Frigatebird behaviour at the ocean–atmosphere interface: integrating animal behaviour with multi-satellite data

Marine top predators such as seabirds are useful indicators of the integrated response of the marine ecosystem to environmental variability at different scales. Large-scale physical gradients constrain seabird habitat. Birds however respond behaviourally to physical heterogeneity at much smaller scales. Here, we use, for the first time, three-dimensional GPS tracking of a seabird, the great frigatebird (Fregata minor), in the Mozambique Channel. These data, which provide at the same time high-resolution vertical and horizontal positions, allow us to relate the behaviour of frigatebirds to the physical environment at the (sub-)mesoscale (10–100 km, days–weeks). Behavioural patterns are classified based on the birds’ vertical displacement (e.g. fast/slow ascents and descents), and are overlaid on maps of physical properties of the ocean–atmosphere interface, obtained by a nonlinear analysis of multi-satellite data. We find that frigatebirds modify their behaviours concurrently to transport and thermal fronts. Our results suggest that the birds’ co-occurrence with these structures is a consequence of their search not only for food (preferentially searched over thermal fronts) but also for upward vertical wind. This is also supported by their relationship with mesoscale patterns of wind divergence. Our multi-disciplinary method can be applied to forthcoming high-resolution animal tracking data, and aims to provide a mechanistic understanding of animals'' habitat choice and of marine ecosystem responses to environmental change.     

Orientational effects in geophysical fluid dynamics

The approach, accounting the interaction between essentially different scales of turbulent fluid motions on a rotating sphere, is developed. Representation of the large-scale oceanic circulation as a turbulent flow with orientational effects due to synoptic (mesoscale) eddies is the basis of this technique. The scale of these eddies is much less than that of the considered problem, their energetic significance however is important. Such representation leads to employment of nontrivial angular momentum equation, i.e. to micropolar or asymmetrical hydrodynamics. It allows to define a function which would characterize the averaged vorticity of mesoscale (subgrid) motions and does not relate to the mean flow vorticity. Using this parameterization, the calculations with barotropic and 2-layer global ocean models have been carried out. The model results do show an increase of basic ocean gyre transports.     

The effect of external flow on the feeding currents of sessile microorganisms

Microscopic sessile suspension feeders live attached to surfaces and, by consuming bacteria-sized prey and by being consumed, they form an important part of aquatic ecosystems. Their environmental impact is mediated by their feeding rate, which depends on a self-generated feeding current. The feeding rate has been hypothesized to be limited by recirculating eddies that cause the organisms to feed from water that is depleted of food particles. However, those results considered organisms in still water, while ambient flow is often present in their natural habitats. We show, using a point-force model, that even very slow ambient flow, with speed several orders of magnitude less than that of the self-generated feeding current, is sufficient to disrupt the eddies around perpendicular suspension feeders, providing a constant supply of food-rich water. However, the feeding rate decreases in external flow at a range of non-perpendicular orientations due to the formation of recirculation structures not seen in still water. We quantify the feeding flow and observe such recirculation experimentally for the suspension feeder Vorticella convallaria in external flows typical of streams and rivers.     

The distribution of water in degrading polyglycolide. Part II: Magnetic resonance imaging and drug release

This paper reports the use of magnetic resonance imaging (MRI) on polyglycolide disks to monitor the change in water ingress with degradation time. Very little response was measured before 13 days, but after this time, water began to penetrate the disks as fronts, starting from the sample surface and moving inwards towards the centre. These results provide more direct evidence in support of the four-stage degradation model for PGA outlined in previous literature, and in particular, that fairly sharp reaction-erosion fronts move in from the sample surface to the centre when the polymer is undergoing significant mass loss and water gain. A combination of MRI and drug release data suggest that fronts originate at the surface at about 7 (±2) days, and proceed at a rate of 0.033 (±0.002) mm/day. These results agree with results obtained from cumulative drug release profiles for different sample thicknesses presented in Part I. They support the hypothesis that drug releases quickly from the swollen regions behind the fronts where the polymer is open and porous, and that release finishes when the fronts meet in the centre of the sample.     

