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  • American Geophysical Union  (75,817)
  • Annual Reviews
  • Copernicus
  • 2005-2009  (44,032)
  • 1990-1994  (23,567)
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  • 101
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    2002–2003 Lava Flow Eruption of Stromboli: A Contribution to Understanding Lava Discharge Mechanisms Using Periodic Digital Photogrammetry Surveys (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Photogrammetric surveys were performed between 5 January and 26 July 2003 for monitoring the NW flank of the Sciara del Fuoco (SdF) during the eruption of Stromboli that started on 28 December 2002. The collected data were used both for controlling morphological changes after the major landslide that occurred on 30 December 2002 and lava flow field evolution until the end of the eruption (22 July 2003). The latter objective was achieved by a quantitative analysis which allowed to estimate the total lava volume (12.51 × 106 m3) emplaced on the SdF slope corresponding to an eruption rate of about 0.69 m3/s. Thanks to the availability of multitemporal data set, which made this event the first well-documented and regularly surveyed Stromboli eruption, the cumulative volume and effusion rate trends were derived. A model for interpreting the behavior of the 2002–2003 Stromboli effusive eruption is also proposed: being the vents located very close to the volcano summit, a typical summit (terminal) basaltic lava flow eruption was expected; on the contrary, the observed effusion rate trend showed an initial peak followed by an exponential decline typical of flank (lateral) eruptions of basaltic volcanoes. We recognized in this trend a transition from a terminal (open conduit system) to a lateral (pressurized dike system) lava discharge followed by a longer period in which the elastic strain energy from the subvolcanic reservoir controlled the effusion rate; this effect counterbalanced the lava cooling at dike tip that tends to close the eruptive fissure causing the eruption end.
    Description: Published
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: reserved
    Keywords: Stromboli ; Digital photogrammetry survey ; lava disharge mechanism ; morphological changes ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 102
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    Potential-Field Forward Modeling and Inversion Using 3D Fast Fourier Transforms (2009)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Although 1D and 2D fast Fourier transforms (FFTs) have long been used for the filtering, interpretation, and modeling of potential-field data, 3D FFTs have not enjoyed similar popularity. This may change with the recent discovery (Caratori Tontini et al, in press, JGR) that simple 3D FFT filters can be used to transform distributions of density (or magnetization) within a box-shaped 3D volume into gravity (or magnetic) fields within the same volume.
    Description: Published
    Description: San Francisco
    Description: 3.4. Geomagnetismo
    Description: open
    Keywords: 3D Fourier transform ; Potential field ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods ; 05. General::05.01. Computational geophysics::05.01.05. Algorithms and implementation
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Poster session
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  • 103
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    CO2/CH4 ratio in fumaroles a powerful tool to detect magma degassing episodes at quiescent volcanoes (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Long time series of fumarolic compositions at Campi Flegrei (Italy), Mammoth Mountain (California), Panarea (Italy) and Nisyros (Greece) show rapid increases, up to orders of magnitude, of the CO2/CH4 ratio systematically with the occurrence of volcanic unrest periods. These easily detected anomalies originate with the arrival of CH4-poor magmatic fluids in the shallower levels of the volcanoes. The data suggest that volcanoes are characterized by magmatic activity at depth also in periods of apparent quiescence. The activity is constituted by the pulsing release of large amount of fluids which either cause unrest periods (seismicity and ground deformation) or possibly could precede volcanic eruption. This type of volcanic activity can be monitored trough the classical geophysical techniques together with the systematic sampling and analysis of fumaroles.
    Description: In press
    Description: 4.5. Degassamento naturale
    Description: JCR Journal
    Description: reserved
    Keywords: fumarole ; magma degassing ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 104
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    A bayesian approach to the real time estimation of magnitude from the early P- and S-wave displacement peaks (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: It has been shown that the initial portion of P and S wave signals can provide information about the final earthquake magnitude in a wide magnitude range. This observation opens the perspective for the real-time determination of source parameters. In this paper we describe a probabilistic evolutionary approach for the real-time magnitude estimation which can have a potential use in earthquake early warning. The technique is based on empirical prediction laws correlating the low-frequency peak ground displacement measured in a few seconds after the P and/or S phase arrival and the final event magnitude. The evidence for such a correlation has been found through the analysis of 256 shallow crustal events in the magnitude range Mjma 4–7.1 located over the entire Japanese archipelago. The peak displacement measured in a 2-s window from the first P phase arrival correlates with magnitude in the range M = [4–6.5]. While a possible saturation effect above M ’ 6.5 is observed, it is less evident in an enlarged window of 4 s. The scaling of S peaks with magnitude is instead also observed at smaller time lapses (i.e., 1 s) after the first S arrival. The different scaling of P and S peaks with magnitude when measured in a 2-s window is explained in terms of different imaged rupture surface by the early portion of the body wave signals. We developed a technique to estimate the probability density function (PDF) of magnitude, at each time step after the event origin. The predicted magnitude value corresponds to the maximum of PDF, while its uncertainty is given by the 95% confidence bound. The method has been applied to the 2007 (Mjma = 6.9) Noto Hanto and 1995 (Mjma = 7.3) Kobe earthquakes. The results of this study can be summarized as follows: (1) The probabilistic algorithm founded on the predictive model of peak displacement versus final magnitude is able to provide a fast and robust estimation of the final magnitude. (2) The information available after a few seconds from the first detection of the P phase at the network can be used to predict the peak ground motion at a given regional target with uncertainties which are comparable to those derived from the attenuation law. (3) The near-source S phase data can be used jointly with P data for regional early warning purposes, thus increasing the accuracy and reliability of magnitude estimation.
    Description: Published
    Description: B12302
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: reserved
    Keywords: Bayesian approach ; P and S wave ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 105
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    Earthquake early warning system in southern Italy: Methodologies and performance evaluation (2009)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We investigate the effect of extended faulting processes and heterogeneous wave propagation on the early warning system capability to predict the peak ground velocity (PGV) from moderate to large earthquakes occurring in the southern Apennines (Italy). Simulated time histories at the early warning network have been used to retrieve early estimates of source parameters and to predict the PGV, following an evolutionary, probabilistic approach. The system performance is measured through the Effective Lead-Time (ELT), i.e., the time interval between the arrival of the first S-wave and the time at which the probability to observe the true PGV value within one standard deviation becomes stationary, and the Probability of Prediction Error (PPE), which provides a measure of PGV prediction error. The regional maps of ELT and PPE show a significant variability around the fault up to large distances, thus indicating that the system's capability to accurately predict the observed peak ground motion strongly depends on distance and azimuth from the fault.
    Description: Published
    Description: L00B07
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: reserved
    Keywords: Seismic early warning ; Southern Italy ; Synthetic seismograph ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 106
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    Characterization and location of infrasonic sources in active volcanoes: Mount Etna, September–November 2007 (2009)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The period September–November 2007 was characterized at Mount Etna by explosive activity and intense degassing. During this time interval, infrasonic signals were recorded by an infrasonic network. By a triggering procedure, about 1000 infrasonic events were found, characterized by very high signal-to-noise ratio and grouped into nine families. Successively, the spectral analysis allowed subdividing these nine families into three clusters based on the peak frequency and the quality factor of the events. Finally, by the location analysis a cluster (cluster 1) was related to the degassing activity of the northeast crater (NEC), while the other two (clusters 2 and 3) to the explosive activity of the southeast crater (SEC). The comparison between the stacked infrasonic waveforms, interpreted as generated by the vibration of large gas bubbles, and the synthetic ones, permitted to calculate radius, length of the bubble, and initial overpressure, by a genetic algorithm method. The higher overpressure values of cluster 3 compared to the cluster 2 values were in good agreement with the stronger intensity of the explosions accompanying the infrasonic events of cluster 3. The variation of both intensities and waveforms is tentatively attributed to the occasional accumulation of lithic clasts (due to moderate landslides?) on the explosive vent. Indeed, events belonging to cluster 3 were no longer observed once the landslides had ended. Finally, the daily emitted gas volume, related to the active degassing, was estimated for NEC and SEC by using the infrasonic data during the studied period.
    Description: Published
    Description: B08308
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Mt. Etna ; Infrasound ; volcano monitoring ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 107
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    The 2007 Stromboli eruption: event chronology and effusion rates using thermal infrared data (2009)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Accepted for publication in Journal of Geophysical Research. Copyright (2009) American Geophysical Union. Further reproduction or electronic distribution is not permitted.
    Description: Using thermal infrared images recorded by a permanent thermal camera network maintained on Stromboli volcano (Italy), together with satellite and helicopter-based thermal image surveys, we have compiled a chronology of the events and processes occurring before and during Stromboli’s 2007 effusive eruption. These digital data also allow us to calculate the effusion rates and lava volumes erupted during the effusive episode. At the onset of the 2007 eruption, two parallel eruptive fissures developed within the North East crater, eventually breaching the NE flank of the summit cone and extending along the eastern margin of the Sciara del Fuoco. These fed a main effusive vent at 400 m a.s.l. to feed lava flows that extended to the sea. The effusive eruption was punctuated, on 15 March, by a paroxysm with features similar to the 5 April paroxysm that occurred during the 2002-03 effusive eruption. A total of between 3.2 x 106 m3 and 11 x 106 m3 of lava was erupted during the 2007 eruption over 34 days of effusive activity. More than half of this volume was emplaced during the first 5.5 days of the eruption. Although the 2007 effusive eruption had a comparable erupted volume to the previous (2002-03) effusive eruption, it had a shorter duration and thus a mean output rate (= total volume divided by eruption duration) that was one order of magnitude greater than the 2002-03 event (~2.4 m3 s-1 compared with 0.32±0.28 m3 s-1). In this paper, we discuss similarities and differences between these two effusive events, and interpret the processes occurring in 2007 in terms of the recent dynamics witnessed at Stromboli.
    Description: This paper was partially supported by a grant to S. Calvari (Project INGV-DPC Paroxysm V2/03, 2008-2010) funded by the Istituto Nazionale di Geofisica e Vulcanologia and by the Italian Civil Protection. Satellite-based effusion rate work by A. Steffke and A. Harris was supported by NASA grant NNG04GO64G "New Tools for Advanced Hot Spot Tracking".
    Description: In press
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: open
    Keywords: Thermal mapping ; Stromboli ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 108
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    Anomalous magmatic degassing prior to the 5th April 2003 paroxysm on Stromboli (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: A major explosion occurred at Stromboli on April 5 2003, being the most powerful event over a period of exceptional eruptive activity lasting from December to July. Here, we describe results from a network of diffusive tubes set up on the Stromboli’s summit area, aimed at a characterisation of plume composition (SO2, HCl, HF) prior to and after April 5. Data analysis revealed anomalous sulphur degassing 2–3 days before the event, when SO2/HCl ratios (9) significantly higher than those typical of quiescent degassing (1) were recorded. We interpret this exceptional plume signature as an evidence of S-rich magmas ascending in the shallow plumbing system, and propose high SO2/HCl as a potential precursor of major explosions on the volcano. The post-April 5 phase was characterised by time-decreasing SO2/HCl and SO2/HF plume ratios, ascribed to declining magma feeding as a prelude to restoration of ‘‘normal’’ Strombolian activity.
    Description: Published
    Description: L14607
    Description: partially_open
    Keywords: magmatic degassing ; paroxysm ; Stromboli ; 04. Solid Earth::04.03. Geodesy::04.03.06. Measurements and monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 109
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    Evidence of a recent input of magmatic gases into the quiescent volcanic edifice of Panarea, Aeolian Islands, Italy (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: On 2nd/3rd November 2002, a huge amount of gas, mainly composed of CO2, was suddenly released from the sea bottom off the coast of Panarea, producing a ‘‘crater’’20 by 10 meters wide and 7 meters deep. The gas output was estimated to be 109 l/d, two orders of magnitude higher than that measured in the 1980s. The anomalous degassing rate lasted for some weeks, slowly decreasing to an almost constant rate of about 4 x 107 l/d after two months. The geothermo- barometric estimations revealed an increase of both the temperature and pressure in the geothermal system feeding the sampled vents. The 3He/4He ratios were similar to those measured in nearby Stromboli. We have monitored the area for the last two decades, and based on our intensive and extensive geochemical measurements, have ascertained that the geothermal reservoir has lost its steady state. We maintain that a new magmatic input caused these phenomena.
    Description: - Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy. - Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Palermo, Italy. - Dipartimento Chimica e Fisica della Terra ed Applicazioni, Palermo, Italy.
    Description: Published
    Description: L07619
    Description: partially_open
    Keywords: Submarine degassing ; magmatic fluids ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.02. Data dissemination::05.02.01. Geochemical data ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 110
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    Evidence of deep magma degassing and ascent by geochemistry of peripheral gas emissions at Mount Etna (Italy): Assessment of the magmatic reservoir pressure (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Five gas discharges in the area of Mount Etna volcano (Italy) and in the near Hyblean plateau have been monitored since 1996. All the emissions displayed low contributions from crustal fluids, whereas magmatic gases were the main component. Selective dissolution of these gases into hydrothermal aquifers has been recognized and modeled, allowing us to calculate the original composition of the magma-released gases. The inferred composition of the magmatic gases exhibits synchronous variations of He/Ne and He/CO2 ratios, which are coherent with the magma degassing process. On the basis of numerical simulations of volatile degassing from Etnean basalts we have computed the initial and final pressures of the magma batches feeding the emissions. We thus can define the levels of the Etna plumbing system where magmas are stored. Pressure values were around 360 and 160 MPa for initial and final stages, respectively, meaning related depths of about 10 and 3 km below sea level, matching those obtained by geophysical investigations for the deep and shallow magma reservoirs. In addition, we have been able to recognize episodes of magma migration from the deeper reservoir toward the shallow one. An important magma injection into the shallow storage volume was detected during the onset of the 2001 eruption (17 July). No further injection had taken place during this period until September 2001, providing a possible reason for the quick exhaustion of the eruption. In view of this we suggest that the sampled emissions are a powerful geochemical tool to investigate the Etna’s plumbing system and its magma dynamics, as well as the development of eruptive events.
    Description: Published
    Description: 2463
    Description: partially_open
    Keywords: gas geochemistry ; magma degassing ; modeling ; 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::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 111
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    Reply to comment by A. Kopf on ‘‘Methane emission from the mud volcanoes of Sicily (Italy)’’, and notice on CH4 flux data from European mud volcanoes (2005)
    American Geophysical Union
    In:  Etiope G., Caracausi A., Favara R., Italiano F., Baciu C. (2002) Methane emission from the mud volcanoes of Sicily (Italy). Geoph. Res. Letters 29, 14340-14343.
    Details
    Publication Date: 2017-04-04
    Description: The paper ‘‘Methane emission from the mud volcanoes of Sicily (Italy)’’ by Etiope et al. [2002] represents the first report ever done on experimental CH4 output data from subaerial mud volcanoes (MV). A review of available CH4 flux data and detailed discussion about the global implications of mud volcanic CH4 emission has been made elsewhere [Etiope and Klusman, 2002; Morner and Etiope, 2002]. [2] The comment by Kopf [2003] contributes to open discussions and to make the readership aware on how important this subject is. In this reply we wish to clarify that precise data of CH4 flux from geologic sources are beginning to be available only now. It would be opportune that the MV-expert community could agree in using a common unit for the gas flux. We propose t y 1 and Mt y 1, and not metres cubed, consistently with the data reported for the methane sources/sinks budget by the IPCC. [3] Sicilian MVs, the first to be measured in detail, are considerably much smaller than the Azeri Ashgil MV, mentioned by Kopf [2003], and it is therefore obvious to expect a lower gas flux. Anyway the Dashgil mud volcano flux data are not based on exact measurements but only on visual estimates of the bubbles [Hovland et al., 1997]. In order to fully reply to Kopf [2003], hereafter we briefly discuss the problem of how to estimate the total number of MVs in the world and present new data from other European MVs, recently investigated. Finally, we outline the global importance of mud volcanic CH4 emission, as Kopf [2003] and recent literature is stressing.
    Description: Published
    Description: 1094
    Description: partially_open
    Keywords: methane ; mud volcanoes ; helium ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate ; 02. Cryosphere::02.03. Ice cores::02.03.02. Atmospheric Chemistry ; 03. Hydrosphere::03.04. Chemical and biological::03.04.02. Carbon cycling ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases
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  • 112
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    Mount Etna: Geochemical signals of magma ascent and unusually extensive plumbing system (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Five years of gas monitoring from selected sites suggest that Mt Etna’s plumbing system is much more extensive than previously reported. It extends at least 40 km SW from the volcano’s boundary along the NE-SW regional fault, where it discharges about 200 tons/day of gas, containing helium with mantle-type isotopic composition. Synchronous variations of 3He/4He isotopic ratios in gas sampled at sites located 60 kilometers apart have allowed us to detect pulses of ascending magma in the plumbing system, thus providing a powerful tool for eruption forecasting. Following summer 2001 eruption, the still increasing trend of the 3He/4He ratios indicates that magma storage is even now occurring at a shallow depth. Hence, the volcano maintains a high capacity to re-erupt within the next few months.
    Description: Published
    Description: 1057
    Description: partially_open
    Keywords: helium isotopes ; geochemical monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 113
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    Active geodynamics of the central Mediterranean Sea: Tensional tectonic evidences in western Sicily from mantle-derived helium (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We report results on the measured high 3He/4He isotope ratio in western Sicily, interpreted together with the heat data. The study of this sector of the Europe-Africa interaction is crucial to a better understanding of the tectonics and the geodynamical evolution of the central Mediterranean area. The estimated mantle-derived helium fluxes in the investigated areas are up to 2–3 orders of magnitude greater than those of a stable continental area. The highest flux, found in the southernmost area near the Sicily Channel, where recent eruptions of the Ferdinandea Island occurred 20 miles out to sea off Sciacca, has been associated with a clear excess of heat flow. Our results indicate that there is an accumulation of magma below the continental crust of western Sicily that is possibly intruding and out-gassing through roughly N-S trending deep fault systems linked to the mantle, that have an extensional component. Although the identification of these faults is not sufficiently constrained by our data, they could possibly be linked to the pre-existing faults that originated during the Mesozoic extensional-transtensional tectonic phases.
    Description: Published
    Description: L04312
    Description: partially_open
    Keywords: helium isotopes ; heat production ; tectonics ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems ; 03. Hydrosphere::03.04. Chemical and biological::03.04.07. Radioactivity and isotopes ; 04. Solid Earth::04.02. Exploration geophysics::04.02.03. Heat flow ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.07. Tectonophysics::04.07.03. Heat generation and transport ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
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  • 114
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    The Stromboli Volcano landslides of December 2002: A seismological description (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We analyse seismograms of the slump episodes at Stromboli on December 30, 2002. Using a simple single force model, we estimate the volume involved in the individual subevents and attempt a chronological reconstruction of the whole process. Our results indicate the occurrence of two main events that could be interpreted as a submarine slump, which caused the observed tsunami, and a subaerial slump, which did not produce destructive sea waves. A total volume of about 20 106 m3 results for the submarine event, which developed over about 2 minutes with several distinct detachments, the first and largest displacing a volume of 10.8 106 m3. The second, subaerial, slump involved at least 2.5 106 m3, in about 90 s. A large long period pulse is also recognizable in the seismograms of the Stromboli station. We tentatively interpret this feature as tilt caused by the water load associated with the inundation in the Ficogrande area, on the northeastern side of the island.
