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  • American Physical Society  (117,175)
  • American Geophysical Union
  • Wiley-Blackwell
  • 2015-2019  (134,347)
  • 1965-1969  (51,452)
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Year
  • 101
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    Clues to the cause of the 2011–2013 Campi Flegrei caldera unrest, Italy, from continuous GPS data (2015)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: From 2006 to spring 2013, Campi Flegrei (CF) caldera, Italy, was mostly uplifting at an increasing rate, particularly high from 2011. We show that the 2011–2013 accelerated uplift and 1980–2010 inflation and deflation phases can be explained by a two-source conceptual model similar to that proposed by Amoruso et al. (2014) (reference model). However, pressurization of the sole thin quasi-horizontal ∼4000 m deep source, responsible for large-scale 1980–2010 deformation, can explain the whole 2011–2013 deformation, while activity of the shallower Solfatara hydrothermal source, responsible for residual 1980–2010 deformation, appears constant. These results suggest a predominantly magmatic unrest in 2011–2013. Near-real-time comparison of observations and reference model predictions can provide additional information for short-term eruption forecasting at CF; a similar approach could be followed also in other volcanic environments.
    Description: Published
    Description: 3081–3088
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: The two sources of 1980–2010 CF deformation satisfy also the 2011–2013 unrest ; Pressurization of the sole ∼4000 m deep source satisfies the whole deformation ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 102
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    Experimental investigation of the aggregation-disaggregation of colliding volcanic ash particles in turbulent, low-humidity suspensions (2015)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We present the results of laboratory experiments on the aggregation and disaggregation of colliding volcanic ash particles. Ash particles of different composition and size 〈90 µm were held in turbulent suspension and filmed in high speed while colliding, aggregating, and disaggregating, forming a growing layer of electrostatically bound particles along a vertical plate. At room conditions and regardless of composition, 60–80% of the colliding particles smaller than 32 µm remained aggregated. In contrast, aggregation of particles larger than 63 µm was negligible, and, when a layer formed, periods when disaggregation (mainly by collisions or drag) exceeded aggregation occurred twice as frequently than for smaller particles. An empirical relationship linking the aggregation index, i.e., the effective fraction of aggregated particles surviving disaggregation, to the mean particle collision kinetic energy is provided. Our results have potential implications on the dynamics of volcanic plumes and ash mobility in the environment.
    Description: INGV-DPC project V1 “Probabilistic evaluation of volcanic hazard”; EU Seventh Programme FP7 “MED-SUV” grant agreement 308665
    Description: Published
    Description: 1068–1075
    Description: 3V. Dinamiche e scenari eruttivi
    Description: 2IT. Laboratori sperimentali e analitici
    Description: JCR Journal
    Description: restricted
    Keywords: volcanic ash ; disaggregation ; experimental modeling ; volcanic plumes ; aggregation processes ; colliding particles ; sticking rate ; 01. Atmosphere::01.01. Atmosphere::01.01.07. Volcanic effects ; 04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism ; 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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  • 103
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    Projected Changes in Discharge in an Agricultural Watershed in Iowa (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: Our improved capability to adapt to future changes in discharge is linked to our capability to predict the magnitude or at least the direction of these changes. For the agricultural U.S. Midwest, too much or too little water has severe socio-economic impacts. Here we focus on the Raccoon River at Van Meter, Iowa, and use a statistical approach to examine projected changes in discharge. We build on statistical models using rainfall and harvested corn and soybean acreage to explain the observed discharge variability. We then use projections of these two predictors to examine the projected discharge response. Results are based on seven global climate models part of the Coupled Model Intercomparison Project Phase 5 and two representative concentration pathways (RCPs 4.5 and 8.5). There is not a strong signal of change in the discharge projections under the RCP 4.5. However the results for the RCP 8.5 point to a stronger changing signal related to larger projected increases in rainfall, resulting in increasing trends in particular in the upper part of the discharge distribution (i.e., 60th percentile and above). Examination of two hypothetical agricultural scenarios indicates that these increasing trends could be alleviated by decreasing the extent of the agricultural production. We also discuss how the methodology presented in this study represents a viable approach to move forward with the concept of return period for engineering design and management in a non-stationary world.
    Description: Published
    Description: 1361–1371
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: restricted
    Keywords: river discharge ; rainfall ; statistical model ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 104
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    Crustal structure of the Ionian basin and eastern Sicily margin: results from a wide-angle seismic survey (2018)
    American Geophysical Union
    Details
    Publication Date: 2019-03-26
    Description: In the Ionian Sea (Central Mediterranean) the slow convergence between Africa and Eurasia results in the formation of a narrow subduction zone. The nature of the crust of the subducting plate remains debated and could represent the last remnants of the Neo-Tethys ocean. The origin of the Ionian basin is also under discussion, especially concerning the rifting mechanisms as the Malta Escarpment could represent a remnant of this opening. This subduction retreat toward the south-east (motion occurring since the last 35 Ma) but is confined to the narrow Ionian Basin. A major lateral slab tear fault is required to accommodate the slab roll-back. This fault is thought to propagate along the eastern Sicily margin but its precise location remains controversial. This study focuses on the deep crustal structure of the Eastern-Sicily margin and the Malta Escarpment. We present two two-dimensional P-wave velocity models obtained from forward modeling of wide-angle seismic data acquired onboard the R/V Meteor during the DIONYSUS cruise in 2014. The results image an oceanic crust within the Ionian basin as well as the deep structure of the Malta Escarpment, which presents characteristics of a transform margin. A deep and asymmetrical sedimentary basin is imaged south of the Messina strait and seems to have opened between the Calabrian and Peloritan continental terranes. The interpretation of the velocity models suggests that the tear fault is located east of the Malta Escarpment, along the Alfeo fault system (AFS).
    Description: The DIONYSUS cruise is funded through the Deutsche Forschungsgemeinschaft DFG.
    Description: Published
    Description: 2090-2114
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Crustal structure ; Subduction ; Crustal structure of the Ionian basin and eastern Sicily margin: results from a wide-angle seismic survey.
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 105
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    New evidence of CO2 soil degassing anomalies on Piton de la Fournaise volcano and the link with volcano tectonic structures (2016)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Piton de la Fournaise (PdF) is recognised as one of the world’s most active volcanoes in terms of eruptive frequency and the substantial quantity of lava produced. Yet, with the sole exception of rather modest intracrateric fumarole activity, this seems to be in contrast with an apparent absence of any type of natural fluid emission during periods of quiescence. Measurement campaigns were undertaken during a long-lasting quiescent period (2012-2014) and just after a short lived summit eruption (June 2014) in order to identify potential degassing areas in relation to the main structural features of the volcano (ex. rift zones) with the aim of developing a broader understanding of the geometry of the plumbing and degassing system. In order to assess the possible existence of anomalous soil CO2 flux, 513 measurements were taken along transects roughly orthogonal to the known tectonic lineaments crossing PdF edifice. In addition, 53 samples of gas for C isotope analysis were taken at measurement points that showed a relatively high CO2 concentration in the soil. CO2 flux values range from 10 to 1300 g m-2 d-1 while 13C are between -26.6 to -8‰. The results of our investigation clearly indicate that there is a strong spatial correlation between the anomalous high values of diffusive soil emissions and the main rift zones cutting the PdF massif and, moreover, that generally high soil CO2 fluxes show a d13C signature clearly related to a magmatic origin.
    Description: INSU (CNRS) and La Réunion Préfecture (Projet pour la quantification de l’aléa volcanique à La Réunion)
    Description: Published
    Description: 4388–4404
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: CO2 soil degassing anomalies at Piton de la Fournaise ; d13C magmatic signature ; Close link between anomalous CO2 degassing and the main seismotectonic structures ; 04. Solid Earth::04.02. Exploration geophysics::04.02.01. Geochemical exploration ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 106
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    Asynchronous changes of CO2, H2 and He concentrations in soil gases: a theoretical model and experimental results (2016)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: This paper focuses on the chemical composition changes in soil gases through both a theoretical model and laboratory experiments. The model describes the one-dimensional mass transfer process, which is triggered by changes in the flux parameters of the system, and the time-dependent evolution of the composition of the soil gases as a function of i) the pristine gas mixture, ii) the diffusivity of the chemicals, and iii) the thickness of the transited medium. Carbon dioxide (CO2), hydrogen (H2), and helium (He) were used in a laboratory-scale flux simulator to investigate the evolution of the gas composition profile in an artificial soil of constant thickness. The agreement between the theoretical calculations and the experimental results supports the validity of the model. Our results indicate a good reproducibility of the transient changes in the concentrations of CO2, He, and H2 in CO2-rich gas mixtures that contain He and H2 as trace gases. Finally, the theoretical results were used to analyze the H2 and CO2 continuous monitoring data collected at Etna volcano in 2010
    Description: Published
    Description: 1565–1583
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: 1IT. Reti di monitoraggio e Osservazioni
    Description: JCR Journal
    Description: open
    Keywords: Soil gases ; Volcanic gas composition ; Hydrogen ; Carbon dioxide ; CO2 ; Helium ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 107
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    Evidence of underground electric current generation during the 2009 L’Aquila earthquake: Real or instrumental? (2016)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We investigate magnetic effects in correspondence of the Mw6.1 L’Aquila earthquake. Magnetic and seismic records are analyzed. Rapid and distinct changes and an offset can be seen in magnetic field components after the main shock. We show that these effects result from electromagnetic induction due to the movement of the sensors through the Earth’s magnetic field and from a permanent displacement of the sensors from their original position caused by the passing seismic waves. A transient signal in total field data from an overhauser magnetometer apparently occurs in correspondence with the earthquake. Our analysis shows that the transient was not observed by other sensors that were operating in close proximity to the overhauser. Thus, the transient signal in the total magnetic field data, and the offset in the magnetic field components, cannot be associated with a hypothetical underground electric current generated by the earthquake, as suggested by Nenovski (2015).
    Description: Published
    Description: 6153–6161
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquake ; seismoelectric effect ; 04. Solid Earth::04.05. Geomagnetism::04.05.99. General or miscellaneous ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies ; 04. Solid Earth::04.05. Geomagnetism::04.05.08. Instruments and techniques
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  • 108
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    A strategy to explore the topography-driven distortions in the tilt field induced by a spherical pressure source. The case of Mt. Etna. (2016)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: We present a strategy to thoroughly investigate the effects of prominent topography on the surface tilt due to a spherical pressure source. We use Etna's topography as a case of study and, for different source positions, we compare the tilt fields calculated through (i) a 3-D boundary element method and (ii) analytical half-space solutions. We systematically determine (i) the source positions leading to the strongest tilt misfits when numerical and analytical results are compared and (ii) the surface areas where the strongest distortions in the tilt field are most likely to be observed. We also demonstrate that, under critical circumstances, in terms of respective positions of pressure source and observation points, results of inversion procedures aimed at retrieving the source parameters can be misleading, if tilt data are analysed using models that do not account for topography.
    Description: Published
    Description: 1471–1481
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Numerical approximations and analysis ; Transient deformation ; Volcano monitoring ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 109
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    Twenty-five years of continuous borehole tilt and vertical displacement data at Mount Etna: Insights on long-term volcanic dynamics (2016)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We report a 25 year-long data set (1990–2014) of combined continuous tilt and GPS vertical displacement series recorded at Etna volcano. To our knowledge, this is the first time that such a data set on an active volcano has been presented. We show the coherence of the two series, which help draw new insights on how the volcano, characterized by frequent flank eruptions, works in the long-term (tens of years). This data set provides evidence that after the 1992–1993 flank eruption (the biggest in the last three centuries) and the following major recharging phase (1994–2001), all the ensuing eruptions fall within a single long-term reequilibrium phase (2001–2014).
    Description: Published
    Description: 10222–10229
    Description: 1V. Storia e struttura dei sistemi vulcanici
    Description: JCR Journal
    Description: restricted
    Keywords: tilt ; gps ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 110
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    Very shallow dyke intrusion and potential slope failure imaged by ground deformation: The 28 December 2014 eruption on Mount Etna (2016)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: On 28 December 2014, eruptive activity resumed at Mount Etna with fire fountain activity feeding two lava flows on the eastern and southwestern upper flanks of the volcano. Unlike all previous summit activity, this eruption produced clear deformation at the summit of the volcano. GPS displacements and Sentinel-1A ascending interferogramswere calculated in order to image the ground deformation pattern accompanying the eruption. The displacements observed by GPS depict a local ground deformation pattern, affecting only the upperpart of the volcano.Despite snowcover onthe summit, differential interferometry synthetic aperture radar (DInSAR) data allowed obtainingmore detail onthe grounddeformation pattern on the upper eastern side of the volcano. Three-dimensional GPS displacements inversion located a very shallow NE-SW intrusion just beneath the New Southeast Crater. However, this model cannot justify all the deformation observed by DInSAR thus revealing a gravitational failure of the lava flow field
    Description: Published
    Description: 2727–2733
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Sentinel-1A interferogram details the ground deformation field ; GPS data are analyzed for modeling the dyke intrusion ; Data comparison highlights an incipient slope failure ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 111
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    High-resolution magnetics reveal the deep structure of a volcanic-arc-related basalt-hosted hydrothermal site (Palinuro, Tyrrhenian Sea) (2016)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: High-resolution magnetic surveys have been acquired over the partially sedimented Palinuro massive sulfide deposits in the Aeolian volcanic arc, Tyrrhenian Sea. Surveys flown close to the seafloor using an autonomous underwater vehicle (AUV) show that the volcanic-arc-related basalt-hosted hydrothermal site is associated with zones of lower magnetization. This observation reflects the alteration of basalt affected by hydrothermal circulation and/or the progressive accumulation of a nonmagnetic deposit made of hydrothermal and volcaniclastic material and/or a thermal demagnetization of titanomagnetite due to the upwelling of hot fluids. To discriminate among these inferences, estimate the shape of the nonmagnetic deposit and the characteristics of the underlying altered area—the stockwork—we use high-resolution vector magnetic data acquired by the AUV Abyss (GEOMAR) above a crater-shaped depression hosting a weakly active hydrothermal site. Our study unveils a relatively small nonmagnetic deposit accumulated at the bottom of the depression and locked between the surrounding volcanic cones. Thermal demagnetization is unlikely but the stockwork extends beyond the limits of the nonmagnetic deposit, forming lobe-shaped zones believed to be a consequence of older volcanic episodes having contributed in generating the cones.
    Description: Published
    Description: 1950–1961
    Description: 4V. Vulcani e ambiente
    Description: 3A. Ambiente Marino
    Description: 7A. Geofisica di esplorazione
    Description: JCR Journal
    Description: restricted
    Keywords: Hydrothermal alteration ; magnetica anomalies ; Palinuro Seamounts ; Tyrrhenian Sea ; 04. Solid Earth::04.04. Geology::04.04.04. Marine geology ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies
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  • 112
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    New insights on the provenance of obsidian fragments of Ustica Island (Palermo, Sicily). (2017)
    Wiley-Blackwell
    Details
    Publication Date: 2017-12-11
    Description: In this study we applied a multidisciplinary approach, coupling geophysical and geochemical measurements, to unveil the provenance of 170 obsidian flakes, collected on the volcanic island of Ustica (Sicily). On this island there are some prehistoric settlements dated from the Neolithic to the Middle Bronze Age. Despite not having geological outcrops of obsidian rocks, the countryside of Ustica is rich in fragments of this volcanic glass, imported from other source areas. The study of obsidian findings was carried out first through visual observations and density measurements. At least two different obsidian families have been distinguished, probably imported from Lipari and Pantelleria islands. Analysing the magnetic properties of the samples, these two main sources were confirmed, but the possibility of other provenances was inferred. Finally, we characterized the geochemical signature of the Ustica obsidians by performing microchemical analyses through electron microprobe (EMPA) and laser ablation (LA–ICP–MS). The results were compared with literature data, confirming the presence of the Lipari and Pantelleria sources (Sicily) and indicating for the first time in this part of Italy a third provenance from Palmarola island (Latium). Our results shed new light on the commercial exchanges in the peri-Tyrrhenian area during the prehistoric age.
    Description: Published
    Description: 435–454
    Description: 1SR. TERREMOTI - Servizi e ricerca per la Società
    Description: 2SR. VULCANI - Servizi e ricerca per la Società
    Description: 3SR. AMBIENTE - Servizi e ricerca per la Società
    Description: JCR Journal
    Description: restricted
    Keywords: obsdian provenance ; LA-ICPMS ; 05. General::05.04. Instrumentation and techniques of general interest::05.04.99. General or miscellaneous
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  • 113
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    Experimental detection of upward going cosmic particles and consequences for correction of density radiography of volcanoes (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-02-16
    Description: Muon tomography measures the flux of cosmic muons crossing geological bodies to determine their density. The telescopes used to perform measurements are exposed to noise fluxes with high intensities relative to the tiny flux of interest. We give experimental evidences of a so far never described source of noise caused by a flux of upward going particles. Data acquired on La Soufrière of Guadeloupe and Mount Etna reveal that upward going particles are detected only when the rear side of the telescope is exposed to a wide volume of atmosphere located below the altitude of the telescope and with a rock obstruction less than several tens of meters. Biases produced on density muon radiographies by upward going fluxes are quantified, and correction procedures are applied to radiographies of La Soufrière.
    Description: Published
    Description: 6334–6339
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
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  • 114
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    Local pattern of stress field and seismogenic sources in the Pergola-Melandro basin and the Agri valley (Southern Italy) (2018)
    Wiley-Blackwell
    Details
    Publication Date: 2018-03-20
    Description: Our study area is a ~50 km long section of the central-southern Apennines tectonic belt that includes the Pergola-Melandro basin and the Agri valley. This region is located between the areas interested by the 1980 Ms=6.9 Irpinia and the 1857 M=7.0 Val d’Agri earthquakes and is characterized by rare historical events and very low and sparse background seismicity. In this study we provide new seismological and geophysical information to identify the characteristics of the seismotectonics in the area, as the prevailing faulting mechanism and the fit of local to regional stress field. These data concern focal mechanisms from waveform modeling and P-wave polarities, analyses of borehole breakouts and detailed investigation of two seismic sequences. All the data cover a significantly broad range of magnitudes and depths and suggest that no important local variation in stress orientation seems to affect this area, which shows a NE-SW direction of extension consistent with that regionally observed in Southern Italy. Such local homogeneity in the stress field pattern is peculiar of the study area; the variations of orientation and/or type of stress observed in the northern Apennines or only less than 100 km toward the northwest within the same tectonic belt are absent here. Furthermore, there is a suggestion for a northeastward sense of dip of the seismogenic faults in the region, an interesting constraint to the characterization of seismic sources
    Description: Published
    Description: 575-583
    Description: 2T. Sorgente Sismica
    Description: JCR Journal
    Keywords: faulting ; seismicity ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress
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  • 115
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    Micromagnetic understanding of the skyrmion Hall angle current dependence in perpendicular magnetized ferromagnets (2019)
    American Physical Society
    Details
    Publication Date: 2019-03-28
    Description: The understanding of the dynamical properties of skyrmion is a fundamental aspect for the realization of a competitive skyrmion based technology beyond CMOS. Most of the theoretical approaches are based on the approximation of a rigid skyrmion. However, thermal fluctuations can drive a continuous change of the skyrmion size via the excitation of thermal modes. Here, by taking advantage of the Hilbert-Huang transform, we demonstrate that at least two thermal modes can be excited which are non-stationary in time. In addition, one limit of the rigid skyrmion approximation is that this hypothesis does not allow for correctly describing the recent experimental evidence of skyrmion Hall angle dependence on the amplitude of the driving force, which is proportional to the injected current. In this work, we show that, in an ideal sample, the combined effect of field-like and damping-like torques on a breathing skyrmion can indeed give rise to such a current dependent skyrmion Hall angle. While here we design and control the breathing mode of the skyrmion, our results can be linked to the experiments by considering that the thermal fluctuations and/or disorder can excite the breathing mode. We also propose an experiment to validate our findings.