Separation in a two-dimensional Stokes flow inside an elliptic cylinder

The two-dimensional Stokes flow due to a line rotlet inside a fixed elliptic cylinder is investigated, where it is assumed that the line rotlet intersects the major axis of each elliptical cross-section of the cylinder. For the case in which the line rotlet coincides with the centre-line of the elliptic cylinder, it is shown that the number of eddies in the flow increases in a roughly linear way with the ratio of length to width of a cross-section of the cylinder. Moreover, results obtained by varying the rotlet position for several different fixed boundary shapes suggest that the aforementioned ratio, and not the rotlet position, is the principal determinant of the number of eddies.     

Mesoscale fronts as foraging habitats: composite front mapping reveals oceanographic drivers of habitat use for a pelagic seabird

The oceanographic drivers of marine vertebrate habitat use are poorly understood yet fundamental to our knowledge of marine ecosystem functioning. Here, we use composite front mapping and high-resolution GPS tracking to determine the significance of mesoscale oceanographic fronts as physical drivers of foraging habitat selection in northern gannets Morus bassanus. We tracked 66 breeding gannets from a Celtic Sea colony over 2 years and used residence time to identify area-restricted search (ARS) behaviour. Composite front maps identified thermal and chlorophyll-a mesoscale fronts at two different temporal scales—(i) contemporaneous fronts and (ii) seasonally persistent frontal zones. Using generalized additive models (GAMs), with generalized estimating equations (GEE-GAMs) to account for serial autocorrelation in tracking data, we found that gannets do not adjust their behaviour in response to contemporaneous fronts. However, ARS was more likely to occur within spatially predictable, seasonally persistent frontal zones (GAMs). Our results provide proof of concept that composite front mapping is a useful tool for studying the influence of oceanographic features on animal movements. Moreover, we highlight that frontal persistence is a crucial element of the formation of pelagic foraging hotspots for mobile marine vertebrates.     

Concerning inviscid solutions for large-scale separated flows

Summary The large-scale separated eddies set up behind a bluff body at high Reynolds number are considered, for steady laminar planar flow. The main eddies are massive and are controlled predominantly by inviscid mechanics, with uniform vorticity inside. Analytical and computational solutions of the massive-eddy (vortex-sheet) problem are then described. A further possibility studied is that, even with lateral symmetry assumed, there may still be an extra degree of nonsymmetry of skewing with respect to the streamwise direction. Small-scale separations, where a Benjamin-Ono equation also possibly yielding nonsymmetric solutions can come into play, are discussed briefly.     

Large-Eddy-Simulation-based analysis of complex flow structures within the volute of a vaneless centrifugal pump

Centrifugal pumps are very common in many fluid handling industrial applications, such as petrochemicals, oil and gas, etc. Although the design practices for centrifugal pumps are well established, efforts are directed towards optimising such systems for better operational efficiencies. In order to optimally design centrifugal pumps, it is beneficial to first understand the complex flow phenomena within different sections of the pump for a variety of operating conditions. This is normally achieved through the use of modern techniques, such as Computational Fluid Dynamics (CFD), where the flow within centrifugal pumps can be numerically modelled and important flow features can be analysed for better understanding of interactions amongst different process variables. CFD offers different turbulence modelling techniques with an aim to predict realistic flow approximations. Large Eddy Simulation (LES) offers a more accurate solution to this, in which the larger eddies are resolved while smaller eddies are modelled; hence predictions using LES are more realistic. Further, in turbulence modelling within centrifugal pumps, it is also important to model the complete interaction amongst different variables rather than a simplistic single blade passage flow analysis. In the present work, the complex blade–tongue interactions and their consequent effects on the pressure fluctuations within the volute have been evaluated. It is seen that the secondary flow features in the near-tongue regions due to blade interactions with the tongue affect the flow characteristics within the volute considerably.     