    Description: Published
    Description: (L02605)
    Description: reserved
    Keywords: Stromboli Volcano ; seismological description ; Fractures and faults ; Structural Geology ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology
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  • 115
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    The 1997 Umbria-Marche (Italy) earthquake sequence: relationship between ground deformation and seismogenic structure (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: A field survey performed during the 1997 Umbria-Marche earthquake sequence led us to recognize ground and pavement ruptures associated with the three largest shocks (M〉= 5.7). The ruptures are concentrated in narrow bands that, in part, are on and near previously mapped high-angle normal fauts. The geometry of the ground deformation is consistent with the NE-trending extension indicated by CMT focal solutions of the mainshocks. The distribution of aftershocks suggests that the three mainshocks occurred on ~40 degree SW-dipping normal faults. Geological investigations, modelling of expected coseismic elevation changes, and seismic data, suggest that the surface deformation is not the direct result of primary rupture of faults at depth.
    Description: Published
    Description: 895-898
    Description: reserved
    Keywords: Structural geology ; Fractures and faults ; Seismology ; Seismicity and seismotectonics ; Europe ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
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    Geochemistry of serpentinized peridotites from the Mariana Forearc Conical Seamount, ODP Leg 125: Implications for the elemental recycling at subduction zones (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Recent examinations of the chemical fluxes through convergent plate margins suggest the existence of significant mass imbalances for many key species: only 20–30% of the to-the-trench inventory of large-ion lithophile elements (LILE) can be accounted for by the magmatic outputs of volcanic arcs. Active serpentinite mud volcanism in the shallow forearc region of the Mariana convergent margin presents a unique opportunity to study a new outflux: the products of shallow-level exchanges between the upper mantle and slab-derived fluids. ODP Leg 125 recovered serpentinized harzburgites and dunites from three sites on the crests and flanks of the active Conical Seamount. These serpentinites have U-shaped rare earth element (REE) patterns, resembling those of boninites. U, Th, and the high field strength elements (HFSE) are highly depleted and vary in concentration by up to 2 orders of magnitude. The low U contents and positive Eu anomalies indicate that fluids from the subducting Pacific slab were probably reducing in nature. On the basis of substantial enrichments of fluid-mobile elements in serpentinized peridotites, we calculated very large slab inventory depletions of B (79%), Cs (32%), Li (18%), As (17%), and Sb (12%). Such highly enriched serpentinized peridotites dragged down to depths of arc magma generation may represent an unexplored reservoir that could help balance the input-output deficit of these elements as observed by Plank and Langmuir (1993, 1998) and others. Surprisingly, many species thought to be mobile in fluids, such as U, Ba, Rb, and to a lesser extent Sr and Pb, are not enriched in the rocks relative to the depleted mantle peridotites, and we estimate that only 1–2% of these elements leave the subducting slabs at depths of 10 to 40 km. Enrichments of these elements in volcanic front and behind-the-front arc lavas point to changes in slab fluid composition at greater depths.
    Description: Published
    Description: 1-24
    Description: partially_open
    Keywords: Serpentinite ; Ocean Drilling Program ; Forearc ; Mantle ; Marianas ; Subduction ; 04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry ; 04. Solid Earth::04.07. Tectonophysics::04.07.06. Subduction related processes
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    An improved stress map for Italy and surrounding regions (central Mediterranean) (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We present an updated present-day stress data compilation for the Italian region and discuss it with respect to the geodynamic setting and the seismicity of the area. We collected and analyzed 190 new stress data from borehole breakouts, seismicity, and active faults and checked in detail the previous compilation [Montone et al., 1999]. Our improved data set consists of 542 data, 362 of which with a reliable quality for stress maps. The Italian region is well sampled, allowing the computation of constrained smoothed stress maps; for surrounding regions we added the World Stress Map 2003 release data. These maps depict the active stress conditions and, in the areas where the data are sparse, contribute to understand the relationship between active stress, past tectonic setting, and the seismicity of the study region. The new data are particularly representative along the northern Apennine front, from the Po Plain to offshore the Adriatic, and along the southern Tyrrhenian Sea, north of Sicily, where they point out a compressive tectonic regime. In the Alps both compressive and transcurrent regimes are observed. Our data also confirm that the whole Apenninic belt and the Calabrian arc are extending. Along the central Adriatic coast, changes from one stress regime to another are shown by abrupt variations in the minimum horizontal stress directions. Other gentler stress rotations, as, for instance, from the southern Apennines to the Calabrian arc or along the northern Apennines, follow the curvature of the arcs and are not associated to a stress regime variation.
    Description: Published
    Description: (B10410)
    Description: partially_open
    Keywords: active stress ; earthquakes ; borehole breakouts ; crust and lithosphere ; 04. Solid Earth::04.07. Tectonophysics::04.07.99. General or miscellaneous ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress
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  • 118
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    Reply to comment by Clifford Thurber and Haijiang Zhang on “The effect of velocity structure errors on double-difference “earthquake location (2005)
    American Geophysical Union
    In:  Reply to a comment
    Details
    Publication Date: 2017-04-04
    Description: We defend the two statements of ours in Michelini and Lomax [2004] about Zhang and Thurber [2003] regarded by Thurber and Zhang as incorrect and misleading.
    Description: Published
    Description: partially_open
    Keywords: earthquake location ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
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  • 119
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    Seismic constraints on the present-day kinematics of the Gargano foreland, Italy, at the transition zone between the southern and northern Apennine belts (2005)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The 1995–2004 seismicity in the Gargano Promontory (hereafter GP) foreland at the transition zone between Southern and Northern Apennine belts (Italy) is analyzed with the aim to put constraints on the present-day kinematics of this key-area of the foreland. The spatial distribution of earthquakes and 54 calculated focal mechanisms show that that the main GP ruptures develop along E-W striking, right-lateral strike-slip faults and NW- SE, normal to left-lateral second-order faults that move in response to a prevailing NW-SE compression (i.e. NE-SW extension). Tacking into account the depth of the relocated seismicity and the available geological information, we propose that the GP shear zone represents an E-W striking, major crustal discontinuity separating sectors of the foreland that move in response to the higher, northeastward propagation velocity of the thrust front of the Northern Apennines with respect to that of the Southern Apennines.
    Description: Published
    Description: open
    Keywords: Seismicity ; seismotectonics ; geodynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.99. General or miscellaneous
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  • 120
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    High quality seismological recordings from the SN-1 deep seafloor observatory in the Mt. Etna region (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We show over 4 months of 3-component broadband seismometer data from the SN-1 seafloor multidisciplinary observatory, deployed offshore of Eastern Sicily (Italy) at 2105 m b.s.l. The SN-1 spectra show background noise levels above 0.1 Hz similar to levels at a nearby ground station. An important noise source below 0.1 Hz is caused by tilt of the sensor induced by sea currents. Seismic noise levels above 0.01 Hz are strongly dependent on Etna volcanic activity. In spite of these intense noise sources, SN-1 recorded many local, regional and global events. The quality of seismic recordings confirms the validity of the installation procedure and good ground coupling of the 3-component broadband sensor, suggesting that SN-1 can be proposed as permanent observatory in this high seismic and volcanic hazard area.
    Description: 2002-2003 Framework Program of the Italian National Group for the Defense against Earthquakes (GNDT)
    Description: Published
    Description: L07303
    Description: reserved
    Keywords: 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 121
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    Crustal motion along the Eurasia-Nubia plate boundary (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-03
    Description: We investigate crustal deformation along the Eurasia-Nubia plate boundary in Calabria and Sicily revealed by the GPS velocity field obtained by the combination of continuous site velocities with previous results from episodic campaigns. We recognize two distinct crustal domains characterized by different motions and styles of deformation. Convergence in Sicily is taken up by crustal shortening along the former Tyrrhenian back arc passive margin, in agreement with seismological data and geological evidence of recent cessation of deformation along the Plio-Pleistocene subduction front. The analysis of the GPS data and the consistency between earthquake slip vectors and convergence direction suggest that Eu-Nu convergence in Sicily does not require intermediate crustal blocks. Significant Eurasia ( 3 mm/yr to NNE) and Nubia-fixed ( 5 mm/yr to ESE) residual velocities in Calabria suggest instead the presence of an intermediate crustal block which can be interpreted as a forearc sliver or as an independent Ionian block. According to the first hypothesis, subduction is still active in the Ionian wedge, although we find no evidence for active back arc spreading in the Tyrrhenian Sea. The N115 E oriented Sicily-Calabria GPS relative motion is consistent with the extension observed during the 1908 Mw 7.1 Messina earthquake. We suggest that up to 3 mm/yr ( 80%) of this estimated relative motion between Sicily and the Calabrian Arc may be taken up in the Messina Straits.
    Description: Published
    Description: 1-16
    Description: reserved
    Keywords: GPS ; Calabria, Sicily, Active tectonics ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 122
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    Active crustal extension in the central Apennines (Italy) (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We present the first GPS estimate of crustal extension in the central Apennines (Italy) through the analysis of the deformation of a sub-network of the National GPS Geodetic network IGM95 in the interval 1994–1999. The selected sub-network spans the entire active deformation belt perpendicularly to its axis and allows the evaluation of (1) the total extension rate absorbed in this sector of the Apennines and (2) the seismogenic potential of the normal faults active in the Late Pleistocene-Holocene interval within the network. Results of this reoccupation are consistent with an extensional strain rate of 0.18×10−6 yr−1 concentrated in an area of about 35 km width, giving an average extension rate of 6±2 mm/yr across the central Apennines. The pattern of active deformation suggests active elastic strain accumulation on the westernmost of the two fault systems active in the Late Pleistocene-Holocene interval and may also suggest the presence of another active fault system not recognized so far.
    Description: Published
    Description: 2121-2124
    Description: reserved
    Keywords: GPS ; Apennines, Active extension ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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    Pyroclastic flow dynamics and hazard in a caldera setting: application to Phlegrean Fields (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Numerical simulation of pyroclastic density currents has developed significantly in recent years and is increasingly applied to volcanological research. Results from physical modeling are commonly taken into account in volcanic hazard assessment and in the definition of hazard mitigation strategies. In this work, we modeled pyroclastic density currents in the Phlegrean Fields caldera, where flows propagating along the flat ground could be confined by the old crater rims that separate downtown Naples from the caldera. The different eruptive scenarios (mass eruption rates, magma compositions, and water contents) were based on available knowledge of this volcanic system, and appropriate vent conditions were calculated for each scenario. Simulations were performed along different topographic profiles to evaluate the effects of topographic barriers on flow propagation. Simulations highlighted interesting features associated with the presence of obstacles such as the development of backflows. Complex interaction between outward moving fronts and backflows can affect flow propagation; if backflows reach the vent, they can even interfere with fountain dynamics and induce a more collapsing behavior. Results show that in the case of large events ( 108 kg/s), obstacles affect flow propagation by reducing flow velocity and hence dynamic pressure in distal regions, but they cannot stop the advancement of flows. Deadly conditions (in terms of temperature and ash concentration) characterize the entire region invaded by pyroclastic flows. In the case of small events (2.5 107 kg/s), flows are confined by distal topographic barriers which provide valuable protection to the region beyond.
    Description: Published
    Description: Q11003
    Description: open
    Keywords: Phlegrean Fields ; multiphase flow ; pyroclastic flows ; dynamic pressure ; volcanic hazard ; caldera ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 124
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    Evidence for departure in self-similarity: a new spectral ratio method using narrowband coda envelopes (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The use of local and regional S-wave coda is shown to provide stable amplitude ratios that better constrains source differences between event pairs. We first compared amplitude ratio performance between local and near regional S and coda waves in the San Francisco Bay region for moderate-sized events, then applied the coda spectral ratio method to the 1999 Hector Mine mainshock and its larger aftershocks. We find (1) average amplitude ratio standard deviations using coda are ~0.05 to 0.12, roughly a factor of 3 smaller than direct S-waves for 0.2 〈 f 〈 15.0 Hz; (2) coda spectral ratios for the Mw 7.0 Hector Mine earthquake and its aftershocks show a clear departure from self-similarity, consistent with other studies using the same datasets; and (3) event-pairs (Green’s function and target events) can be separated by ~25 km for coda amplitudes without any appreciable degradation, in sharp contrast to direct waves.
    Description: Published
    Description: L11303
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: non-self-similarity ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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  • 125
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    Daily variation at Concordia station (Antarctica) and its dependence on IMF conditions (2007)
    Copernicus
    Details
    Publication Date: 2017-04-04
    Description: After some short test surveys, during the 2004–2005 summer expedition in Antarctica, a geomagnetic French-Italian observatory was installed on the plateau (geographic coordinates: 75.1 S, 123.4 E; corrected geomagnetic coordinates: 88.9 S, 54.3 E; UT=LT−8) very close to the geomagnetic pole. In this paper we present some peculiarities of the daily variation as observed at this polar cap observatory during the years 2005 and 2006, taking into account the different Loyd seasons and different interplanetary magnetic field conditions. Some interesting results emerge from the analysis, confirming the dependence of the daily variation (and of the associated polar current systems) on the IMF Bz and By components. In particular the analysis showed that different Bz conditions correspond to different contribution to daily variation of ionospheric and field aligned currents, while particular By conditions lead to a time shift of the diurnal variation, indicating an asymmetry with respect to the noon meridian.
    Description: Published
    Description: 2045–2051
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: 1.6. Osservazioni di geomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: Geomagnetism and paleomagnetism (Time variations, diurnal to secular) ; Magnetospheric physics (Polar cap phenomena; Solar wind-magnetosphere interactions) ; 01. Atmosphere::01.03. Magnetosphere::01.03.99. General or miscellaneous
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  • 126
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    Lava flow identification and aging by means of lidar intensity: Mount Etna case (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: An application of light detection and ranging (lidar) intensity for the identification and mapping of different lava flows from the Mount Etna (Italy) active volcano is described. In September 2004 an airborne lidar survey was flown over summit sectors of Mount Etna. The information derived from lidar intensity values was used to compare the lava flows with respect to their age of emplacement. Analyzed lava flows vary in age between those dating prior to A.D. 1610 and those active during the survey (2004–2005 eruptions). The target-emitter distance, as well as surface roughness and texture at the lidar footprint scale, is the main parameter controlling the intensity response of lava flows. Variations in the roughness and texture of surfaces at a meter scale result from two main processes, initial lava cooling and subsequent surface weathering; both lead to variations in the original surface roughness of the flow. In summary: (1) initially, from the time of emplacement, the lidar intensity of lava flow surfaces decreases and (2) about 6 years after emplacement the lidar intensity of lava surfaces starts to increase with the age of flows. Lidar capability in terms of geometric (accuracy of ∼1 m in plan position and less than 1 m in elevation) and spectral (lidar intensity depends on surface reflection at λ = 1.064 μm) information can thus be effectively used to map lava flows and to define a relative chronology of lava emplacement.
    Description: Published
    Description: B02201
    Description: 3.6. Fisica del vulcanismo
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: JCR Journal
    Description: reserved
    Keywords: lava flows ; mapping ; lidar ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
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    Empirical ground-motion prediction equations for Northwestern Turkey using the aftershocks of the 1999 Kocaeli earthquake (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We present ground motion models for northwestern Turkey using the aftershocks of the Mw 7.4, 1999 Kocaeli earthquake. We consider 4047 velocity and acceleration records for each component of motion, from 528 earthquakes recorded by stations belonging to regional networks. The ground motion models obtained provide peak ground velocity, peak ground acceleration, and spectral accelerations for 8 different frequencies between 1 and 10 Hz. The analysis of the error distribution shows that the record-to-record component of variance is the largest contribution to the standard deviation of the calibrated ground- motion models. Furthermore, a clear dependence of inter-event error on stress drop is observed. The empirical ground-motion prediction equations, derived for both the larger horizontal and vertical components, are valid in the local magnitude range from 0.5 to 5.9, and for hypocentral distances up to 190 km. Citation: Bindi, D., S. Parolai, H. Grosser, C. Milkereit, and E. Durukal (2007), Empirical ground-motion prediction equations for northwestern Turkey using the aftershocks of the 1999 Kocaeli earthquake,
    Description: Published
    Description: L08305
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: partially_open
    Keywords: Attenuation relationship ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
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  • 128
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    Coseismic and postseismic displacements related with the 1997 earthquake sequence in Umbria-Marche (central Italy) (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We study the coseismic and postseismic displacements related with the 1997 Umbria-Marche earthquake sequence by means of leveling lines along a deformed aqueduct located in the epicentral area. Comparing the 1960 and 10/1997 measurements we obtain 0.49 0.10 m of coseismic displacement distributed along 3 km across the normal fault zone. Modeling of the coseismic surface dislocation is obtained from a combination of low angle (38°) faults at depth and high angle (80°) upper fault branches. The best fit model indicates that the upper branches stop at 0.4 km below the ground surface and have 60% of slip with respect to the lower faults. The postseismic displacement measured during 1998 is 0.18 m and represents 36% of the apparent coseismic deformation. Moderate earthquakes in the Apennines and related surface deformation may thus result from curved faults that reflect the brittle-elastic properties of the uppermost crustal structures.
    Description: Data collection was made while both authors were at Istituto di Ricerca per la Tettonica Recente – CNR (GNDT Project), Roma, Italy. M. Copparoni (ASM, Foligno) and M. Raponi and S. Pacico (Studio Topografico s.n.c., Foligno) provided data about aqueduct and leveling lines. Analysis of data and modeling were done while RB was visiting EOST-IPG, Strasbourg, France. Preparation of the paper benefited from discussion with R. Armijo, S. Barba, P. Gomez and G. Valensise. A. Amato and an anonymous reviewer are thanked for their constructive remarks.
