Impact of fish farming facilities on Posidonia oceanica meadows: a review

The impact of fish farming facilities on Posidonia oceanica meadows was assessed from studies of intensive facilities carried out over the last few years. The disturbances caused by these fish farms were measured by means of both abiotic (light, sediment, interstitial water) and biotic variables (meadow density, leaf biometry, lepidochronology, primary production, epiphytes, reserve carbohydrates in the rhizomes), in function of increasing distance from cages and/or inside a geographically close reference site. The results showed significant degradation of these seagrass meadows in all the sectors investigated. When fish farming cages were placed above a P. oceanica bed, the meadow was severely degraded or disappeared and the sediment showed a strong increase in organic matter that could lead to anoxia phenomena. The irreversible impact of fish farming projects on P. oceanica meadows requires the application of the precautionary principle. Several recommendations (site selection, preliminary studies and monitoring over time) are suggested in order to enable piscicultural activities to be incorporated in a global process of Integrated Coastal Zone Management.     

Re-analysis of Lepping’s Fitting Method for Magnetic Clouds: Lundquist Fit Reloaded

The three-dimensional morphology and direction of propagation of coronal mass ejections (CMEs) are essential information for identifying their source on the solar disk, for understanding the processes of their ejection and propagation in the corona, and for forecasting their possible impact with the Earth or any other objects in the solar system. The polarization of the Thomson scattering by an electron is known to provide information on its position with respect to the plane of the sky. This polarimetric technique is applied to reconstruct 15 CMEs on the basis of white-light polarized images obtained with the Large Angle Spectrometric Coronagraph (LASCO) C2, which have been extensively corrected for instrumental effects. It does provide valuable results in spite of the time delays between the three observations required to build the polarization maps. Most of these CMEs exhibit complex structures making a classification in terms of simple shapes such as arcade of loops or flux rope difficult or even questionable. Three of these CMEs benefited from multiple observations allowing us to follow their three-dimensional development as they propagated outward. All CMEs are tracked back to the solar surface and in several instances, active regions are identified as the probable sources. Finally, the projected speeds and masses derived from white-light unpolarized observations have been corrected for the projection angle to produce unbiased values.

     

Provenance and Evolution of the Guarguariiz Complex, Cordillera Frontal, Argentina

The Guarguardz Complex, basement of the Cordillera Frontal, included in the proposed Chilenia Terrane, consists of metasedimentary rocks deposited in clastic and carbonatic platforms. Turbiditic sequences point out to slope or external platform environments. According to geochemical data, the sedimentary protoliths derived through erosion of a mature cratonic continental basement. Volcanic and subvolcanic rocks with N and E-MORB signature were interbeded in the metasedimentary rocks during basin development. A compressional stage, starting with progressive deformation and metamorphism, followed this extensional stage. Continuing deformation led to the emplacement of slices of oceanic crust, conforming an accretionary prism during Late Devonian. The Guarguardz Complex and equivalent units in western Precordillera and also in the Chilean Coastal Cordillera share common evolutional stages, widely represented along the western Gondwana margin. These evidences imply that Chilenia is not an allochthonous terrane to Gondwana, but a portion of its Early Paleozoic margin. Regional configuration indicates that the Guarguardz Complex and equivalent units represent the accretionary prism of the Famatinian arc (Middle Ordovician-Late Devonian).