Drag reduction of turbulent flow over thin rectangular riblets

Direct numerical simulations of low-Reynolds number turbulent channel flow are carried out where thin rectangular riblets are distributed uniformly at only one of the channel walls. A second-order accurate finite volume code is modified in order to reconstruct the adjacent cells to the riblets at Cartesian coordinates. A quadratic interpolation scheme is used to estimate the fluxes at the reformed cells. The riblets height/spacing ratio is fixed at 0.5 which doubles the surface area at the ribbed wall and the thickness/spacing ratio is set to 0.02. The riblet spacing ranges from 13 to 41 viscous units. Comparison with experiments shows excellent agreement in detecting both reduction and the increase of drag at the studied range of spacings. The maximum drag reduction obtained is about 11% which occurs at a spacing of 18 viscous units. The increase of drag is addressed when the spacing is larger than 30 wall units. Wide spacing permits the near-wall eddies to reside inside the riblet-to-riblet span which in turn makes them interacting with larger wetted area and increases the friction drag.     

Discrimination and analysis of phytoplankton using a microfluidic cytometer

Identification and analysis of phytoplankton is important for understanding the environmental parameters that are influenced by the oceans, including pollution and climate change. Phytoplanktons are studied at the single cell level using conventional light-field and fluorescence microscopy, but the technique is labour intensive. Flow cytometry enables rapid and quantitative measurements of single cells and is now used as an analytical tool in phytoplankton analysis. However, it has a number of drawbacks, including high cost and portability. We describe the fabrication of a microfluidic (lab-on-a-chip) device for high-speed analysis of single phytoplankton. The device measures fluorescence (at three wavelength ranges) and the electrical impedance of single particles. The system was tested using a mixture of three algae (Isochrysis Galbana, Rhodosorus m., Synechococcus sp.) and the results compared with predictions from theory and measurements using a commercial flow cytometer (BD FACSAria). It is shown that the microfluidic flow cytometer is able to distinguish and characterise these different taxa and that impedance spectroscopy enables measurement of phytoplankton biophysical properties.     

矩形断面抖振阻力空间分布特性试验研究

为了研究紊流作用下钝体抖振阻力的空间分布特性及流固相互作用机理,以2:1矩形断面为例,通过刚性模型测压试验研究了抖振阻力的跨向相关性及空间能量分布特性。结果表明,当紊流积分尺度与钝体特征尺寸相当时,抖振阻力的相关性高于纵向脉动风,这也许是由漩涡沿展向发生拉伸引起。而在分离点附近,来流漩涡会发生剧烈畸变,顺流向大尺度漩涡会破碎成小尺度漩涡,在此过程中能量由低频向高频的转移,并导致脉动压力的跨向相关性也会有所减弱。与迎风侧不同,背风侧脉动压力主要受钝体尾流中的紊流成分影响,其漩涡沿跨向拉伸程度可能要高于迎风侧,以致背风侧脉动压力的跨向相关性强于迎风侧。顺流向分离涡在由分离点向中部运动过程中,其高频的小尺度漩涡可能并没沿顺流向拉伸,而是直接耗散,从而导致脉动压力谱在低频保持不变,而在高频区下降。     

Knowledge-transfer analysis based on co-citation clustering

Based on co-citation cluster analysis, we propose a knowledge-transfer analysis model for any technology field. In this model, patent data with backward citations to non-patent literature and forward citations by later patents would be analyzed. Co-citation clustering of the cited articles defines scientific knowledge sources, while that of the patents themselves defines technology fronts. According to the citation between the article and patent clusters, the landscape of knowledge-transfer including route and strength between scientific knowledge sources and technology fronts can be mapped out. The model has been applied to the field of transgenic rice. As a result of the analysis, ten scientific knowledge sources and eight technology fronts have emerged, and reasonable links between them have been established, which clearly show how knowledge has been transferred in this field.     