    Description: Published
    Description: 2695–2698
    Description: JCR Journal
    Description: open
    Keywords: Coseismic displacement ; postseismic displacement ; earthquake fault ; Colfiorito, Italy ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
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  • 129
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    Link between major flank slip and 2002–2003 eruption at Mt. Etna (Italy) (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The 2002–2003 Etna eruption is studied through earthquake distributions and surface fracturing. In September 2002, earthquake-induced surface rupture (sinistral offset 0.48 m) occurred along the E-W striking Pernicana Fault (PF), on the NE flank. In late October, a flank eruption accompanied further ( 0.77 m) surface rupturing, reaching a total sinistral offset of 1.25 m; the deformation then propagated for 18 km eastwards to the coastline (sinistral offset 0.03 m) and southwards, along the NW-SE striking Timpe (dextral offset 0.04 m) and, later, Trecastagni faults (dextral offset 0.035 m). Seismicity (〈4 km bsl) on the E flank accompanied surface fracturing: fault plane solutions indicate an overall ESEWNWextension direction, consistent with ESE slip of the E flank also revealed by ground fractures. A three-stage model of flank slip is proposed: inception (September earthquake), climax (accelerated slip and eruption) and propagation (E and S migration of the deformation).
    Description: Published
    Description: 2286
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: 3.2. Tettonica attiva
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: volcano seismology ; surface fracturing ; flank slip ; eruption ; Etna ; 04. Solid Earth::04.01. Earth Interior::04.01.99. General or miscellaneous ; 04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes ; 04. Solid Earth::04.02. Exploration geophysics::04.02.99. 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::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk ; 04. Solid Earth::04.07. Tectonophysics::04.07.99. General or miscellaneous ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
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  • 130
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    Crustal structure at colliding plates boundary from receiver functions analysis: A close look beneath the northern Apennines (Italy) (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Teleseismic receiver functions from a seismic experiment in a small area of the northern Apennines, Italy, reveal strong crustal structure variations across the mountain chain. Receiver functions imaging and full waveform inversion technique are used to constrain the S-wave velocity profile in the crust and to reconstruct the geometry of the main seismic discontinuities at depth. We highlight the presence of the main mode-converting discontinuities in the study area. Most importantly, we identify the crust-mantle transition which is represented, almost everywhere in the study area, by a sharp S-wave velocity increase (over 4 km/s) at depth between 35 and 40 km. However, farther west, the S-wave velocity reaches values typical for the sub-crustal mantle at about 54 km depth, possibly marking the locus where the subducting Adriatic plate starts to dip into the mantle. Here the presence of a shallower discontinuity at about 36 km depth, with S-velocity values around 4 km/s, can be interpreted as the Moho signature of the overriding Tyrrhenian plate.
    Description: Published
    Description: L12304
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: receiver functions ; northern Apennines ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
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    Volcanomagnetic Evidence of the Magmatic Intrusion on 13th May 2008 (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: During the onset of 2008 volcanic crisis at Mt Etna, the near-real time magnetic data provided a continuous updating of the volcano activity state on the northern flank. On the morning of 13th May 2008, significant local magnetic field changes marked the resumption of the eruptive activity characterized by the opening of a fracture field on the northern flank, and an eruptive fissure in the Valle del Bove. In agreement with the northward propagation of seismic events, magnetic signals at 5 stations in the summit area revealed a nearly NNW-SSE oriented magmatic intrusion, which started at about 9:00 GMT, propagated northward for about 2 km, and stopped at 14:00 GMT before reaching the North-East Rift. Magnetic variations, with amplitude ranging between 1.8 nT and -6.5 nT, are consistent with those calculated from piezomagnetic models, where stress-induced changes in rock magnetization are produced by the magmatic intrusion.
    Description: Published
    Description: L22301
    Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive
    Description: JCR Journal
    Description: partially_open
    Keywords: Mt Etna ; volcano monitoring ; piezomagnetic field ; magmatic intrusion ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 132
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    Gravity “steps” at Mt. Etna volcano (Italy). Instrumental effects or evidences of earthquake-triggered magma density changes? (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: On two occasions, sudden gravity changes occurred simultaneously at two summit Etna’s stations, during local low-magnitude earthquakes. A systematic coupling between earthquakes inducing comparable maximum acceleration and displacement at the observation points and gravity steps is missing, implying (a) the non-instrumental nature of the steps and (b) the need for particular underlying conditions for the triggering mechanism(s) to activate. We review some of the volcanological processes that could induce fast underground mass redistributions, resulting in gravity changes at the surface. These processes involve bubbles and crystals present in the magma and require particular conditions in order to be effective as mass-redistributing processes. The gravity steps could be a geophysical evidence of the dynamical stress transfer between tectonic and magmatic systems at a local scale. Given the implications that these transfers may have on the volcanic activity, routine volcano monitoring should include the observation of fast gravity changes.
    Description: In press
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: open
    Keywords: gravity changes ; volcano ; 04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes ; 04. Solid Earth::04.03. Geodesy::04.03.05. Gravity variations ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 133
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    An innovative tsunami detector operating in tsunami generation environment (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: On August 25th 2007 a tsunami detector installed onboard the multi-parameter observatory GEOSTAR was successfully deployed at 3200 b. s. l. in the Gulf of Cadiz, Portugal. This activity is within the NEAREST EC Project (http://nearest.bo.ismar.cnr.it/ ). Among other deliverables, the NEAREST project will produce and test the basic parts of an operational prototype of a near field tsunami warning system. This system includes an onshore warning centre, based on the geophysical monitoring networks which are already operating, and a tsunami detector deployed on board GEOSTAR at the sea bottom. On land the warning centre is in charge of collecting, integrating, and evaluating data recorded at sea. At the sea bottom data is recorded and processed by an advanced type of tsunami detector which includes: a pressure sensor, a seismometer and two accelerometers. The detector communicates acoustically with a surface buoy in two-way mode. The buoy is equipped with meteo station, GPS and tiltmeter and is connected to a shore station via satellite link. The prototype is designed to operate in tsunami generation areas for detection-warning purpose as well as for scientific measurements. The tsunami detector sends a near real time automatic alert message when a seismic or pressure threshold are exceeded. Pressure signals are processed by the tsunami detection algorithm and the water pressure perturbation caused by the seafloor motion is taken into account. The algorithm is designed to detect small tsunami waves, less than one centimetre, in a very noisy environment. Our objective is to combine a novel approach to the tsunami warning problem, with a study of the coupling between the water column perturbations and sea floor motion, together with the long term monitoring of geophysical, geochemical and oceanographic parameters.
    Description: Published
    Description: San Francisco, CA, USA
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: open
    Keywords: Tsunamis and storm surges ; Seismic instruments and networks ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Poster session
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  • 134
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    Mineralogical, geochemical, and isotopic characteristics of the ejecta from the 5 April 2003 paroxysm at Stromboli, Itlay: Inferences on the Preeruptive Magma Dynamics (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The 5 April 2003 explosive eruption at Stromboli emplaced typical basaltic scoria, pumice, and lithic blocks. This paper reports a detailed set of mineralogical, geochemical, and isotopic data on the juvenile ejecta and fresh subvolcanic blocks, including micro-Sr isotope analyses and major and dissolved volatile element contents in olivine-hosted melt inclusions. The juvenile ejecta have compositions similar to those of their analogs from previous paroxysms; the 2003 pumice, however, does not contain stable high-MgO olivine, usually typical of large-scale paroxysms and has lower compatible element contents. Texture, composition, and Sr isotope disequilibrium of crystals in pumice indicate that most of them are inherited from the shallow crystal-rich magma and/or crystal mush. The most primitive magma is recorded as rare melt inclusion in olivine Fo85–86. It has a typical S/Cl (1.1) and a total volatile content of 3.1 wt % from which the total fluid pressure was evaluated ≥240 MPa. Hence, moderate pressure conditions can be envisaged for the mechanism triggering the April 2003 paroxysm. The subvolcanic blocks are shoshonitic basalts with 45–50 vol % of phenocrysts (plagioclase + clinopyroxene + olivine). The late-stage crystallization of the crystal-rich magma lead to the formation of Na-sanidine with plagioclase An60–25 + olivine Fo68–49 + Timagnetite ± apatite ± phlogopite ± ilmenite assemblage. Mineralogy, chemistry, and Sr–Nd isotopic signatures of the subvolcanic blocks indicate they represent the slowly cooled equivalents of batches of crystal-rich basaltic magma stored in the uppermost subvolcanic feeding system. Cooling might be facilitated by short breaks in the summit crater activity.
    Description: Unpublished
    Description: 17
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: open
    Keywords: Stromboli volcano ; Paroxysmal activity ; Basaltic pumice ; Volatile content ; Mineralogy ; Geochemistry ; Sr isotope ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 135
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    Scanning tomography of SO2 distribution in a volcanic gas plume (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Two-dimensional cross sections of the sulphur dioxide (SO2) distribution in the volcanic gas plume of Mt. Etna were reconstructed using tomographic techniques. The data for these projections were generated by a network of five automated scanning spectrometers, positioned on the flanks of the volcano. These measure slant-column amounts of SO2 at 105 different angles, every four minutes. Stable wind conditions allow the plume to be monitored on 82% of days. A time-series of plume cross sections was computed, revealing the potential of this method to track variations in plume position and structure on timescales of minutes to hours, a result of potential importance for air traffic and civil defence in case of eruption, when copious amounts of fine ash can be transported.
    Description: Published
    Description: L17811
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: tomography ; SO2 ; DOAS ; 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
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  • 136
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    Active tectonics of the Adriatic region from GPS and earthquake slip vectors (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: To investigate the kinematics of the Adriatic region we integrate continuous and episodic GPS measurements and ${M_w} 〉 4.5$ earthquake slip vectors selected from the Regional Centroid Moment Tensor (RCMT) catalogue. Coherent motion of GPS sites in the Po Valley, in Apulia and in the Hyblean Plateau allows us to estimate geodetically constrained angular velocities for these regions. The predictions of the GPS-inferred angular velocities are compared with the earthquake slip vectors, showing that the seismically-expressed deformation at the microplate boundaries is consistent with the observed geodetic motion. The remarkable consistency between geodetic, seismological and geological evidence of active tectonics, suggests that active deformation in the Central Adriatic is controlled by the relative motion between the Adria and Apulia microplates. The microplates angular rotation rates are then compared with the rotation rates calculated with a simple block model supporting the hypotheses (1) that Apulia forms a single microplate with the Ionian Sea and possibly with the Hyblean region and (2) that Adria and Apulia rotate in such a way as to accommodate the Eurasia-Nubia relative motion. We suggest that the present-day microplate configuration follows a recent fragmentation of the Adriatic promontory that during the Neogene rigidly transferred the Africa motion to the orogenic belts that now surround the Adriatic region.
    Description: Published
    Description: B12413
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: Adria ; GPS ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 137
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    Earthquake magnitude estimation from early radiated energy (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: From inspection of a large set of Japanese events, we investigate the scaling of the early radiated energy, inferred from the squared velocity integral (IV2) with the final magnitude of the event. We found that the energy can only discriminate whether the event has a magnitude larger or smaller than 5.8, and in the latter case it can allow for realtime magnitude estimation. However, by normalizing IV2 for the rupture area, the initial slip scales with the magnitude between 4 〈 M 〈 7 following the expected scaling laws. We show that the ratio between the squared peak displacement and IV2 is a proxy for the slip following the same scaling but it can be directly derived from the data, without any assumption on the rupture area. The scaling relationship between initial slip and magnitude can be used for early warning applications, when integrated in a probabilistic, evolutionary approach. Citation: Festa, G., A. Zollo, and M. Lancieri (2008), Earthquake magnitude estimation from early radiated energy, Geophys. Res. Lett., 35, L22307, doi:10.1029/ 2008GL035576.
    Description: Published
    Description: L22307
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: reserved
    Keywords: Early Warning ; Rupture initiation ; Seimic Source ; Magnitude estimation ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
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  • 138
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    Insights on the seismogenic layer thickness from the upper crust structure of the Umbria-Marche Apennines (Central Italy) (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: [1] We reconstruct the subsurface geology in a region of the northern Apennines (central Italy) where a protracted extensional sequence occurred in 1997–1998 with maximum magnitude M = 6.0. Our study is mainly based on the interpretation of three reprocessed seismic reflection profiles crossing the epicentral area, which constrain the subsurface geometry to a depth of about 12 km where most of the shallow seismicity occurs. Comparing the subsurface setting with accurately determined earthquake locations, we find that the seismicity is located entirely within the sedimentary cover and does not penetrate the underlying basement. This is explained by considering that the sedimentary cover is rather thick and composed of relatively strong lithologies (platform carbonates and evaporites), while the upper part of the basement consists of weak phyllites and siliciclastic rocks. This weak horizon is also evidenced by the low-Vp values measured in deep wells of the region. Its effect is to decouple the sedimentary cover from the crystalline basement, where only microseismicity occurs. Our study indicates that local structure and stratigraphy can significantly influence the distribution of seismicity within the upper crust, particularly in complex geological environments such as thrust-and-fold belts.
    Description: Published
    Description: TC1010
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: seismogenic layers, northern apennines ; B/D transition ; umbria-marche apennines ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
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  • 139
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    Complex magma dynamics at Mount Etna revealed by seismic, thermal and volcanological data (2009)
    American Geophysical Union
    In:  An edited version of this paper was published by AGU. Copyright (2009) American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Three eruptive episodes during the 2006 summit eruptions of Mount Etna were exceptionally well documented by visual, seismic and thermal monitoring. The first (16 November) was strongly explosive, with vigorous Strombolian activity and ash emission from multiple vents, lava emission, and phreatomagmatic explosions generating pyroclastic density currents (PDCs). The second episode (19 November) had a rather weakly explosive component, with mild Strombolian activity but more voluminous lava emission. The third (24 November) was a moderately explosive paroxysm, with intermittent lava fountaining and generation of a tephra column as well as lava emission and PDCs. Data recorded by a thermal monitoring camera clearly document the different phases of each paroxysm, weather clouds occasionally hampering thermal monitoring. The images show a rapid onset of the volcanic activity, which during each of the paroxysms reached a peak in eruptive and thermal intensity, and then decreased gradually. The stronger phreatomagmatic explosions and PDCs on 16 and 24 November did not yield any seismic signature linked to the opening of new vents, nor were they associated with peculiar characteristics of the seismic signal. Nevertheless, eruptive styles (Strombolian activity, lava emission) and different levels in the intensity of explosive activity were generally well reflected in the amplitude and frequency content of the seismic signal, and in the source location of the volcanic tremor centroid throughout the three eruptive episodes. This multidisciplinary study, therefore, not only provides a key to distinguish between endogenous and exogenous origins of the phenomena observed, but also documents the complex magma dynamics within the volcano.
    Description: Published
    Description: B03211
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: reserved
    Keywords: Volcano monitoring ; Mt Etna ; volcanic hazard ; instruments and techniques ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 140
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    The 5 April 2003 Explosion of Stromboli: Timing of Eruption Dynamics using Thermal Data (2008)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: Stromboli’s 5 April 2003 explosion sent an ash plume to 4 km and blocks to 2 km, representing one of the most powerful events over the last 100 years. A thermal sensor 450 m east of the vent and a helicopter-flown thermal camera captured the event dynamics allowing detailed reconstruction. This review links previous studies providing a complete collation and clarification of the actual event chronology, while showing how relatively inexpensive thermal sensors can be used to provide great insight into processes that cannot be observed from locations outside of the eruption cloud. The eruption progressed through four phases, comprised 29 discrete explosions and lasted 373 s. The opening phase (phase 1) comprised ~30 s of precursory ash emission, with stronger emission beginning after 17 s. This was abruptly terminated by the main blast of phase 2 which comprised emission of a rapidly expanding ash cloud followed, after 0.4 s, by a powerful jet with velocities of up to 320 m/s. A second explosive phase (phase 3) began 38 s later and involved ascent of a phoenix cloud and explosive emission above a lateral vent lasting 75 s. This was followed by a 175-s-long phase of weaker, pulsed emission. The eruption was terminated by a series of three explosions (phase 4) sending ash to ~600 m at velocities of 27-45 m/s and lasting 87 s. Together these results have shown that a low energy opening phase was followed by the highest energy phase. Each phase itself comprised groups of discrete explosions, with energy of the explosions diminishing during the two final phases.
    Description: Published
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: open
    Keywords: Thermal imaging ; Stromboli ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 141
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    Volcanic and seismic activity at Stromboli preceding the 2002-03 eruption (2008)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: Regular surveys with a PM695 FLIR thermal imaging camera from both the ground and from helicopter were conducted on Stromboli from October 2001. These measurements allow us to (i) examine changes in morphology of the summit craters produced by paroxystic explosions and (ii) track the increasing level of magma within the conduits of Stromboli that preceded and led to the 2002/03 effusive eruption. Two geophysical surveys in May and September/October 2002 demonstrated a clear increasing trend in the amplitude of VLP events, consistent with the presence of a higher magma column above the VLP source region. The observed increase in magma level was probably induced by an increase in the pressure of the magma feeding system at Stromboli, controlled by regional tectonic stress. The increased magma level induced strain on the uppermost part of the crater terrace, allowing an increase in soil permeability and therefore CO2 and Radon degassing. Eventually this stress caused the northeast flank of the craters to fracture, allowing lava to flood out at high effusion rates on 28th December. Regular surveys with the thermal imaging camera, combined with geophysical monitoring, are an invaluable addition to the armory of volcanologists attempting to follow the evolution of activity on active volcanoes.
    Description: Published
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: open
    Keywords: Thermal imaging ; Stromboli ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 142
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    Network of Superconducting Gravimeters Benefits a Number of Disciplines (2008)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: abstract - A global network of superconducting gravimeters (SGs) is compiling significant data for a range of important studies spamming a number of disciplines concerned with the Earth's gravity, tides, environment, and geodetics. .......
    Description: Published
    Description: 121-126
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: N/A or not JCR
    Description: open
    Keywords: Gravity ; Gravimeters ; Geodynamics ; Tides ; 04. Solid Earth::04.02. Exploration geophysics::04.02.02. Gravity methods
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  • 143
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    The eruptive activity of 28 and 29 December 2002 (2008)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: At 18:20 of 28 December 2002 an eruptive vent opened on the NE flank of the Sciara del Fuoco at 600 m asl, marking the onset of the 2002-2003 eruptive crisis of Stromboli volcano. The first eruptive hours were characterized by mild spattering and effusive activity from the new vent and the summit vent at crater 1. Gravitational instability processes also determined the partial collapse of NE walls of the summit cone (crater 1). Pyroclastic material partly accumulated on the NE part of the Sciara, and partly flowed down slope and reached the sea at Spiaggia dei Gabbiani forming a ~ 4m-thick, reddish avalanche, that was soon covered by a lava flow emitted in the following hours (Lodato et al., 2007). In this paper, we describe the first hours of activity trough eyewitnesses’ reports, geophysical monitoring, field and laboratory studies and of the erupted pyroclastic material and lava flows. Daily temperature measurements were carried out on the avalanche deposit formed by the flow of scoria along the Sciara, using a handheld thermal camera mainly during helicopter surveys. A fast cooling rate was typical of the deposit surface, and a slow cooling rate was representative of its inner portion.
