Anthropogenic debris on beaches in the SE Pacific (Chile): Results from a national survey supported by volunteers

Anthropogenic marine debris (AMD) is an ubiquitous problem, which has motivated public participation in activities such as beach surveys and clean-up campaigns. While it is known that beaches in the SE Pacific are also affected by this problem, the quantities and types of AMD remain largely unknown. In the context of an outreach project, volunteers (1500 high-school students) participated in a nation-wide survey of AMD on 43 beaches distributed randomly along the entire Chilean coast (18°S to 53°S). The mean density of AMD was 1.8 items m⁻² and the major types were plastics, cigarette butts and glass. Densities in central Chile were lower than in northern and southern Chile, which could be due to different attitudes of beach users or to intense beach cleaning in central regions. We suggest that public participation in surveys and cleaning activities will raise awareness and thereby contribute to an improvement of the situation.     

Contrasting regional discharge evolutions in the Amazon basin (1974–2004)

Former hydrological studies in the Amazon Basin generally describe annual discharge variability on the main stem. However, the downstream Amazon River only represents the mean state of the Amazonian hydrological system. This study therefore uses a new data set including daily discharge in 18 sub-basins to analyze the variability of regional extremes in the Amazon basin, after recalling the diversity of the hydrological annual cycles within the Amazon basin. Several statistical tests are applied in order to detect trends and breaks in the time series. We show that during the 1974–2004 period, the stability of the mean discharge on the main stem in Óbidos is explained by opposite regional features that principally involve Andean rivers: a decrease in the low stage runoff, particularly important in the southern regions, and an increase in the high stage runoff in the northwestern region. Both features are observed from the beginning of the nineties. These features are also observed in smaller meridian sub-basins in Peru and Bolivia. Moreover we show that the changes in discharge extremes are related to the regional pluriannual rainfall variability and the associated atmospheric circulation as well as to tropical large-scale climatic indicators.     

A Burst with Double Radio Spectrum Observed up to 212 GHz

We study a solar flare that occurred on 10 September 2002, in active region NOAA 10105, starting around 14:52 UT and lasting approximately 5 minutes in the radio range. The event was classified as M2.9 in X-rays and 1N in Hα. Solar Submillimeter Telescope observations, in addition to microwave data, give a good spectral coverage between 1.415 and 212 GHz. We combine these data with ultraviolet images, hard and soft X-ray observations, and full-disk magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic Imager data are used to identify the locations of X-ray sources at different energies, and to determine the X-ray spectrum, while ultraviolet images allow us to characterize the coronal flaring region. The magnetic field evolution of the active region is analyzed using Michelson Doppler Imager magnetograms. The burst is detected at all available radio frequencies. X-ray images (between 12 keV and 300 keV) reveal two compact sources. In the 212 GHz data, which are used to estimate the radio-source position, a single compact source is seen, displaced by 25″ from one of the hard X-ray footpoints. We model the radio spectra using two homogeneous sources, and we combine this analysis with that of hard X-rays to understand the dynamics of the accelerated particles. Relativistic particles, observed at radio wavelengths above 50 GHz, have an electron index evolving with the typical soft–hard–soft behavior.     

Terrestrial photogrammetric techniques applied to the control of a parabolic dune in the Liencres dune system,Cantabria (Spain)

The spatial–temporal variations of a dune system can be determined by using diverse ‘geomatic’ methodologies: geodesy, global positioning system (GPS) and photogrammetry. In the case of the Liencres dune system, a study will be carried out using the ‘close‐range’ photogrammetry technique and the topography technique (total station and GPS). In order to determine the dynamic of the dune system it is necessary to repeat the process of study after a specific interval of time. For this reason, three dimensional data should be available in two different time periods, between which the displacement of the object of analysis (the front portion of the dune) will be significant enough to evaluate its magnitude. This work analyses the viability of photogrammetry for the determination of the spatial–temporal changes of a coastal parabolic dune. Two factors have been analysed: first, the comparison of the photogrammetric results with the results obtained from topographic methods (total station and GPS), and second, the quantification of the displacement of the dune system. The analysis of the correspondence between the movement of different parts of the dune and the influence of the intensity and direction of the prevailing wind in the area is also desired. The dune advanced 12·15 ± 0·06 m (an average of 8·5 m/yr), and the partial implications for the dynamic of human modified processes on the natural park have been established. Copyright © 2008 John Wiley & Sons, Ltd.     

