Steady Lateral Growth of Three-Dimensional Particle Laden Density Currents

In this paper the steady lateral growth of three-dimensional turbulent inclined turbidity current is investigated. To simulate the current, an experimental setup is developed to analyze the turbidity current for different regimes in the particle laden density currents environment. The Buckingham's π theorem together with a dimensional analysis is implemented to derive the appropriate non-dimensional variables. The experimental results were normalized and plotted in the form of non-dimensional graphs from which a theoretical model is developed and analyzed. Based on the results obtained for the steady lateral growth, three different regimes, namely, inertia-viscous one as the first regime, buoyancy-viscous and gravity-viscous as the second and third regimes are distinguished within the current.In these regimes, the force balance is between the driving and resisting forces. Namely, in the first regime, the force balance is between the inertia and viscous forces, in the second regime, the buoyancy and viscous forces, and in the third regime, gravity and viscous forces are balanced. The experimental results indicate that the lateral growth rate in the first regime is smaller than that in the second and third regimes due to the magnitude and type of the forces involved in those regimes. According to the graphical results, the three different lateral growth rates appear when the normalized current length is smaller than about 3, between about 3 and 10, and larger than about 10. In those regions,the slopes of the data are different with respect to one another.     

Baikal Electromagnetic Experiment

Izvestiya, Atmospheric and Oceanic Physics - The vertical component of the electric field Ez in the hydrosphere is not contaminated by the telluric component and therefore can effectively be used...     

Extreme Climatic Events in the Altai-Sayan Region as an Indicator of Powerful Volcanic Eruptions

Izvestiya, Atmospheric and Oceanic Physics - Analytic data on anomalies of the tree-ring structure of Siberian larch on the transect, passing through the Russian part of the Altai-Sayan Mountain...     

Authigenic iron oxide formation in the estuarine mixing zone of the Yangtze River

Estuaries are elementary geochemical fronts where river water and seawater mix. Within this mixing zone, iron and other non-conservative elements can undergo complex reactions to form new solid phases. In order to understand authigenic iron oxide formation in the Yangtze River Estuary, two onsite water-mixing sets of experiments were conducted, one by mixing variable amounts of unfiltered Yangtze River water with filtered East China Sea water of different salinity (set 1), the other by mixing variable amounts of filtered Yangtze River water with filtered East China Sea water of different salinity (set 2). In set 2, the minerals newly formed in the course of mixing were investigated by means of a scanning electron microscope fitted with an energy-dispersive X-ray analytical system. It was found that ferrihydrite and lepidocrocite were formed in these mixing experiments, coexisting in nearly equal amounts. These iron oxides appear as aggregated particles with a large grain-size range of several microns to more than 100 μm. The electrolytic properties of seawater played an important role in the formation of these authigenic iron oxides. Kaolinite and organic aggregates were also found in the experimentally mixed pre-filtered waters. Amounts of newly formed suspended matter (set 2) were one to three orders of magnitude lower than those of total suspended matter (TSM) (set 1). This implies that newly formed minerals represent only a very small proportion of TSM in the estuarine mixing zone of the Yangtze River.     

Fishing industry and related perspectives on the issues raised by no-take marine protected area proposals

In the face of growing calls for no-take marine protected areas (NTMPAs), the views of fishing industry representatives in south-west (SW) England on related issues are analysed. Only 23% thought NTMPAs were the way forward and a range of concerns were expressed, e.g. that the ‘terrestrial’ protected areas approach and related biodiversity conservation objectives will be extended to the seas, and that fish yield reductions from the loss of access to NTMPAs are very unlikely to be compensated for through spillover/export. Some interesting approaches to ameliorating these concerns emerged, such as being open and honest that NTMPAs are primarily intended to achieve biodiversity conservation benefits, reducing uncertainty concerning the potential for any secondary fisheries spillover/export benefits, justifying NTMPAs on an objective, rational basis rather than on a subjective, precautionary basis, and the quid pro quo streamlining of wider fisheries management approaches. This research reveals a more diverse range of perspectives amongst fishing industry representatives on the issues raised by NTMPA proposals than is often assumed.     