    Description: Published
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: open
    Keywords: Thermal imaging ; Stromboli ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 144
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    Evolution of the lava flow field by daily thermal and visible airborne surveys (2008)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: On 28 December 2002, an effusive flank eruption started at Stromboli volcano (Aeolian Islands, 15 Italy). This lasted until 22 July 2003 and produced two lava flow fields that were emplaced onto the 16 steep slopes of Sciara del Fuoco. The first flow field was fed by a vent that opened at 500 m 17 elevation and was active between 30 December 2002 and 15 February 2003. The second was 18 supplied by a vent at 670 m and was emplaced mainly between 15 February and 22 July 2003. Here 19 we review the lava flow field emplacement based on daily thermal and visual surveys. The variable 20 slopes on which the lava flowed yielded an uncommon flow field morphology. This resulted in a 21 lava shield in the proximal area where flow stacking and inflation caused piling up of lava due to the 22 relatively flat ground. The proximal area was characterized by a complex network of tumuli and 23 tube-fed flows associated. The medial-distal lava flow field was emplaced on an extremely steep 24 zone. This area showed persistent flow front crumbling, producing a debris field on which emplaced 25 lava flows formed lava channels with excavated debris levées. This eruption provided an exceptional 26 opportunity to examine the evolution of lava flow fields emplaced on steep slopes, and proved the 27 usefulness of thermal imagers for safe and efficient monitoring of the active lava flows. In addition, thermal monitoring allowed calculation of quantitative parameters, such as effusion rate, allowing constraint of the time varying nature of supply to this eruption.
    Description: Published
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: open
    Keywords: thermal imaging ; stromboli ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 145
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    Measurements of 220Rn and 222Rn and CO2 emissions in soil and fumarole gases on Mt. Etna volcano (Italy): Implications for gas transport and shallow ground fracture (2008)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: Measurements of 220Rn and 222Rn activity and of CO2 flux in soil and fumaroles were carried out on Mount Etna volcano in 2005–2006, both in its summit area and along active faults on its flanks. We observe an empirical relationship between (220Rn/222Rn) and CO2 efflux. The higher the flux of CO2, the lower the ratio between 220Rn and 222Rn. Deep sources of gas are characterized by high 222Rn activity and high CO2 efflux, whereas shallow sources are indicated by high 220Rn activity and relatively low CO2 efflux. Excess 220Rn highlights sites of ongoing shallow rock fracturing that could be affected by collapse, as in the case of the rim of an active vent. Depletion both in 220Rn and in CO2 seems to be representative of residual degassing along recently active eruptive vents.
    Description: This work was funded by the Istituto Nazionale di Geofisica e Vulcanologia (S.G., M.N.) and by the Dipartimento per la Protezione Civile (Italy), projects V3_6/28-Etna (M.N.) and V5/08-Diffuse degassing in Italy (S.G.), and NSF EAR 063824101 (K.W.W.S.).
    Description: Published
    Description: Q10001
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: 4.5. Degassamento naturale
    Description: JCR Journal
    Description: reserved
    Keywords: radon ; thoron ; carbon dioxide ; rock stress ; gas transport ; Mount Etna ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.02. Data dissemination::05.02.01. Geochemical data
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  • 146
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    Thermo-rheological magma control on the impact of highly fluid lava flows at Mt. Nyiragongo (2007)
    American Geophysical Union
    Details
    Publication Date: 2020-05-29
    Description: In January 2002 Mount Nyiragongo erupted foiditic lavas that covered the Southern volcano flank devastating vast urban areas. Lava flows originated from vents at different heights on the eruptive fissure displayed different velocities, from tens of km/h at the highest vents to slow-advance (0.1–1 km/h) in Goma town several km away from the volcano. To understand the different behavior of lava flows and their threat to the local population, we undertook a multidisciplinary study involving textural and rheological measurements and numerical simulations of heat transfer during magma ascent. We demonstrate that pre-eruptive cooling and syn-eruptive undercooling of magma determined the different rheological behavior of lava flows erupted from vents at diverse heights. Venting at lower altitudes is expected to produce viscous, slowly advancing lavas, although development of fluid, faster flows should be included among possible future eruptive scenarios.
    Description: Published
    Description: L06301
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Nyiragongo volcano ; textural and rheological measurements ; numerical simulations ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
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  • 147
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    The 5 April 2003 paroxysm at Stromboli: a review of geochemical observations (2008)
    American Geophysical Union
    Details
    Publication Date: 2018-02-01
    Description: This paper reviews the published geochemical variations observed during the 2002–2003 eruption at Stromboli volcano. At the end of 2002, a new eruption began at Stromboli with a lava flow that lasted until the end of July 2003. On 5 April 2003 an explosive paroxysm occurred with the ejection of bombs that reached the village of Ginostra, about 4 km from the craters. During the eruption, specific variations in chemical composition of ground waters and summit fumaroles were recorded before the explosion, most of them for the first time. The water pH decreased significantly (0.5 units) and the dissolved CO2 increased in two thermal wells (Cusolito and Zurro) located near Stromboli harbor from March until 5 April. Peaks in the dissolved He were also observed at all the sampling sites. All of these changes in the thermal aquifer suggested a pressurization of the system due to the degassing of a volatile-rich magma at depth. In the summit area the SO2/HCl and SO2/HF ratios in the plume increased suddenly between 1 and 3 April due to the degassing of an S-rich magma that was approaching the shallow levels of the plumbing system, and this was involved in the explosion that occurred a few days later. This eruption was the first at Stromboli to be analyzed using geochemical models. The variations observed in the basal aquifer and in the summit area occurred on very different timescales: a few weeks and few days, respectively.
    Description: Published
    Description: 347-358
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: open
    Keywords: paroxysm ; geochemical observations ; monitoring ; plume ; thermal aquifer ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 148
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    Shades of White: Explaining Variations in Clear-Sky Snow Albedo (2008)
    American Geophysical Union
    In:  EPIC3American Geophysical Union, Fall Meeting 2008, American Geophysical Union, 2008A(abstra)
    Details
    Publication Date: 2019-12-03
    Description: Multi-year data from four Antarctic automatic weather stations show that clear-sky snow albedo ranges from 0.77 to 0.88, varying in time and space. The broadband albedo of a snowpack under clear-sky conditions is largely determined by snow grain size, solar zenith angle, and the vertical composition of the atmosphere -- but it is not obvious which process contributes what. A model that describes broadband radiative transfer in both the atmosphere and the snowpack is used to show that the observed variations in clear-sky snow albedo is dominated by strong spatial and temporal variation in snow grain size. Average values of snow grain size range from 22 μm on the Antarctic plateau to 64 μm on the ice shelves, whereas maximum values (December, January) are 40--150% higher. The seasonal cycle in solar zenith angle explains at most 0.02 of albedo variation at a location, whereas spatial variation in the atmospheric optical thickness leads to a 0.01 difference between plateau and ice shelf albedos. The most critical success factor for this method is the quality of the radiation observations, which is most notably affected by the horizontal tilt of either the radiation sensors or the snow surface. In order to tie model and observations together, we carried out an experiment at Summit, Greenland, where we simultaneously measured albedos and snow grain sizes, about which results will be presented.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 149
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    Causes of Low Frequency North Atlantic SST Variability in a Coupled GCM (2005)
    American Geophysical Union
    Details
    Publication Date: 2021-05-19
    Description: The low frequency sea surface temperature (SST) variability in the North Atlantic is studied using the Center for Ocean-Land-Atmosphere Studies (COLA) anomaly coupled general circulation model. The main focus is placed on the relative roles of stable and unstable coupled feedbacks in inducing the low frequency SST variability in various regions of the North Atlantic. To examine this question, a recently developed coupling technique, interactive ensembles, is applied to reduce the strength of “weather noise” in the model and isolate the atmospheric feedback to boundary forcing.
    Description: Published
    Keywords: Sea surface temperature
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed , Article
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  • 150
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    Seasonality and stable isotopes in planktonic foraminifera off Cape Cod, Massachusetts (2005)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 20 (2005): PA4011, doi:10.1029/2005PA001150.
    Description: Monthly samples of stratified plankton tows taken from the slope waters off Cape Cod nearly 25 years ago are used to describe the seasonal succession of planktonic foraminifera and their oxygen isotope ratios. The 15°C seasonal cycle of sea surface temperature (SST) accounts for a diverse mixture of tropical to subpolar species. Summer samples include various Globigerinoides and Neogloboquadrina dutertrei, whereas winter and early spring species include Globigerina bulloides and Neogloboquadrina pachyderma (dextral). Globorotalia inflata lives all year but at varying water depths. Compared with the fauna in 1960–1961 (described by R. Cifelli), our samples seem warmer. Because sea surface salinity varies little during the year, δ18O is mostly a function of SST. Throughout the year, there are always species present with δ18O close to the calculated isotopic equilibrium of carbonate with surface seawater. This raises the possibility that seasonality can be estimated directly from the range of δ18O in a sediment sample provided that the δ18O-salinity relationship is the same as today.
    Description: Funding was provided by NSF grant OCE-0117149.
    Keywords: Plankton tow ; Foraminifera ; Stable isotopes
    Repository Name: Woods Hole Open Access Server
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  • 151
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    Spatial and temporal variability of oceanic heat flux to the Arctic ice pack (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 110 (2005): C07021, doi:10.1029/2004JC002293.
    Description: In order to simulate the large-scale structure and temporal variability of oceanic heat flux (F w) to the Arctic perennial ice pack, observations of heat in the mixed layer and ice dynamics are compared with parameterizations and climatologies. Long-term drifting platform observations of seawater temperature and salinity (primarily from automated buoys) are used to describe the annual cycle of temperature above freezing (ΔT f) in the mixed layer beneath the ice pack, which are modulated by ice-ocean friction velocities (u*) determined from the platform drifts to produce estimates of F w between 1975 and 1998. On average, ΔT f is not negligible in winter, especially in the Transpolar Drift, which implies a positive F w to the ice pack by means other than solar heating. A parameterization based solely on the solar zenith angle (with a 1 month lag) is found to largely describe the observed ΔT f (with root mean square error of 0.03°C), despite the lack of an albedo or open water term. A reconstruction of F w from 1979 to 2002 is produced by modulating parameterized ΔT f with u* on the basis of daily ice drift estimates from a composite satellite and in situ data set. The reconstructed estimates are corrected for regional variations and are compared to independent estimates of F w from ice mass balance measurements, indicating annual F w averages between 3 and 4 W m−2 depending on the selection of under-ice roughness length in the ice-ocean stress calculations. Although the interannual variations in ΔT f are fixed by the parameterization in the derived reconstruction, the dynamics indicate an overall positive trend (0.2 W m−2 decade−1) in Arctic F w, with the largest variations found in the southern Beaufort Gyre.
    Description: Portions of this work were prepared with funding provided by the International Arctic Research Center and National Science Foundation ARCSS program (grant OPP-0230184). Analysis of the IOEB data was accomplished as part of the IOEB program, which was supported by the Office of Naval Research, High Latitude Program, and Japan Marine Science and Technology Center.
    Keywords: Oceanic heat flux ; Arctic ice pack ; Ice-ocean interactions
    Repository Name: Woods Hole Open Access Server
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  • 152
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    Growth and composition of high-Mg calcite in the skeleton of a Bermudian gorgonian (Plexaurella dichotoma) : potential for paleothermometry (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 6 (2005): Q08010, doi:10.1029/2005GC000911.
    Description: We used Secondary Ion Mass Spectrometry (SIMS) ion microprobe to analyze magnesium-to-calcium (Mg/Ca) and strontium-to-calcium (Sr/Ca) ratios of high-Mg calcite loculi within the skeleton of a shallow water gorgonian, Plexaurella dichotoma, from Bermuda. A cross-section of the gorgonian skeleton reveals loculi embedded within proteinaceous gorgonin arranged in concentric rings about the axial core. Viewed in cross-section, the loculi are fan-shaped, 10-140 μm in diameter, and composed of bundles of needle-shaped crystals that appear to radiate out from a calcification center. Discrete sample spots, each 20 μm diameter, were sputtered from successive loculi along a sample track 3 mm long. Over this distance, twenty-five bands of high-low density gorgonin couplets were encountered, estimated to represent the period 1963 to 1988. Mg/Ca ratios show an overall, positive correlation with annual sea surface temperatures (SSTs) that is strongest in the autumn months (October- December). High-resolution analyses along the growth axes of individual loculi reveal low variability and no trend, consistent with our interpretation of seasonal growth of these calcite inclusions. The sensitivity of Mg/Ca to interannual changes in average autumn temperatures is 0.47 mmol/mol per ºC. Conversely, interannual variability in calcite Sr/Ca does not follow the interannual variability in SST and may be influenced primarily by growth rate.
    Description: This study was supported by an Independent Study Award from the Woods Hole Oceanographic Institution No. 270051.81; NERC grant GR3/12800; a WHOI Ocean Life Institute grant to ALC; Bermuda Government, in support of the Benthic Ecology Research Programme at BBSR to SRS. Support for the WHOI Northeast National Ion Microprobe Facility was provided by NSF EAR-9628749.
    Keywords: Gorgonian ; Octocoral ; Mg/Ca ; Sr/Ca ; Sea surface temperature ; Biomineralization ; Growth bands ; SIMS ion microprobe ; Bermuda
    Repository Name: Woods Hole Open Access Server
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    Emission of dimethylsulfide from Weddell Sea leads (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. @ American Geophysical Union, 2005. 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 32 (2005): L23610, doi:10.1029/2005GL024242.
    Description: The distribution of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) was examined in lead water in pack ice of the Weddell Sea. Samples were taken by pulling water into a syringe from a series of depths from 0.002 m to 4 m and deeper. Concentrations of DMS, DMSP and DMSO remained low throughout the water column relative to surface water, which was highly enriched. Concentrations of the major sulfur compounds increased by over an order of magnitude during periods with smooth surface water conditions. This increase coincided with a profound stratification of the water column, caused by a decrease in salinity of near surface water. We estimate that the DMS emission from leads and open water in Antarctic sea ice could contribute significantly to the yearly DMS flux from the Southern Ocean.
    Description: This work was financially supported by the Marie Currie Training Site Fellowship (contract number HPMF-CT-2002-01865) and by Natural Environment Research Council, UK (award ref number NER/B/S/2003/00844).
    Repository Name: Woods Hole Open Access Server
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  • 154
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    Channelized lava flows at the East Pacific Rise crest 9°–10°N : the importance of off-axis lava transport in developing the architecture of young oceanic crust (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 6 (2005): Q08005, doi:10.1029/2005GC000912.
    Description: Submarine lava flows are the building blocks of young oceanic crust. Lava erupted at the ridge axis is transported across the ridge crest in a manner dictated by the rheology of the lava, the characteristics of the eruption, and the topography it encounters. The resulting lava flows can vary dramatically in form and consequently in their impact on the physical characteristics of the seafloor and the architecture of the upper 50–500 m of the oceanic crust. We have mapped and measured numerous submarine channelized lava flows at the East Pacific Rise (EPR) crest 9°–10°N that reflect the high-effusion-rate and high-flow-velocity end-member of lava eruption and transport at mid-ocean ridges. Channel systems composed of identifiable segments 50–1000 m in length extend up to 3 km from the axial summit trough (AST) and have widths of 10–50 m and depths of 2–3 m. Samples collected within the channels are N-MORB with Mg# indicating eruption from the AST. We produce detailed maps of lava surface morphology across the channel surface from mosaics of digital images that show lineated or flat sheets at the channel center bounded by brecciated lava at the channel margins. Modeled velocity profiles across the channel surface allow us to determine flux through the channels from 0.4 to 4.7 × 103 m3/s, and modeled shear rates help explain the surface morphology variation. We suggest that channelized lava flows are a primary mechanism by which lava accumulates in the off-axis region (1–3 km) and produces the layer 2A thickening that is observed at fast and superfast spreading ridges. In addition, the rapid, high-volume-flux eruptions necessary to produce channelized flows may act as an indicator of the local magma budget along the EPR. We find that high concentrations of channelized lava flows correlate with local, across-axis ridge morphology indicative of an elevated magma budget. Additionally, in locations where channelized flows are located dominantly to the east or west of the AST, the ridge crest is asymmetric, and layer 2A appears to thicken over a greater distance from the AST toward the side of the ridge crest where the channels are located.
    Description: This work was supported by NSF grant OCE-9819261 (to H.S., M.A.T., and D.J.F.) as well as the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the Penzance Endowed Discretionary Fund.
    Keywords: Channels ; Lava ; Lava morphology ; Ridge-crest ; Submarine
    Repository Name: Woods Hole Open Access Server
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    FOZO, HIMU, and the rest of the mantle zoo (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 6 (2005): Q05007, doi:10.1029/2004GC000824.
    Description: The parameter μ describes the 238U/204Pb ratio of an Earth reservoir. Mantle domains labeled HIMU (high μ) originally defined reservoirs with highly radiogenic Pb isotope ratios observed in basalts from a select number of ocean islands, St. Helena in the Atlantic Ocean and the Cook-Austral islands in the South Pacific Ocean. While some authors use the term HIMU in this original sense, others refer to HIMU as a widespread component in many mid-ocean ridge and ocean island basalt (MORB and OIB) sources. Here we show that highly radiogenic Pb isotope signatures in MORB and OIB originate from two different sources. In addition to the classical HIMU component observed at St. Helena and the South Pacific (named HIMU in the following), we define a component with slightly less radiogenic Pb but significantly more radiogenic Sr isotope signatures. This component lies at the extension of the (Atlantic and Pacific) MORB array in a Sr-Pb isotope ratio diagram and is argued to be a ubiquitous component in MORB and many OIB sources. The inferred role of this component in the mantle and its inferred genetic origin closely resemble those originally suggested for a mantle component termed FOZO by Hart and coworkers. By redefining the composition, the origin, and the role of FOZO in the mantle, we establish a simple conceptual framework that explains the isotopic variability in both MORB and OIB with the lowest number of components. OIB are grouped into HIMU-type OIB and basalts from islands that diverge from the MORB-FOZO array toward various isotopically “enriched” compositions (EM). The apparent ubiquity of FOZO in the mantle and the calculated isotopic evolution of compositionally diverse MORB suggest that normal mantle melting and continuous subduction and aging of that crust during recycling through the mantle are the dominant causes of the MORB-FOZO array. In contrast to FOZO, HIMU-type OIB are quite rare, and if an origin by recycling of oceanic crust is also postulated, the production of HIMU sources has to be a special and rare combination of age and composition of subduction-modified recycled oceanic crust.
    Description: This work is partially supported by the Deutsche Forschungsgmeinschaft (DFG grant STR853/1 to A.S).
    Keywords: FOZO ; HIMU ; MORB ; Oceanic basalts ; OIB
    Repository Name: Woods Hole Open Access Server
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    Evidence for an extensive hydrothermal plume in the Tonga-Fiji region of the South Pacific (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. 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 5 (2004): Q01003, doi:10.1029/2003GC000607.
