An analogue model study of electromagnetic induction in the eastern coastal region of North America

The behavior of electric and magnetic field variations over the eastern coastal region of North America is studied using a scaled laboratory electromagnetic analogue model. The model source frequency used simulates a period of 1 h in the geophysical scale. The results indicate that deflection and conductive channelling of induced electric current is important for both the E-polarization (northeast-southwest direction of the electric field of the source) and the H-polarization (northwest-southeast) of the source field. In the model, conductive channelling occurs through the Strait of Belle Isle, Cabot Strait, and in the St. Lawrence River. Current deflection is particularly prevalent around the southeast coast of Newfoundland for both E- and H-polarization, and around the northeast coastline of Nova Scotia for E-polarization. The model results also show current deflection by cape and bay coastal features, as well as by ocean depth contours.A comparison of model measurements for the cases of a uniform source field and a line current source indicate that the nature of the source field has a measurable but surprisingly small effect on the vertical to horizontal magnetic field ratio for both E- and H-polarizations, and negligible effect on the magnetotelluric ratio for coastal regions.The model fields in coastal regions were found to be strongly influenced by induced currents, deflected and channelled by the coastline and ocean bathymetry, and were dependent on the nature and particularly the polarization of the source field. Thus, along the complex coastline of eastern North America, a wide range of electric and magnetic field values should be expected. In some regions the coast effect, measured by the vertical to horizontal magnetic field ratio at the coast, could be expected to be extremely small or absent, while in other regions the ratio could approach a value as large as unity for variations of 1 h period.     

A method of searching for radial velocity anomalies in the lower mantle using interfering signals

Radial velocity anomalies in the lower mantle that give rise to triplications in the travel-time curve for short-periodP waves will produce arrivals havingdT/d values that differe by roughly 0.2–0.5 s/deg. The first two arrivals associated with such triplications will be separated by less than one second over a distance range of 4°–10° they may not, therefore, be separable visually on single seismograms, so that their presence can only be inferred from some measurable property that depends on their mutual interference. If there are lateral variations in the regions of anomalous velocity gradients, the interfering signals will also have different azimuths of arrival. Using two synthetic wavelets we have investigated the effect of interference on bothdT/d and azimuth measurements at the Yellowknife Array. We found that if the interfering pulses have a dominant frequencyv, there is a range of time separations (0.30/v0.55/v) over which the measureddT/d and azimuth values may fluctuate by much more than the differences indT/d and azimuth between the interfering signals. We have evaluated the following empirically defined functions for three different primary signals, and for three different relative amplitudes of the interfering signals:f (t), the drift function, which expresses how the measured slownesses,p, and azimuths, , differ from the slownesses and azimuths of the primary wavelets; f(), the range function, which describes the behaviour of the upper and lower bounds ofp and as a function of the difference in arrival times of the signals, andf , studied the properties of these functions, and have outlined how these properties provide criteria based on the numerical and statistical characteristics of the arrival vectors, and on the waveform of the signal that will enable small radial velocity anomalies to be more clearly delineated.Contribution No. 863 from the Earth Physics Branch.     

Sedimentation in Lake Biel,an eutrophic,hard-water lake in northwestern Switzerland

A 2-year study of sedimentation in Lake Biel reveals that three major factors can account for the spatial and temporal patterns of tripton sedimentation. Allochthonous inputs of particulate matter mostly derived from the Aare river during spring snowmelt and other high-water periods, provide about 50% of the carbonate and 50% of the siliceous matter collected in sediment traps. Phytoplankton activity in this eutrophic, hard-water lake accounts for the rest of the carbonate and siliceous matter, the latter being mostly diatom frustules. Sedimentation rates are thus highest during periods of maximum river flooding, maximum phytoplankton activity and following the breakdown of the thermocline, at which time trapped particles settle out. Resuspension of sediment is important in at least one basin. Resolution of carbonate appears to be minor.     

Deformation measurements on Kilauea volcano,Hawaii

Repeated electronic distance measurements across Kilauea Caldera with Tellurometers and Geodimeter show definite horizontal expansion related to the vertical uplift and outward tilting of the summit prior to an eruption, and contraction during and after a flank eruption. Measurements started in October 1964, along a 3098 meter line between Uwekahuna and Keanakakoi, indicate a relatively uniform lengthening of 12 centimeters during the interval October 22, 1964 to March 1, 1965. Rapid shortening of the line by 28 centimeters was measured 4 days after the beginning of a flank eruption which involved emission of approximately 29 million cubic meters of lava during the period March 5 to March 15, 1965. During the expansion, the standard deviation of 10 Tellurometer measurements from a least-squares srtaight line solution is ± 2.0 centimeters (6.5 ppm) whereas 9 Geodimeter measurements have a standard deviation of ± 1.1 (3.6 ppm) centimeters. Absolute distance readings between the two instruments differ by 4 centimeters (13 ppm), but relative changes in distance were the same on both instruments. Changes in distance across Kilauea Caldera can, therefore, be easily measured to accuracies of 4 to 7 parts per million with standard electronic distance measuring systems. On active volcanoes where ground surface deformation exceeds 10–100 parts per million with changes in subsurface magma pressure or volume, repeated horizontal distance measurements can be a most useful technique.     