The kaleidoscope ocean

Oceanic plant life is dominated by the microscopic phytoplankton. Regardless of the scale at which they are observed, they display striking heterogeneity in their distribution. At their most dramatic they paint colorful swathes across whole seas. A short history of observations of phytoplankton 'patchiness' is presented, illustrated with some of the many ideas put forward to explain it. Focus is then turned to the mesoscale, covering scales of roughly 1-500 km. It is argued that the spatial variability seen in phytoplankton at these scales gives important information on the biogeochemistry of the ocean. In particular, interplay between the physical circulation and biological processes results in constantly shifting patterns that are strongly related to changes induced in phytoplankton production. It is thought that this physical influence may play a major role in controlling the rate at which new plant material (primary production) is generated in much of the world's oceans. Major questions yet to be addressed are also discussed including the difficulty of quantifying processes on the very limit of what we can model or observe and how these processes may change in response to and exert a feedback on future climate change.     

Optical assessment of particle size and composition in the Santa Barbara Channel, California

The suspended particle assemblage in complex coastal waters is a mixture of living phytoplankton, other autochthonous matter, and materials of terrestrial origin. The characterization of suspended particles is important for understanding regional primary productivity and rates of carbon sequestration, the fate of anthropogenic materials released to the coastal environment, as well as its effects on bulk optical properties, which influence the passive optical remote sensing of the coastal ocean. Here, the extensive bio-optical Plumes and Blooms data set is used to characterize the surface particle assemblage in the Santa Barbara Channel, California, a highly productive, upwelling-dominated, coastal site affected by episodic sediment inputs. Available variables sensitive to characteristics of the particle assemblage include particle beam attenuation and backscattering coefficients, High Performance Liquid Chromatography (HPLC) pigment concentration observations, chlorophyll and particulate organic carbon concentration, particulate and phytoplankton absorption coefficients, and Laser In-situ Scattering and Transmissometry (LISST) 100-X particle sizer observations. Comparisons among these particle assemblage proxy variables indicate good agreement and internal consistency among the data set. Correlations among chlorophyll concentration, particulate organic carbon concentration (POC), HPLC pigments, and proxies sensitive to the entire particle assemblage such as backscattering and LISST data strongly indicate that in spite of its coastal character, variability in the particle assemblage in the Santa Barbara Channel is dominated by its marine biogenic component. Relatively high estimates of the bulk real index of refraction and its positive correlation with chlorophyll and lithogenic silica concentration tentatively indicate that there is minerogenic particle influence in the Santa Barbara Channel that tends to covary with the phytoplankton blooms. Limitations of each particle assemblage proxy and remote-sensing applications are discussed.     

磁性液体管道流动的数值模拟

通过将磁性液体的磁化曲线用一个反正切函数来模拟，并且将磁场体积力写成Az的函数形式来模拟磁性液体在圆管申的流动。结果表明，圆管内的磁性液体有最大流量时，磁性液体流在靠近永磁附近呈紊流状态流动，在圆管的最右端，大致呈层流状态流动；圆管内的磁性液体净流量为零时，靠近永磁的磁性液体在原地呈激烈的涡旋流动状态．     

Satellite observations of the Agulhas Current system

The Agulhas Current system is a complex interplay of currents and eddies with the bathymetry. Components such as the East Madagascar Retroflection and the Agulhas Return Current evolve significantly over a month, and they are thus not adequately resolved by infrequent research-ship cruises. This paper contrasts the abilities of three different spaceborne sensors for monitoring these complex regimes. A key parameter is sea-surface temperature, measured by both infrared and microwave radiometers. Ocean colour observations of chlorophyll can also be used to distinguish between water masses.     