    Description: Several hydrographic stations in the vicinity of the Samoa Islands have 3He/4He above the regional background in the depth range of 1500–1800 m, indicating injection of mantle helium from a local hydrothermal source. The highest δ(3He) = 43.4% was detected at 1726-m depth at 15.0°S, 173.1°W in the bathymetric gap between the Samoa Islands and the northern end of the Tonga-Kermadec Arc. The δ(3He) profile at this station decreases to δ(3He) = 26% at 2500-m depth. The relatively shallow depth of the maximum hydrothermal signal suggests a source different from the conventional Pacific basin helium plume centered at 2500 m that is carried westward from the East Pacific Rise. Stations to the west of this locality show a progressive decrease in the maximum δ(3He) values in the depth range of 1480–1790 m out to 169°E. Stations east of the Tonga-Fiji region show lower 3He values (〈26%) at 1700 m and the profiles are dominated by a deeper maximum at 2500 m, presumably the distal traces of hydrothermal input from East Pacific Rise. This pattern in the 3He distribution suggests that the 1700-m deep helium plume is carried in a northwesterly direction some 2000 km from its source near the northern end of the Tonga-Kermadec Arc. At this time very little is known about the source of this hydrothermal plume or the details of its areal extent. Numerous seamounts and rift zones in the region are possible hydrothermal sources for the plume. The summit crater of Vailulu'u, a young seamount at the eastern end of the Samoa chain, was recently discovered to be hydrothermally active at ∼600 m depth [Hart et al., 2000]. However this shallow hydrothermal field on Vailulu'u is an unlikely source for the deeper 1700-m signal. The most likely source would appear to be the extensional zones of the northern Lau Basin system, such as the Mangatolo Triple Junction. Just as the helium plume emanating from Lo'ihi has helped our understanding of the circulation near the Hawaiian Islands [Lupton, 1996], this helium plume in the Tonga-Fiji region has great potential for delineating circulation in this area of the south Pacific.
    Description: This work was supported by the NOAA Vents Program and by Grants OCE91-05884, OCE92-96237, OCE92-96169, and OCE98-20132 of the Ocean Sciences Division of the National Science Foundation.
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    Quantitative bedrock geology of east and Southeast Asia (Brunei, Cambodia, eastern and southeastern China, East Timor, Indonesia, Japan, Laos, Malaysia, Myanmar, North Korea, Papua New Guinea, Philippines, far-eastern Russia, Singapore, South Korea, Taiwan, Thailand, Vietnam) (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. 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 5 (2004): Q01B06, doi:10.1029/2003GC000619.
    Description: We quantitatively analyze the area-age distribution of sedimentary, igneous and metamorphic bedrock based on data from the most recent digital geologic maps of East and Southeast Asia (Coordinating Committee for Coastal and Offshore Geosciences Programmes in East and Southeast Asia (CCOP) and the Geologic Survey of Japan, 1997; 1:2,000,000), published as Digital Geoscience Map G-2 by the Geological Survey of Japan. Sedimentary rocks, volcanic rocks, plutonic rocks, ultramafic rocks and metamorphic rocks cover 73.3%, 8.5%, 8.8%, 0.9%, and 8.6% of the surface area, respectively. The average ages of major lithologic units, weighted according to bedrock area, are as follows: sedimentary rocks (average stratigraphic age of 123 Myr/median age of 26 Myr), volcanic rocks (84 Myr/20 Myr), intrusive rocks (278 Myr/195 Myr), ultramafic rocks (unknown) and metamorphic rocks (1465 Myr/1118 Myr). The variability in lithologic composition and age structure of individual countries reflects the complex tectonic makeup of this region that ranges from Precambrian cratons (e.g., northeast China and North Korea) to Mesozoic-Cenozoic active margins (e.g., Japan, the Philippines, Indonesia and New Guinea). The spatial resolution of the data varies from 44 km2 per polygon (Japan) to 1659 km2 per polygon (Taiwan) and is, on average (490 km2/polygon), similar to our previous analyses of the United States of America and Canada. The temporal and spatial resolution is sufficiently high to perform age-area analyses of individual river basins larger than ∼10,000 km2 and to quantitatively evaluate the relationship between bedrock geology and river chemistry. As many rivers draining tropical, mountainous islands of East and Southeast Asia have a disproportionate effect on the dissolved and particulate load delivered to the world oceans, bedrock geology in such river drainage basins disproportionately affect ocean chemistry.
    Description: Financial support was provided through the U.S. National Science Foundation (NSF-EAR-0125873) to BPE.
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    Hydrothermal venting at Vailulu'u Seamount : the smoking end of the Samoan chain (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. 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 5 (2004): Q02003, doi:10.1029/2003GC000626.
    Description: The summit crater of Vailulu'u Seamount, the youngest volcano in the Samoan chain, hosts an active hydrothermal system with profound impact on the ocean water column inside and around its crater (2 km wide and 407 m deep at a 593 m summit depth). The turbidity of the ocean water reaches 1.4 NTU, values that are higher than in any other submarine hydrothermal system. The water is enriched in hydrothermal Mn (3.8 ppb) and 3He (1 × 10−11 cc/g) and we measured water temperature anomalies near the crater floor up to 0.2°C. The hydrothermal system shows complex interactions with the ocean currents around Vailulu'u that include tidally-modulated vertical motions of about 40–50 m, and replenishment of waters into the crater through breaches in the upper half of the crater wall. Inside and outside potential density gradients suggest that hydrothermal venting exports substantial amounts of water from the crater (1.3 ± 0.2 × 108 m3/day), which is in good agreement with fluxes obtained from a tracer release experiment inside the crater of Vailulu'u (0.8 × 108 m3/day [Hart et al., 2003]). This mass flux, in combination with the differences in the inside and outside crater temperature, yields a power output of around 760 megawatts, the equivalent of 20–100 MOR black smokers. The Mn output of 300 kg/day is approximately ten times the output of a single black smoker.
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    Composition and structure of the central Aleutian island arc from arc-parallel wide-angle seismic data (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. 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 5 (2004): Q10006, doi:10.1029/2004GC000715.
    Description: New results from wide-angle seismic data collected parallel to the central Aleutian island arc require an intermediate to mafic composition for the middle crust and a mafic to ultramafic composition for the lower crust and yield lateral velocity variations that correspond to arc segmentation and trends in major element geochemistry. The 3-D ray tracing/2.5-D inversion of this sparse wide-angle data set, which incorporates independent phase interpretations and new constraints on shallow velocity structure, produces a faster and smoother result than a previously published velocity model. Middle-crustal velocities of 6.5–7.3 km/s over depths of ∼10–20 km indicate an andesitic to basaltic composition. High lower-crustal velocities of 7.3–7.7 km/s over depths of ∼20–35 km are interpreted as ultramafic-mafic cumulates and/or garnet granulites. The total crustal thickness is 35–37 km. This result indicates that the Aleutian island arc has higher velocities, and thus more mafic compositions, than average continental crust, implying that significant modifications would be required for this arc to be a suitable building block for continental crust. Lateral variations in average crustal velocity (below 10 km) roughly correspond to trends in major element geochemistry of primitive (Mg # 〉 0.6) lavas. The highest lower-crustal velocities (and presumably most mafic material) are detected in the center of an arc segment, between Unmak and Unalaska Islands, implying that arc segmentation exerts control over crustal composition.
    Description: Funding for this work was provided by the University of Wyoming Graduate School.
    Keywords: Continental crust ; Crustal geophysics ; Island arc ; Major element geochemistry
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    Upper crustal structure and axial topography at intermediate spreading ridges : seismic constraints from the southern Juan de Fuca Ridge (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 110 (2005): B12104, doi:10.1029/2005JB003630.
    Description: We use multichannel seismic reflection data to image the upper crustal structure of 0-620 ka crust along the southern Juan de Fuca Ridge (JdFR). The study area comprises two segments spreading at intermediate rate with an axial high morphology with narrow (Cleft) and wide (Vance) axial summit grabens (ASG). Along most of the axis of both segments we image the top of an axial magma chamber (AMC). The AMC along Cleft deepens from south to north, from 2.0 km beneath the RIDGE Cleft Observatory and hydrothermal vents near the southern end of the segment, to 2.3 km at the northern end near the site of the 1980’s eruptive event. Along the Vance segment, the AMC also deepens from south to north, from 2.4 km to 2.7 km. Seismic layer 2A, interpreted as the basaltic extrusive layer, is 250-300 m thick at the ridge axis along the Cleft segment, and 300-350 m thick along the axis of the Vance segment. However off-axis layer 2A is similar in both segments (500-600 m), indicating ~90% and ~60% off-axis thickening at the Cleft and Vance segments, respectively. Half of the thickening occurs sharply at the walls of the ASG, with the remaining thickening occurring within 3-4 km of the ASG. Along the full length of both segments, layer 2A is thinner within the ASG, compared to the ridge flanks. Previous studies argued that the ASG is a cyclic feature formed by alternating periods of magmatism and tectonic extension. Our observations agree with the evolving nature of the ASG. However, we suggest that its evolution is related to large changes in axial morphology produced by small fluctuations in magma supply. Thus the ASG, rather than being formed by excess volcanism, is a rifted flexural axial high. The changes in axial morphology affect the distribution of lava flows along the ridge flanks, as indicated by the pattern of layer 2A thickness. The fluctuations in magma supply may occur at all spreading rates, but its effects on crustal structure and axial morphology are most pronounced along intermediate spreading rate ridges.
    Description: This study was supported by the National Science Foundation grants OCE-0002551 to Woods Hole Oceanographic Institution, OCE-0002488 to Lamont-Doherty Earth Observatory, and OCE-0002600 to Scripps Institution of Oceanography.
    Keywords: Mid-ocean ridge ; Juan de Fuca ; Crustal structure
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  • 161
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    Global temperature calibration of the alkenone unsaturation index (UK′37) in surface waters and comparison with surface sediments (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q02005, doi:10.1029/2005GC001054.
    Description: In this paper, we compile the current surface seawater C37 alkenone unsaturation (UK′37) measurements (n=629, −1 to 30°C temperature range) to derive a global, field-based calibration of UK′37 with alkenone production temperature. A single nonlinear “global” surface water calibration of UK′37 accurately predicts alkenone production temperatures over the diversity of modern-day oceanic environments and alkenone-synthesizing populations (T=−0.957 + 54.293(UK′37) − 52.894(UK′37)2 + 28.321(UK′37)3, r2=0.97, n=567). The mean standard error of estimation is 1.2°C with insignificant bias in estimated production temperature among the different ocean regions sampled. An exception to these trends is regions characterized by strong lateral advection and extreme productivity and temperature gradients (e.g., the Brazil-Malvinas Confluence). In contrast to the surface water data, the calibration of UK′37 in surface sediments with overlying annual mean sea surface temperature (AnnO) is best fit by a linear model (AnnO=29.876(UK′37) − 1.334, r2=0.97, n=592). The standard error of estimation (1.1°C) is similar to that of the surface water production calibration, but a higher degree of bias is observed among the regional data sets. The sediment calibration differs significantly from the surface water calibration. UK′37 in surface sediments is consistently higher than that predicted from AnnO and the surface water production temperature calibration, and the magnitude of the offset increases as the surface water AnnO decreases. We apply the global production temperature calibration to the coretop UK′37 data to estimate the coretop alkenone integrated production temperature (coretop IPT) and compare this with the overlying annual mean sea surface temperature (AnnO). We use simple models to explore the possible causes of the deviation observed between the coretop temperature signal, as estimated by UK′37, and AnnO. Our results indicate that the deviation can best be explained if seasonality in production and/or thermocline production as well as differential degradation of 37:3 and 37:2 alkenones both affect the sedimentary alkenone signal.
    Description: C.R. acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG).
    Keywords: Alkenones ; Paleoproxies ; Sea surface temperature ; UK′37
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  • 162
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    Slope water, Gulf Stream, and seasonal influences on southern Mid-Atlantic Bight circulation during the fall-winter transition (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 110 (2005): C02009, doi:10.1029/2004JC002311.
    Description: Observations from autumn, 2000, near the shelfbreak front in the Middle Atlantic Bight are used to describe the transition from stratified summer conditions to well-mixed winter conditions over the shelf. During the observational period, the front differed dramatically from climatological conditions, with buoyant Gulf Stream water found shoreward over the sub-surface shelfbreak front. Water mass analysis shows a large number of separate water masses with shelf, slope and Gulf Stream origins. The coolest shelf water was located at the shelfbreak and may be related to “cold pool” water masses observed to the north during summer. Shoreward of this shelfbreak water mass, a mid-shelf front was present which intersected the bottom at the 50 m isobath. High volume transports were associated with both the shelfbreak and mid-shelf fronts. Transport estimates from the cross-shelf sections were approximately 1 Sverdrup, which is large relative to previous estimates of shelf transport. The foot of the front was near the 130 m isobath, much deeper than the climatological position near the 75 m isobath, however this is consistent with a recent theory relating the magnitude of alongshelf transport to the depth at which the front intersects the bottom.
    Description: The authors gratefully acknowledge support from the Duke University - University of North Carolina Oceanographic Consortium for ship time aboard the R/V Cape Hatteras. MSL also gratefully acknowledges support from the Office of Naval Research (N00014-01-1-0260).
    Keywords: Shelfbreak front ; Mid-shelf front ; Shelf transport
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  • 163
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    A multiple proxy and model study of Cretaceous upper ocean temperatures and atmospheric CO2 concentrations (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 21 (2206): PA2002, doi:10.1029/2005PA001203.
    Description: We estimate tropical Atlantic upper ocean temperatures using oxygen isotope and Mg/Ca ratios in well-preserved planktonic foraminifera extracted from Albian through Santonian black shales recovered during Ocean Drilling Program Leg 207 (North Atlantic Demerara Rise). On the basis of a range of plausible assumptions regarding seawater composition at the time the data support temperatures between 33° and 42°C. In our low-resolution data set spanning ~84–100 Ma a local temperature maximum occurs in the late Turonian, and a possible minimum occurs in the mid to early late Cenomanian. The relation between single species foraminiferal δ18O and Mg/Ca suggests that the ratio of magnesium to calcium in the Turonian-Coniacian ocean may have been lower than in the Albian-Cenomanian ocean, perhaps coincident with an ocean 87Sr/86Sr minimum. The carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples. The δ13C values of phytane, combined with foraminiferal δ13C and inferred temperatures, were used to estimate atmospheric carbon dioxide concentrations through this interval. Estimates of atmospheric CO2 concentrations range between 600 and 2400 ppmv. Within the uncertainty in the various proxies, there is only a weak overall correspondence between higher (lower) tropical temperatures and more (less) atmospheric CO2. The GENESIS climate model underpredicts tropical Atlantic temperatures inferred from ODP Leg 207 foraminiferal δ18O and Mg/Ca when we specify approximate CO2 concentrations estimated from the biomarker isotopes in the same samples. Possible errors in the temperature and CO2 estimates and possible deficiencies in the model are discussed. The potential for and effects of substantially higher atmospheric methane during Cretaceous anoxic events, perhaps derived from high fluxes from the oxygen minimum zone, are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric CH4 concentrations. With 50 ppm CH4, GENESIS sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when CO2 concentrations specified to the model are near those inferred using the phytane δ13C proxy. However, atmospheric CO2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures.
    Description: Funding for this research was provided by the U.S. Science Support Program of the JOI, the Andrew W. Mellon Foundation Endowed Fund for Innovative Research, and Deutsche Forschungsgemeinschaft through the DFG-Research Center Ocean Margins.
    Keywords: Cretaceous ; Temperature ; Carbon dioxide
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  • 164
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    Radiocarbon constraint on relict organic carbon contributions to Ross Sea sediments (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q04012, doi:10.1029/2005GC001097.
    Description: We estimate the relative contribution of relict organic matter to the acid-insoluble organic carbon (AIOC) fraction of surface sediments from Ross Sea, Antarctica, on the basis of 14C abundance. The bulk isotopic characteristics of AIOC can largely be explained by simple two-source models of modern and relict organic carbon, when samples are grouped according to two geographical regions, namely, southwestern and south central Ross Sea. This spatial variability in relict organic carbon could be controlled by proximity to the edge of the Ross Ice Shelf and ice drainage areas. Radiocarbon abundance in the AIOC is potentially an excellent tool to estimate the contribution of relict organic carbon in the Antarctic margin sediments.
    Description: This work was partly supported by a grant from Japan Society for the Promotion of Science to N.O.
    Keywords: Ross Sea ; Radiocarbon ; Sediment ; Organic carbon
    Repository Name: Woods Hole Open Access Server
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  • 165
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    The Cleft revealed: geologic, magnetic, and morphologic evidence for construction of upper oceanic crust along the southern Juan de Fuca Ridge (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q04003, doi:10.1029/2005GC001038.
    Description: The geology and structure of the Cleft Segment of the Southern Juan de Fuca Ridge (JdFR) have been examined using high-resolution mapping systems, observations by remotely operated vehicle (ROV), ROV-mounted magnetometer, and the geochemical analysis of recovered lavas. Bathymetric mapping using multibeam (EM300) coupled with in situ observations that focused on near-axis and flank regions provides a detailed picture of 0 to 400 ka upper crust created at the southern terminus of the JdFR. A total of 53 rock cores and 276 precisely located rock or glass samples were collected during three cruises that included sixteen ROV dives. Our observations of the seafloor during these dives suggest that many of the unfaulted and extensive lava flows that comprise and/or cap the prominent ridges that flank the axial valley emanate from ridge parallel faults and fissures that formed in the highly tectonized zone that forms the walls of the axial valley. The geochemically evolved and heterogeneous nature of these near-axis and flank eruptions is consistent with an origin within the cooler distal edges of a crustal magma chamber or mush zone. In contrast, the most recent axial eruptions are more primitive (higher MgO), chemically homogeneous lobate, sheet, and massive flows that generate a distinct magnetic high over the axial valley. We suggest that the syntectonic capping volcanics observed off-axis were erupted from near-axis and flank fissures and created a thickened extrusive layer as suggested by the magnetic and seismic data. This model suggests that many of the lavas that comprise the elevated ridges that bound the axial valley of the Cleft Segment were erupted during the collapse of a magmatic cycle not during the robust phase that established a new magmatic cycle.
    Description: This research has been partially supported by a NSF grant to M. Perfit (OCE-0221541). M. Tivey acknowledges support from WHOI’s Mellon grant for Independent Study. Support for D. Stakes, T. Ramirez, D. Caress, and N. Maher and for the entire field program was provided by funds to MBARI from the Lucille and David Packard Foundation.
    Keywords: Basalt ; Ridge
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    Detachment shear zone of the Atlantis Massif core complex, Mid-Atlantic Ridge, 30°N (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q06016, doi:10.1029/2005GC001109.
