ALBERT

Description: For the past 50 years there has been rapid warming in the maritime Antarctic, with concurrent, and probably temperature-mediated, proliferation of the two native plants, Antarctic pearlwort (Colobanthus quitensis) and especially Antarctic hair grass (Deschampsia antarctica). In many terrestrial ecosystems at high latitudes, nitrogen (N) supply regulates primary productivity. Although the predominant view is that only inorganic and amino acid N are important sources of N for angiosperms, most N enters soil as protein. Maritime Antarctic soils have large stocks of proteinaceous N, which is released slowly as decomposition is limited by low temperatures. Consequently, an ability to acquire N at an early stage of availability is key to the success of photosynthetic organisms. Here we show that D. antarctica can acquire N through its roots as short peptides, produced at an early stage of protein decomposition, acquiring N over three times faster than as amino acid, nitrate or ammonium, and more than 160 times faster than the mosses with which it competes. Efficient acquisition of the N released in faster decomposition of soil organic matter as temperatures rise may give D. antarctica an advantage over competing mosses that has facilitated its recent proliferation in the maritime Antarctic.

Description: We applied digestate generated from the anaerobic digestion of slurry, undigested slurry, or inorganic N (ammonium nitrate) or NPK compound fertilizer to pots of grass and a grass–clover mix grown in two soils. Crop yields were equal or enhanced with digestate, and analysis of soil water showed that there was less potential for loss of nutrients via leaching. Replacing inorganic fertilizer with digestate may therefore maintain grassland productivity but with less impact on the environment.

Description: [1]  The shelf circulation off Ningaloo Reef near the North West Cape of Western Australia is driven by complex interactions between the southward flowing Leeuwin Current and wind-driven currents that episodically reverse the coastal flow towards the north. The presence of these northward (equatorward) wind-driven currents is thought to make this section of coast one of the few locations along Western Australia to experience periodic coastal upwelling. We used a combination of field observations and numerical modeling to investigate this summer circulation and upwelling dynamics along Ningaloo Reef. We analyzed current and temperature profiles from moorings at four sites across the shelf and used two Regional Ocean Modeling System (ROMS) sub-models: (1) a coarser model of northwestern Australia forced by a global ocean model and (2) a nested fine-scale model of the Ningaloo region. This nesting significantly improved model skill as it included the offshore mesoscale dynamics that strongly influenced the shelf circulation off Ningaloo. The field observations revealed several northward flow reversals, accompanied by cooling of the coastal waters adjacent to Ningaloo, which were associated with strong northward wind events. Analysis of the coastal heat budget revealed that cooling events were primarily driven by upwelling, whereas warming of coastal waters during relaxation events resulted mostly from along-shelf advection of warm water from the north. Due to the combined effects of its relatively steep (~1/50 slope) shelf and strong summer stratification, upwelled water was sourced from the interior of the water column, likely influencing the sources and fluxes of nutrients to Ningaloo Reef.

Description: We have investigated the seasonal evolution of the internal tide using a yearlong mooring record in the Browse Basin on the Australian North-West Shelf. Using a modal harmonic-decomposition technique, we studied the modulation of the semi-diurnal kinetic energy, potential energy, energy flux, group velocity and sea surface height anomaly for different internal wave modes. A very coherent and energetic, locally generated internal tide dominated the mooring record during spring-tide periods. Relationships amongst the wave variables suggest that the interaction of multiple waves formed a standing wave pattern. To assist in explaining the seasonal variability of this standing wave pattern, we used an analytical model of internal wave generation and propagation in a double-shelf system, representative of the area, to highlight the effects of changes in the stratification and barotropic forcing. A comparison of the low-mode wave energy indicated that the analytical solution overestimated the observed wave energy by a factor of two and failed to detect an apparent seasonal shift in the conversion rate. We discuss potential mechanisms for this discrepancy.

Description: Clear-conservative satellite cloud detection algorithms overestimate cloud fraction (CF), the degree to which depends on instrument resolution and the spatial distribution of cloud area, with boundary layer cumulus carrying the largest overestimation. This is because in the standard method of computing CF, partially cloudy pixels contribute in the amount of the pixel's area rather than the true cloud area. Development of analytical and pattern recognition techniques to reduce overestimation has been limited by the lack of coincident long-term, large scale, and high-resolution satellite data sets. Such data sets are now available from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Multiangle Imaging SpectroRadiometer (MISR) instruments onboard the satellite, Terra. These data sets are used to determine the resolution required to reduce the CF overestimation to ≤0.01 absolute CF using the standard, analytical, and pattern recognition techniques on perfect, clear-conservative cloud masks with future instrument design in mind; investigate the challenges of implementing these techniques on MISR's operational clear-conservative cloud mask; and demonstrate the impact of these techniques on a MISR-derived CF climatology similar to those used to evaluate climate models. Reducing the median CF bias to ≤0.01 requires resolutions of

Description: Barium titanate-20wt% cobalt ferrite ( BaTiO 3 -20wt% CoFe 2 O 4 ) nanocomposites were sintered from nanocrystalline BaTiO 3 and CoFe 2 O 4 powders using spark plasma sintering (SPS) and pressureless sintering (PS) techniques. Using SPS, dense polycrystalline composites were obtained at a sintering temperature as low as 860°C and a time of 5 min whereas PS required a higher sintering temperature (1150°C) and time (120 min) to obtain similarly dense composites. Microstructural analysis of the composites showed that both the techniques retained nanocrystalline grain sizes after sintering. High resolution X-ray diffraction measurements revealed that the BaTiO 3 -20wt% CoFe 2 O 4 composites sintered by the SPS technique did not exhibit formation of any new phase(s) due to reaction between the BaTiO 3 and CoFe 2 O 4 phases during sintering. However, the PS technique resulted in the formation of additional phases (other than the BaTiO 3 and CoFe 2 O 4 phases) in the composites. While the composites synthesized by SPS were of superior phase-purity, evidence of Fe diffusion from the spinel to the perovskite phase was found from X-ray diffraction and permittivity measurements.

