E‐tracers: Development of a low cost wireless technique for exploring sub‐surface hydrological systems

This briefing describes the first deployment of a new electronic tracer (E‐tracer) for obtaining along‐flowpath measurements in subsurface hydrological systems. These low‐cost, wireless sensor platforms were deployed into moulins on the Greenland Ice Sheet. After descending into the moulin, the tracers travelled through the subglacial drainage system before emerging at the glacier portal. They are capable of collecting along‐flowpath data from the point of injection until detection. The E‐tracers emit a radio frequency signal, which enables sensor identification, location and recovery from the proglacial plain. The second generation of prototype E‐tracers recorded water pressure, but the robust sensor design provides a versatile platform for measuring a range of parameters, including temperature and electrical conductivity, in hydrological environments that are challenging to monitor using tethered sensors. Copyright © 2012 John Wiley & Sons, Ltd.     

Black hole shadow image and visibility analysis of Sagittarius A*

The compact dark objects with very large masses residing at the centres of galaxies are believed to be black holes. Due to the gravitational lensing effect, they would cast a shadow larger than their horizon size over the background; the shape and size of this shadow can be calculated. For the supermassive black hole candidate Sgr A*, this shadow spans an angular size of about 50 μas, which is under the resolution attainable with the current astronomical instruments. Such a shadow image of Sgr A* will be observable at about 1 mm wavelength, considering the scatter broadening by the interstellar medium. By simulating the black hole shadow image of Sgr A* with the radiatively inefficient accretion flow model, we demonstrate that analysing the properties of the visibility function can help us determine some parameters of the black hole configuration, which is instructive for the submillimetre Very Long Baseline Interferometry (VLBI) observations of Sgr A* to be made in the near future.     

Comparative analysis of relationships between NLDAS‐2 forcings and model outputs

This study reports results from an analysis of the relationship between atmospheric forcing and model‐simulated water and energy fluxes for the North American Land Data Assimilation System Project Phase 2 (NLDAS‐2). The relationships between mean monthly precipitation and total runoff are stronger in the Sacramento (SAC) and variable infiltration capacity (VIC) models, which grew out of the hydrological community, than in the Noah and Mosaic models, which grew out of the soil‐vegetation‐atmosphere transfer (SVAT) community. The reverse is true for the relationship between mean monthly precipitation and evapotranspiration. In addition, surface energy fluxes in VIC are less sensitive to model forcing (except for air temperature) than those in the Noah and Mosaic model. Notwithstanding these general conclusions, the relationships between forcings and model‐simulated water and energy fluxes for all models vary for different seasons, variables, and regions. These findings will ultimately inspire a combination of SVAT‐type model energy components with hydrological model water components to develop a SVAT‐hydrology model to improve both evapotranspiration and total runoff simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

Application of Laser Ablation ICP-MS to U-Th-Pb Dating of Monazite

Recent advances in laser ablation ICP-MS techniques allow accurate U-Th-Pb age dating of monazites that are as young as several tens of million years to a precision better than 2%. Accuracy of the age determinations has been improved by true real-time mass bias correction via nebulisation of a solution containing enriched ²³³U and natural Tl isotopes. The Tl-U tracer solution eliminates possible effects of variable sample matrices on the precision and accuracy of measured isotopic ratios. Mass bias corrections based on measured ²⁰⁵Tl/²³³U ratios in the tracer solution allow direct measurement of ²³⁵U in monazite. Combined with high-sensitivity laser ablation ICP-MS measurements, direct measurement of ²³⁵U particularly improves the precision of U-Pb dating of young monazites. Correction for laser-induced Pb/U and Pb/Th elemental fractionation is based on a mathematical treatment of time resolved count-rate data that is independent of laser ablation characteristics, does not require external standardisation and allows variable laser pit size or raster patterns for each measurement. The new procedures make the LA ICP-MS technique more flexible for in situ U-Th-Pb analysis.     

Changes in phytoplankton following nitrate and phosphate additions to large enclosures in Marion Lake,British Columbia

The addition of nitrate, phosphate and a nitrate phosphate combination to replicated wooden enclosures in Marion Lake resulted in significant increases in primary productivity and algal standing crop in each of the three types of treated enclosures. This indicated that no single nutrient is likely to simultaneously limit the growth of all phytoplankton species present at any one time in the lake epilimnion. The relevance of this to the detergent controversy is discussed. Canadian Contribution to the International Biological Programme No. CCIBP 208.     

Eradication success down under: heat treatment of a sunken trawler to kill the invasive seaweed Undaria pinnatifida

Eradication of invasive species is difficult in the marine environment, and there have only been a few successes. We report the successful eradication of the invasive seaweed Undaria pinnatifida from a sunken trawler in the Chatham Islands, New Zealand. New heat-treatment methods were developed as the most cost effective and environmentally acceptable option to kill Undaria. Monitoring of the trawler for three years after it sank found no Undaria after the vessel was treated. Key factors in the success of the eradication programme included: early detection, a rapid response, pre-existing knowledge of Undaria, an adaptive management approach, targeting of multiple life history stages, and the cooperation of the vessel's insurer.