The distribution of water in degrading polyglycolide. Part I: Sample size and drug release

The effect of sample thickness on the degradation of polyglycolide (PGA) disks and on their drug release profiles is explored in this paper, and conclusions drawn about the distribution of water across a sample during degradation. The degradation process was monitored by measuring changes in the long period calculated from small angle X-ray scattering profiles, and by following changes in the pH of the buffer solutions. Drug release profiles were obtained using UV-spectrophotometry. The measurements suggest that reaction-erosion fronts form at the surface of all samples after around 7 days of degradation, and that these fronts progress through the sample at a constant rate of 0.032 mm/day. The data are consistent with a model in which drug is released quickly from the porous, hydrated regions behind the front, and reaches 100% release when the fronts meet. ©2003 Kluwer Academic Publisher     

The atmospheric ocean: eddies and jets in the Antarctic Circumpolar Current

Although the Antarctic Circumpolar Current (ACC) is the longest and the strongest oceanic current on the Earth and is the primary means of inter-basin exchange, it remains one of the most poorly represented components of global climate models. Accurately describing the circulation of the ACC is made difficult owing to the prominent role that mesoscale eddies and jets, oceanic equivalents of atmospheric storms and storm tracks, have in setting the density structure and transport properties of the current. The successes and limitations of different representations of eddy processes in models of the ACC are considered, with particular attention given to how the circulation responds to changes in wind forcing. The dynamics of energetic eddies and topographically steered jets may both temper and enhance the sensitivity of different aspects of the ACC's circulation to changes in climate.     

Laboratory experiments on frazil ice growth in supercooled water

Presented herein are the results of a laboratory investigation of the influence of turbulence and water temperature on the nature and rate of frazil ice growth in a turbulent body of supercooled water. The results indicate that the rate and the quantity of frazil ice growth increase with both increasing turbulence intensity and with decreasing water temperature at the instant of seeding, when a small fragment of ice is placed in the supercooled water. The turbulence characteristics of a flow affect the rate of frazil-ice growth by governing the temperature to which the flow can be supercooled; by influencing heat transfer from the frazil ice to surrounding water; and by promoting secondary nucleation, crystal, platelet and floc fracture, thereby increasing the number of nucleation sites available for further frazil ice growth.Larger frazil ice platelets, beginning as single crystals then becoming laminar fusions of crystals, were observed to form in water supercooled to lower temperatures. However, platelet size generally decreased with increasing turbulence intensity, as platelets with a major diameter larger than a certain value tend to break when buffeted by turbulence eddies.The investigation of frazil ice growth involved the use of a simplified analytical model, in which the rate of frazil ice growth is related to temperature rise of a turbulent volume of water due to the release of latent heat of fusion of liquid water to ice. Experiments conducted in a turbulence jar with a heated, vertically oscillating grid served both to guide and to calibrate the analytical model as well as to afford insights into frazil ice growth.     

Spatial variability of oceanic phycoerythrin spectral types derived from airborne laser-induced fluorescence emissions

We report spatial variability of oceanic phycoerythrin spectral types detected by means of a blue spectral shift in airborne laser-induced fluorescence emission. The blue shift of the phycoerythrobilin fluorescence is known from laboratory studies to be induced by phycourobilin chromophore substitution at phycoerythrobilin chromophore sites in some strains of phycoerythrin-containing marine cyanobacteria. The airborne 532-nm laser-induced phycoerythrin fluorescence of the upper oceanic volume showed distinct segregation of cyanobacterial chromophore types in a flight transect from coastal water to the Sargasso Sea in the western North Atlantic. High phycourobilin levels were restricted to the oceanic (oligotrophic) end of the flight transect, in agreement with historical ship findings. These remotely observed phycoerythrin spectral fluorescence shifts have the potential to permit rapid, wide-area studies of the spatial variability of spectrally distinct cyanobacteria, especially across interfacial regions of coastal and oceanic water masses. Airborne laser-induced phytoplankton spectral fluorescence observations also further the development of satellite algorithms for passive detection of phytoplankton pigments. Optical modifications to the NASA Airborne Oceanographic Lidar are briefly described that permitted observation of the fluorescence spectral shifts.