    Description: Near-bottom investigations of the cross section of the Atlantis Massif exposed in a major tectonic escarpment provide an unprecedented view of the internal structure of the footwall domain of this oceanic core complex. Integrated direct observations, sampling, photogeology, and imaging define a mylonitic, low-angle detachment shear zone (DSZ) along the crest of the massif. The shear zone may project beneath the nearby, corrugated upper surface of the massif. The DSZ and related structures are inferred to be responsible for the unroofing of upper mantle peridotites and lower crustal gabbroic rocks by extreme, localized tectonic extension during seafloor spreading over the past 2 m.y. The DSZ is characterized by strongly foliated to mylonitic serpentinites and talc-amphibole schists. It is about 100 m thick and can be traced continuously for at least 3 km in the tectonic transport direction. The DSZ foliation arches over the top of the massif in a convex-upward trajectory mimicking the morphology of the top of the massif. Kinematic indicators show consistent top-to-east (toward the MAR axis) tectonic transport directions. Foliated DSZ rocks grade structurally downward into more massive basement rocks that lack a pervasive outcrop-scale foliation. The DSZ and underlying basement rocks are cut by discrete, anastomosing, normal-slip, shear zones. Widely spaced, steeply dipping, normal faults cut all the older structures and localize serpentinization-driven hydrothermal outflow at the Lost City Hydrothermal Field. A thin (few meters) sequence of sedimentary breccias grading upward into pelagic limestones directly overlies the DSZ and may record a history of progressive rotation of the shear zone from a moderately dipping attitude into its present, gently dipping orientation during lateral spreading and uplift.
    Description: This work was supported by NSF grants OCE-9712430 and 0136816 to Karson and Kelley and Swiss SNF grant 2100-068055 to Früh-Green.
    Keywords: Detachment faults ; Faults ; Oceanic core complex ; Seafloor spreading ; Serpentinite ; Shear zones
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  • 167
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    Bottom boundary layer flow and salt injection from the continental shelf to slope (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 33 (2006): L13608, doi:10.1029/2006GL026311.
    Description: Austral winter oceanographic measurements from the northwest Australian continental shelf reveal salty water forming evaporatively inshore, moving across the wide shelf near the bottom and into the adjacent open ocean when the shelf edge alongshore flow is equatorward. The salt tongue is absent during more normal conditions, when the poleward Leeuwin Current is present. We hypothesize that the flow reversal enables shelf-wide bottom boundary layer (Ekman) transport and thus creates the shelf-edge convergence that accounts for the observed salt tongue. This flow is absent under sustained normal conditions because of buoyancy arrest in the bottom boundary layer.
    Description: This research was supported by the Processes and Prediction Division (Code 322 PO) of the U.S. Office of Naval Research through grant N00014-02-1-0767.
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    Interannual variability of the South China Sea throughflow inferred from wind data and an ocean data assimilation product (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 33 (2006): L14605, doi:10.1029/2006GL026316.
    Description: The Luzon Strait transport, as an index for the South China Sea throughflow, has attracted much attention. In this study the interannual variability of the Luzon Strait transport is examined, using the Island Rule and results from an ocean general circulation model. Transport variability obtained from these two approaches are consistent with each other. Assessment of contribution from each integral segment involved in the Island Rule indicates that wind stress in the western and central equatorial Pacific is the key factor regulating the interannual variability of the Luzon Strait transport, whereas the effect of local wind stress in the vicinity of the Luzon Strait is secondary. Analysis also shows that when the westerly (easterly) wind anomalies in the tropical Pacific break out, the Luzon Strait transport increases (decreases), consistent with the variations in the North Equatorial Current during El Niño (La Niña) events.
    Description: This research was supported by NSF of China (Grants Nos. 40136010 and 40406006). YD and TQ were supported by the National Aeronautics and Space Administration through grant NAG5-12756, and TQ also supported by Japan Agency for Marine-Earth Science and Technology through its sponsorship of the International Pacific Research Center.
    Keywords: Island Rule ; Wind stress ; South China Sea throughflow
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  • 169
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    Heat flow variations on a slowly accreting ridge : constraints on the hydrothermal and conductive cooling for the Lucky Strike segment (Mid-Atlantic Ridge, 37°N) (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q07011, doi:10.1029/2005GC001178.
    Description: We report 157 closely spaced heat flow measurements along the Lucky Strike segment in the Mid-Atlantic Ridge (MAR) for ages of the ocean floor between 0 and 11 Ma. On the eastern flank of a volcanic plateau delimiting off-axis and axial domains, the magnitude of heat flow either conforms to the predictions of conductive lithospheric cooling models or is affected by localized anomalies. On the western flank it is uniformly lower than conductive model predictions. We interpret the observed patterns of heat flow by lateral fluid circulation in a highly permeable oceanic basement. The circulation geometries are probably 3-D rather than 2-D and are determined by the configuration of the basement/sediment interface and the distribution of effectively unsedimented seamounts where water recharge can occur. Two major hydrothermal circulation systems can possibly explain the observations off-axis: the first would involve lateral pore water flow from west to east, and the second would have a reverse flow direction. The wavelengths and magnitudes of heat flow anomalies require Darcy velocities of the order of 1–4 m/year, which are similar to those proposed for fast-accreted crust elsewhere. However, a large proportion of this MAR domain remains unaffected by hydrothermal cooling, which is a relatively unusual observation but confirms the validity of conductive thermal models for seafloor ages between 5 and 10 Ma. Closer to the ridge axis (〈5 Myr old crust), water circulation affects the overall axial domain, as larger proportions of basement are exposed. As much as 80–90% of the heat flux from the axial domain may be transferred to the Lucky Strike vent field, in agreement with the estimated discharge.
    Keywords: Heat flow ; Mid-Atlantic Ridge
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  • 170
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    Meridional circulation during the Last Glacial Maximum explored through a combination of South Atlantic δ18O observations and a geostrophic inverse model (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q11N07, doi:10.1029/2006GC001383.
    Description: The vertical profile of meridional transport in the South Atlantic is examined by combining paleoceanographic observations with a geostrophic circulation model using an inverse method. δ18Ocalcite observations along the margins of the South Atlantic show that upper-ocean cross-basin differences were weaker during the Last Glacial Maximum (LGM) than the Holocene. The δ18Ocalcite observations can be explained by a shift of water-mass properties without any change in the overturning circulation. Alternatively, they may indicate a reduced LGM cross-basin density difference and, via the thermal wind relation, a reduced vertical shear. Model inversions of δ18Ocalcite are found to require meridional transports different from the modern only after three assumptions are made: temperature and salinity distributions are spatially smooth, the relationship between salinity and δ18Owater is linear and spatially invariant, and LGM temperatures are known to within 1°C along the margins. The last assumption is necessary because an independent constraint on temperature or salinity is required to determine density from δ18Ocalcite observations. δ18Ocalcite observations are clearly useful, but before any firm constraints can be placed on LGM meridional transport, it appears necessary to better determine the relationship between δ18Ocalcite and density.
    Description: P.H. was funded by the NOAA postdoctoral program in climate and global change, and G.G. was partially funded by NSF paleoclimate program ATM-0502482.
    Keywords: Inverse modeling ; Last Glacial Maximum ; Meridional ocean circulation ; Geostrophy
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    Submarine volcanic morphology of the western Galapagos based on EM300 bathymetry and MR1 side-scan sonar (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q03010, doi:10.1029/2006GC001464.
    Description: A compilation of high-resolution EM300 multibeam bathymetric and existing MR1 side-scan sonar data was used to investigate the volcanic morphology of the flanks of the western Galápagos Islands. The data portray an assortment of constructional volcanic features on the shallow to deep submarine flanks of Fernandina, Isabela, and Santiago Islands, including rift zones and groups of cones that are considered to be the primary elements in constructing the archipelagic apron. Ten submarine rift zones were mapped, ranging in length from 5 to 20 km, comparable in length to western Canary Island rift zones but significantly shorter than Hawaiian submarine rift zones. A detailed analysis of the northwestern Fernandina submarine rift, including calculated magnetization from a surface-towed magnetic study, suggests that the most recent volcanism has focused at the shallow end of the rift. Small submarine volcanic cones with various morphologies (e.g., pointed, cratered, and occasionally breached) are common in the submarine western Galápagos both on rift zones and on the island flanks where no rifts are present. At depths greater than ∼3000 m, large lava flow fields in regions of low bathymetric relief have been previously identified as a common seafloor feature in the western Galápagos by Geist et al. (2006); however, their source(s) remained enigmatic. The new EM300 data show that a number of the deep lava flows originate from small cones along the mid-lower portion of the NW submarine rift of Fernandina, suggesting that the deep flows owe their origin, at least in part, to submarine rift zone volcanism.
    Description: Data collected on TN188 was funded by NSF grant OCE0326148 and NOAA grant NA04OAR460009 to S.M.W. Support for data collected on previous multibeam and MR1 cruises was provided by NSF grants OCE9811504 and OCE0002461 (D.J.F.).
    Keywords: Galapagos Islands ; EM300 multibeam bathymetry ; MR1 side-scan sonar ; Submarine volcanic cones ; Submarine volcanic rift zones ; Deep lava flows
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  • 172
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    Insights on coccolith chemistry from a new ion probe method for analysis of individually picked coccoliths (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q06020, doi:10.1029/2006GC001546.
    Description: The elemental chemistry of calcareous nannofossils may provide valuable information on past ocean conditions and coccolithophorid physiology, but artifacts from noncoccolith particles and from changing nannofossil assemblages may bias geochemical records from coccolith size fractions. We describe the first method for picking individual coccoliths using a tungsten needle in micromanipulator. Epoxy-mounted individuals and populations of coccoliths can be analyzed by secondary ion mass spectrometry (SIMS). For Paleocene sediments the technique distinguishes the high Sr/Ca ratios of coccoliths (0.3 to 2.8 mmol/mol) from low ratios in abiogenic calcite blades (0.1 mmol/mol). The large heterogeneity of Sr/Ca ratios among different genera suggests that primary geochemical differences have not been homogenized by diagenetic overgrowth and the thick massive coccoliths of the late Paleocene are a primary feature of biomineralization. Sr/Ca ratios for modern genera are on average higher than those of Paleogene genera but exhibit a comparable level of variability.
    Description: Research supported by NSF OCE-0424474 to H. Stoll and a fellowship to H. Stoll from the Spanish Ministry of Education cofunded by the European Social Fund.
    Keywords: Ion probe ; SIMS ; Sr/Ca ; Coccolith
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    Quantitative bedrock geology of the continents and large-scale drainage regions (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q06009, doi:10.1029/2006GC001544.
    Description: We quantitatively analyze the area-age distribution of sedimentary, extrusive volcanic, and endogenous (plutonic and/or metamorphic) bedrock on the basis of data from the most recent digital Geological Map of the World at a scale of 1:25,000,000. The spatial resolution of the digital bedrock data averages 13,905 km2 per polygon. Comparison of certain regions of the world, previously analyzed at higher spatial resolution, with the low-resolution world data reveals general consistency in the areal exposure of major rock types as well as a minor systematic bias toward older average bedrock ages in the global data set. Application of the global bedrock data to 19 large-scale drainage regions and three large, internally drained regions reveals considerable regional variability of Earth's bedrock geology that is consistent with the dominant geotectonic setting of the respective drainage region.
    Description: B.P.E. acknowledges financial support from the United States National Science Foundation (NSF-EAR- 0125873) and from the Woods Hole Oceanographic Institution.
    Keywords: Geologic map ; World ; Age ; Bedrock ; Sediment ; Volcanic rock
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    Evolution of the Southwest Indian Ridge from 55°45′E to 62°E : changes in plate-boundary geometry since 26 Ma (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q06022, doi:10.1029/2006GC001559.
    Description: From 55°45′E to 58°45′E and from 60°30′E to 62°00′E, the ultraslow-spreading Southwest Indian Ridge (SWIR) consists of magmatic spreading segments separated by oblique amagmatic spreading segments, transform faults, and nontransform discontinuities. Off-axis magnetic and multibeam bathymetric data permit investigation of the evolution of this part of the SWIR. Individual magmatic segments show varying magnitudes and directions of asymmetric spreading, which requires that the shape of the plate boundary has changed significantly over time. In particular, since 26 Ma the Atlantis II transform fault grew by 90 km to reach 199 km, while a 45-km-long transform fault at 56°30′E shrank to become an 11 km offset nontransform discontinuity. Conversely, an oblique amagmatic segment at the center of a first-order spreading segment shows little change in orientation with time. These changes are consistent with the clockwise rotation of two ~450-km-wide first-order spreading segments between the Gallieni and Melville transform faults (52–60°E) to become more orthogonal to spreading. We suggest that suborthogonal first-order spreading segments reflect a stable configuration for mid-ocean ridges that maximizes upwelling rates in the asthenospheric mantle and results in a hotter and weaker ridge-axis that can more easily accommodate seafloor spreading.
    Description: Funding for this work came from a JOI-Schlanger Fellowship to Baines and NSF grant 0352054 to Cheadle and John.
    Keywords: Southwest Indian Ridge ; Atlantis II fracture zone ; Asymmetric spreading ; Ridge segmentation
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    Sea surface temperature signatures of oceanic internal waves in low winds (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 112 (2007): C06014, doi:10.1029/2006JC003947.
    Description: In aerial surveys conducted during the Tropical Ocean–Global Atmosphere Coupled Ocean-Atmosphere Response Experiment and the low-wind component of the Coupled Boundary Layer Air-Sea Transfer (CBLAST-Low) oceanographic field programs, sea surface temperature (SST) variability at relatively short spatial scales (O(50 m) to O(1 km)) was observed to increase with decreasing wind speed. A unique set of coincident surface and subsurface oceanic temperature measurements from CBLAST-Low is used to investigate the subsurface expression of this spatially organized SST variability, and the SST variability is linked to internal waves. The data are used to test two previously hypothesized mechanisms for SST signatures of oceanic internal waves: a modulation of the cool-skin effect and a modulation of vertical mixing within the diurnal warm layer. Under conditions of weak winds and strong insolation (which favor formation of a diurnal warm layer), the data reveal a link between the spatially periodic SST fluctuations and subsurface temperature and velocity fluctuations associated with oceanic internal waves, suggesting that some mechanism involving the diurnal warm layer is responsible for the observed signal. Internal-wave signals in skin temperature very closely resemble temperature signals measured at a depth of about 20 cm, indicating that the observed internal-wave SST signal is not a result of modulation of the cool-skin effect. Numerical experiments using a one-dimensional upper ocean model support the notion that internal-wave heaving of the warm-layer base can produce alternating bands of relatively warm and cool SST through the combined effects of surface heating and modulation of wind-driven vertical shear.
    Description: We gratefully acknowledge funding for this research from the Office of Naval Research through the CBLAST Departmental Research Initiative (grants N00014-01-1-0029, N00014-05-10090, N00014-01-1-0081, N00014-04-1-0110, N00014-05-1-0036, N00014-01-1-0080) and the Secretary of the Navy/Chief of Naval Operations Chair (grant N00014-99-1-0090).
    Keywords: Internal waves ; Upper-ocean processes
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    Nonvolcanic seafloor spreading and corner-flow rotation accommodated by extensional faulting at 15°N on the Mid-Atlantic Ridge : a structural synthesis of ODP Leg 209 (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q06015, doi:10.1029/2006GC001567.
    Description: Drilling during ODP Leg 209, dredging, and submersible dives have delineated an anomalous stretch of the Mid-Atlantic Ridge north and south of the 15°20′N Fracture Zone. The seafloor here consists dominantly of mantle peridotite with gabbroic intrusions that in places is covered by a thin, discontinuous extrusive volcanic layer. Thick lithosphere (10–20 km) in this region inhibits magma from reaching shallow levels beneath the ridge axis, thereby causing plate accretion to be accommodated by extensional faulting rather than magmatism. The bathymetry and complex fault relations in the drill-core suggest that mantle denudation and spreading are accommodated by a combination of high-displacement, rolling-hinge normal faults and secondary lower-displacement normal faults. These extensional faults must also accommodate corner flow rotation (up to 90°) of the upwelling mantle within the shallow lithosphere, consistent with remnant magnetic inclinations in denuded peridotite and gabbro from Leg 209 core that indicate up to 90° of sub-Curie-temperature rotation.
    Description: This work was funded by a grant from the Joint Oceanographic Institutions.
    Keywords: Seafloor spreading ; Ocean Drilling Program ; Nonvolcanic mid-ocean ridges ; Extensional faulting
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    Role of carbon cycle observations and knowledge in carbon management (2005)
    Annual Reviews
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    Publication Date: 2022-05-25
    Description: Author Posting. © Annual Reviews, 2003. This article is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Environment and Resources 28 (2003): 521-558, doi:10.1146/annurev.energy.28.011503.163443.
    Description: Agriculture and industrial development have led to inadvertent changes in the natural carbon cycle. As a consequence, concentrations of carbon dioxide and other greenhouse gases have increased in the atmosphere and may lead to changes in climate. The current challenge facing society is to develop options for future management of the carbon cycle. A variety of approaches has been suggested: direct reduction of emissions, deliberate manipulation of the natural carbon cycle to enhance sequestration, and capture and isolation of carbon from fossil fuel use. Policy development to date has laid out some of the general principles to which carbon management should adhere. These are summarized as: how much carbon is stored, by what means, and for how long. To successfully manage carbon for climate purposes requires increased understanding of carbon cycle dynamics and improvement in the scientific capabilities available for measurement as well as for policy needs. The specific needs for scientific information to underpin carbon cycle management decisions are not yet broadly known. A stronger dialogue between decision makers and scientists must be developed to foster improved application of scientific knowledge to decisions. This review focuses on the current knowledge of the carbon cycle, carbon measurement capabilities (with an emphasis on the continental scale) and the relevance of carbon cycle science to carbon sequestration goals.
    Description: The National Center for Atmospheric Research is supported by the National Science Foundation.
    Keywords: Carbon sequestration ; Measurement techniques ; Climate ; Kyoto protocol
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    Spatial variability of mixing in the Southern Ocean (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 32 (2005): L18603, doi:10.1029/2005GL023568.
    Description: Strain variance from standard hydrographic profiles in the southern hemisphere oceans shows that turbulent mixing is vertically and spatially non-uniform. In the South Atlantic, Indian and South Pacific Oceans, enhanced diffusivities are found over rough topography. Consistent with internal tide generated mixing, the water column diffusivity returns to background levels 500 m to 1000 m off the sea floor. In the Southern Ocean, enhanced diffusivities throughout the entire water column below 1500 m are found in the Antarctic Circumpolar Current over complex topography. Differences in the vertical extent of enhanced diffusivity profiles in the Antarctic Circumpolar Current between the parameterizations based on tidal models and topography and of the present estimate of strain variance imply that elevated vertical diffusivity profiles in the Southern Ocean are due to the interaction between the mean geostrophic current and bottom topography.