    Description: Published
    Description: 224418
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: 2IT. Laboratori analitici e sperimentali
    Description: JCR Journal
    Keywords: Physics - Mesoscopic Systems and Quantum Hall Effect ; Physics - Mesoscopic Systems and Quantum Hall Effect
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  • 116
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    Pore Pressure Pulse Drove the 2012 Emilia (Italy) Series of Earthquakes (2019)
    American Geophysical Union
    Details
    Publication Date: 2019-03-29
    Description: Pore Pressure Pulse Drove the 2012 Emilia (Italy)Series of EarthquakesGiuseppe Pezzo1, Pasquale De Gori1, Francesco Pio Lucente1, and Claudio Chiarabba11Istituto Nazionale di Geofisica e Vulcanologia, Rome, ItalyAbstractThe 2012 Emilia earthquakes sequence is thefirst debated case in Italy of destructive eventpossibly induced by anthropic activity. During this sequence, two main earthquakes occurred separated by9 days on contiguous thrust faults. Scientific commissions engaged by the Italian government reportedcomplementary scenarios on the potential trigger mechanism ascribable to exploitation of a nearby oilfield.In this study, we combine a refined geodetic source model constrained by precise aftershock locationsand an improved tomographic model of the area to define the geometrical relation between the activatedfaults and investigate possible triggering mechanisms. An aftershock decay rate that deviates from theclassical Omori-like pattern andVp/Vschanges along the fault system suggests that natural pore pressurepulse drove the space-time evolution of seismicity and the activation of the second main shock
    Description: Published
    Description: 682-690
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
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  • 117
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    Relation Between Near-Fault Ground Motion Impulsive Signals and Source Parameters (2019)
    American Geophysical Union
    Details
    Publication Date: 2019-03-29
    Description: Near-fault ground motion records often present impulsive signals, characterized by a largeamplitude in the velocity wavefield and by the energy concentrated in a short time window as comparedto the total earthquake duration. Thispulse-likebehavior is ascribed to the directivity of the seismic rupture,and it requires a stronger demand to the buildings not predicted by the classical design spectra. In this workwe investigate the pulse occurrence and duration in near-fault synthetic seismograms generated from anensemble ofk 2source models. We exploited the fault geometry of theMw= 6.3, 2009 L’Aquila earthquake,which represents a typical example of normal-fault earthquake for which several records in the fault vicinityare available for comparison with synthetics. We show that impulsive records are sensitive to the rupturevelocity, to the hypocenter depth, and to the station location, whether it is on the hanging wall or on thefootwall. The pulse duration was also shown to be proportional to the risetime, and it scales with thesource-receiver distance and inversely with the rupture velocity. We model these results as an effectof the coupled along-strike and updip directivity
    Description: Published
    Description: 7707-7721
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Evolution of Conduit Geometry and Eruptive Parameters During Effusive Events (2018)
    American Geophysical Union
    Details
    Publication Date: 2019-11-22
    Description: The dynamics of effusive events is controlled by the interplay between conduit geometry and source conditions. Dyke‐like geometries have been traditionally assumed for describing conduits during effusive eruptions, but their depth‐dependent and temporal modifications are largely unknown. We present a novel model which describes the evolution of conduit geometry during effusive eruptions by using a quasi steady state approach based on a 1‐D conduit model and appropriate criteria for describing fluid shear stress and elastic deformation. This approach provides time‐dependent trends for effusion rate, conduit geometry, exit velocity, and gas flow. Fluid shear stress leads to upward widening conduits, whereas elastic deformation becomes relevant only during final phases of effusive eruptions. Simulations can reproduce different trends of effusion rate, showing the effect of magma source conditions and country rock properties on the eruptive dynamics. This model can be potentially applied for data inversion in order to study specific case studies.
    Description: Published
    Description: 7471-7480
    Description: 5V. Processi eruttivi e post-eruttivi
    Description: JCR Journal
    Keywords: Magma ascent ; Effusive eruption ; Conduit geometry ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 119
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    Low-temperature catalytic CO2 hydrogenation with geological quantities of ruthenium: a possible abiotic CH4 source in chromitite-rich serpentinized rocks. (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2020-02-24
    Description: Metal-catalysed CO2 hydrogenation is considered a source of methane in serpentinized (hydrated) igneous rocks and a fundamental abiotic process germane to the origin of life. Iron, nickel, chromium and cobalt are the catalysts typically employed in hydrothermal simulation experiments to obtain methane at temperatures 〉200°C. However, land-based present-day serpentinization and abiotic gas apparently develop below 100°C, down to approximately 40–50°C. Here, we document considerable methane production in thirteen CO2 hydrogenation experiments performed in a closed dry system, from 20 to 90°C and atmospheric pressure, over 0.9–122 days, using concentrations of non-pretreated ruthenium equivalent to those occurring in chromitites in ophiolites or igneous complexes (from 0.4 to 76 mg of Ru, equivalent to the amount occurring approximately in 0.4–760 kg of chromitite). Methane production increased with time and temperature, reaching approximately 87 mg CH4 per gram of Ru after 30 days (2.9 mgCH4/gru/day) at 90°C. At room temperature, CH4 production rate was approximately three orders of magnitude lower (0.003 mgCH4/gru/day). We report the first stable carbon and hydrogen isotope ratios of abiotic CH4 generated below 100°C. Using initial d13CCO2 of -40&, we obtained room temperature d13CCH4 values as 13C depleted as 142&. With time and temperature, the C-isotope separation between CO2 and CH4 decreased significantly and the final d13CCH4 values approached that of initial d13CCO2. The presence of minor amounts of C2-C6 hydrocarbons is consistent with observations in natural settings. Comparative experiments at the same temperatures with iron and nichel catalysts did not generate CH4. Ru-enriched chromitites could potentially generate methane at low temperatures on Earth and on other planets.
    Description: Published
    Description: 438–452
    Description: 7A. Geofisica di esplorazione
    Description: JCR Journal
    Description: restricted
    Keywords: abiotic methane, Sabatier reaction ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
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  • 120
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    Considering uncertainties in the determination of earthquake source parameters from seismic spectra. (2016)
    Wiley-Blackwell
    Details
    Publication Date: 2020-02-05
    Description: In this paper, we present a method for handling uncertainties in the determination of the source parameters of earthquakes from spectral data. We propose a robust framework for estimating earthquake source parameters and relative uncertainties, which are propagated down to the estimation of basic seismic parameters of interest such as the seismic moment, the moment magnitude, the source size and the static stress drop. In practice, we put together a Bayesian approach for model parameter estimation and a weighted statistical mixing of multiple solutions obtained from a network of instruments, providing a useful framework for extracting meaningful data from intrinsically uncertain data sets. The Bayesian approach used to estimate the source spectra parameters is a simple but powerful mechanism for non-linear model fitting, providing also the opportunity to naturally propagate uncertainties and to assess the quality and uniqueness of the solution. Another important added value of such an approach is the possibility of integrating information from the expertise of seismologists. Such data can be encoded in a prior state of information that is then updated with the information provided by seismological data. The performance of the proposed approach is demonstrated analysing data from the 1909 April 23 earthquake occurred near Benavente (Portugal).
    Description: Published
    Description: 691-701
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: open
    Keywords: Fourier analysis ; Probability distributions ; Earthquake source observations ; Seismicity and tectonics ; 04. Solid Earth::04.02. Exploration geophysics::04.02.06. Seismic methods
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    Hydrothermal fluid venting in the offshore sector of Campi Flegrei caldera: A geochemical, geophysical and volcanological study (2016)
    American Geophysical Union
    Details
    Publication Date: 2020-06-03
    Description: The ongoing unrest at the Campi Flegrei caldera (CFc) in southern Italy is prompting exploration of its poorly studied offshore sector. We report on a multidisciplinary investigation of the Secca delle Fumose (SdF), a submarine relief known since antiquity as the largest degassing structure of the offshore sector of CFc. We combined high-resolution morphobathymetric and seismostratigraphic data with onshore geological information to propose that the present-day SdF morphology and structure developed during the initial stages of the last CFc eruption at Monte Nuovo in AD 1538. We suggest that the SdF relief stands on the eastern uplifted border of a N-S-trending graben-like structure formed during the shallow emplacement of the Monte Nuovo feeding dike. We also infer that the high-angle bordering faults that generated the SdF relief now preferentially allow the ascent of hot brines (with an equilibrium temperature of 1798C), thereby sustaining hydrothermal degassing on the seafloor. Systematic vertical seawater profiling shows that hydrothermal seafloor venting generates a sizeable CO2, pH, and temperature anomaly in the overlying seawater column. Data for the seawater vertical profile can be used to estimate the CO2 and energy (heat) outputs from the SdF area at 50 tons/d ( 0.53 kg/s) and 80 MW, respectively. In view of the cause-effect relationship with the Monte Nuovo eruption, and the substantial gas and energy outputs, we consider that the SdF hydrothermal system needs to be included in monitoring programs of the ongoing CFc unrest.
    Description: Published
    Description: 4153–4178
    Description: 1V. Storia e struttura dei sistemi vulcanici
    Description: JCR Journal
    Description: restricted
    Keywords: Hydrothermal fluid ; Campi Flegrei caldera ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
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    How increasing CO2 leads to an increased negative greenhouse effect in Antarctica (2015)
    American Geophysical Union
    In:  EPIC3Geophys. Res. Lett, American Geophysical Union, 42(10), pp. 422-428
    Details
    Publication Date: 2018-06-19
    Description: CO2 is the strongest anthropogenic forcing agent for climate change since pre-industrial times. Like other greenhouse gases, CO2 absorbs terrestrial surface radiation and causes emission from the atmosphere to space. As the surface is generally warmer than the atmosphere, the total long-wave emission to space is commonly less than the surface emission. However, this does not hold true for the high elevated areas of central Antarctica. For this region, the emission to space is higher than the surface emission; and the greenhouse effect of CO2 is around zero or even negative, which has not been discussed so far. We investigated this in detail and show that for central Antarctica an increase in CO2 concentration leads to an increased long-wave energy loss to space, which cools the Earth-atmosphere system. These findings for central Antarctica are in contrast to the general warming effect of increasing CO2.
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  • 123
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    Submarine permafrost depth from ambient seismic noise (2015)
    American Geophysical Union
    In:  EPIC3Geophysical research Letters, American Geophysical Union, 42(18), pp. 7581-7588
    Details
    Publication Date: 2016-01-08
    Description: Permafrost inundated since the last glacial maximum is degrading, potentially releasing trapped or stabilized greenhouse gases, but few observations of the depth of ice-bonded permafrost (IBP) below the seafloor exist for most of the arctic continental shelf. We use spectral ratios of the ambient vibration seismic wavefield, together with estimated shear wave velocity from the dispersion curves of surface waves, for estimating the thickness of the sediment overlying the IBP. Peaks in spectral ratios modeled for three-layered 1-D systems correspond with varying thickness of the unfrozen sediment. Seismic receivers were deployed on the seabed around Muostakh Island in the central Laptev Sea, Siberia. We derive depths of the IBP between 3.7 and 20.7 m ± 15%, increasing with distance from the shoreline. Correspondence between expected permafrost distribution, modeled response, and observational data suggests that the method is promising for the determination of the thickness of unfrozen sediment.
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    Coastal Hazard Vulnerability Assessment: A Case Study of Erosion and Flooding on Herschel Island, Yukon Territory, Canada (2015)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, San Francisco, California, USA, 2015-12-14-2015-12-18San Francisco, CA, American Geophysical Union
    Details
    Publication Date: 2016-01-26
    Description: Coastal infrastructure, cultural, and archeological sites are increasingly vulnerable to erosion and flooding along permafrost coasts. Amplified warming of the Arctic, sea level rise, lengthening of the open water period, and a predicted increase in frequency of major storms compound these threats. Mitigation necessitates decision-making tools at an appropriate scale. We present a study of coastal erosion combining it with a flooding risk assessment for the culturally important historic settlement on Herschel Island, a UNESCO World Heritage candidate site. The resulting map may help local stakeholders devise management strategies to cope with rapidly changing environmental conditions. We analyzed shoreline movement using the Digital Shoreline Analysis System (DSAS) after digitizing shorelines from 1952, 1970, and 2011. Using these data, forecasts of shoreline positions were made for 20 and 50 years into the future. Flooding risk was assessed using a cost-distance map based on a high-resolution Light Detection and Ranging (LiDAR) dataset and current Intergovernmental Panel on Climate Change sea level estimates. Widespread erosion characterizes the study area. The rate of shoreline movement for different periods of the study ranges from -5.5 to 2.7 m·a-1 (mean -0.6 m·a-1). Mean coastal retreat decreased from -0.6 m·a-1 to -0.5 m·a-1, for 1952-1970 and 1970-2000, respectively, and increased to -1.3 m·a-1 in the period 2000-2011. Ice-rich coastal sections, and coastal sections most exposed to wave attack exhibited the highest rates of coastal retreat. The geohazard map resulting from shoreline projections and flood risk analysis indicates that most of the area occupied by the historic settlement is at extreme or very high risk of flooding, and some buildings are vulnerable to coastal erosion. The results of this study indicate a greater threat by coastal flooding than erosion. Our assessment may be applied in other locations where limited data are available.
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    Seasonal evolution of an ice-shelf influenced fast-ice regime, derived from an autonomous thermistor chain (2015)
    American Geophysical Union
    In:  EPIC3Journal of Geophysical Research: Oceans, American Geophysical Union, 120, pp. 1703-1724
    Details
    Publication Date: 2019-12-03
    Description: Ice shelves strongly interact with coastal Antarctic sea ice and the associated ecosystem by creating conditions favorable to the formation of a sub-ice platelet layer. The close investigation of this phenomenon and its seasonal evolution remains a challenge due to logistical constraints and a lack of suitable methodology. In this study, we characterize the seasonal cycle of Antarctic fast ice adjacent to the Ekstr€om Ice Shelf in the eastern Weddell Sea. We used a thermistor chain with the additional ability to record the temperature response induced by cyclic heating of resistors embedded in the chain. Vertical sea-ice temperature and heating profiles obtained daily between November 2012 and February 2014 were analyzed to determine sea-ice and snow evolution, and to calculate the basal energy budget. The residual heat flux translated into an ice-volume fraction in the platelet layer of 0.18+-0.09, which we reproduced by a independent model simulation and agrees with earlier results. Manual drillings revealed an average annual platelet-layer thickness increase of at least 4 m, and an annual maximum thickness of 10 m beneath second-year sea ice. The oceanic contribution dominated the total sea-ice production during the study, effectively accounting for up to 70% of second-year sea-ice growth. In summer, an oceanic heat flux of 21 Wm-2 led to a partial thinning of the platelet layer. Our results further show that the active heating method, in contrast to the acoustic sounding approach, is well suited to derive the fast-ice mass balance in regions influenced by ocean/ice-shelf interaction, as it allows subdiurnal monitoring of the platelet-layer thickness.
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  • 126
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    Thermodynamic sea ice growth in the central Weddell Sea, observed in upward-looking sonar data (2015)
    American Geophysical Union
    In:  EPIC3Journal of Geophysical Research: Oceans, American Geophysical Union, 120(3), pp. 2270-2286, ISSN: 21699275
    Details
    Publication Date: 2018-01-01
    Description: Upward-looking sonar (ULS) data were used to analyze thermodynamic sea ice growth. The study was carried out for an ocean region in the central Weddell Sea, for which data of sea ice thickness variability and of the oceanic heat flux through the ice are rare. In the study area the contribution of sea ice deformation to vertical ice growth is relatively small in some years. This provides the opportunity to simulate thermodynamic sea ice growth considering the influence of a snow cover and of the oceanic heat flux. To this end, a modified version of Stefan’s law was used. The resulting ice thickness variations were then compared with the ULS measurements. For the investigated cases, the best consistency between data and model results was obtained assuming a snow layer of less than 5 cm thickness and average oceanic heat fluxes between 6 and 14 W m^-2. It is demonstrated that in conjunction with ice drift data and analytical models for thermal sea ice growth, ULS ice thickness measurements are useful for studying the seasonal cycle of growth and decay and for inferring the magnitude of the average oceanic heat flux under sea ice.
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  • 127
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    Rates of coastal destruction in areas of tabular ground ice occurrence in the western Russian Arctic (2018)
    American Geophysical Union
    In:  EPIC3American Geophysical Union Fall Meeting, Washington D.C., USA, 2018-12-10-2018-12-14Washington D.C., American Geophysical Union
    Details
    Publication Date: 2018-12-23
    Description: Tabular ground ice bodies are widely spread on Eurasian and North American Arctic plains. Exposed tabular ground ice in coastal bluffs favors the activation of thermal abrasion and thermal denudation, which in turn causes increasing coastal destruction rates. Thermo-denudation under conditions of ground ice exposures includes thawing of ice and frozen sediments along retreating headwalls of retrogressive thaw slumps and their constant enlargement. Thermo-cirques and thermo-terraces are two basic landform types that either feature channelized or broad open outlets, depending on the initial ice body outcrop by the denudation processes inland or in the retreating coastal bluffs. We study key-sites on Kolguev Island (Barents Sea) and on Yugorsky Peninsula (Kara Sea), continuing and extending earlier research efforts on coastal dynamics in the region. New data on thermo-denudation and thermo-abrasion rates for these key-sites have been obtained using a set of multi-temporal satellite images of high and very-high spatial resolution covering the period from 2002 to 2016. For orthorectification purposes of imagery collected prior to TanDEM-X acquisitions, we used an edited version of the 12 m TanDEM-X DEM. Along erosive coastline segments the former relief situation was reconstructed through extrapolation of coastal bluff edge elevation values and restoration of the coastal plain relief towards the sea. On the western coast of Kolguev Island, average coastal bluff retreat rates between 2002 and 2012 varied from 1.7 to 2.4 m/year, while averaged rates of thermo-cirques headwalls retreat were 2.6 m/year. Maximum rates at some sections increased up to 14.5-15.1 m/year in the recent past. High rates of thermo-denudation increase were not only observed on western Kolguev Island, but also on the Yugorsky Peninsula, were rates raised up to 13 m/year in recent years. Activation of thermo-denudation is also noted in other parts of Kara Sea coasts and were generally correlated with changing environmental factors, particularly expressed in an increase on the thaw index during recent years.
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    High-resolution sub-bottom seismic and sediment core records from the Chukchi Abyssal Plain reveal Quaternary glaciation impacts on the western Arctic Ocean (2017)
    American Geophysical Union
    In:  EPIC3American Geophysical Union, Fall Meeting 2017, Poster PP51B-1061, New Orleans, 2017-12-15-2017-12-15New Orleans, USA, American Geophysical Union
    Details
    Publication Date: 2019-05-12
    Description: For regional context of the Quaternary history of Arctic marine glaciations, such as glacial events in northern North America and on the Siberian and Chukchi margins, we used CHIRP sub-bottom profiles (SBP) along with sediment cores, including a 14-m long piston core ARA06-04JPC taken from the Chukchi abyssal plain during the RV Araon expedition in 2015. Based on core correlation with earlier developed Arctic Ocean stratigraphies using distribution of various sedimentary proxies, core 04JPC is estimated to extend to at least Marine Isotope Stage 13 (〉0.5 Ma). The stratigraphy developed for SBP lines from the Chukchi abyssal plain to surrounding slopes can be divided into four major seismostratigraphic units (SSU 1-4). SBP records from the abyssal plain show well preserved stratification, whereas on the surrounding slopes this pattern is disrupted by lens-shaped, acoustically transparent sedimentary bodies interpreted as glaciogenic debris flow deposits. Based on the integration of sediment physical property and SBP data, we conclude that these debris flows were generated during several ice-sheet grounding events on the Chukchi and East Siberian margins, including adjacent ridges and plateaus, during the middle to late Quaternary.
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    The impact of Southern Ocean circulation on the global carbon cycle and Antarctic ice shelf stability (2018)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2018, Washington DC, 2018-12-10-2018-12-14Washington DC, American Geophysical Union
    Details
    Publication Date: 2019-01-06
    Repository Name: EPIC Alfred Wegener Institut
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  • 130
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    P-wave velocity models of continental shelf of East Siberian Sea using the Laplace-domain full waveform inversion (2017)
    American Geophysical Union
    In:  EPIC3AGU, Fall Meeting 2017, Poster T13B-0522, New Orleans, 2017-12-11-2017-12-11New Orleans, USA, American Geophysical Union
    Details
    Publication Date: 2019-05-12
    Description: 2016 IBRV ARAON Arctic Cruise Leg-2, Expedition ARA07C was a multidisciplinary undertaking carried out in the East Siberian Sea (ESS) from August 25 to September 10, 2016. The program was conducted as a collaboration between the Korea Polar Research Institute (KOPRI), P.P. Shirshov Institute of Oceanology (IORAS), and Alfred Wegener Institute (AWI). During this expedition, the multi-channel seismic (MCS) data were acquired on the continental shelf and the upper slope of the ESS, totaling 3 lines with 660 line-kilometers. The continental shelf of ESS is one of the widest shelf seas in the world and it is believed to cover the largest area of sub-sea permafrost in the Arctic. According to the present knowledge of the glacial history of the western Arctic Ocean, it is likely that during the LGM with a sea level approximately 120 m below present, the entire shelf area of the ESS was exposed to very cold air temperatures so that thick permafrost should have formed. Indeed, in water depths shallower than 80 m, sub-bottom profiles in the ESS recorded from the shelf edge to a latitude of 74°30' N in 60 m water depth exhibited acoustic facies, suggesting that at least relicts of submarine permafrost are present. In order to identify the existence and/or non-existence of subsea permafrost in our study area, we analyze the MCS data using the Laplace domain full waveform inversion (FWI). In case of the Canadian continental shelf of the Beaufort Sea, subsea permafrost has high seismic velocity values (over 2.6 km/sec) and strong refraction events were found in the MCS shotgathers. However, in the EES our proposed P-wave velocity models derived from FWI have neither found high velocity structures (over 2.6 km/sec) nor indicate strong refraction events by subsea permafrost. Instead, in 300 m depth below sea floor higher P-wave velocity structures (1.8 2.2 km/s) than normal subsea sediment layers were found, which are interpreted as cemented strata by glaciation activities.
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  • 131
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    Methane oxidation following submarine permafrost degradation: Measurements from a central Laptev Sea shelf borehole (2015)
    American Geophysical Union
    In:  EPIC3Journal of Geophysical Research: Biogeosciences, American Geophysical Union, 120(5), pp. 965-978
    Details
    Publication Date: 2015-06-26
    Description: Submarine permafrost degradation has been invoked as a cause for recent observations of methane emissions from the seabed to the water column and atmosphere of the East Siberian shelf. Sediment drilled 52 m down from the sea ice in Buor Khaya Bay, central Laptev Sea revealed unfrozen sediment overlying ice-bonded permafrost. Methane concentrations in the overlying unfrozen sediment were low (mean 20 µM) but higher in the underlying ice-bonded submarine permafrost (mean 380 µM). In contrast, sulfate concentrations were substantially higher in the unfrozen sediment (mean 2.5 mM) than in the underlying submarine permafrost (mean 0.1 mM). Using deduced permafrost degradation rates, we calculate potential mean methane efflux from degrading permafrost of 120 mg m−2 yr−1 at this site. However, a drop of methane concentrations from 190 µM to 19 µM and a concomitant increase of methane δ13C from −63‰ to −35‰ directly above the ice-bonded permafrost suggest that methane is effectively oxidized within the overlying unfrozen sediment before it reaches the water column. High rates of methane ebullition into the water column observed elsewhere are thus unlikely to have ice-bonded permafrost as their source.
