Degradation of some mechanical current meter measurements byhigh-frequency mooring or wave motion

Comparison of current measurements from moored (paddle-wheel rotor) Aanderaa current meters and acoustic Doppler current profilers in a strong tidal flow on Georges Bank indicates rate under-reading by the Aanderaa meters at some vertical positions. The under-reading may arise from mooring-line vibrations induced by vortex shedding from spherical buoyancy packages, and shielding of the paddle-wheel rotors due to the meters' inability to remain aligned with the fluctuating relative water velocity. Field tests and a simple model are used to investigate this explanation. The authors briefly review the Georges Bank observations that instigated this investigation. An explanation for the degradation of the Aanderaa measurements is proposed, observational information from field tests is discussed, and the model and its implications are presented. The model results support the hypothesis that high-frequency mooring-line vibration causes the degradation of the Aanderaa measurements     

Surface of Miranda: Identification of water ice

Near-infrared spectrophotometry at 5% resolution shows Miranda to have a water-ice surface. Estimates of Miranda's albedo made from the depth of its 2.0-μm absorption band suggest that its visual geometric albedo is likely to be between 10 and 70%, which when combined with the satellite's visual magnitude, yields a diameter of 500 ± 225km. There is some evidence that suggests the visual geometric albedo of Miranda may be ≥0.3, which implies that its diameter may lie near the lower end of the estimated range. With these results all the Uranian satellites are now known to have water-ice surfaces.     

Chemical speciation and fate of tripolyphosphate after application to a calcareous soil

Adsorption and precipitation reactions often dictate the availability of phosphorus in soil environments. Tripolyphosphate (TPP) is considered a form of slow release P fertilizer in P limited soils, however, investigations of the chemical fate of TPP in soils are limited. It has been proposed that TPP rapidly hydrolyzes in the soil solution before adsorbing or precipitating with soil surfaces, but in model systems, TPP also adsorbs rapidly onto mineral surfaces. To study the adsorption behavior of TPP in calcareous soils, a short-term (48 h) TPP spike was performed under laboratory conditions. To determine the fate of TPP under field conditions, two different liquid TPP amendments were applied to a P limited subsurface field site via an in-ground injection system. Phosphorus speciation was assessed using X-ray absorption spectroscopy, total and labile extractable P, and X-ray diffraction. Adsorption of TPP to soil mineral surfaces was rapid (< 48 h) and persisted without fully hydrolyzing to ortho-P. Linear combination fitting of XAS data indicated that the distribution of adsorbed P was highest (~ 30–40%) throughout the site after the first TPP amendment application (high water volume and low TPP concentrations). In contrast, lower water volumes with more concentrated TPP resulted in lower relative fractions of adsorbed P (15–25%), but a significant increase in total P concentrations (~ 3000 mg P kg soil) and adsorbed P (60%) directly adjacent to the injection system. This demonstrates that TPP application increases the adsorbed P fraction of calcareous soils through rapid adsorption reactions with soil mineral surfaces.     

The three-dimensional structure of Saturn’s E ring

Saturn’s diffuse E ring consists of many tiny (micron and sub-micron) grains of water ice distributed between the orbits of Mimas and Titan. Various gravitational and non-gravitational forces perturb these particles’ orbits, causing the ring’s local particle density to vary noticeably with distance from the planet, height above the ring-plane, hour angle and time. Using remote-sensing data obtained by the Cassini spacecraft in 2005 and 2006, we investigate the E-ring’s three-dimensional structure during a time when the Sun illuminated the rings from the south at high elevation angles (>15°). These observations show that the ring’s vertical thickness grows with distance from Enceladus’ orbit and its peak brightness density shifts from south to north of Saturn’s equator plane with increasing distance from the planet. These data also reveal a localized depletion in particle density near Saturn’s equatorial plane around Enceladus’ semi-major axis. Finally, variations are detected in the radial brightness profile and the vertical thickness of the ring as a function of longitude relative to the Sun. Possible physical mechanisms and processes that may be responsible for some of these structures include solar radiation pressure, variations in the ambient plasma, and electromagnetic perturbations associated with Saturn’s shadow.     

Cross‐shelf colour zonation in northern Great Barrier Reef lagoon surficial sediments

A cross‐shelf colour zonation is observed in Great Barrier Reef lagoon surficial sediments from 12 to 18°S, with colours tending to lighten from inner to outer shelf. The phenomenon is particularly well defined south of Cairns where four zones occur. The colour zonation appears to reflect the abrupt facies changes that occur in the lagoon. Visual estimates of relative optical lightness for the zones are strongly related to carbonate content, and lightness class boundaries broadly follow carbonate contours, indicating that the mechanisms leading to the colour zones are related to those governing carbonate distribution.