Food web and fish stock changes in central Chile: comparing the roles of jumbo squid (Dosidicus gigas) predation,the environment,and fisheries

We analyzed recent food web and fish stock changes in the central Chile marine ecosystem, comparing the roles of jumbo squid (Dosidicus gigas) as predator, the environment, and fishing. To accomplish this we used food web modeling and the Ecopath with Ecosim software (EwE). The principal fish stocks have experienced wide decadal fluctuations in the past 30 years, including stock collapses of horse mackerel (Trachurus murphyi) and hake (Merluccius gayi), and there was a large influx of jumbo squid during the mid-2000s. We used two EwE models representing the food web off central Chile to test the hypothesis that predation by jumbo squid has been significant in explaining the dynamics of the main fishing resources and other species in the study area. Results indicate that predation by jumbo squid on fish stocks is lower than that of other predators (e.g. hake) and the fishery. Long-term fluctuations (1978–2004) in the biomass of the main fish stocks (as well as other components of the food web) seem to be related to fishing and to variation in primary production, rather than to predation by jumbo squid alone. Jumbo squid seems to play a role as predator rather than prey in the system, but its impacts are low when compared with the impacts of other predators and fishing. Therefore, we conclude that jumbo squid predation on its prey was not the primary force behind the collapse of important fish stocks off central Chile. Future efforts should be directed to better understanding factors that trigger sudden increases in jumbo squid abundance off central Chile, as well as modeling its trophic impacts.     

Three-dimensional dynamic response of multilayered poroelastic media

ABSTRACT

The dynamic response of a multilayered poroelastic medium under 3D time-harmonic loading is studied using an exact stiffness method. The poroelastic medium under consideration consists of N layers of different thicknesses and properties and an underlying poroelastic half-space. The exact stiffness matrices for each layer and the underlying half-space are derived explicitly using Biot’s poroelastodynamic theory and double-dimensional Fourier transforms. Selected numerical results are presented to demonstrate the influence of various parameters on dynamic response of multilayered poroelastic media under traction and fluid loading. The application of proposed solution scheme to soil–structure interaction problems is also presented.     

Eclogite varieties and petrotectonic evolution of the northern Guatemala Suture Complex

ABSTRACT

Field and petrologic characteristics of two new eclogite localities within the Guatemala Suture Complex (GSC) north of the Motagua Fault are presented. The Tuncaj Hill locality exposes a coherent body of retrogressed eclogite hundreds of metres long that is associated with serpentinite of the North Motagua Unit. The Tanilar River locality exposes numerous bands and lenses of eclogite hosted in sialic gneisses of the Chuacús Complex. The Tuncaj eclogite has a two-stage prograde evolution containing the peak assemblage Grt + Omp + Ttn + Czo + Zo ± Am, formed at temperatures <720°C. In contrast, eclogites of the Tanilar unit are characterized by the paragenesis Omp + Grt + Rt ± Phg ± Qtz ± Ep giving higher peak conditions of T = 720–830°C and P = 2.1–2.7 GPa, near the stability field of coesite. Previously obtained data and our thermobaric calculations suggest distinct petrotectonic evolutions for the various types of eclogites within the suture. The lawsonite eclogites south of the Motagua Fault were probably produced in a mature Farallon subduction zone during the Early Cretaceous. The northern high-pressure (HP) blocks in serpentinite mélange and coherent amphibolite bodies with eclogite relics were generated by the Early Cretaceous subduction of the proto-Caribbean lithosphere under the Great Caribbean Arc. A continental block, the North American passive margin, reached the arc’s trench in the Campanian and was subducted to ca. 80 km depth, producing the eclogites of the Chuacús Complex. As the slab was delaminated and partially exhumed, the continental Chuacús became tectonically juxtaposed with HP blocks of the proto-Caribbean that had been accreted to the Caribbean plate forming the North Motagua Unit. The juxtaposed group migrated to mid-crustal level and was contemporaneously retrogressed under epidote-amphibolite facies conditions.     