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    When and where is thaw slump mass wasting energy limited? A landscape-scale assessment using TanDEM-X single-pass radar interferometry (2017)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, Ernest N. Morial Convention Center, 2017-12-11-2017-12-15New Orleans, Lousinana, USA, American Geophysical Union
    Details
    Publication Date: 2018-04-05
    Description: Thermokarst is expected to drive major changes in ice-rich permafrost regions, but its current and future extent and rates of change remain only partially understood; in part due to limited broad-scale observations. Here we show that time-lapse digital elevation models from single-pass interferometry can provide important synoptic observations of thermokarst-induced terrain changes and novel insight into the drivers and controls of thermokarst. We focus on retrogressive thaw slumps, an important and dynamic form of thermokarst. On sub-seasonal time scales, sparse measurements indicate that mass wasting at active slumps is often limited by the energy available for melting ground ice, but other factors such as rainfall or the formation of an insulating veneer are also thought important. To study the sub-seasonal drivers, we use TanDEM-X observations (12 m resolution) acquired during the Science Phase in summer 2015 over two study regions. The high vertical precision (30 cm), frequent observations (11 days) and large coverage (5000 km2) allow us to track volume losses as drivers (e.g. available energy) vary through time. We find that thaw slumps in the Tuktoyaktuk coastlands, Canada, are not energy limited in June, as they undergo limited mass wasting (height loss of around 0 cm/day) despite the ample available energy, indicating the widespread presence of an insulating snow or debris veneer. Later in summer, height losses generally increase (around 3 cm/day), but they do so in distinct ways. For many slumps, mass wasting tracks the available energy, a temporal pattern that is also observed at coastal yedoma cliffs on the Bykovsky Peninsula, Russia. However, the other two common temporal trajectories are asynchronous with the available energy, as they track strong precipitation events or show a sudden speed-up in late August, respectively. The contrasting temporal behaviour of nearby thaw slumps highlights the importance of complex local and temporally varying controls on mass wasting. This complexity reinforces the need for circum-arctic monitoring efforts, for which remote sensing approaches such as single-pass interferometry are indispensable.
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    Biological and physical controls on N2, O2, and CO2 distributions in contrasting Southern Ocean surface waters (2015)
    American Geophysical Union
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union, 29(7), pp. 994-1013, ISSN: 08866236
    Details
    Publication Date: 2015-08-17
    Repository Name: EPIC Alfred Wegener Institut
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    The Manihiki Plateau—A multistage volcanic emplacement history (2015)
    American Geophysical Union
    In:  EPIC3Geochemistry, Geophysics, Geosystems, American Geophysical Union, 16, pp. 2480-2498
    Details
    Publication Date: 2015-09-17
    Description: The formation history of the Manihiki Plateau, a Large Igneous Province, is poorly understood. New high resolution seismic reflection data across the High Plateau, the largest edifice of the Manihiki Plateau, provides evidence for multistage magmatic emplacement. Improved data quality allows for an identification of an earlier volcanic phase, the initial formation phase (〉125 Ma), in addition to the previously known volcanic formation phases: the expansion phase (125-116) formerly called main-phase and the secondary volcanic phase (100-65 Ma). This enhances the understanding of the emplacement scenario. An intrabasement reflection band IB1 reveals the end of initial volcanic formation and forms the nucleus of the High Plateau. This feature provides indications that it continued beyond the Manihiki Scarp and thus supports the hypothesis of an extension of the Manihiki Plateau to the East during the initial formation and expansion phases. The expansion phase is characterized by massive volcanic outpourings leveling and extending the basement throughout the High Plateau and the neighboring Western Plateaus, which in contrast shows massive tectonic alteration. Extrusion centers formed within the secondary volcanic phase (ending ∼65 Ma) are mainly concentrated along the margins of the High Plateau, suggesting the magmatic sources shifted from those being related to the initial emplacement and expansion phases of the High Plateau to induced volcanism at the tectonically altered margins. This article is protected by copyright. All rights reserved
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    Landforms indicative of former glaciations and permafrost along continental margin of the Chukchi and East Siberian seas (2015)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, San Francisco, 2015-12-14-2015-12-18American Geophysical Union
    Details
    Publication Date: 2016-02-02
    Description: In the western Arctic Ocean glacial landforms are interpreted as a complex pattern of Pleistocene glaciations along the continental margin of the East Siberian Sea and the Chukchi borderland. These landforms include moraines, drumlinized features, glacigenic debris flows, till wedges, mega-scale glacial lineations (MSGL), and iceberg plough marks. Orientations of some of the landforms suggest the presence of former ice sheets on the Chukchi Borderland and the East Siberian shelf. In seismic and sub-bottom profiles as well as sediment cores, there is evidence that glaciations have occurred repeatedly. Typically, several generations of glacial wedges intercalate with well-stratified (interglacial) sediments in ice-distal locations. MSGL of former ice grounding in present water depths of more than 1200 m suggests that some ice sheets developed significant thickness and size. The extent of glacial features and deposits into the Arctic Ocean decreased with time. We interpret this as indication that ice sheets in the western Arctic Ocean were thicker and larger during earlier times of the Pleistocene and became restricted to the Chukchi Borderland during the most recent glaciation (Last Glacial Maximum, LGM). Finally, icebergs intensively ploughed the sediments along the Chukchi and East Siberian margin in a range from 350m to 80m present water depth. In water depth shallower than 80m, sub-bottom profiles in the East Siberian Sea exhibit acoustic facies more typical for submarine permafrost. Discontinuous (permafrost) reflectors mask sub-bottom strata beneath an unfrozen 10m thick top sediment layer. In places, unfrozen sediment-filled depressions (taliks) are visible to about 20m below the seafloor, which may be related to former thermokarst and/or channels. We suggest that only during the LGM permafrost formed in the exposed area of the entire East Siberian Sea, whereas some areas have been largely covered by ice sheets during previous glacial periods.
    Repository Name: EPIC Alfred Wegener Institut
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    Modeling Permafrost Sensitivity in Arctic Forest (2019)
    American Geophysical Union
    In:  EPIC3AGU Fall meeting 2019, San Francisco, CA, 2019-12-09-2019-12-13USA, American Geophysical Union
    Details
    Publication Date: 2021-08-16
    Description: Deciduous larch is a weak competitor when growing in mixed stands with evergreen taxa but is dominant in many boreal forest areas of Eastern Siberia. However, it is hypothesized that certain factors such as a shallow active layer thickness and high fire frequency favor larch dominance. Our aim is to understand how thermohydrological interactions between vegetation, permafrost, and atmosphere stabilize the larch forests and the underlying permafrost in Eastern Siberia. A tailored version of a one-dimensional land surface model (CryoGrid) is adapted for the application in vegetated areas and used to reproduce the energy transfer and thermal regime of permafrost ground in typical boreal larch stands. In order to simulate the responds of Arctic trees to local climate and permafrost conditions we have implemented a multilayer canopy parameterization originally developed for the Community Land Model (CLM-ml_v0). The coupled model is capable of calculating the full energy balance above, within and below the canopy including the radiation budget, the turbulent fluxes and the heat budget of the permafrost ground under several forcing scenarios. We will present first results of simulations performed for different study sites in larch-dominated forests of Eastern Siberia and Mongolia under current and future climate conditions. Model performance is thoroughly evaluated based on comprehensive in-situ soil temperature and radiation measurements at our study sites.
    Repository Name: EPIC Alfred Wegener Institut
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    Noble Gases in Deepwater Oils of the U.S. Gulf of Mexico (2019)
    American Geophysical Union
    Details
    Publication Date: 2019-01-07
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Noble gases in deepwater oils of the U.S. Gulf of Mexico. Geochemistry, Geophysics, Geosystems , 19, 4218 – 4235.(2018): doi:10.1029/2018GC007654.
    Description: Hydrocarbon migration and emplacement processes remain underconstrained despite the vast potential economic value associated with oil and gas. Noble gases provide information about hydrocarbon generation, fluid migration pathways, reservoir conditions, and the relative volumes of oil versus water in the subsurface. Produced gas He-Ne-Ar-Kr-Xe data from two distinct oil fields in the Gulf of Mexico (Genesis and Hoover-Diana) are used to calibrate a model that takes into account both water-oil solubility exchange and subsequent gas cap formation. Reconstructed noble gas signatures in oils reflect simple (two-phase) oil-water exchange imparted during migration from the source rock to the trap, which are subsequently modified by gas cap formation at current reservoir conditions. Calculated, oil to water volume ratios (Vo/Vw) in Tertiary-sourced oils from the Hoover-Diana system are 2–3 times greater on average than those in the Jurassic sourced oils from the Genesis reservoirs. Higher Vo/Vw in Hoover-Diana versus Genesis can be interpreted in two ways: either (1) the Hoover reservoir interval has 2–3 times more oil than any of the individual Genesis reservoirs, which is consistent with independent estimates of oil in place for the respective reservoirs, or (2) Genesis oils have experienced longer migration pathways than Hoover-Diana oils and thus have interacted with more water. The ability to determine a robust Vo/Vw , despite gas cap formation and possible gas cap loss, is extremely powerful. For example, when volumetric hydrocarbon ratios are combined with independent estimates of hydrocarbon migration distance and/or formation fluid volumes, this technique has the potential to differentiate between large and small oil accumulations.
    Description: We thank ExxonMobil for funding and providing the samples. In addition, we thank James Scott and two anonymous reviewers for their comprehensive and constructive reviews, as well as Janne Blichert-Toft for editorial handling.
    Description: 2019-04-10
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    Tectonic control on the petrophysical properties of foredeep sandstone in the Central Apennines, Italy (2015)
    American Geophysical Union
    Details
    Publication Date: 2022-04-29
    Description: Petrophysical properties of rocks and their applicability at larger scale are a challenging topic in Earth sciences. Petrophysical properties of rocks are severely affected by boundary conditions, rock fabric/microstructure, and tectonics that require a multiscale approach to be properly defined. Here we (1) report laboratory measurements of density, porosity, permeability, and P wave velocities at increasing confining pressure conducted on Miocene foredeep sandstones (Frosinone Formation); (2) compare the laboratory results with larger-scale geophysical investigations; and (3) discuss the effect of thrusting on the properties of sandstones. At ambient pressure, laboratory porosity varied from 2.2% to 13.8% and P wave velocities (Vp) from 1.5 km/s to 2.7 km/s. The P wave velocity increased with confining pressure, reaching between 3.3 km/s and 4.7 km/s at 100 MPa. In situ Vp profiles, measured using sonic logs, matched the ultrasonic laboratory measurement well. The permeability varied between 1.4 × 10 15m2 and 3.9 × 10 15m2 and was positively correlated with porosity. The porosity and permeability of samples taken at various distances to the Olevano–Antrodoco fault plane progressively decreased with distance while P wave velocity increased. At about 1 km from the fault plane, the relative variations reached 43%, 65%, and 20% for porosity, permeability, and P wave velocity, respectively. This suggests that tectonic loading changed the petrophysical properties inherited from sedimentation and diagenesis. Using field constraints and assuming overburden-related inelastic compaction in the proximity of the fault plane, we conclude that the fault reached the mechanical condition for rupture in compression at differential stress of 64.8 MPa at a depth of 1500 m.
    Description: Published
    Description: 9077-9094
    Description: 2IT. Laboratori sperimentali e analitici
    Description: JCR Journal
    Description: open
    Keywords: Petrophysical properties of sandstone ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Pond fractals in a tidal flat (2015)
    American Physical Society
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Physical Review E Statistical, Nonlinear, and Soft Matter Physics 92 (2015): 052128, doi: 10.1103/PhysRevE.92.052128.
    Description: Studies over the past decade have reported power-law distributions for the areas of terrestrial lakes and Arctic melt ponds, as well as fractal relationships between their areas and coastlines. Here we report similar fractal structure of ponds in a tidal flat, thereby extending the spatial and temporal scales on which such phenomena have been observed in geophysical systems. Images taken during low tide of a tidal flat in Damariscotta, Maine, reveal a well-resolved power-law distribution of pond sizes over three orders of magnitude with a consistent fractal area-perimeter relationship. The data are consistent with the predictions of percolation theory for unscreened perimeters and scale-free cluster size distributions and are robust to alterations of the image processing procedure. The small spatial and temporal scales of these data suggest this easily observable system may serve as a useful model for investigating the evolution of pond geometries, while emphasizing the generality of fractal behavior in geophysical surfaces.
    Description: This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. 2388357, the Gordon and Betty Moore Foundation, and the National Science Foundation, Award No. OCE-1315201.
    Repository Name: Woods Hole Open Access Server
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    Graphical user interface for interactive seismic ray tracing (2018)
    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 Eos 86 (2005): 90, doi:10.1029/2005EO090004.
    Description: RayGUI 2.0 is a new version of RayGUI, a graphical user interface (GUI) to the seismic travel time modeling program of Zelt and Smith [1992]. It represents a significant improvement over the previous version of RayGUI (RayGUI 1.04; Loss et al.[1998a,1998b]).
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    Overview of the Arctic Sea state and boundary layer physics program (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. 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-Oceans 123(12), (2018): 8674-8687, doi:10.1002/2018JC013766.
    Description: A large collaborative program has studied the coupled air‐ice‐ocean‐wave processes occurring in the Arctic during the autumn ice advance. The program included a field campaign in the western Arctic during the autumn of 2015, with in situ data collection and both aerial and satellite remote sensing. Many of the analyses have focused on using and improving forecast models. Summarizing and synthesizing the results from a series of separate papers, the overall view is of an Arctic shifting to a more seasonal system. The dramatic increase in open water extent and duration in the autumn means that large surface waves and significant surface heat fluxes are now common. When refreezing finally does occur, it is a highly variable process in space and time. Wind and wave events drive episodic advances and retreats of the ice edge, with associated variations in sea ice formation types (e.g., pancakes, nilas). This variability becomes imprinted on the winter ice cover, which in turn affects the melt season the following year.
    Description: This program was supported by the Office of Naval Research, Code 32, under Program Managers Scott Harper and Martin Jeffries. The crew of R/V Sikuliaq provide outstanding support in collecting the field data, and the US National Ice Center, German Aerospace Center (DLR), and European Space Agency facilitated the remote sensing collections and daily analysis products. RADARSAT‐2 Data and Products are from MacDonald, Dettwiler, and Associates Ltd., courtesy of the U.S. National Ice Center. Data, supporting information, and a cruise report can be found at http://www.apl.uw.edu/arcticseastate
    Keywords: Arctic ; waves ; autumn ; sea ice ; Beaufort ; flux
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    Stable Isotope clues to the formation and evolution of refrozen melt ponds on Arctic Sea ice. (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. 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-Oceans 123(12), (2018): 8887-8901, doi:10.1029/2018JC013797.
    Description: Sea ice is one of the determining parameters of the climate system. The presence of melt ponds on the surface of Arctic sea ice plays a critical role in the mass balance of sea ice. A total of nine cores was collected from multiyear ice refrozen melt ponds and adjacent hummocks during the 2015 Arctic Sea State research cruise. The depth profiles of water isotopes, salinity, and ice texture for these sea ice cores were examined to provide information about the development of refrozen melt ponds and water balance generation processes, which are otherwise difficult to acquire. The presence of meteoric water with low oxygen isotope values as relatively thin layers indicates melt pond water stability and little mixing during formation and refreezing. The hydrochemical characteristics of refrozen melt pond and seawater depth profiles indicate little snowmelt enters the upper ocean during melt pond refreezing. Due to the seasonal characters of deuterium excess for Arctic precipitation, water balance calculations utilizing two isotopic tracers (oxygen isotope and deuterium excess) suggest that besides the melt of snow cover, the precipitation input in the melt season may also play a role in the evolution of melt ponds. The dual‐isotope mixing model developed here may become more valuable in a future scenario of increasing Arctic precipitation. The layers of meteoric origin were found at different depths in the refrozen melt pond ice cores. Surface topography information collected at several core sites was examined for possible explanations of different structures of refrozen melt ponds.
    Description: The coauthors (S. F. A., S. S., T. M., and B. W.) wish to thank the other DRI participants and the Captain and crew of the Sikuliaq's October 2015 cruise for their assistance in the sample collections analyzed in the paper. Jim Thomson (Chief Scientist), Scott Harper (ONR Program Manager), and Martin Jeffries (ONR Program Manager) are particularly acknowledged for their unwavering assistance and leadership during the 5 years of the SeaState DRI. We thank Guy Williams for production of the aerial photo mosaic. Funding from the Office of Naval Research N00014‐13‐1‐0435 (S. F. A. and B. W.), N00014‐13‐1‐0434 (S. S.), and N00014‐13‐1‐0446 (T. M.) supported this research through grants to UTSA, UColorado, and WHOI, respectively. This project was also funded (in part) by the University of Texas at San Antonio, Office of the Vice President for Research (Y. G. and S. F. A.). Data for the stable isotope mixing models used in this study are shown in supporting information Tables S1–S3.
    Description: 2019-05-15
    Keywords: Arctic ; sea ice ; isotope tracer ; melt pond ; oxygen isotope ; deuterium excess
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    Geophysical evidence for the evolution of the California Inner Continental Borderland as a metamorphic core complex (2018)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2000. 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: Solid Earth 105 (2000): 5835-5857, doi:10.1029/1999JB900318.
    Description: We use new seismic and gravity data collected during the 1994 Los Angeles Region Seismic Experiment (LARSE) to discuss the origin of the California Inner Continental Borderland (ICB) as an extended terrain possibly in a metamorphic core complex mode. The data provide detailed crustal structure of the Borderland and its transition to mainland southern California. Using tomographic inversion as well as traditional forward ray tracing to model the wide-angle seismic data, we find little or no sediments, low (#6.6 km/s) P wave velocity extending down to the crust-mantle boundary, and a thin crust (19 to 23 km thick). Coincident multichannel seismic reflection data show a reflective lower crust under Catalina Ridge. Contrary to other parts of coastal California, we do not find evidence for an underplated fossil oceanic layer at the base of the crust. Coincident gravity data suggest an abrupt increase in crustal thickness under the shelf edge, which represents the transition to the western Transverse Ranges. On the shelf the Palos Verdes Fault merges downward into a landward dipping surface which separates “basement” from low-velocity sediments, but interpretation of this surface as a detachment fault is inconclusive. The seismic velocity structure is interpreted to represent Catalina Schist rocks extending from top to bottom of the crust. This interpretation is compatible with a model for the origin of the ICB as an autochthonous formerly hot highly extended region that was filled with the exhumed metamorphic rocks. The basin and ridge topography and the protracted volcanism probably represent continued extension as a wide rift until ;13 m.y. ago. Subduction of the young and hot Monterey and Arguello microplates under the Continental Borderland, followed by rotation and translation of the western Transverse Ranges, may have provided the necessary thermomechanical conditions for this extension and crustal inflow.
    Description: The LARSE experiment was funded by NSF EAR-9416774, the U.S. Geological Survey’s Earthquake Hazards and Coastal and Marine Programs, and by the Southern California Earthquake Center (SCEC).
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    Slab tears and intermediate‐depth seismicity (2018)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. 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 40 (2013): 4244-4248, doi:10.1002/grl.50830.
    Description: Active tectonic regions where plate boundaries transition from subduction to strike slip can take several forms, such as triple junctions, acute, and obtuse corners. Well‐documented slab tears that are associated with high rates of intermediate‐depth seismicity are considered here: Gibraltar arc, the southern and northern ends of the Lesser Antilles arc, and the northern end of Tonga trench. Seismicity at each of these locations occurs, at times, in the form of swarms or clusters, and various authors have proposed that each marks an active locus of tear propagation. The swarms and clusters start at the top of the slab below the asthenospheric wedge and extend 30–60 km vertically downward within the slab. We propose that these swarms and clusters are generated by fluid‐related embrittlement of mantle rocks. Focal mechanisms of these swarms generally fit the shear motion that is thought to be associated with the tearing process.
    Keywords: Slab tear ; Intermediate seismicity ; Subduction corner
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    Constraining instantaneous fluxes and integrated compositions of fluvially discharged organic matter (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Freymond, C. V., Lupker, M., Peterse, F., Haghipour, N., Wacker, L., Filip, F., et al. (2018). Constraining instantaneous fluxes and integrated compositions of fluvially discharged organic matter. Geochemistry, Geophysics, Geosystems, 19, 2453 2462. doi: 10.1029/2018GC007539.
    Description: Fluvial export of organic carbon (OC) and burial in ocean sediments comprises an important carbon sink, but fluxes remain poorly constrained, particularly for specific organic components. Here OC and lipid biomarker contents and isotopic characteristics of suspended matter determined in depth profiles across an active channel close to the terminus of the Danube River are used to constrain instantaneous OC and biomarker fluxes and integrated compositions during high to moderate discharges. During high (moderate) discharge, the total Danube exports 8 (7) kg/s OC, 7 (3) g/s higher plant‐derived long‐chain fatty acids (LCFA), 34 (21) g/s short‐chain fatty acids (SCFA), and 0.5 (0.2) g/s soil bacterial membrane lipids (brGDGTs). Integrated stable carbon isotopic compositions were TOC: −28.0 (−27.6)‰, LCFA: −33.5 (−32.8)‰ and Δ14C TOC: −129 (−38)‰, LCFA: −134 (−143)‰, respectively. Such estimates will aid in establishing quantitative links between production, export, and burial of OC from the terrestrial biosphere.
