32181 research outputs found
Sort by
Variability in sulfur isotope composition suggests unique dimethylsulfoniopropionate cycling and microalgae metabolism in Antarctic sea ice
Get PDFSea ice microbial communities produce large amounts of the sulfur metabolite dimethylsulfoniopropionate (DMSP), a precursor of the climate cooling gas dimethylsulfide. Despite their importance to the polar sulfur cycle, drivers and metabolic pathways of sea ice DMSP are uncertain. Here we report the first measurements of sea ice DMSP sulfur isotopic composition (34S/32S ratio, δ34S). δ34S values in ice cores from the Ross Sea and Weddell Sea reveal considerable variability across seasons and between ice horizons (from +10.6 to +23.6‰). We discuss how the most extreme δ34S values observed could be related to unique DMSP cycling in the seasonally extreme physiochemical conditions of isolated brine inclusions in winter-spring. Using cell cultures, we show that part of the DMSP δ34S variability could be explained by distinct DMSP metabolism in sea ice microalgae. These findings advance our understanding of the sea ice sulfur cycle and metabolic adaptations of microbes in extreme environments
Eddy structure and patterns in the oceans and atmospheres
Get PDFThe use of thematic maps derived from a combination of satellite sensors and images are validated between different methods and with on board observations, the topology of the detected features, such as spiral eddies [1, 2], fronts, Langmuir cells, etc.. May be even be used to predict diffusion and local pollution. It is also important to couple satellite information to the multiscale information available, which may be used to infer the turbulent parametrizations needed to predict pollutant and tracer dispersion in the ocean surface. In such a manner, more sophisticated data analysis such as the evaluation of integral length scales or local fractal dimensions of the sea surface appearance, and the detailed information of the position and sizes of the mesoscale dominant eddies provides very useful information on the sub-mesoscale ocean turbulence. The satellite-borne SAR and ASAR seems to be an excellent system not only to detect man-made oil spills and tension active slicks but it also detects dynamic features and the ocean eddies of different sizes. The study of the topology of the regions of different rugosity of the ocean, separating the vortical, elliptical, regions as well as the hyperbolic shear dominated areas, is also a convenient tool. The eddy structures of the Western Mediterranean were also investigated at different resolutions also by means of thermal images and altimetry data. A comparison of 1489 anticyclonic and 782 cyclonic eddy structures identified in the sea surface, to ASAR observations was performed. The (SST) imagery on an analysis of a 3-year period shows that only large anticyclonic eddies exceeding 70 km in diameter are long lived. This analysis, also applied to SAR and in advanced tracking of STT sequences, allows CPIV to extract velocity and vorticity local fields and relate spiral structure to vortex size. In the NW Mediterranean cyclonic eddies depend further on bathymetric effects. Due to the lack of resolution small spatial and temporal scales of such eddies and their non-geostrophic nature, it is difficult to compare basins of different size
A robust PID autotuning method for steam/water loop in large scale ships
No full textDuring the voyage of the ship, disturbances from the sea dynamics are frequently changing, and the ship's operation mode is also varied. Hence, it is necessary to have a good controller for steam/water loop, as the control task is becoming more challenging in large scale ships. In this paper, a robust proportional-integral-derivative (PID) autotuning method is presented and applied to the steam/water loop based on single sine tests for every sub-loop in the steam/water loop. The controller is obtained during which the user-defined robustness margins are guaranteed. Its performance is compared against other PID autotuners, and results indicate its superiority
A close relative of the Amazon river dolphin in marine deposits: a new Iniidae from the late Miocene of Angola
Get PDFA few odontocetes (echolocating toothed cetaceans) have been able to independently colonize freshwater ecosystems. Although some extant species of delphinids (true dolphins) and phocoenids (porpoises) at least occasionally migrate upstream of large river systems, they have close relatives in fully marine regions. This contrasts with the three odontocete families only containing extant species with a strictly freshwater habitat (Iniidae in South America, the recently extinct Lipotidae in China, and Platanistidae in southeast Asia). Among those, the fossil record of Iniidae includes taxa from freshwater deposits of South America, partly overlapping geographically with the extant Amazon river dolphin Inia geoffrensis, whereas a few marine species from the Americas were only tentatively referred to the family, leaving the transition from a marine to freshwater environment poorly understood
Ontogenetic and phylogenetic simplification during white stripe evolution in clownfishes