U–Pb geochronology and geochemistry of late Palaeozoic volcanism in Sardinia (southern Variscides)

The latest Carboniferous to lower Permian volcanism of the southern Variscides in Sardinia developed in a regional continental transpressive and subsequent transtensile tectonic regime.Volcanism produced a wide range of intermediate-silicic magmas including medium-to high-K calc-alkaline andesites,dacites,and rhyolites.A thick late Palaeozoic succession is well exposed in the four most representative Sardinian continental basins(Nurra,Perdasdefogu,Escalaplano,and Seui-Seulo),and contains substantial stratigraphic,geochemical,and geochronological evidence of the area's complex geological evolution from the latest Carboniferous to the beginning of the Triassic.Based on major and trace element data and LA-ICP-MS U-Pb zircon dating,it is possible to reconstruct the timing of postVariscan volcanism.This volcanism records active tectonism between the latest Carboniferous and Permian,and post-dates the unroofing and erosion of nappes in this segment of the southern Variscides.In particular,igneous zircon grains from calc-alkaline silicic volcanic rocks yielded ages between299±1 and 288±3 Ma,thereby constraining the development of continental strike-slip faulting from south(Escalaplano Basin)to north(Nurra Basin).Notably,andesites emplaced in medium-grade metamorphic basement(Mt.Cobingius,Ogliastra)show a cluster of older ages at 332±12 Ma.Despite the large uncertainty,this age constrains the onset of igneous activity in the mid-crust.These new radiometric ages constitute:(1)a consistent dataset for different volcanic events;(2)a precise chronostratigraphic constraint which fits well with the biostratigraphic data and(3)insights into the plate reorganization between Laurussia and Gondwana during the late Palaeozoic evolution of the Variscan chain.     

利用ERA5资料进行桂林地区GNSS水汽反演精度分析

由于桂林地区地基GNSS站并未配置气象传感器，致使大量GNSS观测数据无法在大气水汽（PWV）监测中发挥作用.针对这一情况，本文将欧洲中期天气预报中心（ECMWF）最新发布的ERA5再分析资料中测站处的气压和温度气象数据加入到GNSS水汽反演中，并将反演结果与利用地面气象站反演的GNSS水汽做对比，以此评估ERA5在桂林地区反演GNSS水汽的精度和适用性.结果表明：1）以桂林地区2017年10个地面气象站的实测气压和温度数据为参考值，ERA5地表气压和温度的年均偏差分别为-0.35 hPa和0.86 K，年均均方根误差（RMSE）分别为0.65 hPa和1.66 K，该精度可用于GNSS水汽反演；2）以2017年6—7月GNSS利用地面气象站反演的PWV为参考值，ERA5反演的GNSS PWV的偏差和RMSE分别为0.17 mm和0.35 mm，且两者具较好的相关性和一致性.由此表明，ERA5地表温压产品可应用于桂林地区GNSS水汽反演，这些研究结果可为桂林地区的GNSS水汽反演及数据源的选用提供重要的参考依据.     

Failles normales Paléocène à Lutétien en zone sud-pyrénéenne (Aragon,Espagne) et flexuration de la plaque ibérique

Close to the South Pyrenean thrust front, synsedimentary normal faults develop in the ‘Garumnian’ continental deposits (Maastrichtian to Palaeocene) and in the carbonate platform during the Lutetian. During the Lutetian, this deformation is accompanied by a change in the sedimentation characterized by the deposit of two series of laminated limestones associated to monogenetic breccias. These normal faults would have formed at the bending of the Iberian plate subducting under Europe. They may also be considered as the starting point for the megaturbidites that deposited further north in the Eocene turbiditic basin. To cite this article: Y. Hervouët et al., C. R. Geoscience 337 (2005).     

Analyzing the (mis)fit between the institutional and ecological networks of the Indo-West Pacific

Critical to improving environmental governance is understanding the fit (alignment) between institutional arrangements and key ecological processes. This is particularly true for biodiversity hotpots and ecologically sensitive areas that are subject to significant impacts from human activities. Here, we have developed an innovative approach to quantify ecological-institutional alignment across an environmentally and politically complex large-scale marine social-ecological system. We mapped the trans-boundary networks of marine population dispersal corridors, and intersected these with estimates of cross-country institutional linkages related to marine management and conservation. In integrating large-scale ecological-institutional networks, we identify geopolitical fit and misfit between a region's ecological processes and its governance. We have demonstrated this approach in the Indo-West Pacific region, a global marine biodiversity hotpot in the Indo-West Pacific. We present region-specific institutional and ecological networks, highlight current challenges, and suggest future directions to refine the proposed approach to quantify alignment between ecological processes and governance arrangements. Ultimately, our method has the potential to assist management efforts in prioritizing and strengthening governance to effectively safeguard ecological processes across multiple jurisdictions.     