    Description: This project was funded by the Swiss National Science Foundation SNF. Grant Number: 200021_140850. F.P. acknowledges funding from NWO‐VENI grant 863.13.016. We thank the sampling crews from both field campaigns (Björn Buggle, James Saenz, Alissa Zuijdgeest, Marilu Tavagna, Stefan Eugen Filip, Silvia Lavinia Filip, Mihai, Clayton Magill, Thomas Blattmann, and Michael Albani), Daniel Montluçon for lab support and Hannah Gies for PCGC work. Figures, tables, and equations can be found in supporting information.
    Keywords: Danube River ; organic carbon ; biomarker ; radiocarbon ; ADCP
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    Seismic evidence for a slab tear at the Puerto Rico Trench (2018)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. 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: Solid Earth 105 (2013): 2915-2923, doi:10.1002/jgrb.50227.
    Description: The fore‐arc region of the northeast Caribbean plate north of Puerto Rico and the Virgin Islands has been the site of numerous seismic swarms since at least 1976. A 6 month deployment of five ocean bottom seismographs recorded two such tightly clustered swarms, along with additional events. Joint analyses of the ocean bottom seismographs and land‐based seismic data reveal that the swarms are located at depths of 50–150 km. Focal mechanism solutions, found by jointly fitting P wave first‐motion polarities and S/P amplitude ratios, indicate that the broadly distributed events outside the swarm generally have strike‐ and dip‐slip mechanisms at depths of 50–100 km, while events at depths of 100–150 km have oblique mechanisms. A stress inversion reveals two distinct stress regimes: The slab segment east of 65°W longitude is dominated by trench‐normal tensile stresses at shallower depths (50–100 km) and by trench‐parallel tensile stresses at deeper depths (100–150 km), whereas the slab segment west of 65°W longitude has tensile stresses that are consistently trench normal throughout the depth range at which events were observed (50–100 km). The simple stress pattern in the western segment implies relatively straightforward subduction of an unimpeded slab, while the stress pattern observed in the eastern segment, shallow trench‐normal tension and deeper trench‐normal compression, is consistent with flexure of the slab due to rollback. These results support the hypothesis that the subducting North American plate is tearing at or near these swarms. The 35 year record of seismic swarms at this location and the recent increase in seismicity suggest that the tear is still propagating.
    Keywords: Subduction ; Slab‐tear ; Caribbean ; Focal mechanism ; Stress inversion
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    New seafloor map of the Puerto Rico trench helps assess earthquake and tsunami hazards (2018)
    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 Eos 85 (2004): 349,354, doi:10.1029/2004EO370001 .
    Description: The Puerto Rico Trench, the deepest part of the Atlantic Ocean, is located where the North American (NOAM) plate is subducting under the Caribbean plate (Figure l). The trench region may pose significant seismic and tsunami hazards to Puerto Rico and the U.S.Virgin Islands, where 4 million U.S. citizens reside. Widespread damage in Puerto Rico and Hispaniola from an earthquake in 1787 was estimated to be the result of a magnitude 8 earthquake north of the islands [McCann et al., 2004]. A tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918 [Mercado and McCann, 1998]. Large landslide escarpments have been mapped on the seafloor north of Puerto Rico [Mercado et al., 2002; Schwab et al., 1991],although their ages are unknown.
    Description: Funding was provided by the NOAA Office of Ocean Exploration and the USGS Coastal and Marine Program
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    Dispersal of hydrothermal vent larvae at East Pacific Rise 9-10 degrees N segment (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. 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-Oceans, 123(11), (2018): 7877-7895. doi: 10.1029/2018JC014290.
    Description: A three‐dimensional, primitive‐equation, ocean circulation model coupled with a Lagrangian particle‐tracking algorithm is used to investigate the dispersal and settlement of planktonic larvae released from discrete hydrothermal habitats on the East Pacific Rise segment at 9–10°N. Model outputs show that mean circulation is anticyclonic around the ridge segment, which consists of a northward flow along the western flank and a southward flow along the eastern flank. Those flank jets are dispersal expressways for the along‐ridge larval transport and strongly affect its overall direction and spatial‐temporal variations. It is evident from model results that the transform faults bounding the ridge segment and off axis topography (the Lamont Seamount Chain) act as topographic barriers to larval dispersal in the along‐ridge direction. Furthermore, the presence of an overlapping spreading center and an adjacent local topographic high impedes the southward along‐ridge larval transport. The model results suggest that larval recolonization within ridge‐crest habitats is enhanced by the anticyclonic circulation around the ridge segment, and the overall recolonization rate is higher for larvae having a short precompetency period and an altitude above the bottom sufficient to avoid influence by the near‐bottom currents Surprisingly, for larvae having a long precompetency period (〉10 days), the prolonged travel time allowed some of those larvae to return to their natal vent clusters, which results in an unexpected increase in connectivity among natal and neighboring sites. Overall, model‐based predictions of connectivity are highly sensitive to the larval precompetency period and vertical position in the water column.
    Description: The sediment‐trap data presented in this paper are included in Table S1. The bathymetric data used in the model can be downloaded from the Global Multi‐Resolution Topography (GMRT) Synthesis of Marine Geoscience Data System (MGDS) (https://www.gmrt.org/GMRTMapTool). The ocean current time series data used in this work were acquired in 2006‐2007 by Andreas Thurnherr at the Earth Institute of Columbia University. Those data can be accessed in the supporting information. D.J. McGillicuddy gratefully acknowledges support from the National Science Foundation and the Holger W. Jannasch and Columbus O'Donnell Iselin Shared Chairs for Excellence in Oceanography. L.S. Mullineaux acknowledges with gratitude support from the National Science Foundation and the Woods Hole Oceanographic Institution (WHOI) Ocean life fellowship. We appreciate the operation support from the Captain and crew of R/V Atlantis and the Alvin submersible group. We are thankful to V.K. Kosnyrev for developing the coupling interface between the ocean‐circulation and particle‐tracking models. We are grateful to J.W. Lavelle for his intellectual support for the modeling work presented in this paper. We thank Houshuo Jiang for sponsoring our use of the cluster computer at WHOI.
    Description: 2019-05-06
    Keywords: larva ; dispersal ; hydrothermal vent ; EPR ; connectivity ; supply
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    Melt pond conditions on declining arctic sea ice over 1979-2016: Model development, validation, and results (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. 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-Oceans, 123(11), (2018): 7983-8003. doi:10.1029/2018JC014298.
    Description: A melt pond (MP) distribution equation has been developed and incorporated into the Marginal Ice‐Zone Modeling and Assimilation System to simulate Arctic MPs and sea ice over 1979–2016. The equation differs from previous MP models and yet benefits from previous studies for MP parameterizations as well as a range of observations for model calibration. Model results show higher magnitude of MP volume per unit ice area and area fraction in most of the Canada Basin and the East Siberian Sea and lower magnitude in the central Arctic. This is consistent with Moderate Resolution Imaging Spectroradiometer observations, evaluated with Measurements of Earth Data for Environmental Analysis (MEDEA) data, and closely related to top ice melt per unit ice area. The model simulates a decrease in the total Arctic sea ice volume and area, owing to a strong increase in bottom and lateral ice melt. The sea ice decline leads to a strong decrease in the total MP volume and area. However, the Arctic‐averaged MP volume per unit ice area and area fraction show weak, statistically insignificant downward trends, which is linked to the fact that MP water drainage per unit ice area is increasing. It is also linked to the fact that MP volume and area decrease relatively faster than ice area. This suggests that overall the actual MP conditions on ice have changed little in the past decades as the ice cover is retreating in response to Arctic warming, thus consistent with the Moderate Resolution Imaging Spectroradiometer observations that show no clear trend in MP area fraction over 2000–2011.
    Description: We gratefully acknowledge the support of the NASA Cryosphere Program (grants NNX15AG68G, NNX17AD27G, and NNX14AH61G), the Office of Naval Research (N00014‐12‐1‐0112), the NSF Office of Polar Programs (PLR‐1416920, PLR‐1603259, PLR‐1602521, and ARC‐1203425), and the Department of Homeland Security (DHS, 2014‐ST‐061‐ML‐0002). The DHS grant is coordinated through the Arctic Domain Awareness Center (ADAC), a DHS Center of Excellence, which conducts maritime research and development for the Arctic region. The views and conclusions in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the DHS. MODIS‐derived MP area data are available at https://icdc.cen.uni‐hamburg.de/1/daten/cryosphere/arctic‐meltponds.html. MP area fraction statistics derived from MEDEA images are available from http://psc.apl.uw.edu/melt‐pond‐data/. Sea ice thickness and snow observations are available at http://psc.apl.washington.edu/sea_ice_cdr. CFS forcing data used to drive MIZMAS are available at https://www.ncdc.noaa.gov/data‐access/model‐data/model‐datasets/climate‐forecast‐system‐version2‐cfsv2.
    Description: 2019-04-18
    Keywords: Arctic Ocean ; sea ice ; melt ponds ; numerical modeling ; climate variability
    Repository Name: Woods Hole Open Access Server
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  • 150
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    Interoperability between coastal web atlases using semantic mediation: a case study of the International Coastal Atlas Network (ICAN). (2015)
    American Geophysical Union | Washington, DC
    Details
    Publication Date: 2021-05-19
    Description: Coastal mapping plays an important role in informing marine spatial planning, resource management, maritime safety, hazard assessment and even national sovereignty. As such, there is now a plethora of data/metadata catalogs, pre-made maps, tabular and text information on resource availability and exploitation, and decision-making tools. A recent trend has been to encapsulate these in a special class of web-enabled geographic information systems called a coastal web atlas (CWA). While multiple benefits are derived from tailor-made atlases, there is great value added from the integration of disparate CWAs. CWAs linked to one another can query more successfully to optimize planning and decision-making. If a dataset is missing in one atlas, it may be immediately located in another. Similar datasets in two atlases may be combined to enhance study in either region. But how best to achieve semantic interoperability to mitigate vague data queries, concepts or natural language semantics when retrieving and integrating data and information? We report on the development of a new prototype seeking to interoperate between two initial CWAs: the Marine Irish Digital Atlas (MIDA) and the Oregon Coastal Atlas (OCA). These two mature atlases are used as a testbed for more regional connections, with the intent for the OCA to use lessons learned to develop a regional network of CWAs along the west coast, and for MIDA to do the same in building and strengthening atlas networks with the UK, Belgium, and other parts of Europe. Our prototype uses semantic interoperability via services harmonization and ontology mediation, allowing local atlases to use their own data structures, and vocabularies (ontologies). We use standard technologies such as OGC Web Map Services (WMS) for delivering maps, and OGC Catalogue Service for the Web (CSW) for delivering and querying ISO-19139 metadata. The metadata records of a given CWA use a given ontology of terms called local ontology. Human or machine users formulate their requests using a common ontology of metadata terms, called global ontology. A CSW mediator rewrites the user’s request into CSW requests over local CSWs using their own (local) ontologies, collects the results and sends them back to the user. To extend the system, we have recently added global maritime boundaries and are also considering nearshore ocean observing system data. Ongoing work includes adding WFS, error management, and exception handling, enabling Smart Searches, and writing full documentation. This prototype is a central research project of the new International Coastal Atlas Network (ICAN), a group of 30+ organizations from 14 nations (and growing) dedicated to seeking interoperability approaches to CWAs in support of coastal zone management and the translation of coastal science to coastal decision-making.
    Description: Alternate reference: Eos, Transactions of the American Geophysical Union, 2009 Fall Meeting, American Geophysical Union, Volume 90(52), San Francisco, CA, p.IN21B-1054 (2009)
    Description: Published
    Keywords: Coastal informatics ; Coastal atlas ; Coastal web atlas ; Interoperability ; Ontologies ; Semantic web and semantic integration ; Marine geology and geophysics ; Informatics
    Repository Name: AquaDocs
    Type: Conference Material , Non Refereed
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  • 151
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    The Capo Vaticano (Calabria) coastal terraces and the 1905 M7 earthquake: the geomorphological signature of regional uplift and coseismic slip in southern Italy (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: The elevation of the Capo Vaticano coastal terraces (Tyrrhenian coast, central Calabria) is the result of a combination of regional uplift and repeated coseismic displacement. We subtract the regional uplift from the total uplift (maximum average uplift rates: 0.81–0.97 mm a)1 since c. 0.7 Ma) and obtain the residual fault-related displacement. Then, we model the residual displacement to provide constraints on the location and geometry of the seismogenic source of the 1905 M7 earthquake, the strongest – and still poorly understood – earthquake of the instrumental era in this area. We try four different potential sources for the dislocation modelling and find that (1) three sources are not compatible with the displacement observed along the terraces and (2) the only source consistent with the local deformation is the 100 - striking Coccorino Fault. We calculate average long-term vertical slip rates of 0.2–0.3 mm a)1 on the Coccorino Fault and estimate an average recurrence time of one millennium for a 1905-type earthquake.
    Description: Published
    Description: 378-389
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: restricted
    Keywords: 1905 earthquake ; marine terraces ; coseismic displacement ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 152
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    Coseismic ground deformation of the 6 April 2009 L’Aquila earthquake (central Italy, Mw6.3) (2015)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We provide field data of coseismic ground deformation related to the 6 April Mw 6.3 L’Aquila normal faulting earthquake. Three narrow fracture zones were mapped: Paganica‐Colle Enzano (P‐E), Mt. Castellano‐Mt. Stabiata (C‐S) and San Gregorio (SG). These zones define 13 km of surface ruptures that strike at 130–140°. We mapped four main types of ground deformation (free faces on bedrock fault scarps, faulting along synthetic splays and fissures with or without slip) that are probably due to the near‐surface lithology of the fault walls and the amount of slip that approached the surface coseismically. The P‐E and C‐S zones are characterized by downthrow to the SW (up to 10 cm) and opening (up to 12 cm), while the SG zone is characterized only by opening. Afterslip throw rates of 0.5–0.6 mm/day were measured along the Paganica fault, where paleoseismic evidence reveals recurring paleo‐earthquakes and post‐24.8 kyr slip‐rate ≥ 0.24 mm/yr.
    Description: Published
    Description: L06308
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: restricted
    Keywords: 6 April 2009 L’Aquila earthquake ; Coseismic ground deformation ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
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  • 153
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    Accounting for source effects in the ShakeMap procedure: the 2000 Tottori and the 2008 Miyagi earthquakes (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: Real-time seismology has made significant improvements in recent years, with source parameters now available within a few tens of minutes after an earthquake. It is likely that this time will be further reduced, in the near future, by means of increased efficiency in real-time transmission,increasingdatacoverageandimprovementofthemethodologies.Inthiscontext, together with the development of new ground motion predictive equations (GMPEs) that are abletoaccountforsourcecomplexity,thegenerationofstronggroundmotionshakingmapsin quasi-real time has become ever more feasible after the occurrence of a damaging earthquake. However, GMPEs may not reproduce reliably the ground motion in the near-source region where the finite fault parameters have a strong influence on the shaking. Inthispaperwetestwhetheraccountingforsource-relatedeffectsiseffectiveinbettercharacterizingthegroundmotion.WeintroduceamodificationoftheGMPEswithintheShakeMap softwarepackage,andsubsequentlytesttheaccuracyofthenewlygeneratedshakemapsinpredictingthegroundmotion.ThetestisconductedbycontrollingtheperformanceofShakeMap as we decrease the amount of the available information. We then update ShakeMap with the GMPE modified with a corrective factor accounting for source effects, in order to better constrain these effects that likely influence the level of (near-source) ground shaking. Weinvestigatetwowell-recordedearthquakesfromJapan(the2000Tottori, Mw 6.6,andthe 2008 Iwate-Miyagi, Mw7.0, events) where the instrumental coverage is as dense as needed to ensure an objective appraisal of the results. The results demonstrate that the corrected GMPE can capture only some aspects of the ground shaking in the near-source area, neglecting other multidimensional effects, such as propagation effects and local site amplification.
    Description: Italian Presidenza del Consiglio dei Ministri, Dipartimento della Protezione Civile(DPC)under the contract 2007–2009 DPC-INGVS3project
    Description: Published
    Description: 1836-1848
    Description: 3T. Pericolosità sismica e contributo alla definizione del rischio
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquake ground motions ; Earthquake source observation ; Computational seismology ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
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  • 154
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    On the reliability of the Spatial Scintillation Index to detect earthquake precursors in the ionosphere (2015)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The scientific literature includes many reports of ionospheric phenomena that are retrospectively identified prior to seismic events. These disturbances of the Earth’s ionosphere are considered to be possible precursors of the impending earthquakes. However, a causal relationship between ionospheric phenomena and earthquakes has never been definitively demonstrated and attempts at identifying precursory effects in the ionosphere have been called into question by several studies [see, e.g., Masci and Thomas, 2014; Masci et al., 2014]. Among the candidate indicators of ionospheric precursors there is the Spatial Scintillation Index (SSI) proposed by Pulinets et al. [2007]. The usefulness of this index in the search for precursory effects of earthquakes has been criticized by Thomas et al. [2012] and Masci [2013]. In a recent report, Pulinets and Davidenko [2014] attempt to briefly respond to the remarks of these researchers. Here we cast doubt that Pulinets and Davidenko [2014] have shown that SSI is a reliable indicator of precursory effects of earthquakes in the ionosphere.
    Description: Published
    Description: 745–753
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Ionosphere ; Total Electron Content ; Earthquake precursor ; Short-term earthquake prediction ; 05. General::05.07. Space and Planetary sciences::05.07.01. Solar-terrestrial interaction
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  • 155
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    How fast was the Matuyama-Brunhes geomagnetic reversal? A new subcentennial record from the Sulmona Basin, central Italy (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: A recent study of the Matuyama–Brunhes (M-B) geomagnetic field reversal recorded in exposed lacustrine sediments from the Sulmona Basin (Italy) provided a continuous, highresolution record indicating that the reversal of the field direction at the terminus of the M-B boundary (MBB) occurred in less than a century, about 786 ka ago. In the sediment, thin (4–6 cm) remagnetized horizons were recognized above two distinct tephra layers—SUL2- 19 and SUL2-20—that occur ∼25 and ∼35 cm below the MBB, respectively. Also, a faint, millimetre-thick tephra (SUL2-18) occurs 2–3 cm above the MBB.With the aim of improving the temporal resolution of the previous Sulmona MBB record and understanding the possible influence of cryptotephra on the M-B record in the Sulmona Basin,we performed more detailed sampling and analyses of overlapping standard and smaller samples from a 50 cm-long block that spans the MBB. The new data indicate that (i) the MBB is even sharper than previously reported and occurs ∼2.5 cm below tephra SUL2-18, in agreement with the previous study; (ii) the MBB coincides with the rise of an intensity peak of the natural remanent magnetization (NRM) intensity, which extends across SUL2-18; (iii) except for a 2-cm-thick interval just above tephra SUL2-18, the rock magnetic parameters (k, ARM, Mr, Ms, Bc, Bcr) indicate exactly the same magnetic mineralogy throughout the sampled sequence. We conclude that either SUL2-18 resulted in the remagnetization of an interval of about 6 cm (i.e. during the NRM intensity peak spanning ∼260 ± 110 yr, according to the estimated local sedimentation rate), and thus the detailed MBB record is lost because it is overprinted, or the MBB is well recorded, occurred abruptly about 2.5 cm below SUL2-18 and lasted less than 13 ± 6 yr. Both hypotheses challenge our understanding of the geomagnetic field behaviour during a polarity transition and/or of the NRM acquisition process in the Sulmona lacustrine sediment.
    Description: Published
    Description: 798-812
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Palaeomagnetic secular variation; Rapid time variations; Reversals: process, time scale, magnetostratigraphy; Rock and mineral magnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 156
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    Density-driven transport in the umbrella region of volcanic clouds: Implications for tephra dispersion models (2016)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Large explosive volcanic eruptions can generate ash clouds from rising plumes that spread in the atmosphere around a Neutral Buoyancy Level (NBL). These ash clouds spread as inertial intrusions and are advected by atmospheric winds. For low mass flow rates, tephra transport is mainly dictated by wind advection, because ash cloud spreading due to gravity current effects is negligible (passive transport). For large mass flow rates, gravity-driven transport at the NBL can be the dominant transport mechanism. Conditions under which the passive transport assumption is valid have not yet been critically studied. We analyze the conditions when gravity-driven transport is dominant in terms of the cloud Richardson number. Moreover, we couple an analytical model that describes cloud spreading as a gravity current with an advection-diffusion model. This coupled model is used to simulate the evolution of the volcanic cloud during the climatic phase of the 1991 Pinatubo eruption. Citation: Costa, A., A. Folch, and G. Macedonio (2013), Density-driven transport in the umbrella region of volcanic clouds: Implications for tephra dispersion models.
    Description: This work has benefited from funding provided by the Italian Presidenza del Consiglio dei Ministri - Dipartimento della Protezione Civile (DPC), agreement INGV-DPC 2012-2013. This paper does not necessarily represent DPC official opinion and policies. A.F. acknowledges funding by the Spanish project ATMOST (CGL2009-10244).
