Semisubmersible response to transient ice forces

The paper presents an analytical and experimental study on the transient response of semisubmersibles to bergybit impact and the strength of bergybit ice to high strain-rate loadings. Two approaches have been proposed for the solution of the semisubmersible-bergybit interaction problem, one using the energy approach and the other using the conventional structural dynamics approach with initial velocity conditions. In addition the local behaviour of the impacted regions have been analysed for deformation and failure. Numerical results have been given for local behaviour of an impacted column and global behaviour of semisubmersible-bergybit system. Experimental study has been reported on the impact strength of iceberg ice at strain rates of 10⁻³, 10⁻² and 10⁻¹; the indentation impact strength of ice is found to be 3–4 times the unaixial compressive strength, at the same strain rate.     

Distributions of dissolved and particulate biogenic thiols in the subartic Pacific Ocean

Dissolved and particulate concentrations of the biogenic thiols cysteine (Cys), arginine–cysteine (Arg–Cys), glutamine–cysteine (Gln–Cys), γ-glutamate–cysteine (γ-Glu–Cys) and glutathione (GSH) were measured in the subartic Pacific Ocean in the summer of 2003 using high performance liquid chromatography (HPLC) with precolumn derivatization as reported in previous work. In this study, a preconcentration protocol for the derivatized thiols was utilized to extend detection limits of dissolved thiols to picomolar levels. The measured concentrations of particulate and dissolved thiols were uncoupled, with distinctive depth profiles and large differences in the particulate to dissolved ratios between individual compounds. Glutathione was the most abundant particulate thiol whereas the most abundant dissolved thiol was γ-Glu–Cys, with concentrations as high as 15 nM. Given the relatively small pool of intracellular γ-Glu–Cys and the very low dissolved concentrations of GSH, we hypothesize that glutathione released from cells is rapidly converted to the potentially degradation resistant γ-Glu–Cys outside the cell. The relatively high concentrations of other dissolved thiols compared to particulate concentrations implies both biological exudation and slow degradation rates. Some thiols appear to vary with changes in nutrient availability but this effect is difficult to decouple from changes in community structure inferred from pigment analyses. Dissolved thiol concentrations also exceed typical metal concentrations in the subartic Pacific, supporting previous arguments that they may be important in metal speciation.     

Different cardiac response to copper in limpets from metal polluted and clean shores of Hong Kong

The gastropod limpet, Cellana grata, is common on moderately exposed to exposed Hong Kong rocky shores. On the basis of the existing literature on trace metal contamination in Hong Kong, four sites were identified, representative of highly polluted (Aberdeen and Lei Yue Mun) and clean (Cape d'Aguilar and Clear Water Bay) conditions. Limpets from the two polluted sites showed similar, but significantly higher body concentrations of copper than limpets from the two clean sites, which were also similar. Non-invasive measurements of cardiac activity of limpets from the four sites showed between site differences in baseline heart rates under standard seawater, irrespective of pollution level. When acutely exposed to water borne copper (2 h, 0.5+/-0.06 SD ppm), however, limpets from clean sites showed a significantly higher increase in inter-beating time (bradycardia) than those from polluted sites. These results highlight the potential use of cardiac activity to assess the exposure of natural populations of limpets to trace metal pollution.     

Geologic evolution of the Canarian Islands of Lanzarote, Fuerteventura, Gran Canaria and La Gomera and comparison of landslides at these islands with those at Tenerife, La Palma and El Hierro

In this paper we discuss the results of a swath bathymetric investigation of the Canary archipelago offshore area. These new data indicate that volcanism is pervasive throughout the seafloor in the region, much more that would be suggested by the islands. We have mapped tens of volcanic edifices between Fuerteventura and Gran Canaria and offshore Tenerife, La Gomera, El Hierro and La Palma. Volcanic flows are present between Tenerife and La Gomera and salic necks dominate the eastern insular slope of La Gomera. This bathymetry also supports land geologic studies that indicate that the oceanic archipelago has acquired its present morphology in part by mass wasting, a consequence of the collapse of the volcanic edifices. In the younger islands, Tenerife, La Palma and El Hierro, the Quaternary (1.2 to 0.15 Ma) debris avalanches are readily recognizable and can be traced offshore for distances measured in tens of km. Off the older islands, Lanzarote, Fuerteventura, Gran Canaria and La Gomera (<20 to 3.5 Ma), the avalanches have been obscured by subsequent turbidity current deposition and erosion as well as hemipelagic processes. The failure offshore western Lanzarote is in the form of a ramp at the base of the insular slope bound on the seaward side by a scarp. Its size and the lack of evidence of rotation along its landwards side precludes the possibility that it is a slump. It probably represents a slide whose outer scarp is caused by break-up of the slide. Mounds on the ramp’s surface may represent post-displacement volcanic structures or exotic blocks transported to their present locations by the slide. The failures offshore Fuerteventura are so large that, although they occurred in the Miocene-Pliocene, exotic blocks displaced from upslope are still recognizable in the insular margin morphology. The Canary Island insular margin appears to be a creation of Miocene-Pliocene mass wasting and more recent turbidity current deposition and erosion, and hemilepagic deposition. Failures offshore La Gomera are due to debris flows and/or turbidity currents. These events have obscured earlier mass wasting events. An erratum to this article is available at .     

