Changes in the angular separation of the lensed images PKS 1830-211 NE & SW

We present 8 epochs of 7 mm dual-polarization VLBA observations of the gravitational lens system PKS 1830-211 made over the course of 14 weeks. Clear changes in the relative positions of the cores of up to 80 μarcseconds (μas) were observed between epochs (each separated by ≈2 weeks). A comparison with previous 7 mm VLBA maps shows that the separation of the cores has changed by almost 280 μas over 12 months. This leads us to conclude that changes in the brightness distribution of the mm-VLBI core of the background source must be occurring rapidly. This is the first clear observation of significant radio source evolution in a gravitational lens system. It is also the first time that changes in source structure have been detected in a distant extra-galactic source on such short time-scales. This is partly accounted for by the magnification provided by the lens system.     

Fishery biology and management of Protonibea diacanthus (Sciaenidae) aggregations in far Northern Cape York Peninsula waters

The sciaenid Protonibea diacanthus is a large, long-lived predatory fish of inshore northern Australian waters, which forms annual aggregations that are fished extensively by traditional (subsistence) and recreational fishers. There are now widespread concerns that the resource is being overexploited.     

Temporal variability of phosphorus fractions in Irish karst springs

Transfer pathways of phosphorus (P) from soil to surface waters are the subject of much current research because of concerns about eutrophication. However, P transfer via groundwater discharge has received little attention. Temporal P changes at eight Carboniferous limestone karst springs from two catchments in western Ireland are examined. The eight springs were sampled fortnightly between June and October 1999 and thereafter monthly until February 2000. Each sample was analysed for total P (TP), total dissolved P (TDP) and dissolved reactive P (DRP). Total P exhibited some hydrological response at all springs (e.g. increase from 45 to 107 µg l^–1) reflecting significant changes in particulate P (PP) (e.g. increase from 7 to 44 µg l^–1) and dissolved organic P (DOP) (e.g. increase from 0 to 27 µg l^–1), with DRP displaying greatest temporal stability. Greatest response to rainfall events occurred after the first major autumnal rains in September 1999, when there appeared to be dislodging of loosely bound PP and DOP, which was transported to groundwater. This response to the first autumnal rains probably reflects the hydrological switch where the catchments change from a soil moisture deficit to a soil moisture surplus situation. Daily autosampling demonstrated TP concentrations of up to 1,814 µg l^–1 due to local pollution, highlighting the need to adopt storm event driven sampling rather than discrete sampling in karstic springs. Identification and management of springs in karst areas, with associated point recharge via swallow holes, presents an urgent and demanding challenge.     

Improved detection and mapping of deepwater hydrocarbon seeps: optimizing multibeam echosounder seafloor backscatter acquisition and processing techniques

Marine seep hunting surveys are a current focus of hydrocarbon exploration surveys due to recent advances in offshore geophysical surveying, geochemical sampling, and analytical technologies. Hydrocarbon seeps are ephemeral, small, discrete, and therefore difficult to sample on the deep seafloor. Multibeam echosounders are an efficient seafloor exploration tool to remotely locate and map seep features. Geophysical signatures from hydrocarbon seeps are acoustically-evident in bathymetric, seafloor backscatter, midwater backscatter datasets. Interpretation of these signatures in backscatter datasets is a fundamental component of commercial seep hunting campaigns. Degradation of backscatter datasets resulting from environmental, geometric, and system noise can interfere with the detection and delineation of seeps. We present a relative backscatter intensity normalization method and an oversampling acquisition technique that can improve the geological resolvability of hydrocarbon seeps. We use Green Canyon (GC) Block 600 in the Northern Gulf of Mexico as a seep calibration site for a Kongsberg EM302 30 kHz MBES prior to the start of the Gigante seep hunting program to analyze these techniques. At GC600, we evaluate the results of a backscatter intensity normalization, assess the effectiveness of 2X seafloor coverage in resolving seep-related features in backscatter data, and determine the off-nadir detection limits of bubble plumes using the EM302. Incorporating these techniques into seep hunting surveys can improve the detectability and sampling of seafloor seeps.     

Unexpected waves: Intermediate depth simulations and comparison with observations

In an earlier study, we defined an “unexpected wave” as, for example, a wave twice as high as any of the preceding 30 waves. Here we extend earlier deep water simulations to allow for the greater crest enhancement in water of finite depth and find that the predicted frequency of unexpected waves increases significantly. We also analyze data obtained by wave buoys off the east and west coasts of Canada. In both deep and intermediate depth water, the occurrence of unexpected waves is in reasonable accord with our simulations, supporting our assumption of random superposition of waves though with local crest enhancement by the non-resonant second harmonic.     