    Description: Published
    Description: 4823–4827
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Large explosive eruptions ; Volcanic ash transport ; volcanic modeling ; tephra transport ; 05. General::05.01. Computational geophysics::05.01.99. General or miscellaneous
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  • 157
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    Temporal and spatial correlations between soil CO2 flux and crustal stress (2016)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: In seismically active areas, tectonic stress deforms and breaks the rocks of the crust. Ongoing deformation produces detectable modifications in the shallower portions of the crust, resulting in a wide variety of changes in several parameters. In this paper, we report the results of a large-scale spatial (across an area of 15,000 km2) and temporal (up to 3 years) investigation of the relationship between active crustal stress and soil CO2 flux. We deployed a network of 10 automatic stations in most of the seismically active districts of southern Italy to monitor the soil CO2 fluxes, and we used seismicity data to track crustal stress. The results of the investigation show that the CO2 flux signals varied independently in the districts with low and sporadic seismicity. Conversely, in the only district with nearly continuous seismic activity, almost all of the CO2 flux signals were well correlated with each other, and we recorded a clear synchronous sharp increase of the seismicity and signals recorded by several stations. The high spatial and temporal correlation between seismicity and gas discharge evidenced in this study prove that the crustal stress associated with the seismogenic process is able to effectively modulate the gas release in a seismically active area.
    Description: Published
    Description: 7071–7085
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: Soil CO2 flux ; Crustal stress ; seismotectonic process ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.07. Tectonophysics::04.07.99. General or miscellaneous
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  • 158
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    New structural and seismological evidence and interpretation of a lithospheric-scale shear zone at the southern edge of the Ionian subduction system (central-eastern Sicily, Italy) (2017)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: - We performed an integrative analysis of geological gravimetric and seismological data - Analyzed data depicted a not well-known wrench zone in the central-eastern Sicily - Our findings enabled us to interpret this shear zone as a Plio-Pleistocene STEP fault
    Description: Geological, gravimetric, and seismological data from the central-eastern Sicily (Italy) provide evidences of a NW-SE oriented shear zone at the southern edge of the Ionian subduction system. This structure consists of a near 100 km long lithospheric-scale structural and seismic boundary. In the near-surface, it shows Plio-Pleistocene vertical-axis structural rotations, kilometer-scale topographic imprint, progressive wrenching, and large down-faulting. All these features, together with its location south-west of the subduction system, allow us to interpret the shear zone as the upper plate expression of an abandoned Subduction Transform Edge Propagator fault, working before slab detachment, currently reactivated by elastic rebound or mantle upwelling mechanism triggered by slab detachment, to form an incipient transform belt separating compartments characterized by different motion in the modern context of Africa-Europe convergence
    Description: Published
    Description: 1489–1505
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: abandoned STEP fault ; Sicilian/Calabrian subduction system ; central Mediterranean ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
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  • 159
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    Seismotectonics of northeastern Sicily and southern Calabria (Italy): New constraints on the tectonic structures featuring in a crucial sector for the central Mediterranean geodynamics (2017)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: • Detailed tectonic features are revealed in a crucial sector of the central Mediterranean • Seismic pattern pinpoints the activity of a lithospheric-scale tear fault • The complex of faults enables adjacent compressional and extensional domains
    Description: The purpose of this study is to gain a better understanding on the tectonic structures featuring in a crucial sector of central Mediterranean area, including the Aeolian Islands, southern Calabria, and northeastern Sicily, where the convergence between Eurasian and African Plates has given rise to a complicated collisional/subduction complex. A high-quality data set of about 3000 earthquakes has been exploited for local earthquake tomography and focal mechanisms computation together with available source mechanisms from published catalogues. The results depict new details of a network of faults which enables the concurrent existence of adjacent compressional and extensional domains. In particular, tomographic images, seismic events distribution, and focal mechanisms pinpoint the geometry and activity of a lithospheric-scale tear faults system which, with a NW-SE trend through Sicily and the Tyrrhenian and Ionian Seas, represents the southern edge of the Ionian subduction trench zone. At crustal depth, this tearing is well highlighted by a rotation of the maximum horizontal stress, moving across the area from west toward east. In addition, the shallow normal fault regime, characterizing the southern Calabria and northeastern Sicily mainland, south of the NW-SE lineament, changes in the deeper part of the crust. Indeed, a NE-SW earthquake distribution, gently dipping NW, and inverse fault solutions indicate a still active contractional deformation in eastern Sicily, caused by the Africa-Eurasia convergence and well framed with the current compressive regime along the southern Tyrrhenian zone and at the front of the Sicilian Chain-Foreland.
    Description: Published
    Description: 812-830
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: central Mediterranean ; lateral slab tear fault ; tomography ; focal mechanisms ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
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  • 160
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    Evidence of a shallow persistent magmatic reservoir from joint inversion of gravity and ground deformation data: The 25–26 October 2013 Etna lava fountaining event (2017)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: To evaluate the volcanic processes leading to the 25–26 October 2013 lava fountain at Mount Etna, we jointly investigated gravity, GPS, and DInSARmeasurements covering the late-June to early-November time interval. We used finite element modeling to infer a shallow magmatic reservoir which (i) inflated since July 2013, (ii) fed the volcanic activity at the summit craters during 25–26 October, and (iii) deflated due to magma drainage related to this volcanic activity. We suggested that this reservoir belongs to a shallow volume, which is located beneath the summit area and is replenished by magma rising from deep reservoirs and fed the short-term volcanic activity, representing a persistent shallow magmatic plumbing system of Etna. In addition, the model results show that there is a large discrepancy between the erupted and shallow reservoir deflation volumes, which could be reasonably attributable to a highly compressible volatile-rich magma.
    Description: Published
    Description: 3246–3253
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: open
    Keywords: Gravity and deformation signatures of the 26 October 2013 Mount Etna lava fountain ; Integrated finite element-based inversion of gravity and GPS data ; Inference on a highly compressible volatile-rich magma in the magmatic reservoir ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 161
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    Lidar surveys reveal eruptive volumes and rates at Etna, 2007–2010 (2017)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The quantification of eruptive activity represents one major challenge in volcanology. Digital comparison of lidar-based elevation models of Etna (Italy) was made to quantify the volumes of volcanics emitted in 2007–2010. During this period, Etna produced several summit paroxysms followed by a flank eruption. We integrated the total volume difference resulting from the subtraction of the 2007 and 2010 digital elevation models with volumes of eruptive products based on field and aerial surveys to attribute volumes with hitherto unrealized precision to poorly constrained eruptions. The total erupted volume of 2007–2010 is 〉86 × 106m3, most (~74 × 106m3) of which is made up by the lava flows of the 2008–2009 flank eruption. The survey also reveals the high lava volume (5.73 × 106m3) and average eruption rate (~400m3 s 1) of the 10 May 2008 paroxysm, whose flow front stopped 6.2km from the vent, not far from the town of Zafferana Etnea.
    Description: Published
    Description: 4270–4278
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: LiDAR ; Etna ; 04. Solid Earth::04.03. Geodesy::04.03.99. General or miscellaneous ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous
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  • 162
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    The late Mesozoic‐Cenozoic Arctic Ocean climate and sea ice history: A challenge for past and future scientific ocean drilling (2019)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union
    Details
    Publication Date: 2020-05-14
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 163
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    The Power of the Spectrum: Combining Numerical Proxy System Models with Analytical Error Spectra to Better Understand Timescale Dependent Proxy Uncertainty (2017)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, New Orleans, USA, 2017-12-11-2017-12-15New Orleans, USA, American Geophysical Union
    Details
    Publication Date: 2020-05-26
    Description: Understanding the uncertainties associated with proxy-based reconstructions of past climate is critical if they are to be used to validate climate models and contribute to a comprehensive understanding of the climate system. Here we present two related and complementary approaches to quantifying proxy uncertainty. The proxy forward model (PFM) “sedproxy” bitbucket.org/ecus/sedproxy numerically simulates the creation, archiving and observation of marine sediment archived proxies such as Mg/Ca in foraminiferal shells and the alkenone unsaturation index UK’37. It includes the effects of bioturbation, bias due to seasonality in the rate of proxy creation, aliasing of the seasonal temperature cycle into lower frequencies, and error due to cleaning, processing and measurement of samples. Numerical PFMs have the advantage of being very flexible, allowing many processes to be modelled and assessed for their importance. However, as more and more proxy-climate data become available, their use in advanced data products necessitates rapid estimates of uncertainties for both the raw reconstructions, and their smoothed/derived products, where individual measurements have been aggregated to coarser time scales or time-slices. To address this, we derive closed-form expressions for power spectral density of the various error sources. The power spectra describe both the magnitude and autocorrelation structure of the error, allowing timescale dependent proxy uncertainty to be estimated from a small number of parameters describing the nature of the proxy, and some simple assumptions about the variance of the true climate signal. We demonstrate and compare both approaches for time-series of the last millennia, Holocene, and the deglaciation. While the numerical forward model can create pseudoproxy records driven by climate model simulations, the analytical model of proxy error allows for a comprehensive exploration of parameter space and mapping of climate signal re-constructability, conditional on the climate and sampling conditions.
    Repository Name: EPIC Alfred Wegener Institut
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  • 164
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    Emission of gas and atmospheric dispersion of SO2 during the December 2013 eruption at San Miguel volcano (El Salvador, Central America). (2016)
    American Geophysical Union
    Details
    Publication Date: 2022-05-04
    Description: Abstract San Miguel volcano, El Salvador, erupted on 29 December 2013, after a 46 year period characterized by weak activity. Prior to the eruption a trend of increasing SO2 emission rate was observed, with all values measured after mid-November greater than the average value of the previous year (~310 t d 1). During the eruption, SO2 emissions increased from the level of ~330 t d 1 to 2200 t d 1, dropping after the eruption to an average level of 680 t d 1. Wind measurements and SO2 emission rates during the preeruptive, syneruptive, and posteruptive stages were used to model SO2 dispersion around the volcano. Atmospheric SO2 concentration exceeded the dangerous threshold of 5 ppm in the crater region and in some sectors with medium elevation of the highly visited volcanic cone. Combining the SO2 emission rate with measured CO2/SO2, HCl/SO2, and HF/SO2 plume gas ratios, we estimate the CO2, HCl, and HF outputs for the first time on this volcano.
    Description: Published
    Description: 5847–5854
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: SO2 flux, Clorine and CO2 at San miguel, cloud dispersion and hazard ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Applying a curl-B technique to Swarm vector data to estimate nighttime F region current intensities (2015)
    American Geophysical Union
    Details
    Publication Date: 2022-03-01
    Description: The innovative geometry of European Space Agency Swarm constellation opens the way for new investigations based on magnetic data. Since the knowledge of a vector field on two spherical surfaces allows calculating its curl, we propose a new technique to estimate the curl of the ionospheric magnetic field measured by Swarm satellites A and B, orbiting the Earth at two different altitudes from March to September 2014. Using this technique, we mapped the amplitude of the radial, meridional, and zonal components and of total intensity of the ionospheric current density at the satellite's altitudes, i.e., the F region of the ionosphere, during two local nighttime intervals: before and after midnight. Most of the obtained results are consistent with some of the known features of nighttime F region currents; others need further investigation. The proposed technique could contribute in selecting magnetic data with minimum contamination from nighttime F region electric currents for magnetic modeling purposes.
    Description: Published
    Description: 6162-6169
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Swarm magnetic data ; current density ; F region ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous ; 04. Solid Earth::04.05. Geomagnetism::04.05.08. Instruments and techniques ; 05. General::05.01. Computational geophysics::05.01.01. Data processing
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  • 166
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    Seasonal and solar activity variations of F3 layer and quadruple stratification (StF-4) near the equatorial region (2017)
    American Geophysical Union
    Details
    Publication Date: 2022-02-16
    Description: The study of multiple stratification of the F layer has the initial records in the midtwentieth century. Since then, many studies were focused on F3 layer. The diurnal, seasonal, and solar activity variations of the F3 layer characteristics have been investigated by several researchers. Recently, investigations on multiple stratifications of F layer received an important boost after the quadruple stratification (StF-4) was observed at Palmas (10.3°S, 48.3°W; dip latitude 6.6°S—near-equatorial region), Brazil. The present study reports the latest findings related with the seasonal and solar activity characteristics of the F3 layer and StF-4 near the equatorial region during the period from 2002 to 2006. A significant connection between StF-4 and F3 layer has been noticed, since the StF-4 is always preceded and followed by a F3 layer appearance. However, the F3 layer and the StF-4 present different seasonal and solar cycle variations. At a near-equatorial station Palmas, the F3 layer shows the maximum and minimum occurrences during summer and winter seasons, respectively. On the contrary, the StF-4 presents the maximum and minimum occurrences during winter and summer seasons, respectively. While the F3 layer occurrence is not affected by solar cycle, the StF-4 appearance is instead more frequent during high solar activity.
    Description: Published
    Description: 12116–12125
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Description: open
    Keywords: Ionogram ; F layer ; F3 layer ; F4 layer ; low-latitude ionosphere ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous ; 01. Atmosphere::01.02. Ionosphere::01.02.02. Dynamics ; 01. Atmosphere::01.02. Ionosphere::01.02.04. Plasma Physics ; 01. Atmosphere::01.02. Ionosphere::01.02.05. Wave propagation ; 01. Atmosphere::01.02. Ionosphere::01.02.06. Instruments and techniques
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    Ionospheric response to the 2009 sudden stratospheric warming over the equatorial, low, and middle latitudes in the South American sector (2015)
    American Geophysical Union
    Details
    Publication Date: 2022-02-16
    Description: The present study investigates the ionospheric total electron content (TEC) and F-layer response in the Southern Hemisphere equatorial, low, and middle latitudes due to major sudden stratospheric warming (SSW) event, which took place during January–February 2009 in the Northern Hemisphere. In this study, using 17 ground-based dual frequency GPS stations and two ionosonde stations spanning latitudes from 2.8°N to 53.8°S, longitudes from 36.7°W to 67.8°W over the South American sector, it is observed that the ionosphere was significantly disturbed by the SSW event from the equator to the midlatitudes. During day of year 26 and 27 at 14:00 UT, the TEC was two times larger than that observed during average quiet days. The vertical TEC at all 17 GPS and two ionosonde stations shows significant deviations lasting for several days after the SSWtemperature peak. Using one GPS station located at Rio Grande (53.8°S, 67.8°W, midlatitude South America sector), it is reported for the first time that the midlatitude in the Southern Hemisphere was disturbed by the SSW event in the Northern Hemisphere.
    Description: Published
    Description: 7889–7902
    Description: 2A. Fisica dell'alta atmosfera
    Description: 4A. Clima e Oceani
    Description: 1IT. Reti di monitoraggio e Osservazioni
    Description: 4IT. Banche dati
    Description: JCR Journal
    Description: open
    Keywords: sudden stratospheric warming ; equatorial, low, and middle latitude ionosphere ; GPS ; ionosonde ; TEC ; 01. Atmosphere::01.01. Atmosphere::01.01.99. General or miscellaneous ; 01. Atmosphere::01.01. Atmosphere::01.01.04. Processes and Dynamics ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous ; 01. Atmosphere::01.02. Ionosphere::01.02.02. Dynamics ; 01. Atmosphere::01.02. Ionosphere::01.02.04. Plasma Physics ; 01. Atmosphere::01.02. Ionosphere::01.02.06. Instruments and techniques
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    Source modelling of the M5-6 Emilia-Romagna, Italy, earthquakes (May 20-29, 2012) (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2021-11-25
    Description: On 2012 May 20 and 29, two damaging earthquakes with magnitudes Mw 6.1 and 5.9, respectively, struck the Emilia-Romagna region in the sedimentary Po Plain, Northern Italy, causing 26 fatalities, significant damage to historical buildings and substantial impact to the economy of the region. The earthquake sequence included four more aftershocks with Mw ? 5.0, all at shallow depths (about 7–9 km), with similar WNW–ESE striking reverse mechanism. The timeline of the sequence suggests significant static stress interaction between the largest events. We perform here a detailed source inversion, first adopting a point source approximation and considering pure double couple and full moment tensor source models. We compare different extended source inversion approaches for the two largest events, and find that the rupture occurred in both cases along a subhorizontal plane, dipping towards SSW. Directivity is well detected for the May 20 main shock, indicating that the rupture propagated unilaterally towards SE. Based on the focal mechanism solution, we further estimate the co-seismic static stress change induced by the May 20 event. By using the rate-and-state model and a Poissonian earthquake occurrence, we infer that the second largest event of May 29 was induced with a probability in the range 0.2–0.4. This suggests that the segment of fault was already prone to rupture. Finally, we estimate peak ground accelerations for the two main events as occurred separately or simultaneously. For the scenario involving hypothetical rupture areas of both main events, we estimate Mw = 6.3 and an increase of ground acceleration by 50 per cent. The approach we propose may help to quantify rapidly which regions are invested by a significant increase of the hazard, bearing the potential for large aftershocks or even a second main shock.
    Description: Published
    Description: 1658-1672
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquake dynamics ; Earthquake source observations ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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    Effect of glass on the frictional behavior of basalts at seismic slip rates (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-12-16
    Description: We performed 31 friction experiments on glassy basalts (GB) and glass-free basalts (GFB) at slip rates up to 6.5 m s−1 and normal stress up to 40 MPa (seismic conditions). Frictional weakening was associated to bulk frictional melting and lubrication. The weakening distance (Dw) was about 3 times shorter in GB than in GFB, but the steady state friction was systematically higher in GB than in GFB. The shorter Dw in GB may be explained by the thermal softening occurring at the glass transition temperature (Tg ~500°C), which is lower than the bulk melting temperature (Tm ~1250°C) of GFB. Postexperiment microanalyses suggest that the larger crystal fraction measured in GB melts results in the higher steady state friction value compared to the GFB melts. The effect of interstitial glass is to facilitate frictional instability and rupture propagation in GB with respect to GFB.
    Description: Published
    Description: 348-355
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: embargoed_20160201
    Keywords: Earthquakes ; Friction ; Basalts ; Interstitial glass ; 04. Solid Earth::04.01. Earth Interior::04.01.04. Mineral physics and properties of rocks ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Linked frequency and intensity of persistent volcanic activity at Stromboli (Italy) (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-12-15
    Description: Relationships between frequency and intensity of volcanic eruptions are actively sought by geophysicists for both monitoring and research purposes. By analyzing surveillance videos of persistent volcanic activity at Stromboli (Italy), we derived the frequency and jet height of 〉4000 explosions that occurred in 72 h-long time windows sampled yearly from 2005 to 2009. We found a positive relationship linking explosion frequency and jet height (linked to eruption intensity) when averaging the two parameters over time intervals from hours to days, with a stronger correlation for longer intervals. We interpret this behavior as the response of the magmatic system to variable influx of magma and gas at depth, increased flux at depth causing more frequent and stronger explosions at the surface. This relationship entails concurrent control of source processes over explosion frequency and intensity, directly impacting modeling of explosion sources at persistently active volcanoes in general and hazard assessment at Stromboli in particular.
    Description: DPC-INGV Project V2 “Paroxysm”
    Description: Published
    Description: 1–5
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: reserved
    Keywords: Stromboli ; Strombolian frequency ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 171
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    Spatial variability of volcanic features in early-stage rift settings: the case of the Tanzania Divergence, East African rift system (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2022-05-24
    Description: Close relationships between deformation and volcanism are well documented in relatively late evolutionary stages of con- tinental rifting, whereas these are poorly constrained in less mature rifting stages. To investigate the control of inherited structures on faulting and volcanism, we present a statistical analysis of volcanic features, faults and pre-rift fabric in the Tanzania Divergence, where volcanic features occur exten- sively in in-rift and off-rift areas. Our results show that in mature rift sectors (Natron), magma uprising is mostly con- trolled by fractures/faults responding to the far-field stress, whereas the distribution of volcanism during initial rifting (Eyasi) is controlled by inherited structures oblique to the regional extension direction. Off-rift sectors show a marked control of pre-rift structures on magma emplacement, which may not respond to the regional stress field. Thus, the use of off-rift magmatic features as stress indicators should take into account the role of pre-existing structures.
    Description: Published
    Description: 461-468
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: East Africa Rift System, Tanzania-Kenia, structures and volcanism ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
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  • 172
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    Noble gases in deepwater oils of the U.S. Gulf of Mexico (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-08-31
    Description: Author Posting. © American Geophysical Union, 2018. 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 19(11), (2018): 4218-4235. doi: 10.1029/2018GC007654
    Description: Hydrocarbon migration and emplacement processes remain underconstrained despite the vast potential economic value associated with oil and gas. Noble gases provide information about hydrocarbon generation, fluid migration pathways, reservoir conditions, and the relative volumes of oil versus water in the subsurface. Produced gas He‐Ne‐Ar‐Kr‐Xe data from two distinct oil fields in the Gulf of Mexico (Genesis and Hoover‐Diana) are used to calibrate a model that takes into account both water‐oil solubility exchange and subsequent gas cap formation. Reconstructed noble gas signatures in oils reflect simple (two‐phase) oil‐water exchange imparted during migration from the source rock to the trap, which are subsequently modified by gas cap formation at current reservoir conditions. Calculated, oil to water volume ratios (Vo/Vw) in Tertiary‐sourced oils from the Hoover‐Diana system are 2–3 times greater on average than those in the Jurassic sourced oils from the Genesis reservoirs. Higher Vo/Vw in Hoover‐Diana versus Genesis can be interpreted in two ways: either (1) the Hoover reservoir interval has 2–3 times more oil than any of the individual Genesis reservoirs, which is consistent with independent estimates of oil in place for the respective reservoirs, or (2) Genesis oils have experienced longer migration pathways than Hoover‐Diana oils and thus have interacted with more water. The ability to determine a robust Vo/Vw, despite gas cap formation and possible gas cap loss, is extremely powerful. For example, when volumetric hydrocarbon ratios are combined with independent estimates of hydrocarbon migration distance and/or formation fluid volumes, this technique has the potential to differentiate between large and small oil accumulations.