    Description: BMS was supported by the Ocean and Climate Change Institute at the Woods Hole Oceanographic Institution.
    Keywords: Fine structure and microstructure ; Internal and inertial waves ; Turbulence, diffusion, and mixing processes
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  • 179
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    Extending the record of photosynthetic activity in the eastern United States into the presatellite period using surface diurnal temperature range (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 32 (2005): L08405, doi:10.1029/2005GL022583.
    Description: In this study, we demonstrate that mid-latitude surface measurements of diurnal temperature range (DTR) can be used to reconstruct decadal variability of regional-scale terrestrial photosynthetic activity 1) during and prior to the period with satellite retrievals of land greenness and 2) without the need for moisture data. While the two relative maxima present in the seasonal evolution of DTR can determine the beginning and the end of the growing season, the summertime average DTR can be used as a proxy of summertime terrestrial photosynthesis. In a case study in the eastern United States (1966–1997), the DTR reconstructions indicate significant natural decadal variability in photosynthetic activity, but no secular, long-term trend. The summertime photosynthesis was found to be controlled primarily by moisture availability. Also, contrary to existing model parameterizations, the timing of spring onset was found to depend on both temperature and moisture.
    Description: This work is supported by National Science Foundation grant ATM-9987457, NASA EOS-IDS grants NAG5-9514 and NNG04GK34G, NASA Carbon Cycle Program grant NAG5-11200, and the WHOI Ocean and Climate Change Institute.
    Keywords: Biogeochemical cycles, processes, and modeling ; Water cycles ; Evapotranspiration ; Land/atmosphere interactions ; North America
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  • 180
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    Reflection and tunneling of ocean waves observed at a submarine canyon (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 32 (2005): L10602, doi:10.1029/2005GL022834.
    Description: Ocean surface gravity waves with periods between 20 and 200 s were observed to reflect from a steep-walled submarine canyon. Observations of pressure and velocity on each side of the canyon were decomposed into incident waves arriving from distant sources, waves reflected by the canyon, and waves transmitted across the canyon. The observed reflection is consistent with longwave theory, and distinguishes between cases of normal and oblique angles of incidence. As much as 60% of the energy of waves approaching the canyon normal to its axis was reflected, except for waves twice as long as the canyon width, which were transmitted across with no reflection. Although waves approaching the canyon at oblique angles cannot propagate over the canyon, total reflection was observed only at frequencies higher than 20 mHz, with lower frequency energy partially transmitted across, analogous to the quantum tunneling of a free particle through a classically impenetrable barrier.
    Description: Funding was provided by the Office of Naval Research and the National Science Foundation.
    Keywords: Wave reflection ; Infragravity ; Submarine canyon
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  • 181
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    Seawater-peridotite interactions : first insights from ODP Leg 209, MAR 15°N (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. 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 5 (2004): Q09F26, doi:10.1029/2004GC000744.
    Description: We present first results of a petrographic study of hydrothermally altered peridotites drilled during Ocean Drilling Program (ODP) Leg 209 in the 15°20′N fracture Zone area on the Mid-Atlantic Ridge (MAR). We find that serpentinization is extensive at all drill sites. Where serpentinization is incomplete, phase relations indicate two major reaction pathways. One is reaction of pyroxene to talc and tremolite, and the other is reaction of olivine to serpentine, magnetite, and brucite. We interpret these reactions in the light of recent peridotite-seawater reaction experiments and compositions of fluids venting from peridotite massifs at a range of temperatures. We suggest that the replacement of pyroxene by talc and tremolite takes place at temperatures 〉350°–400°C, where olivine is stable. The breakdown of olivine to serpentine, magnetite, and brucite is favored at temperatures below 250°C, where olivine reacts faster then pyroxene. High-temperature hydrothermal fluids venting at the Logatchev and Rainbow sites are consistent with rapid reaction of pyroxene and little or no reaction of olivine. Moderate-temperature fluids venting at the Lost City site are consistent with ongoing reaction of olivine to serpentine and brucite. Many completely serpentinized peridotites lack brucite and talc because once the more rapidly reacting phase is exhausted, interaction with the residual phase will change fluid pH and silica activity such that brucite or talc react to serpentine. At two sites we see strong evidence for continued fluid flow and fluid-rock interaction after serpentinization was complete. At Site 1268, serpentinites underwent massive replacement by talc under static conditions. This reaction requires either removal of Mg from or addition of Si to the system. We propose that the talc-altered rocks are Si-metasomatized and that the source of Si is likely gabbro-seawater reaction or breakdown of pyroxene deeper in the basement. The basement at Site 1268 is heavily veined, with talc and talc-oxide-sulfide veins being the most common vein types. It appears that the systems evolved from reducing (oxygen fugacity buffered by magnetite-pyrrhotite-pyrite and lower) to oxidizing (dominantly hematite). We propose that this transition is indicative of high fluid flux under retrograde conditions and that the abundance of hematite may relate to the Ca-depleted nature of the basement that prevents near-quantitative removal of seawater sulfate by anhydrite precipitation. At site 1272 we find abundant iowaite partly replacing brucite. While this is the first report of iowaite from a mid-ocean ridge setting, its presence indicates, again, fairly oxidizing conditions. Our preliminary results indicate that peridotite-seawater and serpentinite-seawater interactions can take place under a wider range of temperature and redox conditions than previously appreciated.
    Description: This research used data and/or samples supplied by the Ocean Drilling Program (ODP). ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc.
    Keywords: Hydrothermal system ; Ocean Drilling Program ; Oceanic crust ; Serpentinite ; Water-rock interaction
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    Long nonlinear internal waves (2006)
    Annual Reviews
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    Publication Date: 2022-05-25
    Description: Author Posting. © Annual Reviews, 2006. This article is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Fluid Mechanics 38 (2006): 395-425, doi:10.1146/annurev.fluid.38.050304.092129.
    Description: Over the past four decades, the combination of in situ and remote sensing observations has demonstrated that long nonlinear internal solitary-like waves are ubiquitous features of coastal oceans. The following provides an overview of the properties of steady internal solitary waves and the transient processes of wave generation and evolution, primarily from the point of view of weakly nonlinear theory, of which the Korteweg-de Vries equation is the most frequently used example. However, the oceanographically important processes of wave instability and breaking, generally inaccessible with these models, are also discussed. Furthermore, observations often show strongly nonlinear waves whose properties can only be explained with fully nonlinear models.
    Description: KRH acknowledges support from NSF and ONR and an Independent Study Award from the Woods Hole Oceanographic Institution. WKM acknowledges support from NSF and ONR, which has made his work in this area possible, in close collaboration with former graduate students at Scripps Institution of Oceanography and MIT.
    Keywords: Solitary waves ; Nonlinear waves ; Stratified flow ; Physical Oceanography
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  • 183
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    Near-surface ocean temperature (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 111 (2006): C02004, doi:10.1029/2004JC002689.
    Description: The first open ocean deployment of the Skin Depth Experimental Profiler (SkinDeEP) was from the R/V Melville in the Gulf of California during the Marine Optical Characterization Experiment (MOCE–5). SkinDeEP is an autonomous, vertical profiler for the upper few meters of the ocean. During MOCE–5, SkinDeEP was deployed on 10 separate occasions, and profiles were made at intervals of approximately one minute each. A total of 976 profiles were acquired during the cruise. The ocean skin temperatures were measured by the Marine Atmosphere Emitted Radiance Interferometer (M–AERI), an infrared spectroradiometer. Typical meteorological conditions were of low winds and high insolation. The dataset provided captures the near-surface temperature structure that decouples the skin layer from the conventional in–situ bulk sea surface temperature measurements made at a depth of a few meters. Data from SkinDeEP showed strong diurnal warming within the upper few meters, with one extreme case of 4.6 K. There were large discrepancies when computing the skin–bulk temperature difference with bulk temperatures at different depths. Results also show the strong dependency of estimating air–sea heat flux based on SST, with warm–layer errors of almost 60 Wm-2 associated with intense stratification. This indicates the importance of the inclusion of the skin temperature for accurate calculation of latent, sensible, and net longwave heat fluxes.
    Description: The development of SkinDeEP was funded through the Research Council of Norway (Prosjektnr. 127872/720). Support was provided by the European Commission under the Marie Curie Fellowship contract ERBFMBICT983162. Further supportwas provided by NSF grant OCE–0241834 and National Oceanographic Partnership Program Award No. NNG04GM56G.
    Keywords: Air-sea heat flux ; Cool skin ; Warm layer
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    Effect of historical changes in land use and climate on the water budget of an urbanizing watershed (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 42 (2006): W03426, doi:10.1029/2005WR004131.
    Description: We assessed the effects of historical (1931-1998) changes in both land-use and climate on the water budget of a rapidly urbanizing watershed, Ipswich River basin (IRB), in northeastern Massachusetts. Water diversions and extremely low flow during summer are major issues in the IRB. Our study centers on a detailed analysis of diversions and a combined empirical/modeling treatment of evapotranspiration (ET) response to changes in climate and land-use. A detailed accounting of diversions showed that net diversions increased due to increases in water withdrawals (primarily ground water pumping) and export of sewage. Net diversions constitute a major component of runoff (20% of streamflow). Using a combination of empirical analysis and physically based modeling we related an increase in precipitation (2.7 mm/yr) and changes in other climate variables to an increase in ET (1.7 mm/yr). Simulations with a physically based water-balance model showed that the increase in ET could be attributed entirely to a change in climate, while the effect of land-use change was negligible. The land-use change effect was different from ET and runoff trends commonly associated with urbanization. We generalized these and other findings to predict future streamflow using climate change scenarios. Our study could serve as a framework for studying suburban watersheds, being the first study of a suburban watershed that addresses long-term effects of changes in both land-use and climate, and accounts for diversions and other unique aspects of suburban hydrology.
    Description: This research was partially supported by NSF grants (DEB-9726862, OCE-9726921 and OCE-0423565).
    Keywords: Water budgets ; Evapotranspiration ; Climate change ; Land-use change ; Urbanization ; Water-balance model ; Ipswich River
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    An estimate of the cross-frontal transport at the shelf break of the East China Sea with the Finite Volume Coastal Ocean Model (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 111 (2006): C03012, doi:10.1029/2005JC003290.
    Description: The Finite Volume Coastal Ocean Model (FVCOM) is used to estimate the onshore cross-frontal transport at the shelf break of the East China Sea. Boundary conditions of FVCOM are provided by the Princeton Ocean Model simulating ocean currents in the Yellow Sea and East China Sea realistically. One advantage of this study is that the unstructured triangular cell grid of FVCOM resolves complex bottom topography that may trigger Kuroshio frontal waves. It is anticipated that these nonlinear frontal waves enhance the exchange of seawater between the Kuroshio and shelf regions. Kuroshio frontal waves in the model are excited around the location where the bottom slope changes abruptly, and have the phase speed and amplitude consistent with those observed in the East China Sea. In addition, the model reproduces the onshore transport associated with growing frontal waves in the upper and lower layers. On the basis of passive tracer experiments, the annually averaged onshore-transport integrated along the shelf break is estimated to be 0.85 × 106 m3/s.
    Description: This study was carried out when A. I. stayed at WHOI with the grant of Overseas Advanced Educational Research Practice Support Program supported by the Ministry of Education, Science and Culture, Japan. In addition, the Japan Society for the Promotion of Science supported this study through Grant-in-Aid for Scientific Research.
    Keywords: East China Sea ; Kuroshio frontal wave ; Cross-frontal transport ; FVCOM
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    Primary U distribution in scleractinian corals and its implications for U series dating (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q05022, doi:10.1029/2005GC001138.
    Description: In this study we use microsampling techniques to explore diagenetic processes in carbonates. These processes are important as they can affect the accuracy of U series chronometry. Fission track maps of deep-sea scleractinian corals show a threefold difference between the minimum and maximum [U] in modern corals, which is reduced to a factor of 2 in fossil corals. We use micromilling and MC-ICP-MS to make detailed analyses of the [U] and δ234Uinitial distributions in corals from 218 ka to modern. Within each fossil coral we observe a large range of δ234Uinitial values, with high δ234Uinitial values typically associated with low [U]. A simple model shows that this observation is best explained by preferential movement of alpha-decay produced 234U atoms (alpha-recoil diffusion). Open-system addition of 234U may occur when alpha-recoil diffusion is coupled with a high [U] surface layer, such as organic material. This process can result in large, whole-coral δ234Uinitial elevations with little effect on the final age. The diagenetic pathways that we model are relevant to both shallow-water and deep-sea scleractinian corals since both exhibit primary [U] heterogeneity and may be subject to U addition.
    Description: We gratefully acknowledge The Comer Foundation for Abrupt Climate Change.
    Keywords: Uranium ; Diagenesis ; Coral ; Dating
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    Paleointensity applications to timing and extent of eruptive activity, 9°–10°N East Pacific Rise (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q06006, doi:10.1029/2005GC001141.
    Description: Placing accurate age constraints on near-axis lava flows has become increasingly important given the structural and volcanic complexity of the neovolcanic zone at fast spreading ridges. Geomagnetic paleointensity of submarine basaltic glass (SBG) holds promise for placing quantitative age constraints on near-axis flows. In one of the first extensive tests of paleointensity as a dating tool or temporal marker we present the results of over 550 successful SBG paleointensity estimates from 189 near-axis (〈4 km) sites at the East Pacific Rise, 9°–10°N. Paleointensities range from 6 to 53 μT and spatially correspond to the pattern expected from known temporal variations in the geomagnetic field. Samples within and adjacent to the axial summit trough (AST) have values approximately equal to or slightly higher than the present-day. Samples out to 1–3 km from the AST have values higher than the present-day, and samples farther off axis have values lower than the present-day. The on-axis samples (〈500 m from the AST) provide a test case for using models of paleofield variation for the past few hundred years as an absolute dating technique. Results from samples collected near a well-documented eruption in 1991–1992 suggest there may be a small negative bias in the paleointensity estimates, limiting resolution of the dating technique. Possible explanations for such a bias include local field anomalies produced by preexisting magnetic terrain; anomalously high magnetic unblocking temperatures, leading to a small cooling rate bias; and/or the possibility of a chemical remanence produced by in situ alteration of samples likely to have complicated thermal histories. Paleointensity remains useful in approximating age differences in young flows, and a clear along-axis paleointensity contrast near 9°50′N is suggestive of a ∼150–200 year age difference. Paleointensity values of off-axis samples are generally consistent with rough age interpretations based on side scan data. Furthermore, spatial patterns in the paleointensity suggest extensive off-axis flow emplacement may occur infrequently, with recurrence intervals of 10–20 kyr. Results of a stochastic model of lava emplacement show that this can be achieved with a single distribution of flows, with flow size linked to time between eruptions.
    Description: This work was accomplished with support from NSF grants OCE-0095698 (J. S. G.), OCE-0095342 (D. V. K.), OCE-9912072 (M. R. P.), OCE-0138088 (M. R. P.), and OCE-9819261 (D. J. F.).
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    A pan-arctic evaluation of changes in river discharge during the latter half of the 20th century (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 33 (2006): L06715, doi:10.1029/2006GL025753.
    Description: Several recent publications have documented changes in river discharge from arctic and subarctic watersheds. Comparison of these findings, however, has been hampered by differences in time periods and methods of analysis. Here we compare changes in discharge from different regions of the pan-arctic watershed using identical time periods and analytical methods. Discharge to the Arctic Ocean increased by 5.6 km3/y/y during 1964-2000, the net result of a large increase from Eurasia moderated by a small decrease from North America. In contrast, discharge to Hudson/James/Ungava Bays decreased by 2.5 km3/y/y during 1964-2000. While this evaluation identifies an overall increase in discharge (~120 km3/y greater discharge at the end of the time period as compared to the beginning for Hudson/James/Unvaga Bays and the Arctic Ocean combined), the contrasting regional trends also highlight the need to understand the consequences of adding/removing freshwater from particular regions of the arctic and subarctic oceans.
    Description: This work was supported by the Arctic System Science Program of the National Science Foundation (NSF-OPP-0229302, NSF-OPP-0230211, NSF-OPP-0519840) and by the National Oceanic and Atmospheric Administration (NA17RJ2612).
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    Sea surface temperature pattern reconstructions in the Arabian Sea (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 21 (2006): PA1014, doi:10.1029/2005PA001162.
    Description: Sea surface temperature (SST) and seawater δ18O (δ18Ow) were reconstructed in a suite of sediment cores from throughout the Arabian Sea for four distinct time intervals (0 ka, 8 ka, 15 ka, and 20 ka) with the aim of understanding the history of the Indian Monsoon and the climate of the Arabian Sea region. This was accomplished through the use of paired Mg/Ca and δ18O measurements of the planktonic foraminifer Globigerinoides ruber. By analyzing basin-wide changes and changes in cross-basinal gradients, we assess both monsoonal and regional-scale climate changes. SST was colder than present for the majority of sites within all three paleotime slices. Furthermore, both the Indian Monsoon and the regional Arabian Sea mean climate have varied substantially over the past 20 kyr. The 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2.5°–3.5°C attributable, in part, to the influences of glacial atmospheric CO2 concentrations and large continental ice sheets. The elimination of the cross-basinal SST gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength. Changes in δ18Ow that are smaller than the δ18O signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing. SSTs throughout the Arabian Sea were still cooler than present by an average of 1.4°C in the 8 ka time slice. These cool SSTs, along with lower δ18Ow throughout the basin, are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation. The results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling.
    Description: Analyses were funded by a SGER grant from the NSF (OCE03–34598). Funding was also provided by a Schlanger Ocean Drilling Program Fellowship (to K.A.D.) and NSF Grant OCE02–20776 (to D.W.O.). 16
    Keywords: Arabian Sea ; Mg/Ca ; Indian monsoon
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  • 190
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    Effects of wave rollers and bottom stress on wave setup (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 112 (2007): C02003, doi:10.1029/2006JC003549.
    Description: Setup, the increase in the mean water level associated with breaking waves, observed between the shoreline and about 6-m water depth on an ocean beach is predicted well by a model that includes the effects of wave rollers and the bottom stress owing to the mean flow. Over the 90-day observational period, the measured and modeled setup are correlated (squared correlation above 0.59), and agree within about 30%. Although rollers may affect setup significantly on beaches with large amplitude (several meters high) sandbars and may be important in predicting the details of the cross-shore profile of setup, for the data discussed here, rollers have only a small effect on the amount of setup. Conversely, bottom stress (calculated using eddy viscosity and undertow formulations based on the surface dissipation, and assuming that the eddy viscosity is uniform throughout the water column) significantly affects setup predictions. Neglecting bottom stress results in underprediction of the observed setup in all water depths, with maximum underprediction near the shoreline where the observed setup is largest.
