchange ; Sea ice
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  • 98
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    Modeling surf zone tracer plumes : 1. Waves, mean currents, and low-frequency eddies (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C11027, doi:10.1029/2011JC007210.
    Description: A model that accurately simulates surf zone waves, mean currents, and low-frequency eddies is required to diagnose the mechanisms of surf zone tracer transport and dispersion. In this paper, a wave-resolving time-dependent Boussinesq model is compared with waves and currents observed during five surf zone dye release experiments. In a companion paper, Clark et al. (2011) compare a coupled tracer model to the dye plume observations. The Boussinesq model uses observed bathymetry and incident random, directionally spread waves. For all five releases, the model generally reproduces the observed cross-shore evolution of significant wave height, mean wave angle, bulk directional spread, mean alongshore current, and the frequency-dependent sea surface elevation spectra and directional moments. The largest errors are near the shoreline where the bathymetry is most uncertain. The model also reproduces the observed cross-shore structure of rotational velocities in the infragravity (0.004 〈 f 〈 0.03 Hz) and very low frequency (VLF) (0.001 〈 f 〈 0.004 Hz) bands, although the modeled VLF energy is 2–3 times too large. Similar to the observations, the dominant contributions to the modeled eddy-induced momentum flux are in the VLF band. These eddies are elliptical near the shoreline and circular in the mid surf zone. The model-data agreement for sea swell waves, low-frequency eddies, and mean currents suggests that the model is appropriate for simulating surf zone tracer transport and dispersion.
    Description: This research was supported by SCCOOS, CA Coastal Conservancy, NOAA, NSF, ONR, and CA Sea Grant.
    Description: 2012-05-18
    Keywords: Mixing ; Surf zone ; Tracer dispersion
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  • 99
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    A conduit dilation model of methane venting from lake sediments (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L06408, doi:10.1029/2011GL046768.
    Description: Methane is a potent greenhouse gas, but its effects on Earth's climate remain poorly constrained, in part due to uncertainties in global methane fluxes to the atmosphere. An important source of atmospheric methane is the methane generated in organic-rich sediments underlying surface water bodies, including lakes, wetlands, and the ocean. The fraction of the methane that reaches the atmosphere depends critically on the mode and spatiotemporal characteristics of free-gas venting from the underlying sediments. Here we propose that methane transport in lake sediments is controlled by dynamic conduits, which dilate and release gas as the falling hydrostatic pressure reduces the effective stress below the tensile strength of the sediments. We test our model against a four-month record of hydrostatic load and methane flux in Upper Mystic Lake, Mass., USA, and show that it captures the complex episodicity of methane ebullition. Our quantitative conceptualization opens the door to integrated modeling of methane transport to constrain global methane release from lakes and other shallow-water, organic-rich sediment systems, and to assess its climate feedbacks.
    Description: This work was supported by the U.S. Department of Energy (grants DE‐FC26‐06NT43067 and DE‐AI26‐05NT42496), an NSF Doctoral Dissertation Research grant (0726806), a GSA Graduate Student Research grant, and MIT Martin, Linden and Ippen fellowships.
    Keywords: Greenhouse gas ; Methane flux ; Freshwater methane ; Gas conduits ; Effective stress ; Ebullition
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  • 100
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    An asymmetric upwind flow, Yellow Sea Warm Current : 2. Arrested topographic waves in response to the northwesterly wind (2011)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C04027, doi:10.1029/2010JC006514.
    Description: A warm and salty water mass exists along the Yellow Sea Trough (YST) in winter. This oceanic water mass is distinct from the ambient shelf water and is distributed on the western side of the YST. It has long been reasoned that a Yellow Sea Warm Current (YSWC) must exist. A recent observational study indeed supports the existence of the YSWC and shows that its position moved progressively westward as the warm water intrudes further shoreward toward the northwest. In this paper, we explain mechanisms for sustaining the YSWC and for its westward displacement. The northwesterly monsoonal wind prevails in the winter and is directed against the YSWC. The cross-trough scale is small compared with the spatial scale of monsoonal variation, so one can assume, to the first order, that the wind stress is uniform across the trough. The curl of depth-averaged wind stress has opposite signs on the two sides of the trough. Consequently, two oppositely rotating gyres develop initially and they converge along the trough giving rise to a barotropic upwind flow. But this upwind flow lasts only for a few days as the two gyres evolve and propagate as topographic waves. For a northerly wind, both gyres move westward since the positive (negative) potential vorticity flux on the western (eastern) side of the trough pushes the water toward shore (trough). If the bottom friction is negligible, the steady response becomes a large anticyclonic gyre over the trough and the upwind current is squeezed toward the shore line. In this case, no YSWC is sustained along or near the trough. This runaway warm current can be arrested by a moderate bottom friction. We therefore propose that the YSWC is actually arrested topographic waves in response to local wind stress forcing.
    Description: X.L. has been supported by China’s National Basic Research Priorities Programmer (2007CB411804 and 2005CB422303), the Ministry of Education’s 111 Project (B07036), the Program for New Century Excellent Talents in University (NECT‐07‐ 0781), and the China National Science Foundation (40976004, 40921004, and 40930844). J.Y. has been supported by the U.S. National Science Foundation and the Woods Hole Oceanographic Institution’s Coastal Ocean Institute.
    Keywords: Yellow Sea Warm Current ; Asymmetric upwind flow ; Arrested topographic waves
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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