    Description: We thank ExxonMobil for funding and providing the samples. In addition, we thank James Scott and two anonymous reviewers for their comprehensive and constructive reviews, as well as Janne Blichert‐Toft for editorial handling.
    Description: 2019-04-10
    Repository Name: Woods Hole Open Access Server
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    Xenon hydrate as an analog of methane hydrate in geologic systems out of thermodynamic equilibrium (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2019. 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 20(5), (2019):2462-2472, doi:10.1029/2019GC008250.
    Description: Methane hydrate occurs naturally under pressure and temperature conditions that are not straightforward to replicate experimentally. Xenon has emerged as an attractive laboratory alternative to methane for studying hydrate formation and dissociation in multiphase systems, given that it forms hydrates under milder conditions. However, building reliable analogies between the two hydrates requires systematic comparisons, which are currently lacking. We address this gap by developing a theoretical and computational model of gas hydrates under equilibrium and nonequilibrium conditions. We first compare equilibrium phase behaviors of the Xe·H2O and CH4·H2O systems by calculating their isobaric phase diagram, and then study the nonequilibrium kinetics of interfacial hydrate growth using a phase field model. Our results show that Xe·H2O is a good experimental analog to CH4·H2O, but there are key differences to consider. In particular, the aqueous solubility of xenon is altered by the presence of hydrate, similar to what is observed for methane; but xenon is consistently less soluble than methane. Xenon hydrate has a wider nonstoichiometry region, which could lead to a thicker hydrate layer at the gas‐liquid interface when grown under similar kinetic forcing conditions. For both systems, our numerical calculations reveal that hydrate nonstoichiometry coupled with hydrate formation dynamics leads to a compositional gradient across the hydrate layer, where the stoichiometric ratio increases from the gas‐facing side to the liquid‐facing side. Our analysis suggests that accurate composition measurements could be used to infer the kinetic history of hydrate formation in natural settings where gas is abundant.
    Description: This work was funded in part by the U.S. Department of Energy, DOE [awards DE‐FE0013999 and DE‐SC0018357 (to R. J.) and DOE Interagency Agreement DE‐FE0023495 (to W. F. W.)]. X. F. acknowledges support by the Miller Research Fellowship at the University of California Berkeley. W. F. W. acknowledges support from the U.S. Geological Survey's Gas Hydrate Project and the Survey's Coastal, Marine Hazards and Resources Program. L. C. F. acknowledges funding from the Spanish Ministry of Economy and Competitiveness (grants RYC‐2012‐11704 and CTM2014‐54312‐P). L. C. F. and R. J. acknowledge funding from the MIT International Science and Technology Initiatives, through a Seed Fund grant. The simulation data are available on the UC Berkeley Dash repository at https://doi.org/10.6078/D1G67B.
    Description: 2019-11-06
    Keywords: Methane hydrates ; Xenon hydrates ; Phase behavior ; Growth kinetics ; Nonstoichiometry
    Repository Name: Woods Hole Open Access Server
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    Nitrogen cycle patterns during forest regrowth in an African Miombo woodland landscape (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2019. 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-Biogeosciences, 124(6), (2019): 1591-1603, doi:10.1029/2018JG004803.
    Description: Tropical dry forests in eastern and southern Africa cover 2.5 × 106 km2, support wildlife habitat and livelihoods of more than 150 million people, and face threats from land use and climate change. To inform conservation, we need better understanding of ecosystem processes like nutrient cycling that regulate forest productivity and biomass accumulation. Here we report on patterns in nitrogen (N) cycling across a 100‐year forest regrowth chronosequence in the Tanzanian Miombo woodlands. Soil and vegetation indicators showed that low ecosystem N availability for trees persisted across young to mature forests. Ammonium dominated soil mineral N pools from 0‐ to 15‐cm depth. Laboratory‐measured soil N mineralization rates across 3‐ to 40‐year regrowth sites showed no significant trends and were lower than mature forest rates. Aboveground tree N pools increased at 6 to 7 kg N·ha−1·yr−1, accounting for the majority of ecosystem N accumulation. Foliar δ15N 〈0‰ in an N‐fixing canopy tree across all sites suggested that N fixation may contribute to ecosystem N cycle recovery. These results contrast N cycling in wetter tropical and Neotropical dry forests, where indicators of N scarcity diminish after several decades of regrowth. Our findings suggest that minimizing woody biomass removal, litter layer, and topsoil disturbance may be important to promote N cycle recovery and natural regeneration in Miombo woodlands. Higher rates of N mineralization in the wet season indicated a potential that climate change‐altered rainfall leading to extended dry periods may lower N availability through soil moisture‐dependent N mineralization pathways, particularly for mature forests.
    Description: This study depended on the knowledge, insights, and cooperation of many people and institutions. We thank the Millennium Villages Project‐Mbola site for providing introductions to the landscape and village headmen in many regions. We thank the ARI‐Tumbi staff (now TARI‐Tumbi) in Tabora, Tanzania for providing invaluable logistical support in identifying forest regrowth sites and help with labwork in Tabora, Tanzania. We thank other key local organizations, including Tabora Development Foundation Trust (Dick Mlimuka, Oscar Kisanji) and Tanzania Forest Service (Bw. Relingo), for logistical support and transportation. We thank many village headmen and farmers for access to forest sites within their lands for sampling. Finally, we would like to thank the MBL Stable Isotope laboratory and Dr. Marshall Otter for his expertise with producing and interpreting soil and leaf C, N and stable isotope data. This study was funded in part by NSF PIRE Grant OISE 0968211, a Dissertation Support Grant to Marc Mayes from Brown University (2015–2016), and completed with permission and cooperation from the Tanzania Commission on Science and Technology (COSTECH permits 2013‐261‐NA‐2014‐199 and 2015‐183‐ER‐2014‐199). Data and code for analyses can be accessed at a Github repository: https://github.com/mtm17/MiomboN.git.
    Description: 2019-11-08
    Keywords: Nitrogen ; Africa ; Miombo ; Tropical dry forest ; Carbon ; Secondary forest regrowth
    Repository Name: Woods Hole Open Access Server
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    Role of Greenland freshwater anomaly in the recent freshening of the subpolar North Atlantic (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: The cumulative Greenland freshwater flux anomaly has exceeded 5,000 km3 since the 1990s. The volume of this surplus freshwater is expected to cause substantial freshening in the North Atlantic. Analysis of hydrographic observations in the subpolar seas reveals freshening signals in the 2010s. The sources of this freshening are yet to be determined. In this study, the relationship between the surplus Greenland freshwater flux and this freshening is tested by analyzing the propagation of the Greenland freshwater anomaly and its impact on salinity in the subpolar North Atlantic based on observational data and numerical experiments with and without the Greenland runoff. A passive tracer is continuously released during the simulations at freshwater sources along the coast of Greenland to track the Greenland freshwater anomaly. Tracer budget analysis shows that 44% of the volume of the Greenland freshwater anomaly is retained in the subpolar North Atlantic by the end of the simulation. This volume is sufficient to cause strong freshening in the subpolar seas if it stays in the upper 50–100 m. However, in the model the anomaly is mixed down to several hundred meters of the water column resulting in smaller magnitudes of freshening compared to the observations. Therefore, the simulations suggest that the accelerated Greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of freshwater have contributed to the freshening. Impacts on salinity in the subpolar seas of the freshwater transport through Fram Strait and precipitation are discussed.
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dukhovskoy, D. S., Yashayaev, I., Proshutinsky, A., Bamber, J. L., Bashmachnikov, I. L., Chassignet, E. P., Lee, C. M., & Tedstone, A. J. Role of Greenland freshwater anomaly in the recent freshening of the subpolar North Atlantic. Journal of Geophysical Research-Oceans, 124(5), (2019): 3333-3360, doi:10.1029/2018JC014686.
    Keywords: Greenland ice sheet melting ; freshwater anomaly ; subpolar North Atlantic ; subpolar gyre ; passive tracer numerical experiment ; freshwater budget
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    Water mass evolution and circulation of the northeastern Chukchi Sea in summer: Implications for nutrient distributions (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(7), (2019): 4416-4432, doi: 10.1029/2019JC015185.
    Description: Synoptic and historical shipboard data, spanning the period 1981–2017, are used to investigate the seasonal evolution of water masses on the northeastern Chukchi shelf and quantify the circulation patterns and their impact on nutrient distributions. We find that Alaskan coastal water extends to Barrow Canyon along the coastal pathway, with peak presence in September, while the Pacific Winter Water (WW) continually drains off the shelf through the summer. The depth‐averaged circulation under light winds is characterized by a strong Alaskan Coastal Current (ACC) and northward flow through Central Channel. A portion of the Central Channel flow recirculates anticyclonically to join the ACC, while the remainder progresses northeastward to Hanna Shoal where it bifurcates around both sides of the shoal. All of the branches converge southeast of the shoal and eventually join the ACC. The wind‐forced response has two regimes: In the coastal region the circulation depends on wind direction, while on the interior shelf the circulation is sensitive to wind stress curl. In the most common wind‐forced state—northeasterly winds and anticyclonic wind stress curl—the ACC reverses, the Central Channel flow penetrates farther north, and there is mass exchange between the interior and coastal regions. In September and October, the region southeast of Hanna Shoal is characterized by elevated amounts of WW, a shallower pycnocline, and higher concentrations of nitrate. Sustained late‐season phytoplankton growth spurred by this pooling of nutrients could result in enhanced vertical export of carbon to the seafloor, contributing to the maintenance of benthic hotspots in this region.
    Description: The authors acknowledge the hard work and dedication of the many crew members who sailed on the different cruises of the USCGC Healy and the R/V Palmer. This study would not have been possible without their ongoing efforts to carry out successful science operations. Seth Danielson performed the quality control of the Barrow wind data. Funding was provided by the following sources: National Oceanic and Atmospheric Administration (NOAA) Grant NA14‐OAR4320158 (P. L., R. P., and L. M.), National Science Foundation (NSF) Grants OPP‐1702371 and OPP‐1733564 (R. P. and F. B.) and PLR‐1303617 (R. P., K. A., and K. L.), NSF Graduate Research Fellowship Program DGE‐0645962 (K. L.), National Aeronautics and Space Administration award NNX10AF42G (R. P., K. A., and K. L.), and NOAA's Ocean Observing and Monitoring Division, Climate Program Office Fund 100007298 (C. M.). This publication is partially funded by the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA15OAR4320063 and is contribution EcoFOCI‐0924 to the Ecosystems and Fisheries‐Oceanography Coordinated Investigations, 4944 to PMEL. The CTD and shipboard ADCP data of the eight cruises are available from http://www.rvdata.us/, and the nutrients data can be accessed from https://arcticdata.io/.
    Description: 2019-12-07
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    Submarine permafrost map in the arctic modeled using 1-D transient heat flux (SuPerMAP) (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(6), (2019): 3490-3507, doi:10.1029/2018JC014675.
    Description: Offshore permafrost plays a role in the global climate system, but observations of permafrost thickness, state, and composition are limited to specific regions. The current global permafrost map shows potential offshore permafrost distribution based on bathymetry and global sea level rise. As a first‐order estimate, we employ a heat transfer model to calculate the subsurface temperature field. Our model uses dynamic upper boundary conditions that synthesize Earth System Model air temperature, ice mass distribution and thickness, and global sea level reconstruction and applies globally distributed geothermal heat flux as a lower boundary condition. Sea level reconstruction accounts for differences between marine and terrestrial sedimentation history. Sediment composition and pore water salinity are integrated in the model. Model runs for 450 ka for cross‐shelf transects were used to initialize the model for circumarctic modeling for the past 50 ka. Preindustrial submarine permafrost (i.e., cryotic sediment), modeled at 12.5‐km spatial resolution, lies beneath almost 2.5 ×106km2 of the Arctic shelf. Our simple modeling approach results in estimates of distribution of cryotic sediment that are similar to the current global map and recent seismically delineated permafrost distributions for the Beaufort and Kara seas, suggesting that sea level is a first‐order determinant for submarine permafrost distribution. Ice content and sediment thermal conductivity are also important for determining rates of permafrost thickness change. The model provides a consistent circumarctic approach to map submarine permafrost and to estimate the dynamics of permafrost in the past.
    Description: Boundary condition data are available online via the sources referenced in the manuscript. This work was partially funded by a Helmholtz Association of Research Centres (HGF) Joint Russian‐German Research Group (HGF JRG 100). This study is part of a project that has received funding from the European Unions Horizon 2020 research and innovation program under grant agreement 773421. Submarine permafrost studies in the Kara and Laptev Seas were supported by Russian Foundation for Basic Research (RFBR/RFFI) grants 18‐05‐60004 and 18‐05‐70091, respectively. The International Permafrost Association (IPA) and the Association for Polar Early Career Scientists (APECS) supported research coordination that led to this study. We acknowledge coordination support of the World Climate Research Programme (WCRP) through their core project on Climate and Cryosphere (CliC). Thanks to Martin Jakobsson for providing a digitized version of the preliminary IHO delineation of the Arctic seas and to Guy Masters for access to the observational geothermal database. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
    Description: 2019-10-17
    Keywords: Submarine permafrost ; Arctic ; Cryosphere ; Sea level
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    Hurricanes enhance labile carbon export to the deep ocean (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Geophysical Union, 2019. 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 46 (2019): 10484–10494, doi:10.1029/2019GL083719.
    Description: Tropical cyclones (hurricanes) generate intense surface ocean cooling and vertical mixing resulting in nutrient upwelling into the photic zone and episodic phytoplankton blooms. However, their influence on the deep ocean remains unknown. Here we present evidence that hurricanes also impact the ocean's biological pump by enhancing export of labile organic material to the deep ocean. In October 2016, Category 3 Hurricane Nicole passed over the Bermuda Time Series site in the oligotrophic NW Atlantic Ocean. Following Nicole's passage, particulate fluxes of lipids diagnostic of fresh phytodetritus, zooplankton, and microbial biomass increased by 30–300% at 1,500 m depth and 30–800% at 3,200 m depth. Mesopelagic suspended particles following Nicole were also enriched in phytodetrital material and in zooplankton and bacteria lipids, indicating particle disaggregation and a deepwater ecosystem response. Predicted climate‐induced increases in hurricane frequency and/or intensity may significantly alter ocean biogeochemical cycles by increasing the strength of the biological pump.
    Description: This work and the Oceanic Flux Program time series were supported by the National Science Foundation Chemical Oceanography Program Grant OCE 1536644. The Bermuda Atlantic Time Series and Hydrostation S time series were supported by NSF Grants OCE 1756105 and OCE 1633125, respectively. We acknowledge the contributions of BATS technicians with CTD and pigment analyses. We sincerely thank the officers and crew of R/V Atlantic Explorer (Bermuda Institute of Ocean Sciences) for their expert assistance on the cruises. The data used in this study are listed in the figures, tables, and references, and are also available in the NSF's Biological and Chemical Oceanography Data Management Office (BCO‐DMO, https://doi.org/10.1575/1912/bco‐dmo.775902.1).
    Description: 2020-02-16
    Keywords: Hurricanes ; Carbon cycle ; North Atlantic Ocean ; Deep ocean ; Particle fluxes ; Lipid biomarkers
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  • 179
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    Sea ice meltwater and Circumpolar Deep Water drive contrasting productivity in three Antarctic polynyas (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(5), (2019): 2943-2968, doi:10.1029/2019JC015071.
    Description: In the Southern Ocean, polynyas exhibit enhanced rates of primary productivity and represent large seasonal sinks for atmospheric CO2. Three contrasting east Antarctic polynyas were visited in late December to early January 2017: the Dalton, Mertz, and Ninnis polynyas. In the Mertz and Ninnis polynyas, phytoplankton biomass (average of 322 and 354 mg chlorophyll a (Chl a)/m2, respectively) and net community production (5.3 and 4.6 mol C/m2, respectively) were approximately 3 times those measured in the Dalton polynya (average of 122 mg Chl a/m2 and 1.8 mol C/m2). Phytoplankton communities also differed between the polynyas. Diatoms were thriving in the Mertz and Ninnis polynyas but not in the Dalton polynya, where Phaeocystis antarctica dominated. These strong regional differences were explored using physiological, biological, and physical parameters. The most likely drivers of the observed higher productivity in the Mertz and Ninnis were the relatively shallow inflow of iron‐rich modified Circumpolar Deep Water onto the shelf as well as a very large sea ice meltwater contribution. The productivity contrast between the three polynyas could not be explained by (1) the input of glacial meltwater, (2) the presence of Ice Shelf Water, or (3) stratification of the mixed layer. Our results show that physical drivers regulate the productivity of polynyas, suggesting that the response of biological productivity and carbon export to future change will vary among polynyas.
    Description: This work was cofunded by the Australian Antarctic Division research projects AAS 4131 and 4291. This project was also supported by the Australian Government Cooperative Research Centres Programme through the Antarctic Climate & Ecosystems (ACE CRC). S. Moreau and C. Genovese were supported by the Australian Research Council's Special Research Initiative for Antarctic Gateway Partnership (project ID SR140300001). V. Puigcorbé and M. Roca‐Martí are grateful for the support from Pere Masque and Edith Cowan University. M.C. Arroyo was supported by the Dickhut Fellowship, administered by the Virginia Institute of Marine Science. The authors would like to thank the officers and crew of the R/V Aurora Australis for their logistic support, the CSIRO hydrochemists for their analyses of nutrient concentrations, and E. J. Yang for her microscope analysis of phytoplankton species. We also want to thank two anonymous reviewers for their very good comments on this study. The data presented in this paper are available on the Australian Antarctic Division (AAD) Data Centre at https://data.aad.gov.au/aadc/metadata/metadata_by_parameter.cfm.
    Description: 2019-09-28
    Keywords: Polynyas ; Primary productivity ; Phytoplankton biomass ; Ice shelves ; Sea ice ; Iron
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    Unabated bottom water warming and freshening in the south Pacific Ocean. (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(3), (2019): 1778-1794, doi:10.1029/2018JC014775.
    Description: Abyssal ocean warming contributed substantially to anthropogenic ocean heat uptake and global sea level rise between 1990 and 2010. In the 2010s, several hydrographic sections crossing the South Pacific Ocean were occupied for a third or fourth time since the 1990s, allowing for an assessment of the decadal variability in the local abyssal ocean properties among the 1990s, 2000s, and 2010s. These observations from three decades reveal steady to accelerated bottom water warming since the 1990s. Strong abyssal (z 〉 4,000 m) warming of 3.5 (±1.4) m°C/year (m°C = 10−3 °C) is observed in the Ross Sea, directly downstream from bottom water formation sites, with warming rates of 2.5 (±0.4) m°C/year to the east in the Amundsen‐Bellingshausen Basin and 1.3 (±0.2) m°C/year to the north in the Southwest Pacific Basin, all associated with a bottom‐intensified descent of the deepest isotherms. Warming is consistently found across all sections and their occupations within each basin, demonstrating that the abyssal warming is monotonic, basin‐wide, and multidecadal. In addition, bottom water freshening was strongest in the Ross Sea, with smaller amplitude in the Amundsen‐Bellingshausen Basin in the 2000s, but is discernible in portions of the Southwest Pacific Basin by the 2010s. These results indicate that bottom water freshening, stemming from strong freshening of Ross Shelf Waters, is being advected along deep isopycnals and mixed into deep basins, albeit on longer timescales than the dynamically driven, wave‐propagated warming signal. We quantify the contribution of the warming to local sea level and heat budgets.
    Description: S. G. P. was supported by a U.S. GO‐SHIP postdoctoral fellowship through NSF grant OCE‐1437015, which also supported L. D. T. and S. M. and collection of U.S. GO‐SHIP data since 2014 on P06, S4P, P16, and P18. G. C. J. is supported by the Global Ocean Monitoring and Observation Program, National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce and NOAA Research. B. M. S and S. E. W. were supported by the Australian Government Department of the Environment and CSIRO through the Australian Climate Change Science Programme and by the National Environmental Science Program. We are grateful for the hard work of the science parties, officers, and crew of all the research cruises on which these CTD data were collected. We also thank the two anonymous reviewers for their helpful comments that improve the manuscript. This is PMEL contribution 4870. All CTD data sets used in this analysis are publicly available at the website (https://cchdo.ucsd.edu).
    Description: 2019-08-20
    Keywords: Abyssal warming ; Pacific deep circulation ; Deep steric sea level ; Deep warming variability ; Antarctic Bottom Water
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    Characterizing the transition from balanced to unbalanced motions in the Southern California Current (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(3), (2019): 2088-2109, doi:10.1029/2018JC014583.