Description: The near seabed mean and turbulent processes on the continental slope were measured for a three week period using an array of acoustic-Doppler velocimeters and thermistors over the bottom 30 m at the 400 m isobath. Baroclinic motions with characteristics similar to internal bores or boluses propagated onshore during the flood phase of both spring and neap tides. The arrival time of these internal bores at our measurement site varied amongst tidal cycles and their characteristics were not highly correlated with the amplitude of the barotropic tidal forcing. The passage of the internal bores was associated with large turbulent overturns, enhanced turbulent kinetic energy dissipation ($\epsilon$ 〉 10−6 W kg−1) and intensified currents (〉6 times the barotropic forcing) within meters of the seabed. During the deployment, stratification and shear competed to govern our observed overturning length scale ($\lesssim$4 m) that were characterized by the Ellison length scale LE. Only measurements closest to the seabed (1.7 m) were described by the log law-of-the-wall; generally both buoyancy and the presence of the bottom boundary influenced LE, while sometimes flow-induced shear determined LE. As the distance of our measurements from the seabed increased, the influence of buoyancy became more pronounced. These results highlight that a more general descriptor of the overturning length scale is necessary for complex stratified shear flows.

Description: An accurate assessment of soil respiration is critical for understanding and predicting ecosystem responses to anthropogenic perturbation such as climate change, pollution, and agriculture. Infra-red gas analyzer (IRGA)–based field measurement is the most widely used technique for assessing soil-respiration flux rates. In this study, respiration rates obtained with two common IRGA systems (LI-COR 8100 and PP Systems EGM-4) were compared across three ecosystem types. Our results showed that both methods were highly comparable in their flux estimates, but the associated methodology used (notably the use or absence of a soil collar) resulted in greater uncertainty in flux rates and a greater degree of intrasite variation. Specifically, the use of collars significantly decreased the flux estimate for both IRGAs compared to the no-collar estimate. The disturbance caused by collar insertion was assumed to be a major factor in causing the differing flux estimates, with root and mycorrhizal severance likely being the main contributor. We conclude that the two IRGAs used in this study can be reliably compared for overall flux estimates but emphasis is needed to validate a common measurement methodology.

Description: Pulsating aurora is a common phenomenon generally believed to occur mainly in the aftermath of a substorm, where dim long-period pulsating patches appear. The study determines the temporal and spatial evolution of pulsating events using two THEMIS all-sky imager stations, at Gillam (66.18 magnetic latitude, 332.78 magnetic longitude, magnetic midnight at 0634 UT) and Fort Smith, (67.38 magnetic latitude, 306.64 magnetic longitude, magnetic midnight at 0806 UT) along roughly the same invariant latitude. Parameters have been calculated from a database of 74 pulsating aurora events from 119 days of good optical data within the period from September 2007 through March 2008 as identified with the Gillam camera. It is shown that the source region of pulsating aurora drifts or expands eastward, away from magnetic midnight, for premidnight onsets and that the spatial evolution is more complicated for postmidnight onsets, which has implications for the source mechanism. The most probable duration of a pulsating aurora event is roughly 1.5 h, while the distribution of possible event durations includes many long (several hours) events. This may suggest that pulsating aurora is not strictly a substorm recovery phase phenomenon but rather a persistent, long-lived phenomenon that may be temporarily disrupted by auroral substorms. Observations from the Gillam station show that in fact, pulsating aurora is quite common with the occurrence rate increasing to around 60% for morning hours, with 69% of pulsating aurora onsets occurring after substorm breakup.

Description: Bismuth-based ferroelectric ceramics are currently under intense investigation for their potential as Pb-free alternatives to lead zirconate titanate-based piezoelectrics. The present work evaluated the thermal depoling behavior of various compositions of Na 0.5 Bi 0.5 TiO 3 (NBT), one of the Bi-based materials of broad interest, through in situ and ex situ measurements of the piezoelectric constant ( d 33 ). A range of ceramics was prepared by substituting 0.5–2 at.% of Fe or Mn for Ti. It was found that a low dopant concentration (0.5 at.%) increases the depolarization temperature ( T d ) with a minimal loss in room temperature d 33 , allowing for high piezoelectric coefficients at elevated temperatures. For example, 0.5 at.% Fe substitution leads to an enhanced piezoelectric coefficient of d 33 of 133 pm/V at an elevated temperature of 180°C. However, with further increase of dopant concentration, T d decreases in both Mn- and Fe-doped NBT. The in situ depoling measurements of 0.5 at.% Fe- and Mn-doped NBT in the present work exhibit the potential for higher temperature applications.