Miscellaneous information

Miscellaneous information     

Ecological Differences in the Distribution of two Tethya (Porifera, Demospongiae) Species Coexisting in a Mediterranean Coastal Lagoon

Abstract. In the Sicilian lagoon Stagnone di Marsala, Tethya aurantium and T. citrina show different ecological distributions, although some overlapping occurs. The first species reaches its highest density where linear currents are maximal, and in this habitat it is particularly frequent on Posidonia oceanica rhizomes. The second species is more abundant in still water locations and is equally common on Posidonia rhizomes and on calcareous concretions. Such distributions can be related to water movement, Posidonia shoot density, and associated factors such as sedimentation and food availability. These observations are consistent with an adaptive interpretation of the morphofunctional features distinguishing the two species.     

The State of the Adriatic Sea Centered on the Small Pelagic Fish Populations

Abstract. The paper provides an overview of the state of the small pelagic fish in the Adriatic Sea. The North Adriatic is reviewed for the 1976–1998 period and the South Adriatic for the 1987–1998 period. First the fluctuations in time and in space of the pelagic biomass, as a whole and per species, are presented. Then the dramatic collapse of anchovy stock and its apparent association with the decrease of surface temperature is discussed. Finally the changes of the anchovy and sardine catches are compared and analysed with respect to their abundances in the sea. The conclusion is that acoustic and satellite methods are able to provide a large amount of information on the variability in the pelagic populations; this is essential for an appropriate management of these resources. There is still a need, however, to refine the methods and to integrate this kind of information with further environmental data (including natural predators).     

Structural,stratigraphic, and petrologic aspects of the Arenal-Chato volcanic system,Costa Rica: Evolution of a young stratovolcanic complex

Geologic mapping on a scale of 1:10000 and detailed stratigraphic studies of lava flows and tephra deposits of the Arenal-Chato volcanic system reveal a complex and cyclic volcanic history. This cyclicity provides insight into the evolution of magma batches during the growth of the andesitic volcanic system. The Arenal and Chato volcanoes have a central zone comprised of a lava armor and a distal zone comprised of a tephra apron. During Arenal's last two eruptive periods major craters formed near intersections of regional fractures at the lava armortephra apron transition. We suggest that such intersections are potential sites for future major explosions. The earliest rocks, i.e., the Chato lava flows, range in composition from basaltic andesite to andesite. These rocks, except for the andesitic domes of Chatito and La Espina, appear to have evolved from a common parental magma. The last active period of Chato volcano occurred 3550 B. P. The earliest known activity of Arenal volcano is 2900 B. P. Arenal lava flows have 54–56 wt% SiO₂ and may be subdivided into a high-alumina group (HAG, Al₂O₃ = 20 wt%) and a low-alumina group (LAG, Al₂O₃ = 19 wt%). Compared to the HAG, the LAG also has smaller amounts of incompatible elements and higher amounts of FeO and MgO. Arenal tephra deposits were emplaced by Plinian-Sub-Plinian explosions occurring at 300±150-yr intervals. These deposits are compositionally zoned and alternate between dacite and basalt. The stratigraphy reveals an apparent magmatic cycle consisting of (a) dacitic-andesitic tephra, (b) HAG lava flows, (c) LAG lava flows, and (d) andesitic-basaltic tephra. This magmatic cycle is repeated four times during Arenal's history and is interpreted to have developed by the crystal fractionation and crystal redistribution of a single magma batch. The period of this cycle, and consequently the life of a magma batch, is about 800 years. If the cyclic pattern continues, a basaltic explosive phase may occur in the next 250 years.     