    Description: As observations and models improve their resolution of oceanic motions at ever finer horizontal scales, interest has grown in characterizing the transition from the geostrophically balanced flows that dominate at large‐scale to submesoscale turbulence and waves that dominate at small scales. In this study we examine the mesoscale‐to‐submesoscale (100 to 10 km) transition in an eastern boundary current, the southern California Current System (CCS), using repeated acoustic Doppler current profiler transects, sea surface height from high‐resolution nadir altimetry and output from a (1/48)° global model simulation. In the CCS, the submesoscale is as energetic as in western boundary current regions, but the mesoscale is much weaker, and as a result the transition lacks the change in kinetic energy (KE) spectral slope observed for western boundary currents. Helmholtz and vortex‐wave decompositions of the KE spectra are used to identify balanced and unbalanced contributions. At horizontal scales greater than 70 km, we find that observed KE is dominated by balanced geostrophic motions. At scales from 40 to 10 km, unbalanced contributions such as inertia‐gravity waves contribute as much as balanced motions. The model KE transition occurs at longer scales, around 125 km. The altimeter spectra are consistent with acoustic Doppler current profiler/model spectra at scales longer than 70/125 km, respectively. Observed seasonality is weak. Taken together, our results suggest that geostrophic velocities can be diagnosed from sea surface height on scales larger than about 70 km in the southern CCS.
    Description: This research was funded by NASA (NNX13AE44G, NNX13AE85G, NNX16AH67G, NNX16AO5OH, and NNX17AH53G). We thank Sung Yong Kim for providing the high‐frequency radar spectral estimates and the two anonymous reviewers for providing useful comments and suggestions that greatly improved the manuscript. High‐frequency ALES data for Jason‐1 and Jason‐2 altimeters are available upon request (https://openadb.dgfi.tum.de/en/contact/ALES). Both AltiKa and Sentinel‐3 altimeter products were produced and distributed by the Copernicus Marine and Environment Monitoring Service (CMEMS; http://www.marine.copernicus.eu). D. M. worked on the modeling component of this study at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). High‐end computing resources were provided by the NASA Advanced Supercomputing (NAS) Division of the Ames Research Center. The LLC output can be obtained from the ECCO project (ftp://ecco.jpl.nasa.gov/ECCO2/LLC4320/). The ADCP data are available at the Joint Archive for Shipboard ADCP data (JASADCP; http://ilikai.soest.hawaii.edu/sadcp).
    Description: 2019-08-21
    Keywords: Mesoscale ; Submesoscale ; Internal gravity waves
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    "Petit spot" rejuvenated volcanism superimposed on plume-derived Samoan shield volcanoes: Evidence from a 645-m drill core from Tutuila Island, American Samoa (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. 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 20(3), (2019): 1485-1507, doi:10.1029/2018GC007985.
    Description: In 2015 a geothermal exploration well was drilled on the island of Tutuila, American Samoa. The sample suite from the drill core provides 645 m of volcanic stratigraphy from a Samoan volcano, spanning 1.45 million years of volcanic history. In the Tutuila drill core, shield lavas with an EM2 (enriched mantle 2) signature are observed at depth, spanning 1.46 to 1.44 Ma. These are overlain by younger (1.35 to 1.17 Ma) shield lavas with a primordial “common” (focus zone) component interlayered with lavas that sample a depleted mantle component. Following ~1.15 Myr of volcanic quiescence, rejuvenated volcanism initiated at 24.3 ka and samples an EM1 (enriched mantle 1) component. The timing of the initiation of rejuvenated volcanism on Tutuila suggests that rejuvenated volcanism may be tectonically driven, as Samoan hotspot volcanoes approach the northern terminus of the Tonga Trench. This is consistent with a model where the timing of rejuvenated volcanism at Tutuila and at other Samoan volcanoes relates to their distance from the Tonga Trench. Notably, the Samoan rejuvenated lavas have EM1 isotopic compositions distinct from shield lavas that are geochemically similar to “petit spot” lavas erupted outboard of the Japan Trench and late stage lavas erupted at Christmas Island located outboard of the Sunda Trench. Therefore, like the Samoan rejuvenated lavas, petit spot volcanism in general appears to be related to tectonic uplift outboard of subduction zones, and existing geochemical data suggest that petit spots share similar EM1 isotopic signatures.
    Description: Reviews from Kaj Hoernle and three anonymous reviewers are gratefully acknowledged. M. G. J. acknowledges support from the American Samoa Power Authority and National Science Foundation grants OCE‐1736984 and EAR‐1624840. The Tutuila drill core was the brainchild of Tim Bodell, without whom we would still have no stratigraphic record of Tutuila volcanism. The support of Utu Abe Malae and Matamua Katrina Mariner was instrumental to the project's success. We dedicate this paper to the memory of Abe Malae and his efforts to support science and education in American Samoa. Images of the entire drill core are available online (escholarship.org/uc/item/6gg6p61w). All data presented are either part of this study or previously published and are referenced in text.
    Description: 2019-08-13
    Keywords: Samoa ; Mantle geochemistry ; Petit spot ; EM1 ; Rejuvenated volcanism
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    Deepening of the winter mixed layer in the Canada Basin, Arctic Ocean over 2006-2017 (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(7), (2019): 4618-4630, doi: 10.1029/2019JC014940.
    Description: The Arctic Ocean mixed layer interacts with the ice cover above and warmer, nutrient‐rich waters below. Ice‐Tethered Profiler observations in the Canada Basin of the Arctic Ocean over 2006–2017 are used to investigate changes in mixed layer properties. In contrast to decades of shoaling since at least the 1980s, the mixed layer deepened by 9 m from 2006–2012 to 2013–2017. Deepening resulted from an increase in mixed layer salinity that also weakened stratification at the base of the mixed layer. Vertical mixing alone can explain less than half of the observed change in mixed layer salinity, and so the observed increase in salinity is inferred to result from changes in freshwater accumulation via changes to ice‐ocean circulation or ice melt/growth and river runoff. Even though salinity increased, the shallowest density surfaces deepened by 5 m on average suggesting that Ekman pumping over this time period remained downward. A deeper mixed layer with weaker stratification has implications for the accessibility of heat and nutrients stored in the upper halocline. The extent to which the mixed layer will continue to deepen appears to depend primarily on the complex set of processes influencing freshwater accumulation.
    Description: We gratefully acknowledge J. Toole for helpful conversations. S. Cole was supported by the National Science Foundation under grant PLR‐1602926 and J. Stadler by the Woods Hole Oceanographic Institution Summer Student Fellowship program. Profile data are available via the Ice‐Tethered Profiler program website: http://whoi.edu/itp. SSM/I ice concentration data were downloaded from the National Snow and Ice Data Center.
    Description: 2019-12-22
    Keywords: Arctic Ocean ; Mixed layer ; Freshwater
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    Dissolved organic radiocarbon in the central Pacific Ocean (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Druffel, E. R. M., Griffin, S., Wang, N., Garcia, N. G., McNichol, A. P., Key, R. M., & Walker, B. D. Dissolved organic radiocarbon in the central Pacific Ocean. Geophysical Research Letters, 46(10), (2019):5396-5403, doi:10.1029/2019GL083149.
    Description: We report marine dissolved organic carbon (DOC) concentrations, and DOC ∆14C and δ13C values in seawater collected from the central Pacific. Surface ∆14C values are low in equatorial and polar regions where upwelling occurs and high in subtropical regions dominated by downwelling. A core feature of these data is that 14C aging of DOC (682 ± 86 14C years) and dissolved inorganic carbon (643 ± 40 14C years) in Antarctic Bottom Water between 54.0°S and 53.5°N are similar. These estimates of aging are minimum values due to mixing with deep waters. We also observe minimum ∆14C values (−550‰ to −570‰) between the depths of 2,000 and 3,500 m in the North Pacific, though the source of the low values cannot be determined at this time.
    Description: We thank Jennifer Walker, Xiaomei Xu, and Dachun Zhang for their help with the stable carbon isotope measurements; John Southon and staff of the Keck Carbon Cycle AMS Laboratory for their assistance and advice; the support of chief scientists Samantha Siedlecki, Molly Baringer, Alison Macdonald, and Sabine Mecking; the guidance of Jim Swift and Dennis Hansell for shared ship time; and Sarah Bercovici for collecting water on the GoA cruise. We appreciate the comments of Christian Lewis and Niels Hauksson on this manuscript. This work was supported by NSF (OCE‐141458941 to E. R. M. D. and OCE‐0824864, OCE‐1558654, and Cooperative Agreement OCE1239667 to R. M. K. and A. P. M.), the Fred Kavli Foundation, the Keck Carbon Cycle AMS Laboratory, and the NSF/NOAA‐funded GO‐SHIP Program. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program (to B. D. W.) and an American Chemical Society Petroleum Research Fund New Directions grant (55430‐ND2 to E. R. M. D. and B. D. W.). Data from the P16N cruises are available in Table S2 in the Supporting Information and at the Repeat Hydrography Data Center at the CCHDO website (http://cdiac.esd.ornl.gov/oceans/index.html) using the expo codes 3RO20150329, 3RO20150410, and 3RO20150525. There are no real or perceived financial conflicts of interests for any author.
    Description: 2019-11-02
    Keywords: Dissolved organic carbon ; Radiocarbon ; Pacific Ocean ; Dissolved inorganic carbon ; Deep ocean circulation ; AABW
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    Frontal subduction of the Mid-Atlantic Bight shelf water at the onshore edge of a warm-core ring (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-19
    Description: Author Posting. © American Geophysical Union, 2018. 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-Oceans, 123(11), (2018): 7795-7818. doi: 10.1029/2018JC013794.
    Description: This work studies the subduction of the shelf water along the onshore edge of a warm‐core ring that impinges on the edge of the Mid‐Atlantic Bight continental shelf. The dynamical analysis is based on observations by satellites and from the Ocean Observatories Initiative Pioneer Array observatory as well as idealized numerical model simulations. They together show that frontogenesis‐induced submesoscale frontal subduction with order‐one Rossby and Froude numbers occurs on the onshore edge of the ring. The subduction flow results from the onshore migration of the warm‐core ring that intensifies the density front on the interface of the ring and shelf waters. The subduction is a part of the cross‐front secondary circulation trying to relax the intensifying density front. The dramatically different physical and biogeochemical properties of the ring and shelf waters provide a great opportunity to visualize the subduction phenomenon. Entrained by the ring‐edge current, the subducted shelf water is subsequently transported offshore below a surface layer of ring water and alongside of the surface‐visible shelf‐water streamer. It explains the historical observations of isolated subsurface packets of shelf water along the ring periphery in the slope sea. Model‐based estimate suggests that this type of subduction‐associated subsurface cross‐shelfbreak transport of the shelf water could be substantial relative to other major forms of shelfbreak water exchange. This study also proposes that outward spreading of the ring‐edge front by the frontal subduction may facilitate entrainment of the shelf water by the ring‐edge current and enhances the shelf‐water streamer transport at the shelf edge.
    Description: W. G. Z. was supported by the National Science Foundation under grants OCE‐1657853, OCE‐1657803, and OCE 1634965. JP is grateful for the support of the Woods Hole Oceanographic Institution Summer Student Fellow Program in 2016 and 2017. W. G. Z. thanks Kenneth Brink, Glen Gawarkiewicz, Rocky Geyer, Steven Lentz, Dennis McGillicuddy, Robert Todd, and John Trowbridge for helpful discussions during the course of the study or useful comments on earlier versions of the manuscript. The satellite sea surface temperature data were obtained from the University of Delaware Ocean Exploration, Remote Sensing, Biogeography Lab (led by Matthew Oliver), through the Mid‐Atlantic Coastal Ocean Observing System (MARACOOS) data server (http://tds.maracoos.org/thredds/catalog.html). The OOI Pioneer Array mooring and glider data presented in this paper were downloaded from the National Science Foundation OOI data portal (http://ooinet.oceanobservatories.org) in July–August 2016.
    Description: 2019-04-15
    Keywords: Frontal subduction ; Warm‐core ring ; Mid‐Atlantic Bight ; Shelf‐water streamer ; Cross‐shelf exchange ; OOI Pioneer Array
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    Long-term and seasonal changes of large whale call frequency in the Southern Indian Ocean (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2018. 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 1123(11), (2018): 8568-8580. doi: 10.1029/2018JC014352.
    Description: In the past decades, in the context of a changing ocean submitted to an increasing human activity, a progressive decrease in the frequencies (pitch) of blue whale vocalizations has been observed worldwide. Its causes, of natural or anthropogenic nature, are still unclear. Based on 7 years of continuous acoustic recordings at widespread sites in the southern Indian Ocean, we show that this observation stands for five populations of large whales. The frequency of selected units of vocalizations of fin, Antarctic, and pygmy blue whales has steadily decreased at a rate of a few tenths of hertz per year since 2002. In addition to this interannual frequency decrease, blue whale vocalizations display seasonal frequency shifts. We show that these intra‐annual shifts correlate with seasonal changes in the ambient noise near their call frequency. This ambient noise level, in turn, shows a strong correlation with the seasonal presence of icebergs, which are one of the main sources of oceanic noise in the Southern Hemisphere. Although cause‐and‐effect relationships are difficult to ascertain, wide‐ranging changes in the acoustic environment seem to have a strong impact on the vocal behavior of large baleen whales. Seasonal frequency shifts may be due to short‐term changes in the ambient noise, and the interannual frequency decline to long‐term changes in the acoustic properties of the ocean and/or in postwhaling changes in whale abundances.
    Description: The authors wish to thank the Captains and crews of RV Marion Dufresne for the successful deployments and recoveries of the hydrophones of the DEFLOHYDRO (Royer, 2008) and OHASISBIO (Royer, 2009) experiments. French cruises were funded by the French Polar Institute (IPEV) with additional support from INSU‐CNRS. NOAA/PMEL also contributed to the DEFLOHYDRO project. E. C. L. was supported by a PhD fellowship from the University of Brest and from the Regional Council of Brittany (Conseil Régional de Bretagne). The contribution of Mickael Beauverger at LGO to the logistics and deployment of the OHASISBIO cruises is greatly appreciated. The data underlying this analysis (weekly averaged frequencies of Antarctic blue whales, pygmy blue whales, and fin whales and daily averaged noise levels at each site) are accessible at http://doi.org/10.17882/51007.
    Description: 2019-05-27
    Keywords: Large baleen whales ; Blue whale calls ; Frequency decrease ; Bioacoustics ; Frequency shifts ; Ambient noise
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  • 187
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    A diel method of estimating gross primary production: 1. Validation with a realistic numerical model of Chesapeake Bay (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2018. 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: Oceans 123(11), (2018): 8411-8429, doi: 10.1029/2018JC014178.
    Description: A method for estimating gross primary production (GPP) is presented and validated against a numerical model of Chesapeake Bay that includes realistic physical and biological forcing. The method statistically fits a photosynthesis‐irradiance response curve using the observed near‐surface time rate of change of dissolved oxygen and the incoming solar radiation, yielding estimates of the light‐saturated photosynthetic rate and the initial slope of the photosynthesis‐irradiance response curve. This allows estimation of GPP with 15‐day temporal resolution. The method is applied to the output from a numerical model that has high skill at reproducing both surface and near‐bottom dissolved oxygen variations observed in Chesapeake Bay in 2013. The rate of GPP predicted by the numerical model is known, as are the contributions from physical processes, allowing the proposed diel method to be rigorously assessed. At locations throughout the main stem of the Bay, the method accurately extracts the underlying rate of GPP, including pronounced seasonal variability and spatial variability. Errors associated with the method are primarily the result of contributions by the divergence in turbulent oxygen flux, which changes sign over the surface mixed layer. As a result, there is an optimal vertical location with minimal bias where application of the method is most accurate.
    Description: This paper is the result of research funded in part by NOAA's U.S. Integrated Ocean Observing System (IOOS) Program Office as a subcontract to the Woods Hole Oceanographic Institution under award NA13NOS120139 to the Southeastern University Research Association. All of the model output, as well as both the CBIBS data (2010–2016) and the bottom oxygen data of Scully (2016b), are publicly available through the THREDDS server associated with the IOOS Coastal Modeling Testbed site: https://comt.ioos.us/projects/cb_hypoxia.
    Description: 2019-05-24
    Keywords: Gross primary production ; Vertical mixing ; Numerical model ; Chesapeake Bay
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  • 188
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    Theoretical considerations on factors confounding the interpretation of the oceanic carbon export ratio (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Theoretical considerations on factors confounding the interpretation of the oceanic carbon export ratio. Global Biogeochemical Cycles, 32(11), (2018); 1644-1658, doi:10.1029/2018GB006003.
    Description: The fraction of primary production exported out of the surface ocean, known as the export ratio (ef ratio), is often used to assess how various factors, including temperature, primary production, phytoplankton size, and community structure, affect the export efficiency of an ecosystem. To investigate possible causes for reported discrepancies in the dominant factors influencing the export efficiency, we develop a metabolism‐based mechanistic model of the ef ratio. Consistent with earlier studies, we find based on theoretical considerations that the ef ratio is a negative function of temperature. We show that the ef ratio depends on the optical depth, defined as the physical depth times the light attenuation coefficient. As a result, varying light attenuation may confound the interpretation of ef ratio when measured at a fixed depth (e.g., 100 m) or at the base of the mixed layer. Finally, we decompose the contribution of individual factors on the seasonality of the ef ratio. Our results show that at high latitudes, the ef ratio at the base of mixed layer is strongly influenced by mixed layer depth and surface irradiation on seasonal time scales. Future studies should report the ef ratio at the base of the euphotic layer or account for the effect of varying light attenuation if measured at a different depth. Overall, our modeling study highlights the large number of factors confounding the interpretation of field observations of the ef ratio.
    Description: Z. L was supported by a NASA Earth and Space Science Fellowship (Grant NNX13AN85H) and the Postdoctoral Scholarship Program at Woods Hole Oceanographic Institution. N. C. was supported by NASA Grant 5109296. Satellite data, nutrient concentration, and monthly MLD climatology are downloaded from NASA ocean color (http://oceancolor.gsfc.nasa.gov/cms/), World Ocean Atlas (https://www.nodc.noaa.gov/OC5/woa13/), and http://www.ifremer.fr/cerweb/deboyer/mld/home.php, respectively.
    Description: 2019-04-13
    Keywords: Oceanic carbon export ratio ; Net community production ; Export production ; Net primary production
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  • 189
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    Bigger tides, less flooding: Effects of dredging on barotropic dynamics in a highly modified estuary. (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124 (2019): 196-211, doi:10.1029/2018JC014313.
    Description: Since the late nineteenth century, channel depths have more than doubled in parts of New York Harbor and the tidal Hudson River, wetlands have been reclaimed and navigational channels widened, and river flow has been regulated. To quantify the effects of these modifications, observations and numerical simulations using historical and modern bathymetry are used to analyze changes in the barotropic dynamics. Model results and water level records for Albany (1868 to present) and New York Harbor (1844 to present) recovered from archives show that the tidal amplitude has more than doubled near the head of tides, whereas increases in the lower estuary have been slight (〈10%). Channel deepening has reduced the effective drag in the upper tidal river, shifting the system from hyposynchronous (tide decaying landward) to hypersynchronous (tide amplifying). Similarly, modeling shows that coastal storm effects propagate farther landward, with a 20% increase in amplitude for a major event. In contrast, the decrease in friction with channel deepening has lowered the tidally averaged water level during discharge events, more than compensating for increased surge amplitude. Combined with river regulation that reduced peak discharges, the overall risk of extreme water levels in the upper tidal river decreased after channel construction, reducing the water level for the 10‐year recurrence interval event by almost 3 m. Mean water level decreased sharply with channel modifications around 1930, and subsequent decadal variability has depended both on river discharge and sea level rise. Channel construction has only slightly altered tidal and storm surge amplitudes in the lower estuary.
    Description: Funding for D. K. R., W. R. G., and C. K. S. was provided by NSF Coastal SEES awards OCE-1325136 and OCE-1325102. Funding for S.T. and H. Z. was provided by the U.S. Army Corps of Engineers (award W1927 N-14-2-0015), and NSF (Career Award 1455350). Data supporting this study are posted to Zenodo (https://doi.org/10.5281/zenodo.1298636).
    Description: 2019-06-11
    Keywords: Barotropic tides ; Flood frequency ; Storm surge ; Dredging ; Estuary ; Tidal river
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  • 190
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    Wave generation, dissipation, and disequilibrium in an embayment with complex bathymetry (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Wave generation, dissipation, and disequilibrium in an embayment with complex bathymetry. Journal of Geophysical Research-Oceans, 123(11), (2018): 7856-7876, doi:10.1029/2018JC014381.
    Description: Heterogeneous, sharply varying bathymetry is common in estuaries and embayments, and complex interactions between the bathymetry and wave processes fundamentally alter the distribution of wave energy. The mechanisms that control the generation and dissipation of wind waves in an embayment with heterogeneous, sharply varying bathymetry are evaluated with an observational and numerical study of the Delaware Estuary. Waves in the lower bay depend on both local wind forcing and remote wave forcing from offshore, but elsewhere in the estuary waves are controlled by the local winds and the response of the wavefield to bathymetric variability. Differences in the wavefield with wind direction highlight the impacts of heterogeneous bathymetry and limited fetch. Under the typical winter northwest wind conditions waves are fetch‐limited in the middle estuary and reach equilibrium with local water depth only in the lower bay. During southerly wind conditions typical of storms, wave energy is near equilibrium in the lower bay, and midestuary waves are attenuated by the combination of whitecapping and bottom friction, particularly over the steep, longitudinal shoals. Although the energy dissipation due to bottom friction is generally small relative to whitecapping, it becomes significant where the waves shoal abruptly due to steep bottom topography. In contrast, directional spreading keeps wave heights in the main channel significantly less than local equilibrium. The wave disequilibrium in the deep navigational channel explains why the marked increase in depth by dredging of the modern channel has had little impact on wave conditions.
