Search results for "oceanography"
showing 10 items of 1567 documents
Nonlinear air dynamics of a surface effect ship in small-amplitude waves
2022
In many existing works, the seakeeping motions and air dynamics of a surface effect ship (SES) were assumed to be linear under small-amplitude waves (wave amplitude to wave length ratio ≤ 5%) to enhance the computational efficiency. However, according to SES model test results, it was found that even in small-amplitude waves, the fluctuating air cushion pressure shows significantly nonlinear effects. To precisely reveal this distinctive feature, the origin of nonlinearity was carefully investigated and the air leakage was considered as the main source of nonlinearity based on mathematical analysis in this paper. The reason is that the variance of clearance height under seals is comparable t…
Temporal dynamic of biofilms enhances the settlement of the central-Mediterranean reef-builder Dendropoma cristatum (Biondi, 1859).
2021
Abstract Research on marine invertebrate settlement provides baseline knowledge for restoration technique implementation, especially for biogenic engineers with limited dispersion ability. Previously, we determined that the maturity of a biofilm strongly enhances the settlement of the vermetid reef-builder Dendropoma cristatum. To elucidate settlement-related biofilm features, here we analyse the structure and composition of marine biofilms over time, through microscopic observations, eukaryotic and prokaryotic fingerprinting analyses and 16S rDNA Illumina sequencing. The vermetid settlement temporal increase matched with the higher biofilm coverage on the substratum and the reduction of th…
Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high-frequency gas monitoring
2016
OVSICORI Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high‐frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO2‐rich gas (CO2/Stotal > 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are acc…
Continuous SO2 flux measurements for Vulcano Island, Italy
2012
<p>The La Fossa cone of Vulcano Island (Aeolian Archipelago, Italy) is a closed conduit volcano. Today, Vulcano Island is characterized by sulfataric activity, with a large fumarolic field that is mainly located in the summit area. A scanning differential optical absorption spectroscopy instrument designed by the Optical Sensing Group of Chalmers University of Technology in Göteborg, Sweden, was installed in the framework of the European project "Network for Observation of Volcanic and Atmospheric Change", in March 2008. This study presents the first dataset of SO<sub>2</sub> plume fluxes recorded for a closed volcanic system. Between 2008 and 2010, the SO<sub>2</…
Metallic nanoparticle enrichment at low temperature, shallow CO2 seeps in Southern Italy
2012
We report on metal enrichment along a natural pH gradient owing to increased CO2 degassing at cold, shallow seeps of Vulcano Island in the Mediterranean Sea, off Sicily. We assessed composition of unfiltered and filtered seawater (<100 nm) along acidic zones ranging between ambient and pH 5, and showed that most seep derived elements are present as nanoclusters which then aggregate into larger colloids while mixing with ambient seawater along a pH gradient. Size and elemental composition of such naturally occurring nanoparticles assessed by modern characterisation methods were in good agreement with the results from conventional analytical methods. We provide analytical evidence for the pre…
Natural and artificial radioactivity levels in Livingston Island (Antarctic regions).
1994
Radioactive contamination of the sea and land is due, on the one hand, to fallout from atmospheric atomic explosions since 1945, and, on the other, to emissions produced by nuclear and radioactive facilities. Given its geographic position far distant from the aforementioned main sources of radioactive contamination, Antarctica should have the lowest levels that can be measured on the Earth of artificial radionuclides in the various receptor media which are characteristic of the trophic chain. In the case of Antarctica, these are melt-water, sea-water, mosses, algae, and lichens. With the aim of contributing basic information on the radiation levels present in the Antarctic ecosystem, we hav…
Pseudo-diel vertical migration in zooplankton: a whole-lake 15N tracer experiment
2012
Diel vertical migration (DVM) of zooplankton is commonly considered an adaptation for feeding in food-rich and warm surface waters at night and avoiding visual predators during the day. However, the critical assessment of migration patterns frequently suggests that: (i) zooplankton may leave deeper waters with rich, deepchlorophyll layers and move into the epilimnion where food resources are lower and/or (ii) the night-time increase in epilimnetic plankton abundance is not matched by a density decrease in deeper strata. To study these discrepancies, we measured DVM of zooplankton in a 1.3-ha Spanish karst lake (Laguna del Tejo) where the phytoplankton in the deep chlorophyll layer had been …
Evolution of neodymium isotopic signature of seawater during the Late Cretaceous: implications for intermediate and deep circulation.
2016
20 pages; International audience; Neodymium isotopic compositions (εNd) have been largely used for the last fifty years as a tracer of past ocean circulation, and more intensively during the last decade to investigate ocean circulation during the Cretaceous period. Despite a growing set of data, circulation patterns still remain unclear during this period. In particular, the identification of the deep-water masses and their spatial extension within the different oceanic basins are poorly constrained. In this study we present new deep-water εNd data inferred from the Nd isotope composition of fish remains and Fe–Mn oxyhydroxide coatings on foraminifera tests, along with new εNd data of resid…
Distribution patterns of particulate trace metals in the water column and nepheloid layer of the Gulf of Riga.
2004
The dynamics (fate) of trace metals in suspended particulate matter within the Gulf of Riga has not yet been adequately addressed in the scientific literature. Therefore, during a two year period (2001-2002) samples of suspended particulate matter and surface sediments for trace metal analysis were collected in the Gulf of Riga and the Daugava river, and these data were combined with background information from the national marine monitoring program in Latvia. This paper presents a descriptive study of solid phase trace metals (aluminium, iron, cadmium, chromium, copper, manganese, nickel, lead and zinc) dynamics and their spatial distribution within the Gulf of Riga based on Principal Comp…
Ba/Ca evolution in water masses of the Mediterranean late Neogene
2008
[1] A Mediterranean composite sedimentary record was analyzed for Ba/Ca ratios on carbonate shells of Orbulina universa planktonic foraminifer (Ba/Ca)carb providing the opportunity to study and assess the extent of freshwater inputs on the basin and possible impacts on its dynamics during the Tortonian to Recent period. A number of scanning electron microscope analyses and auxiliary trace element measurements (Mn, Sr, and Mg), obtained from the same samples, exclude important diagenetic effects on the studied biogenic carbonates and corroborate the reliability of (Ba/Ca)carb ratios in foraminifera calcite as indicators of seawater source components during the studied interval. A long-term t…