Transport and retention of a conservative tracer in an isolated creek–marsh system

A study of tracer transport and retention in a small tidal creek and marsh system located in the southeastern US was conducted using a three-dimensional hydrodynamic model and data from a dye tracer release. The model simulated tidally driven flow, including inundation and drying out of the marshes and the dispersal of the dye tracer. Flow measurements in the tidal creek showed that the simulations appeared to generally duplicate the tidally driven flow into and out of the tidal creeks and marshes. The dye tracer experiment was conducted to test the hydrodynamic model's ability to simulate dispersal of a point release of pollutants into the creek during an incoming tide. The simulations reproduced much of the experimental measurements, but bathymetric errors and lack of resolution of the smallest arms of the tidal creeks affected the ability to faithfully reproduce the initial peak in measured dye tracer concentrations at a sampling location far from the boundary. The lack of the smallest tidal creeks led to some trapping of water and dye in the marshes. Two independent estimates of flushing time yielded values between 1.6 and 2.4 days. An uncertainty analysis indicates that model simulations are sensitive to variations in parameters such as water depth and marsh grass density. On the other hand, omission of the smallest tidal creeks in simulations may be partially offset by decreasing marsh grass density. Further improvements must rely on more accurate and detailed bathymetric data that resolves the smaller arms of the tidal creeks and includes quantitative information about the density and distribution of marsh grass.     

Helical motions in the jet of blazar 1156+295

The blazar 1156+295 was observed by VLBA and EVN + MERLIN at 5 GHz in June 1996 and February 1997 respectively. The results show that the jet of the source has structural oscillations on the milliarcsecond scale and turns through a large angle to the direction of the arcsecond-scale extension. A helical jet model can explain most of the observed properties of the radio structure in 1156+295.     

Using Hydroacoustics to Understand Fish Presence and Vertical Distribution in a Tidally Dynamic Region Targeted for Energy Extraction

The use of tidal currents by fishes for movements to and from onshore spawning, foraging, and nursery grounds is well documented. However, fishes’ use of the water column in tidal currents frequently exceeding 1.5 m?·?s^-1 is largely unknown. With growing interest in extracting energy from the tides, understanding animal use of these dynamic environments has become essential to determining environmental effects of tidal energy devices. To assess the effects of a tidal energy device on fishes, we used down-looking single-beam hydroacoustic technology to collect pre-deployment data on the presence and vertical distribution of fishes at a pilot project site and a control site in Cobscook Bay, ME. Twenty-four-hour stationary surveys were conducted in each season of 2010 and 2011. Relative fish density and vertical distribution were analyzed for variation with respect to site, year, month, and diel and tidal cycles. A seasonal pattern in fish density was apparent in both years at both sites, with maxima in spring and late fall. Fish density was generally highest near the sea floor. Diel changes in vertical distribution were frequently observed, but changes in distribution related to tidal cycle were inconsistent. Results from the project and control sites were very similar, demonstrating that the control site provides a reference for quantifying changes in fish density and vertical distribution related to the tidal device. This approach and baseline dataset will be used to compare hydroacoustic data collected at the project and control sites after device deployment.     

Are there basic physical constraints on future anthropogenic emissions of carbon dioxide?

Global Circulation Models (GCMs) provide projections for future climate warming using a wide variety of highly sophisticated anthropogenic CO₂ emissions scenarios as input, each based on the evolution of four emissions ??drivers??: population p, standard of living g, energy productivity (or efficiency) f and energy carbonization c (IPCC WG III 2007). The range of scenarios considered is extremely broad, however, and this is a primary source of forecast uncertainty (Stott and Kettleborough, Nature 416:723?C725, 2002). Here, it is shown both theoretically and observationally how the evolution of the human system can be considered from a surprisingly simple thermodynamic perspective in which it is unnecessary to explicitly model two of the emissions drivers: population and standard of living. Specifically, the human system grows through a self-perpetuating feedback loop in which the consumption rate of primary energy resources stays tied to the historical accumulation of global economic production??or p×g??through a time-independent factor of 9.7±0.3 mW per inflation-adjusted 1990 US dollar. This important constraint, and the fact that f and c have historically varied rather slowly, points towards substantially narrowed visions of future emissions scenarios for implementation in GCMs.