Timescales of successful and failed subduction: insights from numerical modelling

The relatively short duration of the early stages of subduction results in a poor geological record, limiting our understanding of this critical stage. Here, we utilize a 2D numerical model of incipient subduction, that is the stage after a plate margin has formed with a slab tip that extends to a shallow depth and address the conditions under which subduction continues or fails. We assess energy budgets during the evolution from incipient subduction to either a failed or successful state, showing how the growth of potential energy, and slab pull, is resisted by the viscous dissipation within the lithosphere and the mantle. The role of rheology is also investigated, as deformation mechanisms operating in the crust and mantle facilitate subduction. In all models, the onset of subduction is characterized by high lithospheric viscous dissipation and low convergence velocities, whilst successful subduction sees the mantle become the main area of viscous dissipation. In contrast, failed subduction is defined by the lithospheric viscous dissipation exceeding the lithospheric potential energy release rate and velocities tend towards zero. We show that development of a subduction zone depends on the convergence rate, required to overcome thermal diffusion and to localise deformation along the margin. The results propose a minimum convergence rate of ∼ 0.5 cm yr−1 is required to reach a successful state, with 100 km of convergence over 20 Myr, emphasizing the critical role of the incipient stage

The two INTEGRAL X-ray transients IGR J17091--3624 and IGR J17098--3628: a multi-wavelength long term campaign

IGR J17091-3624 and IGR J17098-3628 are two X-ray transients discovered by INTEGRAL and classified as possible black hole candidates (BHCs). We present here the results obtained from the analysis of multi-wavelength data sets collected by different instruments from 2005 until the end of 2007 on both sources. IGR J17098-3628 has been regularly detected by INTEGRAL and RXTE over the entire period of the observational campaign; it was also observed with pointed observations by XMM and Swift/XRT in 2005 and 2006 and exhibited flux variations not linked with the change of any particular spectral features. IGR J17091-3624 was initially in quiescence (after a period of activity between 2003 April and 2004 April) and it was then detected again in outburst in the XRT field of view during a Swift observation of IGR J17098--3628 on 2007 July 9. The observations during quiescence provide an upper limit to the 0.2-10 keV luminosity, while the observations in outburst cover the transition from the hard to the soft state. Moreover, we obtain a refined X-ray position for IGR J17091-3624 from the Swift/XRT observations during the outburst in 2007. The new position is inconsistent with the previously proposed radio counterpart. We identify in VLA archive data a compact radio source consistent with the new X-ray position and propose it as the radio counterpart of the X-ray transient.Comment: Accepted for publication in Ap

Agricultural Insurance in the DOCG Area of Conegliano—Valdobbiadene: An Assessment of Policy Measures

Agricultural insurance stands prominant in the protection of crop products. In Italy, the increasing occurrence of extreme weather events has had an important impact on the crop insurance market’s dynamics by lowering insurance companies propensity to take on climate risks. In this context, the main aim of the study is to focus on an economic assessment of the demand for insurance in the Controlled and Guaranteed Designation of Origin (DOCG) area of Conegliano-Valdobbiadene, exploiting the economic effects of public contributions for the three main subjects involved in the market: winegrowers, public stakeholders, and insurance companies. The results showed that the more favorable conditions laid down in the Omnibus Regulation in favor of producers do not appear justified in the area investigated. As regards the goodness of public intervention, the overall positivity of the Indicator Efficiency Subsidies (IES) underlines the relative efficiency of the subsidized contribution. As for the insurance companies, the financial equilibrium appears precarious, closed between falling tariffs and increasing quotas in consideration of the feared climate change

Potenciales presas zooplanctónicas (Copepoda y Appendicularia) para Engraulis anchoita en relación con las distribuciones de larvas tempranas y de desove en la región frontal patagónica (océano Atlántico sudoccidental)

We investigated the spatial distribution of the abundance, biomass and size of zooplankton (nauplii, calanoids, cyclopoids and appendicularians) in relation to the distribution of first-feeding larvae and eggs of Engraulis anchoita across the frontal system of Peninsula Valdés. Twelve samples of zooplankton and ichthyoplankton were taken with small Bongo (67 μm) and Pairovet (200 μm) nets during the spring of 2004 along two transects. The total abundance of zooplankton and the chlorophyll a concentration were higher in homogeneous waters, while total biomasses were higher in stratified waters. Temperature was negatively correlated with biological variables and was the main factor affecting the zooplankton distribution. In both transects, abundance peaks of first-feeding larvae were detected at coastal stations along with the smallest fraction of zooplankton ( < 500 μm), while the largest fraction was dominant at the external stations, coinciding with the highest egg abundance. The physical structure of this front generates different levels of food availability for first-feeding larvae. Calanoids (southern transect) and cyclopoids (northern transect) are predominant followed by nauplii and appendicularians. The biomass of zooplankton preys contributes to the carbon transfer to the upper trophic levels and is probably important for the survival and growth of anchovy larvae in this frontal system.Se investigó la distribución espacial de la abundancia, biomasa y las tallas del zooplancton (nauplii, calanoideos, ciclopoideos y apendicularias) en relación con la distribución de las larvas en estadio de primera alimentación y los huevos de Engraulis anchoita en el sistema frontal de Península Valdés. Se tomaron 12 muestras de zooplancton e ictioplancton durante la primavera de 2004 a lo largo de dos transectos, mediante una red Minibongo (67 μm) y una Pairovet (200 μm) respectivamente. La abundancia total del zooplancton y la concentración de clorofila fue mayor en aguas homogéneas, mientras que la biomasa fue mayor en aguas estratificadas. La temperatura se correlacionó negativamente con las variables biológicas siendo ésta el principal factor que afectó la distribución del zooplancton. En las estaciones costeras de ambos transectos, se encontró la mayor abundancia de larvas en coincidencia con la fracción más pequeña de zooplancton ( < 500 μm), mientras que la fracción más grande fue dominante en las estaciones externas, en coincidencia con la mayor abundancia de huevos. La estructura física de este frente genera diferente disponibilidad de alimento para las larvas siendo los calanoideos (transecto sur) y los ciclopoideos (transecto norte) predominantes, seguidos por nauplii y apendicularias. La biomasa de dicho alimento zooplanctónico podría contribuir a la transferencia de carbono a los niveles tróficos superiores y esto sería importante para la supervivencia y crecimiento de la anchoita en este sistema frontal

