The fine structure of lysosomal membranes and endoplasmic reticulum in the digestive cells of Mytilus edulis exposed to anthracene and phenanthrene

The stability of lysosomes in the digestive cells of Mytilus edulis is affected by changes in both the chemical and physical conditions of the environment.¹ This type of response must reflect, at least in part, some change in the organisation of the lysosomal membrane, which is a structure which can be resolved by the electron microscope. However, conventional methods of tissue preparation have produced low contrast images of the digestive gland and damage to the lysosomal membranes. Recently a cryopreparation technique² has produced lysosomal membrane preparations in the digestive cells of the digestive gland of Mytilus which have high contrast and structural integrity (Fig. 1) in control animals. This method has been used to demonstrate pathological alterations in the lysosomal membrane induced by the polynuclear aromatic hydrocarbon (PNAH) phenanthrene. Anthracene, an isomeric PNAH, had no effect on the morphology of the lysosomal membrane. Phenanthrene also induced apparent proliferation of smooth endoplasmic reticulum in the digestive cells.     

Automated drainage extraction in mapping the Monterey submarine drainage system,California margin

Drainage-extraction algorithms traditionally used for extracting river networks and watersheds from gridded land topography are applied to gridded multibeam bathymetry of the mid-California margin. The algorithms are used to automatically map two regional tributary networks of submarine canyons and deepsea channels draining Monterey Bay, the principal conduits of which are Acension and Monterey Canyons. The algorithms reliably map subaqueous drainage areas, but are prone to error in mapping the extent of submarine canyon and channel thalwegs due to operator subjectivity and algorithm limitations. A geomorphic comparison of the Acension and Monterey Canyon networks, with 12 river networks in the continental U.S., illustrates both the potential and weaknesses of using drainage extraction algorithms to analyze sediment pathways in gridded bathymetry.     

Offset Spreading Centers near 12°53′ N on the East Pacific Rise: Submersible observations and composition of the volcanics

The Offset Spreading Center located between 12°52 and 12°54 N on the East Pacific Rise (Macdonald and Fox, 1983) has been studied in 1982 and 1984 with submersible Cyana and in 1983 with the deep towed vehicle Seamarc I. The two O.S.C. segments, about 1.5 km apart and 4 km in length, separated by a depression (about 100 m in depth) show different volcano-tectonic settings. The Western Spreading Center (WSC) segment is characterised mainly by recent volcanic constructional features, while the Eastern Spreading Center (ESC) is highly fissured and consists essentially of older pillow-lava terrain. The intervening depression located between the two segments is floored by small constructional mounds (<10 m in height) of pillow lava. The crust of both segments becomes older along strike towards their respective tips. However, the W.S.C. comprises generally younger flows than does the E.S.C. A small central volcano (80 m in height and 1 km in diameter) located near 12°51 N near the Southern tip of the W.S.C. contains a different type of volcanics than that found on both spreading centers. The volcanics collected along the O.S.C. ridges are depleted tholeiites, with low K₂O (<0.15%), Na₂O (<3%) and TiO₂ (<1.76%) contents, comparable to other MORB from the axial graben of the E.P.R. south of the area of overlap. Instead the specimen from the small volcano is enriched in K₂O (>0.2%), Na₂O (>3%) and TiO₂ (2%).Although there is a morphological overlap of the spreading centers in the study area there is no overlap in the present active axial volcanic zones. The bottom observations suggest that the Western spreading center is younger than the E.S.C. and thus that the W.S.C. could be propagating to the south.Contribution N^o 39 du Centre de Brest de L'IFREMER.     

Asymmetrical turbid surface-plume deposition near ice-outlets of the Pleistocene Laurentide ice sheet in the Labrador Sea

 Ice-sheet drainage of glacial detritus into the sea involves size fractionation by ice-margin winnowing on a giant scale caused by the lower density of meltwater entering cold seawater. Despite its load of suspended sediment, the fresh water rises to or stays at the sea surface forming turbid surface plumes, whereas the coarse-grained sediment forms bed load. On the Labrador Slope south of the Hudson Strait turbid plumes were supplied by meltwater from the Pleistocene ice sheet (LIS). Sediments with the seismic characteristics of plume deposits occur in a 200-km-long slope sector up to 130 km seawards from the strait. The widespread distribution of these deposits is attributed to entrainment of the surface plumes by the south-flowing Labrador Current and suppressed flocculation due to the high detrital carbonate-content of the suspended sediment. Deposits with typical characteristics of surface plume deposits have been recovered within 20 km from former ice margin south of or in front of outlets, but not north of outlets. They consist of 1 to 2-cm-thick alternations of fine sandy silt/coarse silt layers with finer-grained clayey silt/silty clay, and for brevity are called plumites. Received: 6 August 1996/Revision received: 21 January 1997     

Linking watershed disturbance with nearshore sedimentation and the shell beds of Lake Tanganyika (Mahale Mountains,Tanzania)