    Description: Funding was provided by the Office of Naval Research, the National Science Foundation, and the Army Research Office.
    Keywords: Setup ; Rollers ; Bottom stress
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  • 191
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    Current subsidence rates due to compaction of Holocene sediments in southern Louisiana (2007)
    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 33 (2006): L11403, doi:10.1029/2006GL026300.
    Description: Relative contributions of geologic and anthropogenic processes to subsidence of southern Louisiana are vigorously debated. Of these, shallow sediment compaction is often considered dominant, although this has never been directly observed or effectively demonstrated. Quantitative understanding of subsidence is important for predicting relative sea level rise, storm surge flooding due to hurricanes, and for successful wetland restoration. Despite many shallow borings, few appropriate stratigraphic and geotechnical data are available for site-specific calculations. We overcome this by determining present compaction rates from Monte Carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the Holocene of southern Louisiana. This approach generates distributions of present compaction rates that are not expected to exceed 5 mm/yr, but may locally. Locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes.
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  • 192
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    Hydrothermal sediments as a potential record of seawater Nd isotope compositions : the Rainbow vent site (36°14′N, Mid-Atlantic Ridge) (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 21 (2006): PA3012, doi:10.1029/2006PA001273.
    Description: Geochemical compositions and Sr and Nd isotopes were measured in two cores collected ~2 and 5 km from the Rainbow hydrothermal vent site on the Mid-Atlantic Ridge. Overall, the cores record enrichments in Fe and other metals from hydrothermal fallout, but sequential dissolution of the sediments allows discrimination between a leach phase (easily leachable) and a residue phase (refractory). The oxy-anion and transition metal distribution combined with rare earth element (REE) patterns suggest that 1) the leach fraction is a mixture of biogenic carbonate and hydrothermal Fe-Mn oxy-hydroxide with no significant contribution from detrital material, and 2) 〉99.5% of the REE content of the leach fraction is of seawater origin. In addition, the leach fraction has an average 87Sr/86Sr ratio indistinguishable from modern seawater at 0.70916. Although we lack the εNd value of present day deep water at the Rainbow vent site, we believe that the REE budget of the leach fraction is predominantly of seawater origin. We suggest, therefore, that the leach fraction provides a record of local seawater εNd values. Nd isotope data from these cores span the period of 4-14 ka (14C ages) and yield εNd values for North East Atlantic Deep Water (NEADW) that are higher (-9.3 to -11.1) than those observed in the nearby Madeira Abyssal Plain from the same depth (-12.4 ± 0.9). This observation suggests that either the Iceland-Scotland Overflow Water (ISOW) and Lower Deep Water (LDW) contributions to the formation of NEADW are higher along the Mid-Atlantic Ridge than in the surrounding basins, or that the relative proportion of ISOW was higher during this period than is observed today. This study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water εNd values, and hence deep-water circulation patterns in the oceans, than is possible from other types of sediments.
    Description: VC is funded by the 2000 National Oceanography Centre, Southampton fellowship. Hydrothermal research at NOCS is funded through NERC core strategic science.
    Keywords: Nd isotope ; Hydrothermal ; Seawater
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  • 193
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    Evidence for asymmetric nonvolcanic rifting and slow incipient oceanic accretion from seismic reflection data on the Newfoundland margin (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 111 (2006): B09402, doi:10.1029/2005JB003981.
    Description: Prestack depth migrations of seismic reflection data collected around the Ocean Drilling Program (ODP) Leg 210 transect on the Newfoundland nonvolcanic margin delineate three domains: (1) extended continental crust, (2) transitional basement, and (3) apparent slow spreading oceanic basement beyond anomaly M3 and indicate first-order differences between this margin and its well-studied conjugate, the Iberia margin. Extended continental crust thins abruptly with few observed faults, in stark contrast with the system of seaward dipping normal faults and detachments imaged within continental crust off Iberia. Transition zone basement typically appears featureless in seismic reflection profiles, but where its character can be discerned, it does not resemble most images of exhumed peridotite off Iberia. Seismic observations allow three explanations for transitional basement: (1) slow spreading oceanic basement produced by unstable early seafloor spreading, (2) exhumed, serpentinized mantle with different properties from that off Iberia, and (3) thinned continental crust, likely emplaced by one or more detachment or rolling-hinge faults. Although we cannot definitively discriminate between these possibilities, seismic reflection profiles together with coincident wide-angle seismic refraction data tentatively suggest that the majority of transitional basement is thinned continental crust emplaced during the late stages of rifting. Finally, seismic profiles image abundant faults and significant basement topography in apparent oceanic basement. These observations, together with magnetic anomaly interpretations and the recovery of mantle peridotites at ODP Site 1277, appear to be best explained by the interplay of extension and magmatism during the transition from nonvolcanic rifting to a slow spreading oceanic accretion system.
    Description: The SCREECH program was funded by U.S. National Science Foundation grant OCE-9819053 to Woods Hole Oceanographic Institution, by the Danish Research Foundation (Danmarks Grundforskningsfond), and by the Natural Science and Engineering Council of Canada. D. Shillington was also supported by NSF grant OCE-0241940 and by the University of Wyoming Graduate School. B. Tucholke acknowledges additional support from NSF grant OCE-0326714 and the Henry Bryant Bigelow Chair in Oceanography at Woods Hole Oceanographic Institution.
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    The St. Lawrence polynya and the Bering shelf circulation : new observations and a model comparison (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 111 (2006): C09023, doi:10.1029/2005JC003268.
    Description: Using 14 year-long instrumented moorings deployed south of St. Lawrence Island, along with oceanographic drifters, we investigate the circulation over the central Bering shelf and the role of polynyas in forming and disseminating saline waters over the shelf. We focus also on evaluating the Gawarkiewicz and Chapman [1995] model of eddy production within coastal polynyas. Principal results include: 1) The northern central shelf near-surface waters exhibit westward flow carrying low-salinity waters from the Alaskan coast in fall and early winter, with consequences for water mass formation and biological production. 2) Within the St. Lawrence polynya, the freshening effect of winter advection is about half as large as the salting effect of surface brine flux resulting from freezing. 3) Brine production over the Bering shelf occurs primarily offshore, rather than within coastal polynyas, even though ice production per unit area is much larger within the polynyas. 4) We find little evidence for the geostrophic flow adjustment predicted by recent polynya models. 5) In contrast to the theoretical prediction that dense water from the polynya is carried offshore by eddies, we find negligible cross-shelf eddy density fluxes within and surrounding the polynya and very low levels of eddy energy that decreased from fall to winter, even though dense water accumulated within the polynya and large cross-shore density gradients developed. 6) It is possible that dense polynya water was advected downstream of our array before appreciable eddy fluxes materialized.
    Description: This work was supported by National Science Foundation grant OCE9730697 to the University of Alaska and grant OCE9730823 to the University of Washington. S. M. acknowledges the support of the National Science Foundation under OCE9811097 and of NASA under grant NNG04GM69G. The University of Hamburg contributions were funded by the Bundesminister für Bildung und Wissenschaft. Funding for the drifter deployment was made possible by the North Pacific Research Board, grant NPMRI T2130. Manuscript preparation was additionally supported by Office of Naval Research grants N00014-99-1-0345 and N00014-02-1-0305 to the University of Washington.
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    Linkages among runoff, dissolved organic carbon, and the stable oxygen isotope composition of seawater and other water mass indicators in the Arctic Ocean (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. 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 110 (2005): G02013, doi:10.1029/2005JG000031.
    Description: Concentrations of dissolved organic carbon (DOC) and δ18O values have been determined following sampling of runoff from a number of major arctic rivers, including the Ob, Yenisey, Lena, Kolyma, Mackenzie and Yukon in 2003-2004. These data are considered in conjunction with marine data for DOC, δ18O values, nutrients, salinity, and fluorometric indicators of DOC that were obtained as part of the Shelf-Basin Interactions program at the continental shelf-basin boundary of the Chukchi and Beaufort Seas. These marine data indicate that the freshwater component is most likely derived from regional sources, such as the Mackenzie, the Bering Strait inflow and possibly eastern Siberian rivers, including the Kolyma, or the Lena but not rivers further west in the Eurasian arctic. Contributions of freshwater from melted sea ice to marine surface waters appeared to be insignificant over annual cycles compared to runoff, although on a seasonal basis, freshwater from melted sea ice was locally dominant following a major sea-ice retreat into the Canada Basin in 2002. DOC concentrations were correlated with the runoff fraction, with an apparent meteoric water DOC concentration of 174 ± 1 μM (standard error). This concentration is lower than the flow-weighted concentrations measured at river mouths of the five largest Arctic rivers (358 to 917 μM), indicating that removal of terrigenous DOC during transport through estuaries, shelves and in the deep basin. DOC data indicate that flow-weighted concentrations in the two largest North American arctic rivers, the Yukon (625μM) and the Mackenzie (382 μM), are lower than in the three largest Eurasian arctic rivers, the Ob (825 μM), the Yenesey (858 μM) and the Lena (917 μM). A fluorometric indicator of chromophoric dissolved organic matter (CDOM) that has provided estimates of terrigenous DOC concentrations in the Eurasian Arctic was not correlated with DOC concentrations in the Amerasian marine waters studied, except below the upper Arctic Ocean halocline. Nutrient distributions and concentrations as well as derived nutrient ratios suggest the CDOM fluorometer may be responding to the release of chromophoric materials from continental shelf sediments. Shipboard incubation experiments with undisturbed sediment cores indicate that continental shelf sediments on the Bering and Chukchi Sea shelves are likely to be a net source of DOC to the Arctic Ocean.
    Description: The PARTNERS and SBI projects have been supported by the Office of Polar Programs of the U.S. National Science Foundation.
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  • 196
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    Meridional overturning circulation in the South Atlantic at the last glacial maximum (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q10N03, doi:10.1029/2005GC001226.
    Description: The geostrophic shear associated with the meridional overturning circulation is reflected in the difference in density between the eastern and western margins of the ocean basin. Here we examine how the density difference across 30°S in the upper 2 km of the Atlantic Ocean (and thus the magnitude of the shear associated with the overturning circulation) has changed between the last glacial maximum and the present. We use oxygen isotope measurements on benthic foraminifera to reconstruct density. Today, the density in upper and intermediate waters along the eastern margin in the South Atlantic is greater than along the western margin, reflecting the vertical shear associated with the northward flow of surface and intermediate waters and the southward flowing North Atlantic Deep Waters below. The greater density along the eastern margin is reflected in the higher δ 18O values for surface sediment benthic foraminifera than those found on the western margin for the upper 2 km. For the last glacial maximum the available data indicate that the eastern margin foraminifera had similar δ 18O to those on the western margin between 1 and 2 km and that the gradient was reversed relative to today with the higher δ 18O values in the western margin benthic foraminifera above 1 km. If this reversal in benthic foraminifera δ 18O gradient reflects a reversal in seawater density gradient, these data are not consistent with a vigorous but shallower overturning cell in which surface waters entering the Atlantic basin are balanced by the southward export of Glacial North Atlantic Intermediate Water.
    Description: This work was supported by NSF award OCE-9984989/OCE-0428803 to J.L.-S., NSF award OCE-9986748 to D.W.O. and W.B.C., NSF OCE-0222111 to C.D.C., and SEGRF fellowship at LLNL to J.M.
    Keywords: Last Glacial Maximum ; South Atlantic ; Meridional overturning circulation ; Oxygen isotopes ; Benthic foraminifera
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    Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 111 (2006): B11404, doi:10.1029/2005JB004156.
    Description: We present a compressional seismic velocity profile of the crust of the eastern margin of the Grand Banks of Newfoundland, Canada. This velocity model was obtained by a tomographic inversion of wide-angle data recorded on a linear array of 24 ocean-bottom seismometers (OBSs). At the landward side, we imaged a crustal thickness of 27 km in Flemish Pass and beneath Beothuk Knoll, which is thinner than the 35-km-thick crust of the central Grand Banks. We therefore assume that the eastern rim of the Grand Banks stretched uniformly by 25%. Farther seaward, the continental crust tapers rapidly beneath the continental slope to ~6 km thickness. In the distal margin we find a 60-km-wide zone with seismic velocities between 5.0 and 6.5 km/s that thins to the southeast from 6 km to 2 km, which we interpret as highly extended continental crust. Contrary to other seismic studies of the margins of the Grand Banks, we find seismic velocities of 8 km/s and higher beneath this thin crustal layer in the continent-ocean transition. We conclude that mantle was locally emplaced at shallow levels without significant hydration from seawater, or serpentinized mantle was removed along a décollement in the final stages of continental rifting. The outer edge of highly extended continental crust borders a 25-km-wide zone where seismic velocities increase gradually from 6.3 km/s just below the top of acoustic basement to 7.7 km/s at 5 km below basement. We interpret this area as a relatively narrow zone of exhumed and serpentinized continental mantle. Seawards, we imaged a thin and laterally heterogeneous layer with a seismic velocity that increases sharply from 5.0 km/s in basement ridges to 7.0 km/s at its base, overlying mantle velocities between 7.8 and 8.2 km/s. We interpret this area as unroofed mantle and very thin oceanic crust that formed at an incipient, magmastarved, ultraslow spreading ridge. A comparison of the conjugate rifted margins of the eastern Grand Banks and the Iberia Abyssal Plain show that they exhibit a similar seaward progression from continental crust to mantle to oceanic crust. This indicates that before continental breakup, rifting exhumed progressively deeper sections of the continental lithosphere on both conjugate margins. A comparison between the continent-ocean transition of the Grand Banks and Flemish Cap shows that the final phase of continental rifting and the formation of the first oceanic crust required more time at the Grand Banks margin than at the southeastern margin of Flemish Cap.
    Description: The SCREECH program was funded by the U.S. National Science Foundation grant OCE-9819053 to Woods Hole Oceanographic Institution, by the Danish Research Foundation (Danmarks Grundforskningsfond), and by the Natural Science and Engineering Council of Canada. HVA received support from the University of Texas Institute for Geophysics and a Jackson School of Geosciences Fellow award. BET acknowledges additional support from NSF grant OCE-0326714 and the Henry Bryant Bigelow Chair in Oceanography at Woods Hole Oceanographic Institution.
    Keywords: Continental rifting ; Marine geophysics ; Passive margin
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    Temporal stability of the neodymium isotope signature of the Holocene to glacial North Atlantic (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 21 (2006): PA4102, doi:10.1029/2006PA001294.
    Description: The neodymium isotopic composition of marine precipitates is increasingly recognized as a powerful tool for identifying changes in ocean circulation and mixing on million year to millennial time-scales. Unlike nutrient proxies such as δ13C or Cd/Ca, Nd isotopes are not thought to be altered in any significant way by biological processes, and thus can serve as a quasi-conservative water mass tracer. However, the application of Nd isotopes in understanding the role of thermohaline circulation in rapid climate change is currently hindered by the lack of direct constraints on the signature of the North Atlantic end-member through time. Here we present the first results of Nd isotopes measured in U-Th dated deep-sea corals from the New England seamounts in the northwest Atlantic Ocean. Our data are consistent with the conclusion that the Nd isotopic composition of North Atlantic deep and intermediate water has remained nearly constant through the last glacial cycle. The results address longstanding concerns that there may have been significant changes in the Nd isotopic composition of the North Atlantic end member during this interval, and substantiate the applicability of this novel tracer on millennial time-scales for palaeoceanography research.
    Description: This study was supported by the Comer Science and Education Foundation and the Vetlesen Foundation Climate Center at L-DEO.
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    Compositional variability in a cold-water scleractinian, Lophelia pertusa : new insights into “vital effects” (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q12004, doi:10.1029/2006GC001354.
    Description: We analyzed Sr/Ca and Mg/Ca ratios in the thecal wall of Lophelia pertusa, a cold-water coral, using SIMS ion microprobe techniques. The wall grows by simultaneous upward extension and outward thickening. Compositional variability displays similar trends along the upward and outward growth axes. Sr/Ca and Mg/Ca ratios oscillate systematically and inversely. The sensitivity of Lophelia Sr/Ca ratios to the annual temperature cycle (−0.18 mmol · mol−1/°C) is twice as strong as that exhibited by tropical reef corals, and four times as strong as the temperature dependence of Sr/Ca ratios of abiogenic aragonites precipitated experimentally from seawater. A comparison of the skeletal composition of Lophelia with results from precipitation calculations carried out using experimentally determined partition coefficients suggests that both temperature-dependent element partitioning and seasonal changes in the mass fraction of aragonite precipitated from the calcifying fluid influence the composition of Lophelia skeleton. Results from calculations that combine these effects reproduce both the exaggerated amplitude of the Sr/Ca and Mg/Ca oscillations and the inverse relationship between Sr/Ca and Mg/Ca ratios.
    Description: This study was supported in part by a WHOI Ocean Life Institute fellowship to ALC, by NSF grant OCE-0527350 to G.A.G. and A.L.C., and by the EU 6FP project HERMES, EC contract GOCE-CT-2005-511234 to T.L.
    Keywords: Coral ; Aragonite ; Vital effects ; Sr/Ca ; Mg/Ca ; Deep-sea
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    Hydrothermal exploration of the Fonualei Rift and Spreading Center and the Northeast Lau Spreading Center (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 7 (2006): Q11022, doi:10.1029/2006GC001324.
    Description: We report evidence for active hydrothermal venting along two back-arc spreading centers of the NE Lau Basin: the Fonualei Rift and Spreading Center (FRSC) and the Northeast Lau Spreading Center (NELSC). The ridge segments investigated here are of particular interest as the potential source of a mid-water hydrothermal plume (1500–2000 m depth) which extends more than 2000 km across the SW Pacific Ocean dispersing away from an apparent origin close to the most northeastern limits of the Lau Basin. Our results indicate the presence of at least four new hydrothermal plume sources, three along the FRSC and one on the NELSC, the latter situated within 150 km of the maximum for the previously identified SW Pacific regional-scale plume. However, TDFe and TDMn concentrations in the southernmost FRSC plume that we have identified only reach values of 19 and 13 nmol/L and dissolved 3He anomalies in the same plume are also small, both in relation to the SW Pacific plume and to local background, which shows evidence for extensive 3He enrichment throughout the entire Lau Basin water column. Our results reveal no evidence for a single major point hydrothermal source anywhere in the NE Lau Basin. Instead, we conclude that the regional-scale SW Pacific hydrothermal plume most probably results from the cumulative hydrothermal output of the entire topographically restricted Lau Basin, discharging via its NE-most corner.
    Description: This research was funded jointly by NSF's Ridge 2000 Program (OCE-0242002 and OCE-0242618), by the NOAA Vents Program, and by core strategic funding from the Natural Environment Research Council to the National Oceanography Centre, Southampton (UK).
    Keywords: Hydrothermal ; Exploration ; Lau Basin ; SW Pacific
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