Dissolved iron in the Australian sector of the Southern Ocean (CLIVAR SR3 section): Meridional and seasonal trends

We report measurements of dissolved iron (dFe, <0.4 μm) in seawater collected from the upper 300 m of the water column along the CLIVAR SR3 section south of Tasmania in March 1998 (between 42°S and 54°S) and November–December 2001 (between 47°S and 66°S). Results from both cruises indicate a general north-to-south decrease in mixed-layer dFe concentrations, from values as high as 0.76 nM in the Subtropical Front to uniformly low concentrations (<0.1 nM) between the Polar Front and the Antarctic continental shelf. Samples collected from the seasonal sea-ice zone in November–December 2001 provide no evidence of significant dFe inputs from the melting pack ice, which may explain the absence of pronounced ice-edge algal blooms in this sector of the Southern Ocean, as implied by satellite ocean-color images. Our data also allow us to infer changes in the dFe concentration of surface waters during the growing season. South of the Polar Front, a comparison of near-surface with subsurface (150 m depth) dFe concentrations in November–December 2001 suggests a net seasonal biological uptake of at least 0.14–0.18 nM dFe, of which 0.05–0.12 nM is depleted early in the growing season (before mid December). A comparison of our spring 2001 and fall 1998 data indicates a barely discernible seasonal depletion of dFe (0.03 nM) within the Polar Frontal Zone. Further north, most of our iron profiles do not exhibit near-surface depletions, and mixed-layer dFe concentrations are sometimes higher in samples from fall 1998 compared to spring 2001; here, the near-surface dFe distributions appear to be dominated by time-varying inputs of aerosol iron or advection of iron-rich subtropical waters from the north.     

Influence of nutritional stress on digestive enzyme activities in juveniles of two marine clam species, Ruditapes decussatus and Venerupis pullastra

The potential use of digestive activities as indicators of the nutritional status in bivalves is discussed in relation to the results obtained in two clam species exposed to starvation and refeeding. Activities of some digestive enzymes (amylase, laminarinase, cellulase, and protease) were measured in juveniles of two commercially interesting species of clams, Ruditapes decussatus and Venerupis pullastra. The specimens were fed normally, being after subjected to a 15-days starvation and a further refeeding period. Samples were obtained at different moments of such feeding schedule to evaluate enzymes as well as weight (live, dry and organic) and length, in order to calculate growth rates and feeding efficiencies. Starvation led to a major decrease in clam growth as measured by dry weight and a negative growth as measured by organic weight, this coinciding with a certain degree of growth of the shell and a consumption of soft tissue. This response occurred more rapidly in R. decussatus but was of a lower magnitude than in V. pullastra. Activity of carbohydrases decreased rapidly in both species with starvation, although protease activity was maintained in R. decussatus. Recovery after the end of starvation was not similar in both species; while R. decussatus attained similar growth rates and enzyme activities to those measured prior to nutritional stress, V. pullastra only recovered 50% of its initial values. For both species of bivalves it can be concluded that digestive enzymes, and more specifically amylase, could be used as indicative of their nutritional condition.     

Network analysis to inform invasive species spread among lakes

Often facilitated by human-mediated pathways,aquatic invasive species are a threat to the health and biodiversity of global ecosystems.We present a novel approach incorporating survey data of watercraft movement in a social network analysis to reconstruct potential pathways of aquatic invasive species spread between lakes.As an example,we use the green alga Nitellopsis obtusa,also known as starry stonewort,an aquatic invasive species affecting the Great Lakes region in the United States and Canada.The movement of algal fragments via human-mediated pathways(i.e.,watercraft)has been hypothesized as the primary driver of starry stonewort invasion.We used survey data collected at boat ramps during the 2013 and 2014 openwater seasons to describe the flow of watercraft from Lake Koronis,where N.obtusa was first detected in Minnesota,to other lakes in the state.Our results suggest that the risk of N.obtusa expansion is not highly constrained by geographic proximity and management efforts should consider highly connected lakes.Estimating human movement via network analysis may help to explain past and future routes of aquatic invasive species infestation between lakes and can improve evidence-based prevention and control efforts.