Get PDFBackground: Biologists have long been fascinated by the striking diversity of complex color patterns in tropical reef fishes. However, the origins and evolution of this diversity are still poorly understood. Disentangling the evolution of simple color patterns offers the opportunity to dissect both ultimate and proximate causes underlying color diversity. Results: Here, we study clownfishes, a tribe of 30 species within the Pomacentridae that displays a relatively simple color pattern made of zero to three vertical white stripes on a dark body background. Mapping the number of white stripes on the evolutionary tree of clownfishes reveals that their color pattern diversification results from successive caudal to rostral losses of stripes. Moreover, we demonstrate that stripes always appear with a rostral to caudal stereotyped sequence during larval to juvenile transition. Drug treatments (TAE 684) during this period leads to a dose-dependent loss of stripes, demonstrating that white stripes are made of iridophores and that these cells initiate the stripe formation. Surprisingly, juveniles of several species (e.g., Amphiprion frenatus) have supplementary stripes when compared to their respective adults. These stripes disappear caudo-rostrally during the juvenile phase leading to the definitive color pattern. Remarkably, the reduction of stripe number over ontogeny matches the sequences of stripe losses during evolution, showing that color pattern diversification among clownfish lineages results from changes in developmental processes. Finally, we reveal that the diversity of striped patterns plays a key role for species recognition. Conclusions: Overall, our findings illustrate how developmental, ecological, and social processes have shaped the diversification of color patterns during the radiation of an emblematic coral reef fish lineage
Pharmacological and chemical properties of some marine echinoderms
Get PDFEchinoderms have attracted the attention of scientists over the past few years after identifying a variety of unique structures endowed by interesting biological properties. However, the Moroccan coast biodiversity is still uninvestigated. In our ongoing attempts to valorize the rich Moroccan marine environment, this study aimed at assessing the antimicrobial activity of extracts obtained from three echinoderms Astropecten irregularis, Luidia sarsi and Ophiura albida against the human pathogens: Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica and Bacillus subtilis. Moreover, their antioxidant activities were tested using standard methods in addition to the antidiabetic activity which has been evaluated in vitro against α-amylase and α-glucosidase enzymes. HPLC-DAD-QTOF-MS analysis revealed a significant content of some phenolic compounds such as pyrogallol, gallic, sinapic, ferulic, p-hydroxybenzoic and salicylic acids whose existence can be related to the endophytic fungi and/or dietary intake whereas GC-MS analysis exhibited diverse chemical structures such as cholesterol, oleic acid and glycerol 1-palmitate
Fish value chain and its impact on rural households' income: lessons learned from northern Ethiopia
Get PDFThese days, one of the global challenges is the growing demand for food. To be more specific, seafood bases play a key role in filling the nutritional requirements of human beings. In Africa (Ethiopia) the public expenses to improve productive capacity in aquatic food are increasing. Additionally, the expenses in dams and in fishers' capacity building have increased households' engagement in the fishery sector in Ethiopia. Cooperatives' productive capacity has been strengthened by the government and other non-government organizations with the supply of fishing boats, refrigerators, fish nets and other office supplies. However, the effect of such public expenses in bringing changes in the households' livelihood and welfare has never been assessed in this study area. This paper aims to investigate what motivates the households to fish and assess the effect of fisheries on the households' livelihood and welfare. A structured survey consisting of 313 rural households was administered using trained enumerators in two kebeles located close to the Tekeze dam, Northern Ethiopia. The result indicates that socioeconomic characteristics, such as age (young), sex, education, and active family size were driving the households to fishing. Access to market and access to support are driving farmers to fisheries. There is a significant difference in fishing households' income which is higher than non-fishing households. The results also indicate that there are lesser income inequalities among fishery households operating in cooperatives compared to private fishery households
Improving the coexistence of offshore wind farms and shipping: an international comparison of navigational risk assessment processes
Get PDFThe continued growth and evolution of the offshore wind industry, and the emergence of other novel marine uses such as wave and tidal generators, have upped the ante for spatial planners, as well as consenting and approval authorities in various coastal states. These stakeholders rely on processes such as navigational risk assessments (NRAs) to balance safety and efficiency requirements and to make optimal decisions over use of space. Given the increasingly complex and crowded seascape, however, there are some apprehensions about potential shortcomings in these NRA processes. There is also some concern that these inadequacies may lead to unsafe or inefficient marine spatial use. To understand how NRA processes can be improved further, a literature review is conducted, followed by a survey of respondents who are involved in the planning, consenting and/or approval of offshore wind farms across seven different countries. A summary of the NRA processes in these seven countries is presented, and several shortcomings are identified. Based on the findings of the survey, a list of recommendations is presented to enhance existing NRA processesand to improve the coexistence of shipping and offshore wind farms (OWFs)