Reconstruction of the mid-Devonian HP-HT metamorphic event in the Bohemian Massif (European Variscan belt)

Mid-Devonian high-pressure (HP) and high-temperature (HT) metamorphism represents an enigmatic early phase in the evolution of the Variscan Orogeny. Within the Bohemian Massif this metamorphism is recorded mostly in allochthonous complexes with uncertain relationship to the major tectonic units. In this regard, the Mariánské Lázně Complex (MLC) is unique in its position at the base of its original upper plate (Teplá-Barrandian Zone). The MLC is composed of diverse, but predominantly mafic, magmatic-metamorphic rocks with late Ediacaran to mid-Devonian protolith ages. Mid-Devonian HP eclogite-facies metamorphism was swiftly followed by a HT granulite-facies overprint contemporaneous with the emplacement of magmatic rocks with apparent supra-subduction affinity. New Hf in zircon isotopic measurements combined with a review of whole-rock isotopic and geochemical data reveals that the magmatic protoliths of the MLC, as well as in the upper plate Teplá-Barrandian Zone, developed above a relatively unaltered Neoproterozoic lithospheric mantle. They remained coupled with this lithospheric mantle throughout a geological timeframe that encompasses separate Ediacaran and Cambrian age arc magmatism, protracted early Paleozoic rifting, and the earliest phases of the Variscan Orogeny. These results are presented in the context of reconstructing the original architecture of the Variscan terranes up to and including the mid-Devonian HP-HT event.     

In situ Lu–Hf phosphate geochronology: Progress towards a new tool for space exploration

Geochronology is fundamental to understanding planetary evolution. However, as space exploration continues to expand, traditional dating methods, involving complex laboratory processes, are generally not realistic for unmanned space applications. Campaign-style planetary exploration missions require dating methods that can (1) rapidly resolve age information on small samples, (2) be applied to minerals common in mafic rocks, and (3) be based on technologies that could be installed on future rover systems. We demonstrate the application of rapid in situ microanalytical Lu–Hf phosphate geochronology using samples of pallasite meteorites, which are representative examples of the deep interiors of differentiated planetoids that are generally difficult to date. Individual pallasites were dated by laser ablation tandem mass-spectrometry (LA-ICP-MS/MS), demonstrating a rapid novel method for exploring planetary evolution. Derived formation ages for individual pallasites agree with traditional methods and have <2% uncertainty, opening an avenue of opportunity for remote micro-analytical space exploration.     

Petrology and isotopic evolution of granulites from central Madurai Block (southern India): reference to Ediacaran crustal evolution

The Madurai Block, constituting part of the southern granulite terrain in southern India, has contributed significantly towards understanding the UHT (ultrahigh-temperature) granulites that serve as a window into the mid-lower continental crust. The dominant rock types are charnockites, sapphirine-bearing granulites, garnet cordierite gneisses, and quartzites. Significant textural relations reveal multiphase reactions responsible for the formation of diverse mineral parageneses during prolonged metamorphic history of the area. Prograde reaction is evident from the textural relationship where biotite/sillimanite relics are seen as inclusion in garnet/orthopyroxene, suggesting dehydration reactions. The symplectitic assemblages that formed during isothermal decompression involve a series of cordierite-forming reactions, followed by retrogression and cooling. Variety of mineral assemblages present in the rocks of this area offer a wide spectrum of P–T sensors that provide details on the physical conditions of metamorphism. For the rigorous interpretation of the P–T path in the Perumalmalai area, quantitative phase diagrams (P–T pseudosections) have been constructed and contoured for the compositional as well as modal isopleths of involved mineral phases. The rocks of Perumalmalai area document a clockwise decompression P–T trajectory, consistent with crustal thickening followed by extensional collapse. SHRIMP U–Pb ages from zircon associated with sapphirine-bearing granulite facies rocks of Perumalmalai area suggest a widespread Ediacaran tectonothermal event. The occurrence of Ediacaran UHT metamorphism followed by isothermal decompression in the Madurai Block is consistent with the timing and physical conditions associated with the formation of East African Orogen during the amalgamation of Gondwana.