Detection of ocean waves by microwave radar; The modulation of short gravity-capillary waves

Short gravity-capillary waves, the predominant radar scatterers under many oceanic and radar-viewing conditions, are modulated in amplitude, velocity and orientation by the larger-scale motions of the ocean surface. These modulations render the larger scales observable to microwave radar. The high data rate and advanced technology of modern radar systems make it possible to measure these modulations and, in some cases, to display them as images of the ocean surface. While the modulation of orientation and velocity are straightforward to understand, the amplitude modulation is a dynamic response of the equilibrium short gravity-capillary waves to larger scale driving forces including straining by orbital velocities of large waves. Microwave studies of the growth and equilibrium of short wind-generated waves are reviewed. It is shown that the response of these waves to straining can produce modulations in radar cross-section greater than those due to tilting but which are wind-speed dependent. The net modulation depends strongly on the direction as well as the magnitude of the wind speed. Quantitative determination of ocean wave-height spectra from measured modulations will therefore be a complicated procedure. Measurements of ocean waves with CW Doppler and Synthetic Aperture radars are discussed in the light of these findings.     

A deep seismic profile of 800 km length recorded in southern Queensland, Australia

Summary. In 1984, the Australian Bureau of Mineral Resources and the Geological Survey of Queensland recorded a regional seismic reflection profile of over 800 km length from the eastern part of the Eromanga Basin to the Beenleigh Block east of the Clarence Moreton Basin. A relatively transparent upper crustal basement with an underlying, more reflective lower crust is characteristic of much of the region. Prominent westerly dipping reflectors occur well below the sediments of the eastern margin of the Clarence Moreton Basin and the adjacent Beenleigh Block, and provide some of the most interesting features of the entire survey. A wide angle reflection/refraction survey of 192 km length and an expanding reflection spread of 25 km length were recorded across the Nebine Ridge. The only clear deep reflectors are interpreted as P-to-SV or SV-to-P converted reflections from a mid-crustal boundary at a depth of about 17 km. The combined Nebine Ridge data provide well-constrained P and S wave velocity models of the upper crust, and suggest a crustal structure quite different from that beneath the adjacent Mesozoic basins.     

Genetic structure of the tall sea pen Funiculina quadrangularis in NW Scottish sea lochs

The tall sea pen Funiculina quadrangularis has a patchy distribution around the UK, being found in sheltered waters below 20 m depth on the northwest coast of Scotland and Ireland. The limited distribution and sensitivity to bottom fishing activities make F. quadrangularis vulnerable to reduction in population numbers that may lead to genetic isolation and reduced diversity. Because of this vulnerability and low resilience to physical disturbance, the tall sea pen is recognised as a Species of Principle Importance under the Natural Environment and Rural Communities Act, 2006, UK. ( http://www.legislation.gov.uk/ukpga/2006/16/contents ) and is also on the Biodiversity Action Plan list of Priority Species for the UK. In the Mediterranean it is recognised as a sensitive and essential fish habitat because it forms habitat for several commercially important crustaceans. The aim of this study was to understand the current state of the genetic structure and gene flow of F. quadrangularis in areas of NW Scotland. We developed 10 microsatellite markers and used them to genotype 176 samples from four populations. Overall, our results suggest that there is high genetic diversity and high gene flow between colonies of F. quadrangularis in and among locations in Loch Linnhe and Loch Duich. As a result of the high rates of gene flow, genetic differentiation between sites was low. This may provide resilience to human impacts if distant populations have a high connectivity. However, care must be taken, as small but significant isolation by distance was found between the most geographically distant sites and only a small part of the species range was examined in this study. The genetic tools developed here will provide a foundation for wider studies of this vulnerable species.     

Quantitative Research Performing other Worlds: lessons from sustainable agriculture in the Philippines

For those interested in ethical research, quantitative methods are often dismissed as apolitical; as unreflective exercises in ‘mere counting’. If, however, in doing research, we bring into being the very worlds we purport to describe, the question begs: what kinds of worlds might quantitative methods bring into being? Is there space for a reflexive, quantitative research agenda? In this paper, I will discuss an action-based predominantly quantitative research project that aimed to investigate the diverse impacts of sustainable agriculture on small-scale farmers in the Philippines. The study, one of the largest ever undertaken on organic rice production, was consciously designed, not merely to describe, but to perform organic agriculture differently. While most quantitative, and indeed much qualitative, research ignores its performativity, this research was intended to enact a reality of sustainable agriculture as a viable and vital alternative to mainstream, capitalist agriculture.     

Two rapid assays for screening of patulin biodegradation

The mycotoxin patulin is produced by the blue mould pathogen Penicillium expansum in rotting apples during postharvest storage. Patulin is toxic to a wide range of organisms, including humans, animals, fungi and bacteria. Wash water from apple packing and processing houses often harbours patulin and fungal spores, which can contaminate the environment. Ubiquitous epiphytic yeasts, such as Rhodosporidium kratochvilovae strain LS11 which is a biocontrol agent of P. expansum in apples, have the capacity to resist the toxicity of patulin and to biodegrade it. Two non-toxic products are formed. One is desoxypatulinic acid. The aim of the work was to develop rapid, high-throughput bioassays for monitoring patulin degradation in multiple samples. Escherichia coli was highly sensitive to patulin, but insensitive to desoxypatulinic acid. This was utilized to develop a detection test for patulin, replacing time-consuming thin layer chromatography or high-performance liquid chromatography. Two assays for patulin degradation were developed, one in liquid medium and the other in semi-solid medium. Both assays allow the contemporary screening of a large number of samples. The liquid medium assay utilizes 96-well microtiter plates and was optimized for using a minimum of patulin. The semi-solid medium assay has the added advantage of slowing down the biodegradation, which allows the study and isolation of transient degradation products. The two assays are complementary and have several areas of utilization, from screening a bank of microorganisms for biodegradation ability to the study of biodegradation pathways.