Ultrafast force-clamp spectroscopy of single molecules reveals load dependence of myosin working stroke

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Sub-arcsecond radio and optical observations of the likely counterpart to the gamma-ray source 2FGL J2056.7+4939

We have searched and reviewed all multi- wavelength data available for the region towards the gamma-ray source 2FGL J2056.7+4939 in order to con- strain its possible counterpart at lower energies. As a result, only a point-like optical/infrared source with flat-spectrum radio emission is found to be consistent with all X-ray and gamma-ray error circles. Its struc- ture is marginally resolved at radio wavelengths at the sub-arcsecond level. An extragalactic scenario appears to be the most likely interpretation for this object.Comment: 5 pages, 3 figures, 1 tabl

The 3rd IBIS/ISGRI soft gamma-ray survey catalog

In this paper we report on the third soft gamma-ray source catalog obtained with the IBIS/ISGRI gamma-ray imager on board the INTEGRAL satellite. The scientific dataset is based on more than 40 Ms of high quality observations performed during the first three and a half years of Core Program and public IBIS/ISGRI observations. Compared to previous IBIS/ISGRI surveys, this catalog includes a substantially increased coverage of extragalactic fields, and comprises more than 400 high-energy sources detected in the energy range 17-100 keV, including both transients and faint persistent objects which can only be revealed with longer exposure times.Comment: Accepted for publication in ApJ Suppl.; 11 pages; 4 figures Minor changes to conten

The Impact of a Very Weak and Thin Upper Asthenosphere on Subduction Motions

Recent geophysical observations report the presence of a very weak and thin upperasthenosphere underneath subducting oceanic plates at convergent margins. Along these margins, trenchmigrations are significantly slower than plate convergence rates. We use numerical models to assess therole of a weak upper asthenospheric layer on plate and trench motions. We show that the presence of thislayer alone can enhance an advancing trend for the motion of the plate and hamper trench retreat. Thismechanism provides a novel and alternative explanation for the slow rates of trench migration andfast-moving plates observed globally at natural subduction zones

An early cretaceous subduction-modified mantle underneath the ultraslow spreading Gakkel Ridge, Arctic Ocean

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Richter, M., Nebel, O., Maas, R., Mather, B., Nebel-Jacobsen, Y., Capitanio, F. A., Dick, H. J. B., & Cawood, P. A. An early cretaceous subduction-modified mantle underneath the ultraslow spreading Gakkel Ridge, Arctic Ocean. Science Advances, 6(44), (2020): eabb4340, doi:10.1126/sciadv.abb4340.Earth’s upper mantle, as sampled by mid-ocean ridge basalts (MORBs) at oceanic spreading centers, has developed chemical and isotopic heterogeneity over billions of years through focused melt extraction and re-enrichment by recycled crustal components. Chemical and isotopic heterogeneity of MORB is dwarfed by the large compositional spectrum of lavas at convergent margins, identifying subduction zones as the major site for crustal recycling into and modification of the mantle. The fate of subduction-modified mantle and if this heterogeneity transmits into MORB chemistry remains elusive. Here, we investigate the origin of upper mantle chemical heterogeneity underneath the Western Gakkel Ridge region in the Arctic Ocean through MORB geochemistry and tectonic plate reconstruction. We find that seafloor lavas from the Western Gakkel Ridge region mirror geochemical signatures of an Early Cretaceous, paleo-subduction zone, and conclude that the upper mantle can preserve a long-lived, stationary geochemical memory of past geodynamic processes.O.N. was supported by the Australian Research Council (grant FT140101062). P.A.C. was supported by the Australian Research Council (grant FL160100168). H.J.B.D. was supported by the NSF (grants PLR 9912162, PLR 0327591, OCE 0930487, and OCE 1434452). M.R. was supported by a graduate scholarship of Monash University and the SEAE