New sets of wavelet-forming functions

One of the most efficient tools of studying meteorological and climatic time series is wavelet analysis, which allows local properties of a nonstationary time series to be examined. New sets of continuous and discrete wavelet-forming functions are proposed. All proposed wavelets are finite (have a bounded carrier), even, and well localized in the spectral space.     

Bioerosion by chemosynthetic biological communities on Holocene submarine slide scars

Geomorphic, stratigraphic, and faunal observations of submarine slide scars that occur along the flanks of Monterey Canyon in 2.0–2.5 km water depths were made to identify the processes that continue to alter the surface of a submarine landslide scar after the initial slope failure. Deep-sea chemosynthetic biological communities and small caves are common on the sediment-free surfaces of the slide scars, especially along the headwall. The chemosynthetic organisms observed on slide scars in Monterey Canyon undergo a faunal succession based in part on their ability to maintain their access to the redox boundaries in the sediment on which they depend on as an energy source. By burrowing into the seafloor, these organisms are able to follow the retreating redox boundaries as geochemical re-equilibration occurs on the sole of the slide. As these organisms dig into the seafloor on the footwall, they often generate small caves and weaken the remaining seafloor. While chemosynthetic biological communities are typically used as indicators of fluid flow, these communities may be supported by methane and hydrogen sulfide that are diffusing out of the fresh seafloor exposed at the sole of the slide by the slope failure event. If so, these chemosynthetic biological communities may simply mark sites of recent seafloor exhumation, and are not reliable fluid seepage indicators.     

Seagrass landscape-scale changes in response to disturbance created by the dynamics of barrier-islands: A case study from Ria Formosa (Southern Portugal)

This study documents long-term changes of a Zostera noltii landscape induced by a natural cyclic event in a coastal lagoon. The barrier-islands forming this system are very dynamic with drifting movements controlling ecological patterns and processes occurring in this area. Changes in the areal extent of the Z. noltii meadows were assessed using historical aerial photographs from 1940, 1980, 1989, 1996 and 1998. Landscape indices such as total patch area (TA), mean patch size (MPS), number of patches (NP), mean shape coefficient of variation (CV) and landscape fractal dimension (D) were calculated for each year and related to an index of disturbance intensity. The spatial distribution of the Z. noltii meadows varied greatly during the studied period and changes observed were related to the disturbance created by the barrier-islands' spatial dynamics. After an artificial inlet relocation the Z. noltii area, number of patches, patch mean size and coefficient of variation decreased. The fractal dimension of the Z. noltii landscape increased by 50% showing that besides a decrease in total area, number of patches, and patch mean area, patch fragmentation was an important consequence of this anthropogenic disturbance.Seagrass natural distribution patterns changed in response to natural and human-induced activities. This study emphasizes the importance of the landscape approach and the historical perspective when studying seagrass changes and the importance of taking into consideration long-term changes in seagrass landscapes to avoid confusion between man-induced effects with natural cyclic events.     

Spatial heterogeneity of epibenthos on artificial reefs: fouling communities in the early stages of colonization on an East Australian shipwreck

Artificial reefs are spatially complex habitats and serve as good model systems to study patterns of community succession and the response of epibiota to environmental clines over small spatial scales. Here, we quantified spatial heterogeneity in community composition and diversity of fouling communities across a number of environmental gradients that included water depth, surface orientation of habitats, exposure to currents, and shelter. Assemblage structure was quantified by spatially replicated photo transects on a recently scuttled large navy ship off the East Australian coast, lying in 27 m of water. A rich assemblage of epifauna had colonized the wreck within a year, dominated by barnacles, sponges and bryozoans. Community structure varied significantly over small spatial scales of meters to tens of meters. Depth, surface orientation and exposure were the major environmental drivers. Assemblages were substantially less diverse and abundant on the deepest (23 m near the seafloor) part of the hull with residual antifouling paint, on sheltered surfaces inside the wreck, and on the sediment‐laden horizontal surfaces. Overall, the wrecks’ habitat complexity corresponds with small‐scale heterogeneity in the fouling communities. This study supports the notion that wrecks enhance local diversity and biomass within the habitat mosaic of their location, and habitat complexity may be an important mechanism for this, as demonstrated by the large spatial variability in the assemblages documented here.