    Description: Funding was provided by National Science Foundation Coastal SEES: Toward Sustainable Urban Estuaries in the Anthropocene (OCE 1325136) and Ministry of Science and Technology (MOST 107‐2611‐M‐006‐004). We thank James Kirby, Fengyan Shi, and the two anonymous reviewers for their careful reading of our manuscript and their insightful comments. We thank Tracy Quirk for providing wave measurements in Bombay Hook, DE and Stow Creek, NJ. We thank Katie Pijanowski for compiling historical and modern bathymetric data for the estuary. Data supporting this study are posted to Zenodo (http://doi.org/10.5281/zenodo.1433055).
    Description: 2019-04-04
    Keywords: Estuarine hydrodynamics ; Wave energy ; Equilibrium wave ; Anthropogenic impact
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  • 191
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    Using carbon isotope fractionation to constrain the extent of methane dissolution into the water column surrounding a natural hydrocarbon gas seep in the northern Gulf of Mexico (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Using carbon isotope fractionation to constrain the extent of methane dissolution into the water column surrounding a natural hydrocarbon gas seep in the northern gulf of Mexico. Geochemistry Geophysics Geosystems, 19(11), (2018); 4459-4475., doi:10.1029/2018GC007705.
    Description: A gas bubble seep located in the northern Gulf of Mexico was investigated over several days to determine whether changes in the stable carbon isotopic ratio of methane can be used as a tracer for methane dissolution through the water column. Gas bubble and water samples were collected at the seafloor and throughout the water column for isotopic ratio analysis of methane. Our results show that changes in methane isotopic ratios are consistent with laboratory experiments that measured the isotopic fractionation from methane dissolution. A Rayleigh isotope model was applied to the isotope data to determine the fraction of methane dissolved at each depth. On average, the fraction of methane dissolved surpasses 90% past an altitude of 400 m above the seafloor. Methane dissolution was also investigated using a modified version of the Texas A&M Oil spill (Outfall) Calculator (TAMOC) where changes in methane isotopic ratios could be calculated. The TAMOC model results show that dissolution depends on depth and bubble size, explaining the spread in measured isotopic ratios during our investigations. Both the Rayleigh and TAMOC models show that methane bubbles quickly dissolve following emission from the seafloor. Together, these results show that it is possible to use measurements of natural methane isotopes to constrain the extent of methane dissolution following seafloor emission.
    Description: This research was made possible by two grants from the Gulf of Mexico Research Initiative: Gulf Integrated Spill Response (GISR) Consortium (awarded to J. D. K. and S. A. S.) and Center for Integrated Modeling and Assessment of the Gulf Ecosystem (C‐IMAGE) II (awarded to S. A. S.). Additional support was provided by the U.S. Department of Energy (DE‐FE0028980; awarded to J. D. K.). Data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC). Methane concentration and isotopic ratio data can be found at https://data.gulfresearchinitiative.org/data/R1.x137.000:0025, and TAMOC model scripts and results are found at https://data.gulfresearchinitiative.org/data/R1.x137.000:0026. The coversion of methane isotopic ratio data used in this manuscript can be found at https://data.gulfresearchinitiative.org/data/R1.x137.000:0028. We want to thank the captain and crew of the E/V Nautilus and the operators of ROV Hercules and Argus during the GISR G08 cruise and Nicole Raineault for their outstanding support at sea. Acoustically identifying the bubble flare was managed by Andone Lavery, and support for collecting gas and water samples was provided by John Bailey. We also want to thank Sean Sylva for analytical assistance on shore, Inok Jun for helping create the sampling schematics, and David Brink‐Roby for helping create the sample site map.
    Description: 2019-04-20
    Keywords: Methane ; Bubble ; Hydrate ; Dissolution ; Isotope
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  • 192
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    A diel method of estimating gross primary production: 2. Application to 7 years of near-surface dissolved oxygen data in Chesapeake Bay. (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2018. 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: Oceans 123(11), (2018): 8430-8443, doi: 10.1029/2018JC014179.
    Description: A diel method for estimating gross primary production (GPP) is applied to nearly continuous measurements of near‐surface dissolved oxygen collected at seven locations throughout the main stem of Chesapeake Bay. The data were collected through the Chesapeake Bay Interpretive Buoy System and span the period 2010–2016. At all locations, GPP exhibits pronounced seasonal variability consistent temperature‐dependent phytoplankton growth. At the Susquehanna Buoy, which is located within the estuarine turbidity maximum, rates of GPP are negatively correlated with uncalibrated turbidity data consistent with light limitation at this location. The highest rates of GPP are located immediately down Bay from the estuarine turbidity maximum and decrease moving seaward consistent with nutrient limitation. Rates of GPP at the mouth (First Landing Buoy) are roughly a factor of 3 lower than the rates in the upper Bay (Patapsco). At interannual time scales, the summer (June–July) rate of GPP averaged over all stations is positively correlated (r2 = 0.62) with the March Susquehanna River discharge and a multiple regression model that includes spring river discharge, and summer water temperature can explain most (r2 = 0.88) of the interannual variance in the observed rate of GPP. The correlation with river discharge is consistent with an increase in productivity fueled by increased nutrient loading. More generally, the spatial and temporal patterns inferred using this method are consistent with our current understanding of primary production in the Bay, demonstrating the potential this method has for making highly resolved measurements in less well studied estuarine systems.
    Description: This paper is the result of research funded in part by NOAA's U.S. Integrated Ocean Observing System (IOOS) Program Office as a subcontract to the Woods Hole Oceanographic Institution under award NA13NOS120139 to the Southeastern University Research Association. All of the data analyzed in this paper are publicly available including the CBIBS data (http://buoybay.noaa.gov), the NCEP NARR data (https://www.esrl.noaa.gov/psd), and the Kd‐490 MODIS data (ftp://ftp.star.nesdis.noaa.gov/pub/socd1/ecn/data/modis/k490noaa/monthly/cd/). Model output analyzed in this paper is publicly available through the THREDDS server associated with the IOOS Coastal and Ocean Modeling Testbed (COMT) site (https://comt.ioos.us/projects/cb_hypoxia). Postprocessed and compiled data for all seven CBIBS locations including the interpolated values of incoming solar radiation and satellite‐derived Kd‐490 can also be download from the COMT site.
    Description: 2019-05-25
    Keywords: Gross primary production ; Chesapeake Bay ; Observing system ; Diel variability
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  • 193
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    Effects of locally generated wind waves on the momentum budget and subtidal exchange in a coastal plain estuary (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(2), (2019):1005-1028, doi:10.1029/2018JC014585.
    Description: A numerical model with a vortex force formalism is used to study the role of wind waves in the momentum budget and subtidal exchange of a shallow coastal plain estuary, Delaware Bay. Wave height and age in the bay have a spatial distribution that is controlled by bathymetry and fetch, with implications for the surface drag coefficient in young, underdeveloped seas. Inclusion of waves in the model leads to increases in the surface drag coefficient by up to 30% with respect to parameterizations in which surface drag is only a function of wind speed, in agreement with recent observations of air‐sea fluxes in estuaries. The model was modified to prevent whitecapping wave dissipation from generating breaking forces since that contribution is integrally equivalent to the wind stress. The proposed adjustment is consistent with previous studies of wave‐induced nearshore currents and with additional parameterizations for breaking forces in the model. The mean momentum balance during a simulated wind event was mainly between the pressure gradient force and surface stress, with negligible contributions by vortex, wave breaking (i.e., depth‐induced), and Stokes‐Coriolis forces. Modeled scenarios with realistic Delaware bathymetry suggest that the subtidal bay‐ocean exchange at storm time scales is sensitive to wave‐induced surface drag coefficient, wind direction, and mass transport due to the Stokes drift. Results herein are applicable to shallow coastal systems where the typical wave field is young (i.e., wind seas) and modulated by bathymetry.
    Description: This work was supported by National Science Foundation Coastal SEES grant 1325136. We acknowledge Christopher Sommerfield's Group, Jia‐Lin Chen, and Julia Levin who provided assistance with the model configuration. We also thank Nirnimesh Kumar, Greg Gerbi, Melissa Moulton, and the Rutgers Ocean Modeling group for constructive feedback. Insightful comments by two anonymous reviewers helped improve the manuscript. Model files are available in an open access repository (https://doi.org/10.5281/zenodo.1695900).
    Description: 2019-07-28
    Keywords: Bathymetry ; Vortex forces ; Subtidal exchange ; Wind waves ; Surface drag
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  • 194
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    Response to channel deepening of the salinity intrusion, estuarine circulation, and stratification in an urbanized estuary (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(7), (2019): 4784-4802, doi: 10.1029/2019JC015006.
    Description: Modifications for navigation since the late 1800s have increased channel depth (H) in the lower Hudson River estuary by 10–30%, and at the mouth the depth has more than doubled. Observations along the lower estuary show that both salinity and stratification have increased over the past century. Model results comparing predredging bathymetry from the 1860s with modern conditions indicate an increase in the salinity intrusion of about 30%, which is roughly consistent with the H5/3 scaling expected from theory for salt flux dominated by steady exchange. While modifications including a recent deepening project have been concentrated near the mouth, the changes increase salinity and threaten drinking water supplies more than 100 km landward. The deepening has not changed the responses to river discharge (Qr) of the salinity intrusion (~Qr−1/3) or mean stratification (Qr2/3). Surprisingly, the increase in salinity intrusion with channel deepening results in almost no change in the estuarine circulation. This contrasts sharply with local scaling based on local dynamics of an H2 dependence, but it is consistent with a steady state salt balance that allows scaling of the estuarine circulation based on external forcing factors and is independent of depth. In contrast, the observed and modeled increases in stratification are opposite of expectations from the steady state balance, which could be due to reduction in mixing with loss of shallow subtidal regions. Overall, the mean shift in estuarine parameter space due to channel deepening has been modest compared with the monthly‐to‐seasonal variability due to tides and river discharge.
    Description: Funding was provided by NSF Coastal SEES (OCE 1325136). Data supporting this study are posted to Zenodo (https://doi.org/10.5281/zenodo.2551285) or are available by contacting the author.
    Description: 2019-12-07
    Keywords: Estuarine circulation ; Salinity intrusion ; Stratification ; Dredging ; Hudson River
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  • 195
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    Parameterizing air-water gas exchange in the shallow, microtidal New River estuary (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution-NonCommercial‐NoDerivs License. The definitive version was published in Van Dam, B. R., Edson, J. B., & Tobias, C. Parameterizing air-water gas exchange in the shallow, microtidal New River estuary. Journal of Geophysical Research-Biogeosciences, 124(7), (2019): 2351-2363, doi: 10.1029/2018JG004908.
    Description: Estuarine CO2 emissions are important components of regional and global carbon budgets, but assessments of this flux are plagued by uncertainties associated with gas transfer velocity (k) parameterization. We combined direct eddy covariance measurements of CO2 flux with waterside pCO2 determinations to generate more reliable k parameterizations for use in small estuaries. When all data were aggregated, k was described well by a linear relationship with wind speed (U10), in a manner consistent with prior open ocean and estuarine k parameterizations. However, k was significantly greater at night and under low wind speed, and nighttime k was best predicted by a parabolic, rather than linear, relationship with U10. We explored the effect of waterside thermal convection but found only a weak correlation between convective scale and k. Hence, while convective forcing may be important at times, it appears that factors besides waterside thermal convection were likely responsible for the bulk of the observed nighttime enhancement in k. Regardless of source, we show that these day‐night differences in k should be accounted for when CO2 emissions are assessed over short time scales or when pCO2 is constant and U10 varies. On the other hand, when temporal variability in pCO2 is large, it exerts greater control over CO2 fluxes than does k parameterization. In these cases, the use of a single k value or a simple linear relationship with U10 is often sufficient. This study provides important guidance for k parameterization in shallow or microtidal estuaries, especially when diel processes are considered.
    Description: We thank SERDP and DCERP for funding and support. Dennis Arbige assisted with EC tower construction, and Susan Cohen provided invaluable logistical support. I also thank Marc Alperin (UNC Chapel Hill) for his thoughtful guidance and encouragement with this project. All data sets for this manuscript are available at FigShare (https://doi.org/10.6084/m9.figshare.7276877.v1). Additional funding for this project was provided by DAAD (57429828) from funds of the German Federal Ministry of Education and Research (BMBF).
    Keywords: Air‐water CO2 exchange ; Gas transfer velocity ; Convective ; Eddy covariance ; Estuary ; Gas exchange
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  • 196
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    Mesoscale eddies modulate mixed layer depth globally. (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2019. 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 46(3), (2019):1505-1512, doi:10.1029/2018GL080006.
    Description: Mesoscale eddies, energetic vortices covering nearly a third of the ocean surface at any one time, modulate the spatial and temporal evolution of the mixed layer. We present a global analysis of concurrent satellite observations of mesoscale eddies with hydrographic profiles by autonomous Argo floats, revealing rich geographic and seasonal variability in the influence of eddies on mixed layer depth. Anticyclones deepen the mixed layer depth, whereas cyclones thin it, with the magnitude of these eddy‐induced mixed layer depth anomalies being largest in winter. Eddy‐centric composite averages reveal that the largest anomalies occur at the eddy center and decrease with distance from the center. Furthermore, the extent to which eddies modulate mixed layer depth is linearly related to the sea surface height amplitude of the eddies. Finally, large eddy‐mediated mixed layer depth anomalies are more common in anticyclones when compared to cyclones. We present candidate mechanisms for this observed asymmetry.
    Description: This project was supported by NASA grants NNX13AE47G and NNX16AH9G. This manuscript was improved as a result of helpful discussions with Jeffery Early, Johnathan Lilly, and Eric Kunze of Northwest Research Associates. D. J. M. also gratefully acknowledges support of the National Science Foundation. The eddy data set used here is distributed by AVISO at https://www.aviso.altimetry.fr/en/data/products/value-added-products/global-mesoscale-eddy-trajectoryproduct.html. The MLD data can be accessed at http://mixedlayer.ucsd.edu.
    Description: 2019-06-06
    Keywords: Mesoscale eddies ; Ocean mixing ; Satellite ; Floats ; Mixed layer
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  • 197
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    Extremely low frequency (0.1 to 1.0 mHz) surf zone currents. (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: Author Posting. © American Geophysical Union, 2019. 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 46(3), (2019):1531-1536, doi:10.1029/2018GL081106.
    Description: Low‐frequency surf zone eddies disperse material between the shoreline and the continental shelf, and velocity fluctuations with frequencies as low as a few mHz have been observed previously on several beaches. Here spectral estimates of surf zone currents are extended to an order of magnitude lower frequency, resolving an extremely low frequency peak of approximately 0.5 mHz that is observed for a range of beaches and wave conditions. The magnitude of the 0.5‐mHz peak increases with increasing wave energy and with spatial inhomogeneity of bathymetry or currents. The 0.5‐mHz peak may indicate the frequency for which nonlinear energy transfers from higher‐frequency, smaller‐scale motions are balanced by dissipative processes and thus may be the low‐frequency limit of the hypothesized 2‐D cascade of energy from breaking waves to lower frequency motions.
    Description: We thank R. Guza, T. Herbers, and T. Lippmann for their leadership roles during the SandyDuck and NCEX projects and the CCS (SIO), PVLAB (WHOI), and FRF (USACE) field teams for deploying, maintaining, and recovering sensors in harsh conditions over many years. Funding was provided by ASD(R&E), NSF, and ONR. The data can be obtained via https://chlthredds.erdc.dren.mil/thredds/catalog/frf/catalog.html and https://pv‐lab.org.
    Description: 2019-07-02
    Keywords: Surf zone currents ; Nearshore processes ; Breaking waves ; Vorticity
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    Diurnal surface flux variability over western boundary currents (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution-NonCommercial‐NoDerivs License. The definitive version was published in Clayson, C. A., & Edson, J. B. Diurnal surface flux variability over western boundary currents. Geophysical Research Letters, 46(15), (2019): 9174-9182, doi:10.1029/2019GL082826.
    Description: An analysis of a satellite ocean surface turbulent flux product demonstrated that, as expected, the western boundary current regions dominate the seasonal cycle amplitude. Surprisingly, our analysis of the global ocean diurnal flux variability also demonstrated a regional maximum in the winter over the western boundary current regions. We conducted comparisons with in situ data from several buoys located in these regions. The buoy data were in general agreement with the relative magnitude, timing, and importance of each of the bulk parameters driving the latent and sensible heat fluxes. Further analysis demonstrated that the strength and timing of the diurnal signal is related to the location of the buoy relative to the region of maximum heat flux and sea surface temperature gradient. In both regions, the timing of the higher winds coincides with the moistest surface layer, indicating that surface fluxes rather than entrainment mixing play a key role in this phenomenon.
    Description: CAC gratefully acknowledges funding from the NASA MAP and NEWS programs (NNX13AN48G and NNX15AI47A). CLIMODE data were funded by the U.S. National Science Foundation (http://uop.whoi.edu/projects/CLIMODE/climodedata.html). KEO data are provided by the OCS Project Office of NOAA/PMEL (https://www.pmel.noaa.gov/ocs/data/disdel/). JKEO data are provided by RIGC/JAMSTEC and PMEL/NOAA (http://www.jamstec.go.jp/iorgc/ocorp/ktsfg/data/jkeo/). SeaFlux data are provided by the U.S. NOAA Climate Data Record Program (https://www.ncdc.noaa.gov/cdr).
    Keywords: Diurnal variability ; Western boundary currents ; Surface fluxes ; Atmospheric boundary layer
    Repository Name: Woods Hole Open Access Server
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  • 199
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    On the mechanical effects of poroelastic crystal mush in classical magma chamber models (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2018. 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: Solid Earth 123(11), (2018): 9376-9406. doi: 10.1029/2018JB015985.
    Description: Improved constraints on the mechanical behavior of magma chambers is essential for understanding volcanic processes; however, the role of crystal mush on the mechanical evolution of magma chambers has not yet been systematically studied. Existing magma chamber models typically consider magma chambers to be isolated melt bodies surrounded by elastic crust. In this study, we develop a physical model to account for the presence and properties of crystal mush in magma chambers and investigate its impact on the mechanical processes during and after injection of new magma. Our model assumes the magma chamber to be a spherical body consisting of a liquid core of fluid magma within a shell of crystal mush that behaves primarily as a poroelastic material. We investigate the characteristics of time‐dependent evolution in the magma chamber, both during and after the injection, and find that quantities such as overpressure and tensile stress continue to evolve after the injection has stopped, a feature that is absent in elastic (mushless) models. The time scales relevant to the postinjection evolution vary from hours to thousands of years, depending on the micromechanical properties of the mush, the viscosity of magma, and chamber size. We compare our poroelastic results to the behavior of a magma chamber with an effectively viscoelastic shell and find that only the poroelastic model displays a time scale dependence on the size of the chamber for any fixed mush volume fraction. This study demonstrates that crystal mush can significantly influence the mechanical behaviors of crustal magmatic reservoirs.
    Description: We thank James Rice, Tushar Mittal, Chris Huber and Helge Gonnerman for useful discussions in the early stages of this work. S. Adam Soule was supported by National Science Foundation Grant OCE‐1333492. Meghan Jones was supported by the U.S. Department of Defense through the National Defense Science and Engineering Graduate Fellowship (NDSEG) Program. The numerical codes used for computing the results in the work can be found at https://github.com/YangVol/MushyChamber.
    Description: 2019-03-30
    Keywords: Magma chamber ; Crystal mush ; Poroelasticity
    Repository Name: Woods Hole Open Access Server
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  • 200
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    A numerical study of interannual variability in the North Icelandic Irminger Current (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2018. 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-Oceans 123(12), (2018): 8994-9009, doi:10.1029/2018JC013800.
    Description: The North Icelandic Irminger Current (NIIC) is an important component of the Atlantic Water (AW) inflow to the Nordic Seas. In this study, both observations and a high‐resolution (1/12°) numerical model are used to investigate the seasonal to interannual variability of the NIIC and its forcing mechanisms. The model‐simulated velocity and hydrographic fields compare well with the available observations. The water mass over the entire north Icelandic shelf exhibits strong seasonal variations in both temperature and salinity, and such variations are closely tied to the AW seasonality in the NIIC. In addition to seasonal variability, there is considerable variation on interannual time scales, including a prominent event in 2003 when the AW volume transport increased by about 0.5 Sv. To identify and examine key forcing mechanisms for this event, we analyzed outputs from two additional numerical experiments: using only the seasonal climatology for buoyancy flux (the momentum case) and using only the seasonal climatology for wind stress (the buoyancy case). It is found that changes in the wind stress are predominantly responsible for the interannual variations in the AW volume transport, AW fraction in the NIIC water, and salinity. Temperature changes on the shelf, however, are equally attributable to the buoyancy flux and wind forcing. Correlational analyses indicate that the AW volume transport is most sensitive to the wind stress southwest of Iceland.
    Description: This work is supported by the U.S. National Science Foundation (NSF) under grants OCE‐1634886 (J. Zhao and J. Yang) and OCE‐1558742 (R. Pickart), and by the Bergen Research Foundation grant BFS2016REK01 (K. Våge and S. Semper). We thank Xiaobiao Xu at Florida State University for providing the initial model configuration. Comments from anonymous reviewers help to improve the manuscript. The altimeter products are produced and distributed by the Copernicus Marine and Environment Monitoring Service (CMEMS, http://www.marine.copernicus.eu). The hydrographic maps along the Hornbanki section are available at http://www.hafro.is/Sjora/.
    Description: 2019-04-11
    Keywords: Irminger Current ; Interannual ; Wind ; Numerical modeling
    Repository Name: Woods Hole Open Access Server
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