Underground Temperature Measurements as a Tool for Volcanic Activity Monitoring in the Island of Tenerife, Canary Islands

The spatial distribution of groundwater temperatures in the volcanic island of Tenerife, Canary Islands, has been inferred through measurements of water temperatures collected in the vast network of wells and subhorizontal tunnels, locally called “galleries,” which constitutes the main water supply of the island. The spatial coverage of the network of galleries allows us to reach from depth almost any geological feature of the island. The complex spatial distribution of temperatures in the interior of Tenerife is the result of the complex geological evolution of the island. Groundwater temperatures are greatly affected by groundwater flow and are considerably warmer in those galleries located in areas where water circulation is reduced due to the low permeability of materials and/or to the low infiltration rate of cooling meteoric water. In this sense, groundwater temperature should be characterized in quiescent conditions (background level), in order to facilitate monitoring changes in heat flow, such as those induced by ascending gases expected with an increase in volcanic activity.     

Impact of natural (waves and currents) and anthropogenic (trawl) resuspension on the export of particulate matter to the open ocean: Application to the Gulf of Lion (NW Mediterranean)

Modern sediment deposits on continental margins form a vast reservoir of particulate matter that is regularly affected by resuspension processes. Resuspension by bottom trawling on shelves with strong fishing activity can modify the scale of natural disturbance by waves and currents. Recent field data show that the impact of bottom trawls on fine sediment resuspension per unit surface is comparable with that of the largest storms.     

Sediment accumulation in the western Gulf of Lions,France: The role of Cap de Creus Canyon in linking shelf and slope sediment dispersal systems

Previous work in the Gulf of Lions (western Mediterranean Sea) has suggested that significant amounts of sediment escape through the western part of this tectonically passive margin, despite it being far removed from the primary sediment source (the Rhone River, ∼160 km to the NE). The primary mechanism behind this export is hypothesized to be the interaction of a regional, southwestward sediment-transport path with a canyon deeply incising the southwestern part of the shelf, Cap de Creus Canyon.     

Seasonal closures as a measure of trawling effort control in two Mediterranean trawling grounds: effects on epibenthic communities

Within the framework of ecosystem-based management, we focused on the use of seasonal closures as effective measures to minimise the degradation of benthic communities by trawling. These closures imply the complete cessation of trawling fleet activity and are commonly used in the Mediterranean to reduce the annual fishing effort, with the ultimate goal of effective resource management. In this study, we aimed to investigate how epibenthic communities respond to seasonal closures. The potential benefits of short-term annual closures in two Mediterranean fishing grounds were evaluated by analysing changes in community structure and composition that were linked to the closure. A decrease of faunal abundance was observed with the resumption of fishing activity after the closure at both fishing grounds. Remarkably, results indicated that some large and mobile fauna were able to respond to these closures. We concluded that the currently planned closures are too short to benefit benthic communities.     

New insights into Late Pleistocene explosive volcanic activity and caldera formation on Ischia (southern Italy)

A new pyroclastic stratigraphy is presented for the island of Ischia, Italy, for the period ∼75–50 ka BP. The data indicate that this period bore witness to the largest eruptions recorded on the island and that it was considerably more volcanically active than previously thought. Numerous vents were probably active during this period. The deposits of at least 10 explosive phonolite to basaltic-trachyandesite eruptions are described and interpreted. They record a diverse range of explosive volcanic activity including voluminous fountain-fed ignimbrite eruptions, fallout from sustained eruption columns, block-and-ash flows, and phreatomagmatic eruptions. Previously unknown eruptions have been recognised for the first time on the island. Several of the eruptions produced pyroclastic density currents that covered the whole island as well as the neighbouring island of Procida and parts of the mainland. The morphology of Ischia was significantly different to that seen today, with edifices to the south and west and a submerged depression in the centre. The largest volcanic event, the Monte Epomeo Green Tuff (MEGT) resulted in caldera collapse across all or part of the island. It is shown to comprise at least two thick intracaldera ignimbrite flow-units, separated by volcaniclastic sediments that were deposited during a pause in the eruption. Extracaldera deposits of the MEGT include a pumice fall deposit emplaced during the opening phases of the eruption, a widespread lithic lag breccia outcropping across much of Ischia and Procida, and a distal ignimbrite in south-west Campi Flegrei. During this period the style and magnitude of volcanism was dictated by the dynamics of a large differentiated magma chamber, which was partially destroyed during the MEGT eruption. This contrasts with the small-volume Holocene and historical effusive and explosive activity on Ischia, the timing and distribution of which has been controlled by the resurgence of the Monte Epomeo block. The new data contribute to a clearer understanding of the long-term volcanic and magmatic evolution of Ischia.