Intercomparison of Boron Isotope and Concentration Measurements. Part I: Selection, Preparation and Homogeneity Tests of the Intercomparison Materials

In 1999 the Istituto di Geoscienze e Georisorse (IGG), with the support of the International Atomic Energy Agency (IAEA), undertook the collection, preparation and distribution of eight geological materials intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials came from Italian sources and consist of three natural waters (Mediterranean seawater and two groundwaters) and five rocks and minerals (tourmaline, basalt, obsidian, limestone and clay). The solid materials were crushed, milled and mixed, in preparation for distribution. Extensive assays performed at the IGG on these materials demonstrated that their boron isotopic and chemical compositions are homogeneous.
Additional homogeneity tests were carried out on solid material fragments at the GeoForschungsZentrum Potsdam, with the specific objective of investigating the suitability of some of them for the calibration in situ of micro-analytical techniques. Two materials, B4 (tourmaline) and B6 (obsidian), proved to be isotopically homogeneous and may become excellent references for in situ microanalyses of boron isotopes.
The materials described here were used as the basis of a major laboratory intercomparison study and are now available for further distribution from either the IAEA (solid materials) or the IGG (waters).     

Cosmological radiative transfer codes comparison project – I. The static density field tests

Radiative transfer (RT) simulations are now at the forefront of numerical astrophysics. They are becoming crucial for an increasing number of astrophysical and cosmological problems; at the same time their computational cost has come within reach of currently available computational power. Further progress is retarded by the considerable number of different algorithms (including various flavours of ray tracing and moment schemes) developed, which makes the selection of the most suitable technique for a given problem a non-trivial task. Assessing the validity ranges, accuracy and performances of these schemes is the main aim of this paper, for which we have compared 11 independent RT codes on five test problems: (0) basic physics; (1) isothermal H  ii region expansion; (2) H  ii region expansion with evolving temperature; (3) I-front trapping and shadowing by a dense clump and (4) multiple sources in a cosmological density field. The outputs of these tests have been compared and differences analysed. The agreement between the various codes is satisfactory although not perfect. The main source of discrepancy appears to reside in the multifrequency treatment approach, resulting in different thicknesses of the ionized-neutral transition regions and the temperature structure. The present results and tests represent the most complete benchmark available for the development of new codes and improvement of existing ones. To further this aim all test inputs and outputs are made publicly available in digital form.     

An efficient algorithm for prioritizing NEA physical observations

The present near‐Earth asteroids (NEA) discovery rate has surpassed 1500 objects per year, thus calling for extensive observation campaigns devoted to physical characterization in order to define successful mitigation strategies in case of possible impactors. A tool is presented which, through a prioritization algorithm, aims to optimize the planning and the execution of NEA physical observations. Two ranking criteria are introduced, Importance and Urgency, accounting for the need of satisfying the two basic observational modes for physical characterization, that is, rapid response and large observing programs, aimed at selecting targets for exploration and mitigation space missions. The resulting tool generates a daily table of observable targets and it can also be run as a stand‐alone tool in order to provide future observing opportunities at a specific date of interest. It has been developed and implemented within the framework of the NEOShield‐2 EU/HORIZON 2020 Project; the output of the prioritization algorithm is publicly available, in tabular format, on the NEOShield‐2 NEO Properties Portal ( http://www.neoshield.net/the-neoshield-project/project-activities/neo-properties-portal ), reachable from the main page of the Project website ( http://www.neoshield.eu ).     

Long-term change in the structure of a Posidonia oceanica landscape and its reference for a monitoring plan

Abstract On the basis of a detailed cartographic survey carried out by Side Scan Sonar and a towed underwater video camera during 2005, and from a series of historical maps (1959, 1980, 1990), an extensive regression of Posidonia oceanica (L.) Delile beds was evidenced for a vast area of the central Tyrrhenian Sea (Latium coast, Italy). The total loss of P. oceanica surface was assessed through GIS estimate. In 1959, the Posidonia beds extended over 7290 ha, while in the 2005 survey they had regressed to 2899 ha, a loss of about 60% of their coverage. Also the seagrass lower limit showed a general depth decrease in time. Total seagrass coverage loss and lower limit regression were not uniform along the whole investigated areas and three main sub-areas have been identified with different degrees of regression somehow related with coastal potential human-mediated impacts. From different coverage estimates of the present survey and of the previous maps, minimum sampling areas were calculated through bootstrapping simulation routines from small sampling areas (Landscape Units) to reach the nearest estimate of the observed condition in the different periods.