Extensive deposits of shell-rich sediments in the nearshore environment of Lake Tanganyika, Africa, form a unique habitat for a diverse group of endemic gastropods, crustaceans, fish and sponges, among other organisms. Anthropogenic alteration of the lake’s hinterland from deforestation, fires, and agriculture threaten this crucial habitat through sediment pollution of the littoral environment. This study examines the sedimentology of these nearshore shell beds along a study area north of the Mahale Mountains (Tanzania) to test whether varying levels of watershed disturbance, determined by analysis of satellite imagery, within three moderately sized watersheds (>?100 km²) results in sedimentological differences offshore. The results show that shell beds adjacent to disturbed watersheds (Lagosa and Rukoma) contain more fine-grained sediment compared to shell beds offshore of the undisturbed watershed (Katumbi). Widespread burning, clearance, and land cultivation, and rains of the wet season are causal factors that result in significant differences in fine-grained sedimentation, larger sediment plumes offshore, and increased shoreline progradation. In areas most affected by sedimentation, sponges are largely absent, and shell coverage, which is a measure of fish-nesting capabilities, is lower. The discovery of a small population of live Neothauma tanganyicense offshore of the Katumbi river suggests that the presence of shell-bed forming gastropods in front of a relatively low disturbance watershed, and their conspicuous absence offshore of the other two watersheds, could be related to recent watershed disturbance and increased sedimentation. The increased fine-grained sedimentation and limited shell production by the reduced modern gastropod populations may signal that the shell-bed ecosystem of Lake Tanganyika is at risk.     

Landslide databases in the Geological Surveys of Europe

Landslides are one of the most widespread geohazards in Europe, producing significant social and economic impacts. Rapid population growth in urban areas throughout many countries in Europe and extreme climatic scenarios can considerably increase landslide risk in the near future. Variability exists between European countries in both the statutory treatment of landslide risk and the use of official assessment guidelines. This suggests that a European Landslides Directive that provides a common legal framework for dealing with landslides is necessary. With this long-term goal in mind, this work analyzes the landslide databases from the Geological Surveys of Europe focusing on their interoperability and completeness. The same landslide classification could be used for the 849,543 landslide records from the Geological Surveys, from which 36% are slides, 10% are falls, 20% are flows, 11% are complex slides, and 24% either remain unclassified or correspond to another typology. Most of them are mapped with the same symbol at a scale of 1:25,000 or greater, providing the necessary information to elaborate European-scale susceptibility maps for each landslide type. A landslide density map was produced for the available records from the Geological Surveys (LANDEN map) showing, for the first time, 210,544 km² landslide-prone areas and 23,681 administrative areas where the Geological Surveys from Europe have recorded landslides. The comparison of this map with the European landslide susceptibility map (ELSUS 1000 v1) is successful for most of the territory (69.7%) showing certain variability between countries. This comparison also permitted the identification of 0.98 Mkm² (28.9%) of landslide-susceptible areas without records from the Geological Surveys, which have been used to evaluate the landslide database completeness. The estimated completeness of the landslide databases (LDBs) from the Geological Surveys is 17%, varying between 1 and 55%. This variability is due to the different landslide strategies adopted by each country. In some of them, landslide mapping is systematic; others only record damaging landslides, whereas in others, landslide maps are only available for certain regions or local areas. Moreover, in most of the countries, LDBs from the Geological Surveys co-exist with others owned by a variety of public institutions producing LDBs at variable scales and formats. Hence, a greater coordination effort should be made by all the institutions working in landslide mapping to increase data integration and harmonization.     

Rockfall risk management using a pre-failure deformation database

Terrestrial laser scanning (TLS) monitoring has been used to estimate the location, volume, and kinematics of a variety of small magnitude rockfalls before failure (1–1000 m³ range), and in some cases, potential failure time has been assessed through the application of inverse velocity methods. However, our current understanding of rock slope pre-failure behavior for this magnitude range and prediction ability is based on observations of a small number of failure case histories. In this study, a pre-failure deformation database was constructed for rockfall volumes exceeding 0.1 m³, observed over a 1252-day study interval at the Goldpan rock slope, British Columbia, Canada, in order to better understand the pre-failure behavior of rock slopes and provide an empirical means of estimating temporal failure ranges. Repeated TLS datasets were acquired at an average scanning interval of 2–3 months. A total of 90 rockfall events were recorded at this site, during this time period, of which 64 (71%) exhibited measurable deformation prior to failure. Classification of rockfalls by volume suggests that a scale dependency may exist, as deformation was detected for a greater proportion of rockfalls >?5 m³ (92%) than for smaller rockfalls in the range of 0.1–0.5 m³ (61%). A lower rate of pre-failure deformation detection was also reported for planar sliding failures as compared with wedge or toppling failures, suggesting that deformation was less easily detected for these failure types. This study proposes and implements a framework for rockfall assessment and forecasting that does not require continuous monitoring of deformation.     

Petrogenetic and geodynamic origin of the Neoarchean Doré Lake Complex,Abitibi subprovince,Superior Province,Canada

International Journal of Earth Sciences - The Neoarchean (ca. 2728&nbsp;Ma) anorthosite-bearing Doré Lake Complex in the northeastern Abitibi subprovince, Quebec, was emplaced into an...